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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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< html > < head > < title > LLVM Assembly Language Reference Manual< / title > < / head >
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< body bgcolor = white >
< table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
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< tr > < td > < font size = +5 color = "#EEEEFF" face = "Georgia,Palatino,Times,Roman" > < b > LLVM Language Reference Manual< / b > < / font > < / td >
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< / tr > < / table >
< ol >
< li > < a href = "#abstract" > Abstract< / a >
< li > < a href = "#introduction" > Introduction< / a >
< li > < a href = "#identifiers" > Identifiers< / a >
< li > < a href = "#typesystem" > Type System< / a >
< ol >
< li > < a href = "#t_primitive" > Primitive Types< / a >
< ol >
< li > < a href = "#t_classifications" > Type Classifications< / a >
< / ol >
< li > < a href = "#t_derived" > Derived Types< / a >
< ol >
< li > < a href = "#t_array" > Array Type< / a >
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< li > < a href = "#t_function" > Function Type< / a >
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< li > < a href = "#t_pointer" > Pointer Type< / a >
< li > < a href = "#t_struct" > Structure Type< / a >
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<!-- <li><a href="#t_packed" >Packed Type</a> -->
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< / ol >
< / ol >
< li > < a href = "#highlevel" > High Level Structure< / a >
< ol >
< li > < a href = "#modulestructure" > Module Structure< / a >
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< li > < a href = "#globalvars" > Global Variables< / a >
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< li > < a href = "#functionstructure" > Function Structure< / a >
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< / ol >
< li > < a href = "#instref" > Instruction Reference< / a >
< ol >
< li > < a href = "#terminators" > Terminator Instructions< / a >
< ol >
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< li > < a href = "#i_ret" > '< tt > ret< / tt > ' Instruction< / a >
< li > < a href = "#i_br" > '< tt > br< / tt > ' Instruction< / a >
< li > < a href = "#i_switch" > '< tt > switch< / tt > ' Instruction< / a >
< li > < a href = "#i_invoke" > '< tt > invoke< / tt > ' Instruction< / a >
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< li > < a href = "#i_unwind" > '< tt > unwind< / tt > ' Instruction< / a >
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< / ol >
< li > < a href = "#binaryops" > Binary Operations< / a >
< ol >
< li > < a href = "#i_add" > '< tt > add< / tt > ' Instruction< / a >
< li > < a href = "#i_sub" > '< tt > sub< / tt > ' Instruction< / a >
< li > < a href = "#i_mul" > '< tt > mul< / tt > ' Instruction< / a >
< li > < a href = "#i_div" > '< tt > div< / tt > ' Instruction< / a >
< li > < a href = "#i_rem" > '< tt > rem< / tt > ' Instruction< / a >
< li > < a href = "#i_setcc" > '< tt > set< i > cc< / i > < / tt > ' Instructions< / a >
< / ol >
< li > < a href = "#bitwiseops" > Bitwise Binary Operations< / a >
< ol >
< li > < a href = "#i_and" > '< tt > and< / tt > ' Instruction< / a >
< li > < a href = "#i_or" > '< tt > or< / tt > ' Instruction< / a >
< li > < a href = "#i_xor" > '< tt > xor< / tt > ' Instruction< / a >
< li > < a href = "#i_shl" > '< tt > shl< / tt > ' Instruction< / a >
< li > < a href = "#i_shr" > '< tt > shr< / tt > ' Instruction< / a >
< / ol >
< li > < a href = "#memoryops" > Memory Access Operations< / a >
< ol >
< li > < a href = "#i_malloc" > '< tt > malloc< / tt > ' Instruction< / a >
< li > < a href = "#i_free" > '< tt > free< / tt > ' Instruction< / a >
< li > < a href = "#i_alloca" > '< tt > alloca< / tt > ' Instruction< / a >
< li > < a href = "#i_load" > '< tt > load< / tt > ' Instruction< / a >
< li > < a href = "#i_store" > '< tt > store< / tt > ' Instruction< / a >
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< li > < a href = "#i_getelementptr" > '< tt > getelementptr< / tt > ' Instruction< / a >
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< / ol >
< li > < a href = "#otherops" > Other Operations< / a >
< ol >
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< li > < a href = "#i_phi" > '< tt > phi< / tt > ' Instruction< / a >
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< li > < a href = "#i_cast" > '< tt > cast .. to< / tt > ' Instruction< / a >
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< li > < a href = "#i_call" > '< tt > call< / tt > ' Instruction< / a >
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< li > < a href = "#i_vanext" > '< tt > vanext< / tt > ' Instruction< / a >
< li > < a href = "#i_vaarg" > '< tt > vaarg< / tt > ' Instruction< / a >
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< / ol >
< / ol >
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< li > < a href = "#intrinsics" > Intrinsic Functions< / a >
< ol >
< li > < a href = "#int_varargs" > Variable Argument Handling Intrinsics< / a >
< ol >
< li > < a href = "#i_va_start" > '< tt > llvm.va_start< / tt > ' Intrinsic< / a >
< li > < a href = "#i_va_end" > '< tt > llvm.va_end< / tt > ' Intrinsic< / a >
< li > < a href = "#i_va_copy" > '< tt > llvm.va_copy< / tt > ' Intrinsic< / a >
< / ol >
< / ol >
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< p > < b > Written by < a href = "mailto:sabre@nondot.org" > Chris Lattner< / a > and < A href = "mailto:vadve@cs.uiuc.edu" > Vikram Adve< / a > < / b > < p >
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< / ol >
<!-- *********************************************************************** -->
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< p > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "abstract" > Abstract
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
< blockquote >
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This document is a reference manual for the LLVM assembly language. LLVM is
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an SSA based representation that provides type safety, low-level operations,
flexibility, and the capability of representing 'all' high-level languages
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cleanly. It is the common code representation used throughout all phases of
the LLVM compilation strategy.
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< / blockquote >
<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "introduction" > Introduction
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
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The LLVM code representation is designed to be used in three different forms: as
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an in-memory compiler IR, as an on-disk bytecode representation (suitable for
fast loading by a Just-In-Time compiler), and as a human readable assembly
language representation. This allows LLVM to provide a powerful intermediate
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representation for efficient compiler transformations and analysis, while
providing a natural means to debug and visualize the transformations. The three
different forms of LLVM are all equivalent. This document describes the human
readable representation and notation.< p >
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The LLVM representation aims to be a light-weight and low-level while being
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expressive, typed, and extensible at the same time. It aims to be a "universal
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IR" of sorts, by being at a low enough level that high-level ideas may be
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cleanly mapped to it (similar to how microprocessors are "universal IR's",
allowing many source languages to be mapped to them). By providing type
information, LLVM can be used as the target of optimizations: for example,
through pointer analysis, it can be proven that a C automatic variable is never
accessed outside of the current function... allowing it to be promoted to a
simple SSA value instead of a memory location.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "wellformed" > < h4 > < hr size = 0 > Well Formedness< / h4 > < ul >
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It is important to note that this document describes 'well formed' LLVM assembly
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language. There is a difference between what the parser accepts and what is
considered 'well formed'. For example, the following instruction is
syntactically okay, but not well formed:< p >
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< pre >
%x = < a href = "#i_add" > add< / a > int 1, %x
< / pre >
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...because the definition of < tt > %x< / tt > does not dominate all of its uses. The
LLVM infrastructure provides a verification pass that may be used to verify that
an LLVM module is well formed. This pass is automatically run by the parser
after parsing input assembly, and by the optimizer before it outputs bytecode.
The violations pointed out by the verifier pass indicate bugs in transformation
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passes or input to the parser.< p >
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<!-- Describe the typesetting conventions here. -->
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<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "identifiers" > Identifiers
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
LLVM uses three different forms of identifiers, for different purposes:< p >
< ol >
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< li > Numeric constants are represented as you would expect: 12, -3 123.421, etc.
Floating point constants have an optional hexidecimal notation.
< li > Named values are represented as a string of characters with a '%' prefix.
For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
regular expression used is '< tt > %[a-zA-Z$._][a-zA-Z$._0-9]*< / tt > '. Identifiers
which require other characters in their names can be surrounded with quotes. In
this way, anything except a < tt > "< / tt > character can be used in a name.
< li > Unnamed values are represented as an unsigned numeric value with a '%'
prefix. For example, %12, %2, %44.
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< / ol > < p >
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LLVM requires the values start with a '%' sign for two reasons: Compilers don't
need to worry about name clashes with reserved words, and the set of reserved
words may be expanded in the future without penalty. Additionally, unnamed
identifiers allow a compiler to quickly come up with a temporary variable
without having to avoid symbol table conflicts.< p >
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Reserved words in LLVM are very similar to reserved words in other languages.
There are keywords for different opcodes ('< tt > < a href = "#i_add" > add< / a > < / tt > ',
'< tt > < a href = "#i_cast" > cast< / a > < / tt > ', '< tt > < a href = "#i_ret" > ret< / a > < / tt > ',
etc...), for primitive type names ('< tt > < a href = "#t_void" > void< / a > < / tt > ',
'< tt > < a href = "#t_uint" > uint< / a > < / tt > ', etc...), and others. These reserved
words cannot conflict with variable names, because none of them start with a '%'
character.< p >
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Here is an example of LLVM code to multiply the integer variable '< tt > %X< / tt > '
by 8:< p >
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The easy way:
< pre >
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%result = < a href = "#i_mul" > mul< / a > uint %X, 8
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< / pre >
After strength reduction:
< pre >
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%result = < a href = "#i_shl" > shl< / a > uint %X, ubyte 3
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< / pre >
And the hard way:
< pre >
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< a href = "#i_add" > add< / a > uint %X, %X < i > ; yields {uint}:%0< / i >
< a href = "#i_add" > add< / a > uint %0, %0 < i > ; yields {uint}:%1< / i >
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%result = < a href = "#i_add" > add< / a > uint %1, %1
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< / pre >
This last way of multiplying < tt > %X< / tt > by 8 illustrates several important lexical features of LLVM:< p >
< ol >
< li > Comments are delimited with a '< tt > ;< / tt > ' and go until the end of line.
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< li > Unnamed temporaries are created when the result of a computation is not
assigned to a named value.
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< li > Unnamed temporaries are numbered sequentially
< / ol > < p >
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...and it also show a convention that we follow in this document. When
demonstrating instructions, we will follow an instruction with a comment that
defines the type and name of value produced. Comments are shown in italic
text.< p >
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The one non-intuitive notation for constants is the optional hexidecimal form of
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floating point constants. For example, the form '< tt > double
0x432ff973cafa8000< / tt > ' is equivalent to (but harder to read than) '< tt > double
4.5e+15< / tt > ' which is also supported by the parser. The only time hexadecimal
floating point constants are useful (and the only time that they are generated
by the disassembler) is when an FP constant has to be emitted that is not
representable as a decimal floating point number exactly. For example, NaN's,
infinities, and other special cases are represented in their IEEE hexadecimal
format so that assembly and disassembly do not cause any bits to change in the
constants.< p >
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<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "typesystem" > Type System
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
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The LLVM type system is one of the most important features of the intermediate
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representation. Being typed enables a number of optimizations to be performed
on the IR directly, without having to do extra analyses on the side before the
transformation. A strong type system makes it easier to read the generated code
and enables novel analyses and transformations that are not feasible to perform
on normal three address code representations.< p >
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<!-- The written form for the type system was heavily influenced by the
syntactic problems with types in the C language< sup > < a
href="#rw_stroustrup">1< / a > < / sup > .< p > -->
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<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "t_primitive" > Primitive Types
< / b > < / font > < / td > < / tr > < / table > < ul >
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The primitive types are the fundemental building blocks of the LLVM system. The
current set of primitive types are as follows:< p >
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< table border = 0 align = center > < tr > < td >
< table border = 1 cellspacing = 0 cellpadding = 4 align = center >
< tr > < td > < tt > void< / tt > < / td > < td > No value< / td > < / tr >
< tr > < td > < tt > ubyte< / tt > < / td > < td > Unsigned 8 bit value< / td > < / tr >
< tr > < td > < tt > ushort< / tt > < / td > < td > Unsigned 16 bit value< / td > < / tr >
< tr > < td > < tt > uint< / tt > < / td > < td > Unsigned 32 bit value< / td > < / tr >
< tr > < td > < tt > ulong< / tt > < / td > < td > Unsigned 64 bit value< / td > < / tr >
< tr > < td > < tt > float< / tt > < / td > < td > 32 bit floating point value< / td > < / tr >
< tr > < td > < tt > label< / tt > < / td > < td > Branch destination< / td > < / tr >
< / table >
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< / td > < td valign = top >
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< table border = 1 cellspacing = 0 cellpadding = 4 align = center >
< tr > < td > < tt > bool< / tt > < / td > < td > True or False value< / td > < / tr >
< tr > < td > < tt > sbyte< / tt > < / td > < td > Signed 8 bit value< / td > < / tr >
< tr > < td > < tt > short< / tt > < / td > < td > Signed 16 bit value< / td > < / tr >
< tr > < td > < tt > int< / tt > < / td > < td > Signed 32 bit value< / td > < / tr >
< tr > < td > < tt > long< / tt > < / td > < td > Signed 64 bit value< / td > < / tr >
< tr > < td > < tt > double< / tt > < / td > < td > 64 bit floating point value< / td > < / tr >
< / table >
< / td > < / tr > < / table > < p >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "t_classifications" > < h4 > < hr size = 0 > Type Classifications< / h4 > < ul >
These different primitive types fall into a few useful classifications:< p >
< table border = 1 cellspacing = 0 cellpadding = 4 align = center >
< tr > < td > < a name = "t_signed" > signed< / td > < td > < tt > sbyte, short, int, long, float, double< / tt > < / td > < / tr >
< tr > < td > < a name = "t_unsigned" > unsigned< / td > < td > < tt > ubyte, ushort, uint, ulong< / tt > < / td > < / tr >
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< tr > < td > < a name = "t_integer" > integer< / td > < td > < tt > ubyte, sbyte, ushort, short, uint, int, ulong, long< / tt > < / td > < / tr >
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< tr > < td > < a name = "t_integral" > integral< / td > < td > < tt > bool, ubyte, sbyte, ushort, short, uint, int, ulong, long< / tt > < / td > < / tr >
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< tr > < td > < a name = "t_floating" > floating point< / td > < td > < tt > float, double< / tt > < / td > < / tr >
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< tr > < td > < a name = "t_firstclass" > first class< / td > < td > < tt > bool, ubyte, sbyte, ushort, short,< br > uint, int, ulong, long, float, double, < a href = "#t_pointer" > pointer< / a > < / tt > < / td > < / tr >
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< / table > < p >
<!-- ======================================================================= -->
< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 > < tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
< a name = "t_derived" > Derived Types
< / b > < / font > < / td > < / tr > < / table > < ul >
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The real power in LLVM comes from the derived types in the system. This is what
allows a programmer to represent arrays, functions, pointers, and other useful
types. Note that these derived types may be recursive: For example, it is
possible to have a two dimensional array.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "t_array" > < h4 > < hr size = 0 > Array Type< / h4 > < ul >
< h5 > Overview:< / h5 >
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The array type is a very simple derived type that arranges elements sequentially
in memory. The array type requires a size (number of elements) and an
underlying data type.< p >
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< h5 > Syntax:< / h5 >
< pre >
[< # elements> x < elementtype> ]
< / pre >
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The number of elements is a constant integer value, elementtype may be any type
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with a size.< p >
< h5 > Examples:< / h5 >
< ul >
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< tt > [40 x int ]< / tt > : Array of 40 integer values.< br >
< tt > [41 x int ]< / tt > : Array of 41 integer values.< br >
< tt > [40 x uint]< / tt > : Array of 40 unsigned integer values.< p >
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< / ul >
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Here are some examples of multidimensional arrays:< p >
< ul >
< table border = 0 cellpadding = 0 cellspacing = 0 >
< tr > < td > < tt > [3 x [4 x int]]< / tt > < / td > < td > : 3x4 array integer values.< / td > < / tr >
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< tr > < td > < tt > [12 x [10 x float]]< / tt > < / td > < td > : 12x10 array of single precision floating point values.< / td > < / tr >
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< tr > < td > < tt > [2 x [3 x [4 x uint]]]< / tt > < / td > < td > : 2x3x4 array of unsigned integer values.< / td > < / tr >
< / table >
< / ul >
<!-- _______________________________________________________________________ -->
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< / ul > < a name = "t_function" > < h4 > < hr size = 0 > Function Type< / h4 > < ul >
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< h5 > Overview:< / h5 >
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The function type can be thought of as a function signature. It consists of a
return type and a list of formal parameter types. Function types are usually
used when to build virtual function tables (which are structures of pointers to
functions), for indirect function calls, and when defining a function.< p >
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< h5 > Syntax:< / h5 >
< pre >
< returntype> (< parameter list> )
< / pre >
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Where '< tt > < parameter list> < / tt > ' is a comma-separated list of type
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specifiers. Optionally, the parameter list may include a type < tt > ...< / tt > ,
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which indicates that the function takes a variable number of arguments.
Variable argument functions can access their arguments with the < a
href="#int_varargs">variable argument handling intrinsic< / a > functions.
< p >
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< h5 > Examples:< / h5 >
< ul >
< table border = 0 cellpadding = 0 cellspacing = 0 >
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< tr > < td > < tt > int (int)< / tt > < / td > < td > : function taking an < tt > int< / tt > , returning
an < tt > int< / tt > < / td > < / tr >
< tr > < td > < tt > float (int, int *) *< / tt > < / td > < td > : < a href = "#t_pointer" > Pointer< / a >
to a function that takes an < tt > int< / tt > and a < a href = "#t_pointer" > pointer< / a >
to < tt > int< / tt > , returning < tt > float< / tt > .< / td > < / tr >
< tr > < td > < tt > int (sbyte *, ...)< / tt > < / td > < td > : A vararg function that takes at
least one < a href = "#t_pointer" > pointer< / a > to < tt > sbyte< / tt > (signed char in C),
which returns an integer. This is the signature for < tt > printf< / tt > in
LLVM.< / td > < / tr >
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< / table >
< / ul >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "t_struct" > < h4 > < hr size = 0 > Structure Type< / h4 > < ul >
< h5 > Overview:< / h5 >
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The structure type is used to represent a collection of data members together in
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memory. The packing of the field types is defined to match the ABI of the
underlying processor. The elements of a structure may be any type that has a
size.< p >
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Structures are accessed using '< tt > < a href = "#i_load" > load< / a > < / tt > and '< tt > < a
href="#i_store">store< / a > < / tt > ' by getting a pointer to a field with the '< tt > < a
href="#i_getelementptr">getelementptr< / a > < / tt > ' instruction.< p >
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< h5 > Syntax:< / h5 >
< pre >
{ < type list> }
< / pre >
< h5 > Examples:< / h5 >
< table border = 0 cellpadding = 0 cellspacing = 0 >
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< tr > < td > < tt > { int, int, int }< / tt > < / td > < td > : a triple of three < tt > int< / tt >
values< / td > < / tr >
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< tr > < td > < tt > { float, int (int) * }< / tt > < / td > < td > : A pair, where the first
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element is a < tt > float< / tt > and the second element is a < a
href="#t_pointer">pointer< / a > to a < a href = "t_function" > function< / a > that takes
an < tt > int< / tt > , returning an < tt > int< / tt > .< / td > < / tr >
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< / table >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "t_pointer" > < h4 > < hr size = 0 > Pointer Type< / h4 > < ul >
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< h5 > Overview:< / h5 >
As in many languages, the pointer type represents a pointer or reference to
another object, which must live in memory.< p >
< h5 > Syntax:< / h5 >
< pre >
< type> *
< / pre >
< h5 > Examples:< / h5 >
< table border = 0 cellpadding = 0 cellspacing = 0 >
< tr > < td > < tt > [4x int]*< / tt > < / td > < td > : < a href = "#t_pointer" > pointer< / a > to < a
href="#t_array">array< / a > of four < tt > int< / tt > values< / td > < / tr >
< tr > < td > < tt > int (int *) *< / tt > < / td > < td > : A < a href = "#t_pointer" > pointer< / a > to a
< a href = "t_function" > function< / a > that takes an < tt > int< / tt > , returning an
< tt > int< / tt > .< / td > < / tr >
< / table >
< p >
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<!-- _______________________________________________________________________ -->
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<!--
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< / ul > < a name = "t_packed" > < h4 > < hr size = 0 > Packed Type< / h4 > < ul >
Mention/decide that packed types work with saturation or not. Maybe have a packed+saturated type in addition to just a packed type.< p >
Packed types should be 'nonsaturated' because standard data types are not saturated. Maybe have a saturated packed type?< p >
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-->
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<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "highlevel" > High Level Structure
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "modulestructure" > Module Structure
< / b > < / font > < / td > < / tr > < / table > < ul >
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LLVM programs are composed of "Module"s, each of which is a translation unit of
the input programs. Each module consists of functions, global variables, and
symbol table entries. Modules may be combined together with the LLVM linker,
which merges function (and global variable) definitions, resolves forward
declarations, and merges symbol table entries. Here is an example of the "hello world" module:< p >
< pre >
< i > ; Declare the string constant as a global constant...< / i >
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< a href = "#identifiers" > %.LC0< / a > = < a href = "#linkage_internal" > internal< / a > < a href = "#globalvars" > constant< / a > < a href = "#t_array" > [13 x sbyte]< / a > c"hello world\0A\00" < i > ; [13 x sbyte]*< / i >
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< i > ; External declaration of the puts function< / i >
< a href = "#functionstructure" > declare< / a > int %puts(sbyte*) < i > ; int(sbyte*)* < / i >
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< i > ; Definition of main function< / i >
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int %main() { < i > ; int()* < / i >
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< i > ; Convert [13x sbyte]* to sbyte *...< / i >
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%cast210 = < a href = "#i_getelementptr" > getelementptr< / a > [13 x sbyte]* %.LC0, long 0, long 0 < i > ; sbyte*< / i >
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< i > ; Call puts function to write out the string to stdout...< / i >
< a href = "#i_call" > call< / a > int %puts(sbyte* %cast210) < i > ; int< / i >
< a href = "#i_ret" > ret< / a > int 0
}
< / pre >
This example is made up of a < a href = "#globalvars" > global variable< / a > named
"< tt > .LC0< / tt > ", an external declaration of the "< tt > puts< / tt > " function, and a
< a href = "#functionstructure" > function definition< / a > for "< tt > main< / tt > ".< p >
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< a name = "linkage" >
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In general, a module is made up of a list of global values, where both functions
and global variables are global values. Global values are represented by a
pointer to a memory location (in this case, a pointer to an array of char, and a
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pointer to a function), and have one of the following linkage types:< p >
< dl >
< a name = "linkage_internal" >
< dt > < tt > < b > internal< / b > < / tt >
< dd > Global values with internal linkage are only directly accessible by objects
in the current module. In particular, linking code into a module with an
internal global value may cause the internal to be renamed as necessary to avoid
collisions. Because the symbol is internal to the module, all references can be
updated. This corresponds to the notion of the '< tt > static< / tt > ' keyword in C,
or the idea of "anonymous namespaces" in C++.< p >
< a name = "linkage_linkonce" >
< dt > < tt > < b > linkonce< / b > < / tt > :
< dd > "< tt > linkonce< / tt > " linkage is similar to < tt > internal< / tt > linkage, with
the twist that linking together two modules defining the same < tt > linkonce< / tt >
globals will cause one of the globals to be discarded. This is typically used
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to implement inline functions. Unreferenced < tt > linkonce< / tt > globals are
allowed to be discarded.< p >
< a name = "linkage_weak" >
< dt > < tt > < b > weak< / b > < / tt > :
< dd > "< tt > weak< / tt > " linkage is exactly the same as < tt > linkonce< / tt > linkage,
except that unreferenced < tt > weak< / tt > globals may not be discarded. This is
used to implement constructs in C such as "< tt > int X;< / tt > " at global scope.< p >
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< a name = "linkage_appending" >
< dt > < tt > < b > appending< / b > < / tt > :
< dd > "< tt > appending< / tt > " linkage may only applied to global variables of pointer
to array type. When two global variables with appending linkage are linked
together, the two global arrays are appended together. This is the LLVM,
typesafe, equivalent of having the system linker append together "sections" with
identical names when .o files are linked.< p >
< a name = "linkage_external" >
< dt > < tt > < b > externally visible< / b > < / tt > :
< dd > If none of the above identifiers are used, the global is externally visible,
meaning that it participates in linkage and can be used to resolve external
symbol references.< p >
< / dl > < p >
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For example, since the "< tt > .LC0< / tt > " variable is defined to be internal, if
another module defined a "< tt > .LC0< / tt > " variable and was linked with this one,
one of the two would be renamed, preventing a collision. Since "< tt > main< / tt > "
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and "< tt > puts< / tt > " are external (i.e., lacking any linkage declarations), they
are accessible outside of the current module. It is illegal for a function
< i > declaration< / i > to have any linkage type other than "externally visible".< p >
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<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
< a name = "globalvars" > Global Variables
< / b > < / font > < / td > < / tr > < / table > < ul >
Global variables define regions of memory allocated at compilation time instead
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of run-time. Global variables may optionally be initialized. A variable may
be defined as a global "constant", which indicates that the contents of the
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variable will never be modified (opening options for optimization). Constants
must always have an initial value.< p >
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As SSA values, global variables define pointer values that are in scope
(i.e. they dominate) for all basic blocks in the program. Global variables
always define a pointer to their "content" type because they describe a region
of memory, and all memory objects in LLVM are accessed through pointers.< p >
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<!-- ======================================================================= -->
< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "functionstructure" > Functions
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< / b > < / font > < / td > < / tr > < / table > < ul >
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LLVM functions definitions are composed of a (possibly empty) argument list, an
opening curly brace, a list of basic blocks, and a closing curly brace. LLVM
function declarations are defined with the "< tt > declare< / tt > " keyword, a
function name and a function signature.< p >
A function definition contains a list of basic blocks, forming the CFG for the
function. Each basic block may optionally start with a label (giving the basic
block a symbol table entry), contains a list of instructions, and ends with a < a
href="#terminators">terminator< / a > instruction (such as a branch or function
return).< p >
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The first basic block in program is special in two ways: it is immediately
executed on entrance to the function, and it is not allowed to have predecessor
basic blocks (i.e. there can not be any branches to the entry block of a
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function). Because the block can have no predecessors, it also cannot have any
< a href = "#i_phi" > PHI nodes< / a > .< p >
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<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "instref" > Instruction Reference
< / b > < / font > < / td > < / tr > < / table > < ul >
<!-- *********************************************************************** -->
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The LLVM instruction set consists of several different classifications of
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instructions: < a href = "#terminators" > terminator instructions< / a > , < a
href="#binaryops">binary instructions< / a > , < a href = "#memoryops" > memory
instructions< / a > , and < a href = "#otherops" > other instructions< / a > .< p >
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<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "terminators" > Terminator Instructions
< / b > < / font > < / td > < / tr > < / table > < ul >
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As mentioned < a href = "#functionstructure" > previously< / a > , every basic block in a
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program ends with a "Terminator" instruction, which indicates which block should
be executed after the current block is finished. These terminator instructions
typically yield a '< tt > void< / tt > ' value: they produce control flow, not values
(the one exception being the '< a href = "#i_invoke" > < tt > invoke< / tt > < / a > '
instruction).< p >
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There are five different terminator instructions: the '< a
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href="#i_ret">< tt > ret< / tt > < / a > ' instruction, the '< a
href="#i_br">< tt > br< / tt > < / a > ' instruction, the '< a
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href="#i_switch">< tt > switch< / tt > < / a > ' instruction, the '< a
href="#i_invoke">< tt > invoke< / tt > < / a > ' instruction, and the '< a
href="#i_unwind">< tt > unwind< / tt > < / a > ' instruction.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_ret" > < h4 > < hr size = 0 > '< tt > ret< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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ret < type> < value> < i > ; Return a value from a non-void function< / i >
ret void < i > ; Return from void function< / i >
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > ret< / tt > ' instruction is used to return control flow (and a value) from
a function, back to the caller.< p >
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There are two forms of the '< tt > ret< / tt > ' instructruction: one that returns a
value and then causes control flow, and one that just causes control flow to
occur.< p >
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< h5 > Arguments:< / h5 >
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The '< tt > ret< / tt > ' instruction may return any '< a href = "#t_firstclass" > first
class< / a > ' type. Notice that a function is not < a href = "#wellformed" > well
formed< / a > if there exists a '< tt > ret< / tt > ' instruction inside of the function
that returns a value that does not match the return type of the function.< p >
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< h5 > Semantics:< / h5 >
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When the '< tt > ret< / tt > ' instruction is executed, control flow returns back to
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the calling function's context. If the caller is a "< a
href="#i_call">< tt > call< / tt > < / a > instruction, execution continues at the
instruction after the call. If the caller was an "< a
href="#i_invoke">< tt > invoke< / tt > < / a > " instruction, execution continues at the
beginning "normal" of the destination block. If the instruction returns a
value, that value shall set the call or invoke instruction's return value.< p >
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< h5 > Example:< / h5 >
< pre >
ret int 5 < i > ; Return an integer value of 5< / i >
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ret void < i > ; Return from a void function< / i >
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< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_br" > < h4 > < hr size = 0 > '< tt > br< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
br bool < cond> , label < iftrue> , label < iffalse>
br label < dest> < i > ; Unconditional branch< / i >
< / pre >
< h5 > Overview:< / h5 >
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The '< tt > br< / tt > ' instruction is used to cause control flow to transfer to a
different basic block in the current function. There are two forms of this
instruction, corresponding to a conditional branch and an unconditional
branch.< p >
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< h5 > Arguments:< / h5 >
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The conditional branch form of the '< tt > br< / tt > ' instruction takes a single
'< tt > bool< / tt > ' value and two '< tt > label< / tt > ' values. The unconditional form
of the '< tt > br< / tt > ' instruction takes a single '< tt > label< / tt > ' value as a
target.< p >
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< h5 > Semantics:< / h5 >
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Upon execution of a conditional '< tt > br< / tt > ' instruction, the '< tt > bool< / tt > '
argument is evaluated. If the value is < tt > true< / tt > , control flows to the
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'< tt > iftrue< / tt > ' < tt > label< / tt > argument. If "cond" is < tt > false< / tt > ,
control flows to the '< tt > iffalse< / tt > ' < tt > label< / tt > argument.< p >
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< h5 > Example:< / h5 >
< pre >
Test:
%cond = < a href = "#i_setcc" > seteq< / a > int %a, %b
br bool %cond, label %IfEqual, label %IfUnequal
IfEqual:
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< a href = "#i_ret" > ret< / a > int 1
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IfUnequal:
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< a href = "#i_ret" > ret< / a > int 0
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< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_switch" > < h4 > < hr size = 0 > '< tt > switch< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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switch uint < value> , label < defaultdest> [ int < val> , label &dest> , ... ]
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > switch< / tt > ' instruction is used to transfer control flow to one of
several different places. It is a generalization of the '< tt > br< / tt > '
instruction, allowing a branch to occur to one of many possible destinations.< p >
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< h5 > Arguments:< / h5 >
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The '< tt > switch< / tt > ' instruction uses three parameters: a '< tt > uint< / tt > '
comparison value '< tt > value< / tt > ', a default '< tt > label< / tt > ' destination, and
an array of pairs of comparison value constants and '< tt > label< / tt > 's.< p >
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< h5 > Semantics:< / h5 >
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The < tt > switch< / tt > instruction specifies a table of values and destinations.
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When the '< tt > switch< / tt > ' instruction is executed, this table is searched for
the given value. If the value is found, the corresponding destination is
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branched to, otherwise the default value it transfered to.< p >
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< h5 > Implementation:< / h5 >
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Depending on properties of the target machine and the particular < tt > switch< / tt >
instruction, this instruction may be code generated as a series of chained
conditional branches, or with a lookup table.< p >
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< h5 > Example:< / h5 >
< pre >
< i > ; Emulate a conditional br instruction< / i >
%Val = < a href = "#i_cast" > cast< / a > bool %value to uint
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switch uint %Val, label %truedest [int 0, label %falsedest ]
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< i > ; Emulate an unconditional br instruction< / i >
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switch uint 0, label %dest [ ]
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< i > ; Implement a jump table:< / i >
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switch uint %val, label %otherwise [ int 0, label %onzero,
int 1, label %onone,
int 2, label %ontwo ]
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< / pre >
<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_invoke" > < h4 > < hr size = 0 > '< tt > invoke< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = invoke < ptr to function ty> %< function ptr val> (< function args> )
to label < normal label> except label < exception label>
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< / pre >
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< h5 > Overview:< / h5 >
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The '< tt > invoke< / tt > ' instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the
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'< tt > normal< / tt > ' < tt > label< / tt > label or the '< tt > exception< / tt > '
< tt > label< / tt > . If the callee function returns with the "< tt > < a
href="#i_ret">ret< / a > < / tt > " instruction, control flow will return to the
"normal" label. If the callee (or any indirect callees) returns with the "< a
href="#i_unwind">< tt > unwind< / tt > < / a > " instruction, control is interrupted, and
continued at the dynamically nearest "except" label.< p >
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< h5 > Arguments:< / h5 >
This instruction requires several arguments:< p >
< ol >
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< li > '< tt > ptr to function ty< / tt > ': shall be the signature of the pointer to
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function value being invoked. In most cases, this is a direct function
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invocation, but indirect < tt > invoke< / tt > s are just as possible, branching off
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an arbitrary pointer to function value.
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< li > '< tt > function ptr val< / tt > ': An LLVM value containing a pointer to a
function to be invoked.
< li > '< tt > function args< / tt > ': argument list whose types match the function
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signature argument types. If the function signature indicates the function
accepts a variable number of arguments, the extra arguments can be specified.
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< li > '< tt > normal label< / tt > ': the label reached when the called function executes
a '< tt > < a href = "#i_ret" > ret< / a > < / tt > ' instruction.
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< li > '< tt > exception label< / tt > ': the label reached when a callee returns with the
< a href = "#i_unwind" > < tt > unwind< / tt > < / a > instruction.
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< / ol >
< h5 > Semantics:< / h5 >
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This instruction is designed to operate as a standard '< tt > < a
href="#i_call">call< / a > < / tt > ' instruction in most regards. The primary
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difference is that it establishes an association with a label, which is used by the runtime library to unwind the stack.< p >
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This instruction is used in languages with destructors to ensure that proper
cleanup is performed in the case of either a < tt > longjmp< / tt > or a thrown
exception. Additionally, this is important for implementation of
'< tt > catch< / tt > ' clauses in high-level languages that support them.< p >
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< h5 > Example:< / h5 >
< pre >
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%retval = invoke int %Test(int 15)
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to label %Continue
except label %TestCleanup < i > ; {int}:retval set< / i >
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< / pre >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_unwind" > < h4 > < hr size = 0 > '< tt > unwind< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
unwind
< / pre >
< h5 > Overview:< / h5 >
The '< tt > unwind< / tt > ' instruction unwinds the stack, continuing control flow at
the first callee in the dynamic call stack which used an < a
href="#i_invoke">< tt > invoke< / tt > < / a > instruction to perform the call. This is
primarily used to implement exception handling.
< h5 > Semantics:< / h5 >
The '< tt > unwind< / tt > ' intrinsic causes execution of the current function to
immediately halt. The dynamic call stack is then searched for the first < a
href="#i_invoke">< tt > invoke< / tt > < / a > instruction on the call stack. Once found,
execution continues at the "exceptional" destination block specified by the
< tt > invoke< / tt > instruction. If there is no < tt > invoke< / tt > instruction in the
dynamic call chain, undefined behavior results.
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<!-- ======================================================================= -->
< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 > < tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
< a name = "binaryops" > Binary Operations
< / b > < / font > < / td > < / tr > < / table > < ul >
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Binary operators are used to do most of the computation in a program. They
require two operands, execute an operation on them, and produce a single value.
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The result value of a binary operator is not necessarily the same type as its
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operands.< p >
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There are several different binary operators:< p >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_add" > < h4 > < hr size = 0 > '< tt > add< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = add < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > add< / tt > ' instruction returns the sum of its two operands.< p >
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > add< / tt > ' instruction must be either < a href = "#t_integer" > integer< / a > or < a href = "#t_floating" > floating point< / a > values. Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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The value produced is the integer or floating point sum of the two operands.< p >
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< h5 > Example:< / h5 >
< pre >
< result> = add int 4, %var < i > ; yields {int}:result = 4 + %var< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_sub" > < h4 > < hr size = 0 > '< tt > sub< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = sub < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
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The '< tt > sub< / tt > ' instruction returns the difference of its two operands.< p >
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Note that the '< tt > sub< / tt > ' instruction is used to represent the '< tt > neg< / tt > '
instruction present in most other intermediate representations.< p >
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< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > sub< / tt > ' instruction must be either < a
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href="#t_integer">integer< / a > or < a href = "#t_floating" > floating point< / a >
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values. Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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The value produced is the integer or floating point difference of the two
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operands.< p >
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< h5 > Example:< / h5 >
< pre >
< result> = sub int 4, %var < i > ; yields {int}:result = 4 - %var< / i >
< result> = sub int 0, %val < i > ; yields {int}:result = -%var< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_mul" > < h4 > < hr size = 0 > '< tt > mul< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = mul < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > mul< / tt > ' instruction returns the product of its two operands.< p >
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > mul< / tt > ' instruction must be either < a href = "#t_integer" > integer< / a > or < a href = "#t_floating" > floating point< / a > values. Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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The value produced is the integer or floating point product of the two
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operands.< p >
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There is no signed vs unsigned multiplication. The appropriate action is taken
based on the type of the operand. < p >
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< h5 > Example:< / h5 >
< pre >
< result> = mul int 4, %var < i > ; yields {int}:result = 4 * %var< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_div" > < h4 > < hr size = 0 > '< tt > div< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = div < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
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The '< tt > div< / tt > ' instruction returns the quotient of its two operands.< p >
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > div< / tt > ' instruction must be either < a
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href="#t_integer">integer< / a > or < a href = "#t_floating" > floating point< / a >
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values. Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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The value produced is the integer or floating point quotient of the two
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operands.< p >
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< h5 > Example:< / h5 >
< pre >
< result> = div int 4, %var < i > ; yields {int}:result = 4 / %var< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_rem" > < h4 > < hr size = 0 > '< tt > rem< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = rem < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > rem< / tt > ' instruction returns the remainder from the division of its two operands.< p >
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > rem< / tt > ' instruction must be either < a href = "#t_integer" > integer< / a > or < a href = "#t_floating" > floating point< / a > values. Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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This returns the < i > remainder< / i > of a division (where the result has the same
sign as the divisor), not the < i > modulus< / i > (where the result has the same sign
as the dividend) of a value. For more information about the difference, see: < a
href="http://mathforum.org/dr.math/problems/anne.4.28.99.html">The Math
Forum< / a > .< p >
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< h5 > Example:< / h5 >
< pre >
< result> = rem int 4, %var < i > ; yields {int}:result = 4 % %var< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_setcc" > < h4 > < hr size = 0 > '< tt > set< i > cc< / i > < / tt > ' Instructions< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = seteq < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< result> = setne < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< result> = setlt < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< result> = setgt < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< result> = setle < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< result> = setge < ty> < var1> , < var2> < i > ; yields {bool}:result< / i >
< / pre >
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< h5 > Overview:< / h5 > The '< tt > set< i > cc< / i > < / tt > ' family of instructions returns a
boolean value based on a comparison of their two operands.< p >
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< h5 > Arguments:< / h5 > The two arguments to the '< tt > set< i > cc< / i > < / tt > '
instructions must be of < a href = "#t_firstclass" > first class< / a > or < a
href="#t_pointer">pointer< / a > type (it is not possible to compare
'< tt > label< / tt > 's, '< tt > array< / tt > 's, '< tt > structure< / tt > ' or '< tt > void< / tt > '
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values, etc...). Both arguments must have identical types.< p >
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< h5 > Semantics:< / h5 >
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The '< tt > seteq< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
both operands are equal.< br >
The '< tt > setne< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
both operands are unequal.< br >
The '< tt > setlt< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
the first operand is less than the second operand.< br >
The '< tt > setgt< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
the first operand is greater than the second operand.< br >
The '< tt > setle< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
the first operand is less than or equal to the second operand.< br >
The '< tt > setge< / tt > ' instruction yields a < tt > true< / tt > '< tt > bool< / tt > ' value if
the first operand is greater than or equal to the second operand.< p >
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< h5 > Example:< / h5 >
< pre >
< result> = seteq int 4, 5 < i > ; yields {bool}:result = false< / i >
< result> = setne float 4, 5 < i > ; yields {bool}:result = true< / i >
< result> = setlt uint 4, 5 < i > ; yields {bool}:result = true< / i >
< result> = setgt sbyte 4, 5 < i > ; yields {bool}:result = false< / i >
< result> = setle sbyte 4, 5 < i > ; yields {bool}:result = true< / i >
< result> = setge sbyte 4, 5 < i > ; yields {bool}:result = false< / i >
< / pre >
<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "bitwiseops" > Bitwise Binary Operations
< / b > < / font > < / td > < / tr > < / table > < ul >
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Bitwise binary operators are used to do various forms of bit-twiddling in a
program. They are generally very efficient instructions, and can commonly be
strength reduced from other instructions. They require two operands, execute an
operation on them, and produce a single value. The resulting value of the
bitwise binary operators is always the same type as its first operand.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_and" > < h4 > < hr size = 0 > '< tt > and< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = and < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > and< / tt > ' instruction returns the bitwise logical and of its two operands.< p >
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > and< / tt > ' instruction must be < a
href="#t_integral">integral< / a > values. Both arguments must have identical
types.< p >
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< h5 > Semantics:< / h5 >
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The truth table used for the '< tt > and< / tt > ' instruction is:< p >
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< center > < table border = 1 cellspacing = 0 cellpadding = 4 >
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< tr > < td > In0< / td > < td > In1< / td > < td > Out< / td > < / tr >
< tr > < td > 0< / td > < td > 0< / td > < td > 0< / td > < / tr >
< tr > < td > 0< / td > < td > 1< / td > < td > 0< / td > < / tr >
< tr > < td > 1< / td > < td > 0< / td > < td > 0< / td > < / tr >
< tr > < td > 1< / td > < td > 1< / td > < td > 1< / td > < / tr >
< / table > < / center > < p >
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< h5 > Example:< / h5 >
< pre >
< result> = and int 4, %var < i > ; yields {int}:result = 4 & %var< / i >
< result> = and int 15, 40 < i > ; yields {int}:result = 8< / i >
< result> = and int 4, 8 < i > ; yields {int}:result = 0< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_or" > < h4 > < hr size = 0 > '< tt > or< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = or < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
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< h5 > Overview:< / h5 > The '< tt > or< / tt > ' instruction returns the bitwise logical
inclusive or of its two operands.< p >
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< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > or< / tt > ' instruction must be < a
href="#t_integral">integral< / a > values. Both arguments must have identical
types.< p >
2001-06-06 22:29:01 +02:00
< h5 > Semantics:< / h5 >
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The truth table used for the '< tt > or< / tt > ' instruction is:< p >
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< center > < table border = 1 cellspacing = 0 cellpadding = 4 >
2002-06-25 20:03:17 +02:00
< tr > < td > In0< / td > < td > In1< / td > < td > Out< / td > < / tr >
< tr > < td > 0< / td > < td > 0< / td > < td > 0< / td > < / tr >
< tr > < td > 0< / td > < td > 1< / td > < td > 1< / td > < / tr >
< tr > < td > 1< / td > < td > 0< / td > < td > 1< / td > < / tr >
< tr > < td > 1< / td > < td > 1< / td > < td > 1< / td > < / tr >
< / table > < / center > < p >
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< h5 > Example:< / h5 >
< pre >
< result> = or int 4, %var < i > ; yields {int}:result = 4 | %var< / i >
< result> = or int 15, 40 < i > ; yields {int}:result = 47< / i >
< result> = or int 4, 8 < i > ; yields {int}:result = 12< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_xor" > < h4 > < hr size = 0 > '< tt > xor< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = xor < ty> < var1> , < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
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The '< tt > xor< / tt > ' instruction returns the bitwise logical exclusive or of its
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two operands. The < tt > xor< / tt > is used to implement the "one's complement"
operation, which is the "~" operator in C.< p >
2001-06-06 22:29:01 +02:00
< h5 > Arguments:< / h5 >
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The two arguments to the '< tt > xor< / tt > ' instruction must be < a
href="#t_integral">integral< / a > values. Both arguments must have identical
types.< p >
2001-06-06 22:29:01 +02:00
< h5 > Semantics:< / h5 >
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The truth table used for the '< tt > xor< / tt > ' instruction is:< p >
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< center > < table border = 1 cellspacing = 0 cellpadding = 4 >
2002-06-25 20:03:17 +02:00
< tr > < td > In0< / td > < td > In1< / td > < td > Out< / td > < / tr >
< tr > < td > 0< / td > < td > 0< / td > < td > 0< / td > < / tr >
< tr > < td > 0< / td > < td > 1< / td > < td > 1< / td > < / tr >
< tr > < td > 1< / td > < td > 0< / td > < td > 1< / td > < / tr >
< tr > < td > 1< / td > < td > 1< / td > < td > 0< / td > < / tr >
< / table > < / center > < p >
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< h5 > Example:< / h5 >
< pre >
< result> = xor int 4, %var < i > ; yields {int}:result = 4 ^ %var< / i >
< result> = xor int 15, 40 < i > ; yields {int}:result = 39< / i >
< result> = xor int 4, 8 < i > ; yields {int}:result = 12< / i >
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< result> = xor int %V, -1 < i > ; yields {int}:result = ~%V< / i >
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< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_shl" > < h4 > < hr size = 0 > '< tt > shl< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = shl < ty> < var1> , ubyte < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
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The '< tt > shl< / tt > ' instruction returns the first operand shifted to the left a
specified number of bits.
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< h5 > Arguments:< / h5 >
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The first argument to the '< tt > shl< / tt > ' instruction must be an < a
2002-09-03 02:52:52 +02:00
href="#t_integer">integer< / a > type. The second argument must be an
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'< tt > ubyte< / tt > ' type.< p >
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< h5 > Semantics:< / h5 >
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The value produced is < tt > var1< / tt > * 2< sup > < tt > var2< / tt > < / sup > .< p >
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< h5 > Example:< / h5 >
< pre >
< result> = shl int 4, ubyte %var < i > ; yields {int}:result = 4 < < %var< / i >
< result> = shl int 4, ubyte 2 < i > ; yields {int}:result = 16< / i >
< result> = shl int 1, ubyte 10 < i > ; yields {int}:result = 1024< / i >
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_shr" > < h4 > < hr size = 0 > '< tt > shr< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< result> = shr < ty> < var1> , ubyte < var2> < i > ; yields {ty}:result< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > shr< / tt > ' instruction returns the first operand shifted to the right a specified number of bits.
< h5 > Arguments:< / h5 >
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The first argument to the '< tt > shr< / tt > ' instruction must be an < a href = "#t_integer" > integer< / a > type. The second argument must be an '< tt > ubyte< / tt > ' type.< p >
2001-06-06 22:29:01 +02:00
< h5 > Semantics:< / h5 >
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If the first argument is a < a href = "#t_signed" > signed< / a > type, the most
significant bit is duplicated in the newly free'd bit positions. If the first
argument is unsigned, zero bits shall fill the empty positions.< p >
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< h5 > Example:< / h5 >
< pre >
< result> = shr int 4, ubyte %var < i > ; yields {int}:result = 4 >> %var< / i >
2003-06-18 23:30:51 +02:00
< result> = shr uint 4, ubyte 1 < i > ; yields {uint}:result = 2< / i >
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< result> = shr int 4, ubyte 2 < i > ; yields {int}:result = 1< / i >
2003-06-18 23:30:51 +02:00
< result> = shr sbyte 4, ubyte 3 < i > ; yields {sbyte}:result = 0< / i >
< result> = shr sbyte -2, ubyte 1 < i > ; yields {sbyte}:result = -1< / i >
2001-06-06 22:29:01 +02:00
< / pre >
<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "memoryops" > Memory Access Operations
< / b > < / font > < / td > < / tr > < / table > < ul >
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A key design point of an SSA-based representation is how it represents memory.
In LLVM, no memory locations are in SSA form, which makes things very simple.
This section describes how to read, write, allocate and free memory in LLVM.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_malloc" > < h4 > < hr size = 0 > '< tt > malloc< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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< result> = malloc < type> , uint < NumElements> < i > ; yields {type*}:result< / i >
< result> = malloc < type> < i > ; yields {type*}:result< / i >
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< / pre >
< h5 > Overview:< / h5 >
The '< tt > malloc< / tt > ' instruction allocates memory from the system heap and returns a pointer to it.< p >
< h5 > Arguments:< / h5 >
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The the '< tt > malloc< / tt > ' instruction allocates
< tt > sizeof(< type> )*NumElements< / tt > bytes of memory from the operating
system, and returns a pointer of the appropriate type to the program. The
second form of the instruction is a shorter version of the first instruction
that defaults to allocating one element.< p >
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'< tt > type< / tt > ' must be a sized type.< p >
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< h5 > Semantics:< / h5 >
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Memory is allocated using the system "< tt > malloc< / tt > " function, and a pointer
is returned.< p >
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< h5 > Example:< / h5 >
< pre >
%array = malloc [4 x ubyte ] < i > ; yields {[%4 x ubyte]*}:array< / i >
%size = < a href = "#i_add" > add< / a > uint 2, 2 < i > ; yields {uint}:size = uint 4< / i >
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%array1 = malloc ubyte, uint 4 < i > ; yields {ubyte*}:array1< / i >
%array2 = malloc [12 x ubyte], uint %size < i > ; yields {[12 x ubyte]*}:array2< / i >
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< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_free" > < h4 > < hr size = 0 > '< tt > free< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
free < type> < value> < i > ; yields {void}< / i >
< / pre >
< h5 > Overview:< / h5 >
The '< tt > free< / tt > ' instruction returns memory back to the unused memory heap, to be reallocated in the future.< p >
< h5 > Arguments:< / h5 >
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'< tt > value< / tt > ' shall be a pointer value that points to a value that was
allocated with the '< tt > < a href = "#i_malloc" > malloc< / a > < / tt > ' instruction.< p >
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< h5 > Semantics:< / h5 >
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Access to the memory pointed to by the pointer is not longer defined after this instruction executes.< p >
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< h5 > Example:< / h5 >
< pre >
%array = < a href = "#i_malloc" > malloc< / a > [4 x ubyte] < i > ; yields {[4 x ubyte]*}:array< / i >
free [4 x ubyte]* %array
< / pre >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_alloca" > < h4 > < hr size = 0 > '< tt > alloca< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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< result> = alloca < type> , uint < NumElements> < i > ; yields {type*}:result< / i >
< result> = alloca < type> < i > ; yields {type*}:result< / i >
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > alloca< / tt > ' instruction allocates memory on the current stack frame of
the procedure that is live until the current function returns to its caller.< p >
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< h5 > Arguments:< / h5 >
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The the '< tt > alloca< / tt > ' instruction allocates
< tt > sizeof(< type> )*NumElements< / tt > bytes of memory on the runtime stack,
returning a pointer of the appropriate type to the program. The second form of
the instruction is a shorter version of the first that defaults to allocating
one element.< p >
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'< tt > type< / tt > ' may be any sized type.< p >
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< h5 > Semantics:< / h5 >
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Memory is allocated, a pointer is returned. '< tt > alloca< / tt > 'd memory is
automatically released when the function returns. The '< tt > alloca< / tt > '
instruction is commonly used to represent automatic variables that must have an
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address available. When the function returns (either with the < tt > < a
href="#i_ret">ret< / a > < / tt > or < tt > < a href = "#i_invoke" > invoke< / a > < / tt >
instructions), the memory is reclaimed.< p >
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< h5 > Example:< / h5 >
< pre >
%ptr = alloca int < i > ; yields {int*}:ptr< / i >
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%ptr = alloca int, uint 4 < i > ; yields {int*}:ptr< / i >
< / pre >
<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_load" > < h4 > < hr size = 0 > '< tt > load< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = load < ty> * < pointer>
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< result> = volatile load < ty> * < pointer>
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > load< / tt > ' instruction is used to read from memory.< p >
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< h5 > Arguments:< / h5 >
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The argument to the '< tt > load< / tt > ' instruction specifies the memory address to
load from. The pointer must point to a < a href = "t_firstclass" > first class< / a >
type. If the < tt > load< / tt > is marked as < tt > volatile< / tt > then the optimizer is
not allowed to modify the number or order of execution of this < tt > load< / tt >
with other volatile < tt > load< / tt > and < tt > < a href = "#i_store" > store< / a > < / tt >
instructions. < p >
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< h5 > Semantics:< / h5 >
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The location of memory pointed to is loaded.
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< h5 > Examples:< / h5 >
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< pre >
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%ptr = < a href = "#i_alloca" > alloca< / a > int < i > ; yields {int*}:ptr< / i >
< a href = "#i_store" > store< / a > int 3, int* %ptr < i > ; yields {void}< / i >
%val = load int* %ptr < i > ; yields {int}:val = int 3< / i >
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< / pre >
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<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_store" > < h4 > < hr size = 0 > '< tt > store< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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store < ty> < value> , < ty> * < pointer> < i > ; yields {void}< / i >
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volatile store < ty> < value> , < ty> * < pointer> < i > ; yields {void}< / i >
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > store< / tt > ' instruction is used to write to memory.< p >
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< h5 > Arguments:< / h5 >
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There are two arguments to the '< tt > store< / tt > ' instruction: a value to store
and an address to store it into. The type of the '< tt > < pointer> < / tt > '
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operand must be a pointer to the type of the '< tt > < value> < / tt > ' operand.
If the < tt > store< / tt > is marked as < tt > volatile< / tt > then the optimizer is not
allowed to modify the number or order of execution of this < tt > store< / tt > with
other volatile < tt > load< / tt > and < tt > < a href = "#i_store" > store< / a > < / tt >
instructions.< p >
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< h5 > Semantics:< / h5 > The contents of memory are updated to contain
'< tt > < value> < / tt > ' at the location specified by the
'< tt > < pointer> < / tt > ' operand.< p >
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< h5 > Example:< / h5 >
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< pre >
%ptr = < a href = "#i_alloca" > alloca< / a > int < i > ; yields {int*}:ptr< / i >
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< a href = "#i_store" > store< / a > int 3, int* %ptr < i > ; yields {void}< / i >
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%val = load int* %ptr < i > ; yields {int}:val = int 3< / i >
< / pre >
<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_getelementptr" > < h4 > < hr size = 0 > '< tt > getelementptr< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = getelementptr < ty> * < ptrval> {, long < aidx> |, ubyte < sidx> }*
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > getelementptr< / tt > ' instruction is used to get the address of a
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subelement of an aggregate data structure.< p >
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< h5 > Arguments:< / h5 >
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This instruction takes a list of < tt > long< / tt > values and < tt > ubyte< / tt >
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constants that indicate what form of addressing to perform. The actual types of
the arguments provided depend on the type of the first pointer argument. The
'< tt > getelementptr< / tt > ' instruction is used to index down through the type
levels of a structure.< p >
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For example, lets consider a C code fragment and how it gets compiled to
LLVM:< p >
< pre >
struct RT {
char A;
int B[10][20];
char C;
};
struct ST {
int X;
double Y;
struct RT Z;
};
int *foo(struct ST *s) {
return & s[1].Z.B[5][13];
}
< / pre >
The LLVM code generated by the GCC frontend is:
< pre >
%RT = type { sbyte, [10 x [20 x int]], sbyte }
%ST = type { int, double, %RT }
int* "foo"(%ST* %s) {
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%reg = getelementptr %ST* %s, long 1, ubyte 2, ubyte 1, long 5, long 13
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ret int* %reg
}
< / pre >
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< h5 > Semantics:< / h5 >
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The index types specified for the '< tt > getelementptr< / tt > ' instruction depend on
the pointer type that is being index into. < a href = "t_pointer" > Pointer< / a > and
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< a href = "t_array" > array< / a > types require '< tt > long< / tt > ' values, and < a
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href="t_struct">structure< / a > types require '< tt > ubyte< / tt > '
< b > constants< / b > .< p >
In the example above, the first index is indexing into the '< tt > %ST*< / tt > ' type,
which is a pointer, yielding a '< tt > %ST< / tt > ' = '< tt > { int, double, %RT }< / tt > '
type, a structure. The second index indexes into the third element of the
structure, yielding a '< tt > %RT< / tt > ' = '< tt > { sbyte, [10 x [20 x int]], sbyte
}< / tt > ' type, another structure. The third index indexes into the second
element of the structure, yielding a '< tt > [10 x [20 x int]]< / tt > ' type, an
array. The two dimensions of the array are subscripted into, yielding an
'< tt > int< / tt > ' type. The '< tt > getelementptr< / tt > ' instruction return a pointer
to this element, thus yielding a '< tt > int*< / tt > ' type.< p >
Note that it is perfectly legal to index partially through a structure,
returning a pointer to an inner element. Because of this, the LLVM code for the
given testcase is equivalent to:< p >
< pre >
int* "foo"(%ST* %s) {
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%t1 = getelementptr %ST* %s , long 1 < i > ; yields %ST*:%t1< / i >
%t2 = getelementptr %ST* %t1, long 0, ubyte 2 < i > ; yields %RT*:%t2< / i >
%t3 = getelementptr %RT* %t2, long 0, ubyte 1 < i > ; yields [10 x [20 x int]]*:%t3< / i >
%t4 = getelementptr [10 x [20 x int]]* %t3, long 0, long 5 < i > ; yields [20 x int]*:%t4< / i >
%t5 = getelementptr [20 x int]* %t4, long 0, long 13 < i > ; yields int*:%t5< / i >
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ret int* %t5
}
< / pre >
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< h5 > Example:< / h5 >
< pre >
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< i > ; yields [12 x ubyte]*:aptr< / i >
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%aptr = getelementptr {int, [12 x ubyte]}* %sptr, long 0, ubyte 1
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< / pre >
<!-- ======================================================================= -->
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< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
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< a name = "otherops" > Other Operations
< / b > < / font > < / td > < / tr > < / table > < ul >
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The instructions in this catagory are the "miscellaneous" instructions, which defy better classification.< p >
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<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_phi" > < h4 > < hr size = 0 > '< tt > phi< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = phi < ty> [ < val0> , < label0> ], ...
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > phi< / tt > ' instruction is used to implement the φ node in the SSA
graph representing the function.< p >
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< h5 > Arguments:< / h5 >
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The type of the incoming values are specified with the first type field. After
this, the '< tt > phi< / tt > ' instruction takes a list of pairs as arguments, with
one pair for each predecessor basic block of the current block.< p >
There must be no non-phi instructions between the start of a basic block and the
PHI instructions: i.e. PHI instructions must be first in a basic block.< p >
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< h5 > Semantics:< / h5 >
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At runtime, the '< tt > phi< / tt > ' instruction logically takes on the value
specified by the parameter, depending on which basic block we came from in the
last < a href = "#terminators" > terminator< / a > instruction.< p >
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< h5 > Example:< / h5 >
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< pre >
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Loop: ; Infinite loop that counts from 0 on up...
%indvar = phi uint [ 0, %LoopHeader ], [ %nextindvar, %Loop ]
%nextindvar = add uint %indvar, 1
br label %Loop
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< / pre >
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<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_cast" > < h4 > < hr size = 0 > '< tt > cast .. to< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = cast < ty> < value> to < ty2> < i > ; yields ty2< / i >
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > cast< / tt > ' instruction is used as the primitive means to convert
integers to floating point, change data type sizes, and break type safety (by
casting pointers).< p >
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< h5 > Arguments:< / h5 >
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The '< tt > cast< / tt > ' instruction takes a value to cast, which must be a first
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class value, and a type to cast it to, which must also be a first class type.< p >
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< h5 > Semantics:< / h5 >
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This instruction follows the C rules for explicit casts when determining how the
data being cast must change to fit in its new container.< p >
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When casting to bool, any value that would be considered true in the context of
a C '< tt > if< / tt > ' condition is converted to the boolean '< tt > true< / tt > ' values,
all else are '< tt > false< / tt > '.< p >
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When extending an integral value from a type of one signness to another (for
example '< tt > sbyte< / tt > ' to '< tt > ulong< / tt > '), the value is sign-extended if the
< b > source< / b > value is signed, and zero-extended if the source value is
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unsigned. < tt > bool< / tt > values are always zero extended into either zero or
one.< p >
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< h5 > Example:< / h5 >
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< pre >
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%X = cast int 257 to ubyte < i > ; yields ubyte:1< / i >
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%Y = cast int 123 to bool < i > ; yields bool:true< / i >
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< / pre >
<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_call" > < h4 > < hr size = 0 > '< tt > call< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< result> = call < ty> * < fnptrval> (< param list> )
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > call< / tt > ' instruction represents a simple function call.< p >
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< h5 > Arguments:< / h5 >
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This instruction requires several arguments:< p >
< ol >
< li > '< tt > ty< / tt > ': shall be the signature of the pointer to function value being
invoked. The argument types must match the types implied by this signature.< p >
< li > '< tt > fnptrval< / tt > ': An LLVM value containing a pointer to a function to be
invoked. In most cases, this is a direct function invocation, but indirect
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< tt > call< / tt > s are just as possible, calling an arbitrary pointer to function
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values.< p >
< li > '< tt > function args< / tt > ': argument list whose types match the function
signature argument types. If the function signature indicates the function
accepts a variable number of arguments, the extra arguments can be specified.
< / ol >
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< h5 > Semantics:< / h5 >
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The '< tt > call< / tt > ' instruction is used to cause control flow to transfer to a
specified function, with its incoming arguments bound to the specified values.
Upon a '< tt > < a href = "#i_ret" > ret< / a > < / tt > ' instruction in the called function,
control flow continues with the instruction after the function call, and the
return value of the function is bound to the result argument. This is a simpler
case of the < a href = "#i_invoke" > invoke< / a > instruction.< p >
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< h5 > Example:< / h5 >
< pre >
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%retval = call int %test(int %argc)
call int(sbyte*, ...) *%printf(sbyte* %msg, int 12, sbyte 42);
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< / pre >
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<!-- _______________________________________________________________________ -->
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< / ul > < a name = "i_vanext" > < h4 > < hr size = 0 > '< tt > vanext< / tt > ' Instruction< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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< resultarglist> = vanext < va_list> < arglist> , < argty>
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > vanext< / tt > ' instruction is used to access arguments passed through
the "variable argument" area of a function call. It is used to implement the
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< tt > va_arg< / tt > macro in C.< p >
< h5 > Arguments:< / h5 >
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This instruction takes a < tt > valist< / tt > value and the type of the argument. It
returns another < tt > valist< / tt > .
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< h5 > Semantics:< / h5 >
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The '< tt > vanext< / tt > ' instruction advances the specified < tt > valist< / tt > past
an argument of the specified type. In conjunction with the < a
href="#i_vaarg">< tt > vaarg< / tt > < / a > instruction, it is used to implement the
< tt > va_arg< / tt > macro available in C. For more information, see the variable
argument handling < a href = "#int_varargs" > Intrinsic Functions< / a > .< p >
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It is legal for this instruction to be called in a function which does not take
a variable number of arguments, for example, the < tt > vfprintf< / tt > function.< p >
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< tt > vanext< / tt > is an LLVM instruction instead of an < a
href="#intrinsics">intrinsic function< / a > because it takes an type as an
argument.< / p >
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< h5 > Example:< / h5 >
See the < a href = "#int_varargs" > variable argument processing< / a > section.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_vaarg" > < h4 > < hr size = 0 > '< tt > vaarg< / tt > ' Instruction< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
< resultval> = vaarg < va_list> < arglist> , < argty>
< / pre >
< h5 > Overview:< / h5 >
The '< tt > vaarg< / tt > ' instruction is used to access arguments passed through
the "variable argument" area of a function call. It is used to implement the
< tt > va_arg< / tt > macro in C.< p >
< h5 > Arguments:< / h5 >
This instruction takes a < tt > valist< / tt > value and the type of the argument. It
returns a value of the specified argument type.
< h5 > Semantics:< / h5 >
The '< tt > vaarg< / tt > ' instruction loads an argument of the specified type from
the specified < tt > va_list< / tt > . In conjunction with the < a
href="#i_vanext">< tt > vanext< / tt > < / a > instruction, it is used to implement the
< tt > va_arg< / tt > macro available in C. For more information, see the variable
argument handling < a href = "#int_varargs" > Intrinsic Functions< / a > .< p >
It is legal for this instruction to be called in a function which does not take
a variable number of arguments, for example, the < tt > vfprintf< / tt > function.< p >
< tt > vaarg< / tt > is an LLVM instruction instead of an < a
href="#intrinsics">intrinsic function< / a > because it takes an type as an
argument.< / p >
< h5 > Example:< / h5 >
See the < a href = "#int_varargs" > variable argument processing< / a > section.< p >
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<!-- *********************************************************************** -->
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< / ul > < table width = "100%" bgcolor = "#330077" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td align = center > < font color = "#EEEEFF" size = +2 face = "Georgia,Palatino" > < b >
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< a name = "intrinsics" > Intrinsic Functions
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< / b > < / font > < / td > < / tr > < / table > < ul >
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<!-- *********************************************************************** -->
LLVM supports the notion of an "intrinsic function". These functions have well
known names and semantics, and are required to follow certain restrictions.
Overall, these instructions represent an extension mechanism for the LLVM
language that does not require changing all of the transformations in LLVM to
add to the language (or the bytecode reader/writer, the parser, etc...).< p >
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Intrinsic function names must all start with an "< tt > llvm.< / tt > " prefix, this
prefix is reserved in LLVM for intrinsic names, thus functions may not be named
this. Intrinsic functions must always be external functions: you cannot define
the body of intrinsic functions. Intrinsic functions may only be used in call
or invoke instructions: it is illegal to take the address of an intrinsic
function. Additionally, because intrinsic functions are part of the LLVM
language, it is required that they all be documented here if any are added.< p >
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Unless an intrinsic function is target-specific, there must be a lowering pass
to eliminate the intrinsic or all backends must support the intrinsic
function.< p >
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<!-- ======================================================================= -->
< / ul > < table width = "100%" bgcolor = "#441188" border = 0 cellpadding = 4 cellspacing = 0 >
< tr > < td > < / td > < td width = "100%" > < font color = "#EEEEFF" face = "Georgia,Palatino" > < b >
< a name = "int_varargs" > Variable Argument Handling Intrinsics
< / b > < / font > < / td > < / tr > < / table > < ul >
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Variable argument support is defined in LLVM with the < a
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href="#i_vanext">< tt > vanext< / tt > < / a > instruction and these three intrinsic
functions. These functions are related to the similarly named macros defined in
the < tt > < stdarg.h> < / tt > header file.< p >
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All of these functions operate on arguments that use a target-specific value
type "< tt > va_list< / tt > ". The LLVM assembly language reference manual does not
define what this type is, so all transformations should be prepared to handle
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intrinsics with any type used.< p >
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This example shows how the < a href = "#i_vanext" > < tt > vanext< / tt > < / a > instruction
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and the variable argument handling intrinsic functions are used.< p >
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< pre >
int %test(int %X, ...) {
; Initialize variable argument processing
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%ap = call sbyte*()* %< a href = "#i_va_start" > llvm.va_start< / a > ()
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; Read a single integer argument
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%tmp = vaarg sbyte* %ap, int
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; Advance to the next argument
%ap2 = vanext sbyte* %ap, int
; Demonstrate usage of llvm.va_copy and llvm.va_end
%aq = call sbyte* (sbyte*)* %< a href = "#i_va_copy" > llvm.va_copy< / a > (sbyte* %ap2)
call void %< a href = "#i_va_end" > llvm.va_end< / a > (sbyte* %aq)
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; Stop processing of arguments.
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call void %< a href = "#i_va_end" > llvm.va_end< / a > (sbyte* %ap2)
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ret int %tmp
}
< / pre >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_va_start" > < h4 > < hr size = 0 > '< tt > llvm.va_start< / tt > ' Intrinsic< / h4 > < ul >
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< h5 > Syntax:< / h5 >
< pre >
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call va_list ()* %llvm.va_start()
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< / pre >
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< h5 > Overview:< / h5 >
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The '< tt > llvm.va_start< / tt > ' intrinsic returns a new < tt > < arglist> < / tt >
for subsequent use by the variable argument intrinsics.< p >
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< h5 > Semantics:< / h5 >
The '< tt > llvm.va_start< / tt > ' intrinsic works just like the < tt > va_start< / tt >
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macro available in C. In a target-dependent way, it initializes and returns a
< tt > va_list< / tt > element, so that the next < tt > vaarg< / tt > will produce the first
variable argument passed to the function. Unlike the C < tt > va_start< / tt > macro,
this intrinsic does not need to know the last argument of the function, the
compiler can figure that out.< p >
Note that this intrinsic function is only legal to be called from within the
body of a variable argument function.< p >
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<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_va_end" > < h4 > < hr size = 0 > '< tt > llvm.va_end< / tt > ' Intrinsic< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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call void (va_list)* %llvm.va_end(va_list < arglist> )
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< / pre >
< h5 > Overview:< / h5 >
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The '< tt > llvm.va_end< / tt > ' intrinsic destroys < tt > < arglist> < / tt > which has
been initialized previously with < tt > < a
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href="#i_va_start">llvm.va_start< / a > < / tt > or < tt > < a
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href="#i_va_copy">llvm.va_copy< / a > < / tt > .< p >
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< h5 > Arguments:< / h5 >
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The argument is a < tt > va_list< / tt > to destroy.< p >
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< h5 > Semantics:< / h5 >
The '< tt > llvm.va_end< / tt > ' intrinsic works just like the < tt > va_end< / tt > macro
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available in C. In a target-dependent way, it destroys the < tt > va_list< / tt > .
Calls to < a href = "#i_va_start" > < tt > llvm.va_start< / tt > < / a > and < a
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href="#i_va_copy">< tt > llvm.va_copy< / tt > < / a > must be matched exactly with calls
to < tt > llvm.va_end< / tt > .< p >
<!-- _______________________________________________________________________ -->
< / ul > < a name = "i_va_copy" > < h4 > < hr size = 0 > '< tt > llvm.va_copy< / tt > ' Intrinsic< / h4 > < ul >
< h5 > Syntax:< / h5 >
< pre >
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call va_list (va_list)* %llvm.va_copy(va_list < destarglist> )
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< / pre >
< h5 > Overview:< / h5 >
The '< tt > llvm.va_copy< / tt > ' intrinsic copies the current argument position from
the source argument list to the destination argument list.< p >
< h5 > Arguments:< / h5 >
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The argument is the < tt > va_list< / tt > to copy.
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< h5 > Semantics:< / h5 >
The '< tt > llvm.va_copy< / tt > ' intrinsic works just like the < tt > va_copy< / tt > macro
available in C. In a target-dependent way, it copies the source
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< tt > va_list< / tt > element into the returned list. This intrinsic is necessary
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because the < tt > < a href = "i_va_start" > llvm.va_start< / a > < / tt > intrinsic may be
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arbitrarily complex and require memory allocation, for example.< p >
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<!-- *********************************************************************** -->
< / ul >
<!-- *********************************************************************** -->
< hr >
< font size = -1 >
< address > < a href = "mailto:sabre@nondot.org" > Chris Lattner< / a > < / address >
<!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
<!-- hhmts start -->
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Last modified: Tue Oct 21 10:43:36 CDT 2003
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<!-- hhmts end -->
< / font >
< / body > < / html >
