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Re-factor TableGen docs

Browse Source 
This is mainly a movement of content around to give place to new content
allowing different people to add bits to it in the right place. There is some
new content, but mostly to fill the gaps left by text movement.

I'm dropping the old syntax documentation as it has the problem of being
quickly outdated by changes and largely unnecessary to people not involved
in creating the language, but using it, which is the whole point of the
documentation.

llvm-svn: 204351
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=================
TableGen BackEnds
=================
.. contents::
:local:
Introduction
============
TableGen backends are at the core of TableGen's functionality. The source files
provide the semantics to a generated (in memory) structure, but it's up to the
backend to print this out in a way that is meaningful to the user (normally a
C program including a file or a textual list of warnings, options and error
messages).
TableGen is used by both LLVM and Clang with very different goals. LLVM uses it
as a way to automate the generation of massive amounts of information regarding
instructions, schedules, cores and architecture features. Some backends generate
output that is consumed by more than one source file, so they need to be created
in a way that is easy to use pre-processor tricks. Some backends can also print
C code structures, so that they can be directly included as-is.
Clang, on the other hand, uses it mainly for diagnostic messages (errors,
warnings, tips) and attributes, so more on the textual end of the scale.
LLVM BackEnds
=============
.. warning::
This document is raw. Each section below needs three sub-sections: description
of its purpose with a list of users, output generated from generic input, and
finally why it needed a new backend (in case there's something similar).
Emitter
-------
Generate machine code emitter.
RegisterInfo
------------
Generate registers and register classes info.
InstrInfo
---------
Generate instruction descriptions.
AsmWriter
---------
Generate calling convention descriptions.
AsmMatcher
----------
Generate assembly writer.
Disassembler
------------
Generate disassembler.
PseudoLowering
--------------
Generate pseudo instruction lowering.
CallingConv
-----------
Generate assembly instruction matcher.
DAGISel
-------
Generate a DAG instruction selector.
DFAPacketizer
-------------
Generate DFA Packetizer for VLIW targets.
FastISel
--------
Generate a "fast" instruction selector.
Subtarget
---------
Generate subtarget enumerations.
Intrinsic
---------
Generate intrinsic information.
TgtIntrinsic
------------
Generate target intrinsic information.
OptParserDefs
-------------
Print enum values for a class.
CTags
-----
Generate ctags-compatible index.
Clang BackEnds
==============
ClangAttrClasses
----------------
Generate clang attribute clases.
ClangAttrParserStringSwitches
-----------------------------
Generate all parser-related attribute string switches.
ClangAttrImpl
-------------
Generate clang attribute implementations.
ClangAttrList
-------------
Generate a clang attribute list.
ClangAttrPCHRead
----------------
Generate clang PCH attribute reader.
ClangAttrPCHWrite
-----------------
Generate clang PCH attribute writer.
ClangAttrSpellingList
---------------------
Generate a clang attribute spelling list.
ClangAttrSpellingListIndex
--------------------------
Generate a clang attribute spelling index.
ClangAttrASTVisitor
-------------------
Generate a recursive AST visitor for clang attribute.
ClangAttrTemplateInstantiate
----------------------------
Generate a clang template instantiate code.
ClangAttrParsedAttrList
-----------------------
Generate a clang parsed attribute list.
ClangAttrParsedAttrImpl
-----------------------
Generate the clang parsed attribute helpers.
ClangAttrParsedAttrKinds
------------------------
Generate a clang parsed attribute kinds.
ClangAttrDump
-------------
Generate clang attribute dumper.
ClangDiagsDefs
--------------
Generate Clang diagnostics definitions.
ClangDiagGroups
---------------
Generate Clang diagnostic groups.
ClangDiagsIndexName
-------------------
Generate Clang diagnostic name index.
ClangCommentNodes
-----------------
Generate Clang AST comment nodes.
ClangDeclNodes
--------------
Generate Clang AST declaration nodes.
ClangStmtNodes
--------------
Generate Clang AST statement nodes.
ClangSACheckers
---------------
Generate Clang Static Analyzer checkers.
ClangCommentHTMLTags
--------------------
Generate efficient matchers for HTML tag names that are used in documentation comments.
ClangCommentHTMLTagsProperties
------------------------------
Generate efficient matchers for HTML tag properties.
ClangCommentHTMLNamedCharacterReferences
----------------------------------------
Generate function to translate named character references to UTF-8 sequences.
ClangCommentCommandInfo
-----------------------
Generate command properties for commands that are used in documentation comments.
ClangCommentCommandList
-----------------------
Generate list of commands that are used in documentation comments.
ArmNeon
-------
Generate arm_neon.h for clang.
ArmNeonSema
-----------
Generate ARM NEON sema support for clang.
ArmNeonTest
-----------
Generate ARM NEON tests for clang.
AttrDocs
--------
Generate attribute documentation.
How to write a back-end
=======================
TODO.
Until we get a step-by-step HowTo for writing TableGen backends, you can at
least grab the boilerplate (build system, new files, etc.) from Clang's
r173931.
TODO: How they work, how to write one. This section should not contain details
about any particular backend, except maybe ``-print-enums`` as an example. This
should highlight the APIs in ``TableGen/Record.h``.

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=====================
TableGen Deficiencies
=====================
.. contents::
:local:
Introduction
============
Despite being very generic, TableGen has some deficiencies that have been
pointed out numerous times. The common theme is that, while TableGen allows
you to build Domain-Specific-Languages, the final languages that you create
lack the power of other DSLs, which in turn increase considerably the size
and complexity of TableGen files.
At the same time, TableGen allows you to create virtually any meaning of
the basic concepts via custom-made back-ends, which can pervert the original
design and make it very hard for newcomers to understand it.
There are some in favour of extending the semantics even more, but making sure
back-ends adhere to strict rules. Others suggesting we should move to more
powerful DSLs designed with specific purposes, or even re-using existing
DSLs.
Known Problems
==============
TODO: Add here frequently asked questions about why TableGen doesn't do
what you want, how it might, and how we could extend/restrict it to
be more use friendly.

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TableGen Language Reference
===========================
.. sectionauthor:: Sean Silva <silvas@purdue.edu>
.. contents::
:local:
@ -18,369 +16,587 @@ This document is meant to be a normative spec about the TableGen language
in and of itself (i.e. how to understand a given construct in terms of how
it affects the final set of records represented by the TableGen file). If
you are unsure if this document is really what you are looking for, please
read :doc:`/TableGenFundamentals` first.
read :doc:`the introduction <index>` first.
Notation
========
TableGen syntax
===============
The lexical and syntax notation used here is intended to imitate
`Python's`_. In particular, for lexical definitions, the productions
operate at the character level and there is no implied whitespace between
elements. The syntax definitions operate at the token level, so there is
implied whitespace between tokens.
TableGen doesn't care about the meaning of data (that is up to the backend to
define), but it does care about syntax, and it enforces a simple type system.
This section describes the syntax and the constructs allowed in a TableGen file.
.. _`Python's`: http://docs.python.org/py3k/reference/introduction.html#notation
TableGen primitives
-------------------
Lexical Analysis
================
TableGen comments
^^^^^^^^^^^^^^^^^
TableGen supports BCPL (``// ...``) and nestable C-style (``/* ... */``)
comments.
TableGen supports C++ style "``//``" comments, which run to the end of the
line, and it also supports **nestable** "``/* */``" comments.
The following is a listing of the basic punctuation tokens::
.. _TableGen type:
- + [ ] { } ( ) < > : ; . = ? #
The TableGen type system
^^^^^^^^^^^^^^^^^^^^^^^^
Numeric literals take one of the following forms:
TableGen files are strongly typed, in a simple (but complete) type-system.
These types are used to perform automatic conversions, check for errors, and to
help interface designers constrain the input that they allow. Every `value
definition`_ is required to have an associated type.
.. TableGen actually will lex some pretty strange sequences an interpret
them as numbers. What is shown here is an attempt to approximate what it
"should" accept.
TableGen supports a mixture of very low-level types (such as ``bit``) and very
high-level types (such as ``dag``). This flexibility is what allows it to
describe a wide range of information conveniently and compactly. The TableGen
types are:
.. productionlist::
TokInteger: `DecimalInteger` | `HexInteger` | `BinInteger`
DecimalInteger: ["+" | "-"] ("0"..."9")+
HexInteger: "0x" ("0"..."9" | "a"..."f" | "A"..."F")+
BinInteger: "0b" ("0" | "1")+
``bit``
A 'bit' is a boolean value that can hold either 0 or 1.
One aspect to note is that the :token:`DecimalInteger` token *includes* the
``+`` or ``-``, as opposed to having ``+`` and ``-`` be unary operators as
most languages do.
``int``
The 'int' type represents a simple 32-bit integer value, such as 5.
TableGen has identifier-like tokens:
``string``
The 'string' type represents an ordered sequence of characters of arbitrary
length.
.. productionlist::
ualpha: "a"..."z" | "A"..."Z" | "_"
TokIdentifier: ("0"..."9")* `ualpha` (`ualpha` | "0"..."9")*
TokVarName: "$" `ualpha` (`ualpha` | "0"..."9")*
``bits<n>``
A 'bits' type is an arbitrary, but fixed, size integer that is broken up
into individual bits. This type is useful because it can handle some bits
being defined while others are undefined.
Note that unlike most languages, TableGen allows :token:`TokIdentifier` to
begin with a number. In case of ambiguity, a token will be interpreted as a
numeric literal rather than an identifier.
``list<ty>``
This type represents a list whose elements are some other type. The
contained type is arbitrary: it can even be another list type.
TableGen also has two string-like literals:
Class type
Specifying a class name in a type context means that the defined value must
be a subclass of the specified class. This is useful in conjunction with
the ``list`` type, for example, to constrain the elements of the list to a
common base class (e.g., a ``list<Register>`` can only contain definitions
derived from the "``Register``" class).
.. productionlist::
TokString: '"' <non-'"' characters and C-like escapes> '"'
TokCodeFragment: "[{" <shortest text not containing "}]"> "}]"
``dag``
This type represents a nestable directed graph of elements.
:token:`TokCodeFragment` is essentially a multiline string literal
delimited by ``[{`` and ``}]``.
To date, these types have been sufficient for describing things that TableGen
has been used for, but it is straight-forward to extend this list if needed.
.. note::
The current implementation accepts the following C-like escapes::
.. _TableGen expressions:
\\ \' \" \t \n
TableGen values and expressions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TableGen also has the following keywords::
TableGen allows for a pretty reasonable number of different expression forms
when building up values. These forms allow the TableGen file to be written in a
natural syntax and flavor for the application. The current expression forms
supported include:
bit bits class code dag
def foreach defm field in
int let list multiclass string
``?``
uninitialized field
TableGen also has "bang operators" which have a
wide variety of meanings:
``0b1001011``
binary integer value
.. productionlist::
BangOperator: one of
:!eq !if !head !tail !con
:!add !shl !sra !srl
:!cast !empty !subst !foreach !strconcat
``07654321``
octal integer value (indicated by a leading 0)
Syntax
======
``7``
decimal integer value
TableGen has an ``include`` mechanism. It does not play a role in the
syntax per se, since it is lexically replaced with the contents of the
included file.
``0x7F``
hexadecimal integer value
.. productionlist::
IncludeDirective: "include" `TokString`
``"foo"``
string value
TableGen's top-level production consists of "objects".
``[{ ... }]``
usually called a "code fragment", but is just a multiline string literal
.. productionlist::
TableGenFile: `Object`*
Object: `Class` | `Def` | `Defm` | `Let` | `MultiClass` | `Foreach`
``[ X, Y, Z ]<type>``
list value. <type> is the type of the list element and is usually optional.
In rare cases, TableGen is unable to deduce the element type in which case
the user must specify it explicitly.
``class``\es
------------
``{ a, b, c }``
initializer for a "bits<3>" value
.. productionlist::
Class: "class" `TokIdentifier` [`TemplateArgList`] `ObjectBody`
``value``
value reference
A ``class`` declaration creates a record which other records can inherit
from. A class can be parametrized by a list of "template arguments", whose
values can be used in the class body.
``value{17}``
access to one bit of a value
A given class can only be defined once. A ``class`` declaration is
considered to define the class if any of the following is true:
``value{15-17}``
access to multiple bits of a value
.. break ObjectBody into its consituents so that they are present here?
``DEF``
reference to a record definition
#. The :token:`TemplateArgList` is present.
#. The :token:`Body` in the :token:`ObjectBody` is present and is not empty.
#. The :token:`BaseClassList` in the :token:`ObjectBody` is present.
``CLASS<val list>``
reference to a new anonymous definition of CLASS with the specified template
arguments.
You can declare an empty class by giving and empty :token:`TemplateArgList`
and an empty :token:`ObjectBody`. This can serve as a restricted form of
forward declaration: note that records deriving from the forward-declared
class will inherit no fields from it since the record expansion is done
when the record is parsed.
``X.Y``
reference to the subfield of a value
.. productionlist::
TemplateArgList: "<" `Declaration` ("," `Declaration`)* ">"
``list[4-7,17,2-3]``
A slice of the 'list' list, including elements 4,5,6,7,17,2, and 3 from it.
Elements may be included multiple times.
Declarations
------------
``foreach <var> = [ <list> ] in { <body> }``
.. Omitting mention of arcane "field" prefix to discourage its use.
``foreach <var> = [ <list> ] in <def>``
Replicate <body> or <def>, replacing instances of <var> with each value
in <list>. <var> is scoped at the level of the ``foreach`` loop and must
not conflict with any other object introduced in <body> or <def>. Currently
only ``def``\s are expanded within <body>.
The declaration syntax is pretty much what you would expect as a C++
programmer.
``foreach <var> = 0-15 in ...``
.. productionlist::
Declaration: `Type` `TokIdentifier` ["=" `Value`]
``foreach <var> = {0-15,32-47} in ...``
Loop over ranges of integers. The braces are required for multiple ranges.
It assigns the value to the identifer.
``(DEF a, b)``
a dag value. The first element is required to be a record definition, the
remaining elements in the list may be arbitrary other values, including
nested ```dag``' values.
Types
-----
``!strconcat(a, b)``
A string value that is the result of concatenating the 'a' and 'b' strings.
.. productionlist::
Type: "string" | "code" | "bit" | "int" | "dag"
:| "bits" "<" `TokInteger` ">"
:| "list" "<" `Type` ">"
:| `ClassID`
ClassID: `TokIdentifier`
``str1#str2``
"#" (paste) is a shorthand for !strconcat. It may concatenate things that
are not quoted strings, in which case an implicit !cast<string> is done on
the operand of the paste.
Both ``string`` and ``code`` correspond to the string type; the difference
is purely to indicate programmer intention.
``!cast<type>(a)``
A symbol of type *type* obtained by looking up the string 'a' in the symbol
table. If the type of 'a' does not match *type*, TableGen aborts with an
error. !cast<string> is a special case in that the argument must be an
object defined by a 'def' construct.
The :token:`ClassID` must identify a class that has been previously
declared or defined.
``!subst(a, b, c)``
If 'a' and 'b' are of string type or are symbol references, substitute 'b'
for 'a' in 'c.' This operation is analogous to $(subst) in GNU make.
Values
------
``!foreach(a, b, c)``
For each member 'b' of dag or list 'a' apply operator 'c.' 'b' is a dummy
variable that should be declared as a member variable of an instantiated
class. This operation is analogous to $(foreach) in GNU make.
.. productionlist::
Value: `SimpleValue` `ValueSuffix`*
ValueSuffix: "{" `RangeList` "}"
:| "[" `RangeList` "]"
:| "." `TokIdentifier`
RangeList: `RangePiece` ("," `RangePiece`)*
RangePiece: `TokInteger`
:| `TokInteger` "-" `TokInteger`
:| `TokInteger` `TokInteger`
``!head(a)``
The first element of list 'a.'
The peculiar last form of :token:`RangePiece` is due to the fact that the
"``-``" is included in the :token:`TokInteger`, hence ``1-5`` gets lexed as
two consecutive :token:`TokInteger`'s, with values ``1`` and ``-5``,
instead of "1", "-", and "5".
The :token:`RangeList` can be thought of as specifying "list slice" in some
contexts.
``!tail(a)``
The 2nd-N elements of list 'a.'
``!empty(a)``
An integer {0,1} indicating whether list 'a' is empty.
:token:`SimpleValue` has a number of forms:
``!if(a,b,c)``
'b' if the result of 'int' or 'bit' operator 'a' is nonzero, 'c' otherwise.
``!eq(a,b)``
'bit 1' if string a is equal to string b, 0 otherwise. This only operates
on string, int and bit objects. Use !cast<string> to compare other types of
objects.
.. productionlist::
SimpleValue: `TokIdentifier`
Note that all of the values have rules specifying how they convert to values
for different types. These rules allow you to assign a value like "``7``"
to a "``bits<4>``" value, for example.
The value will be the variable referenced by the identifier. It can be one
of:
Classes and definitions
-----------------------
.. The code for this is exceptionally abstruse. These examples are a
best-effort attempt.
As mentioned in the :doc:`introduction <index>`, classes and definitions (collectively known as
'records') in TableGen are the main high-level unit of information that TableGen
collects. Records are defined with a ``def`` or ``class`` keyword, the record
name, and an optional list of "`template arguments`_". If the record has
superclasses, they are specified as a comma separated list that starts with a
colon character ("``:``"). If `value definitions`_ or `let expressions`_ are
needed for the class, they are enclosed in curly braces ("``{}``"); otherwise,
the record ends with a semicolon.
* name of a ``def``, such as the use of ``Bar`` in::
Here is a simple TableGen file:
def Bar : SomeClass {
int X = 5;
}
.. code-block:: llvm
def Foo {
SomeClass Baz = Bar;
}
class C { bit V = 1; }
def X : C;
def Y : C {
string Greeting = "hello";
}
This example defines two definitions, ``X`` and ``Y``, both of which derive from
the ``C`` class. Because of this, they both get the ``V`` bit value. The ``Y``
definition also gets the Greeting member as well.
In general, classes are useful for collecting together the commonality between a
group of records and isolating it in a single place. Also, classes permit the
specification of default values for their subclasses, allowing the subclasses to
override them as they wish.
* value local to a ``def``, such as the use of ``Bar`` in::
.. _value definition:
.. _value definitions:
Value definitions
^^^^^^^^^^^^^^^^^
Value definitions define named entries in records. A value must be defined
before it can be referred to as the operand for another value definition or
before the value is reset with a `let expression`_. A value is defined by
specifying a `TableGen type`_ and a name. If an initial value is available, it
may be specified after the type with an equal sign. Value definitions require
terminating semicolons.
.. _let expression:
.. _let expressions:
.. _"let" expressions within a record:
'let' expressions
^^^^^^^^^^^^^^^^^
A record-level let expression is used to change the value of a value definition
in a record. This is primarily useful when a superclass defines a value that a
derived class or definition wants to override. Let expressions consist of the
'``let``' keyword followed by a value name, an equal sign ("``=``"), and a new
value. For example, a new class could be added to the example above, redefining
the ``V`` field for all of its subclasses:
.. code-block:: llvm
class D : C { let V = 0; }
def Z : D;
In this case, the ``Z`` definition will have a zero value for its ``V`` value,
despite the fact that it derives (indirectly) from the ``C`` class, because the
``D`` class overrode its value.
.. _template arguments:
Class template arguments
^^^^^^^^^^^^^^^^^^^^^^^^
TableGen permits the definition of parameterized classes as well as normal
concrete classes. Parameterized TableGen classes specify a list of variable
bindings (which may optionally have defaults) that are bound when used. Here is
a simple example:
.. code-block:: llvm
class FPFormat<bits<3> val> {
bits<3> Value = val;
}
def NotFP : FPFormat<0>;
def ZeroArgFP : FPFormat<1>;
def OneArgFP : FPFormat<2>;
def OneArgFPRW : FPFormat<3>;
def TwoArgFP : FPFormat<4>;
def CompareFP : FPFormat<5>;
def CondMovFP : FPFormat<6>;
def SpecialFP : FPFormat<7>;
In this case, template arguments are used as a space efficient way to specify a
list of "enumeration values", each with a "``Value``" field set to the specified
integer.
The more esoteric forms of `TableGen expressions`_ are useful in conjunction
with template arguments. As an example:
.. code-block:: llvm
class ModRefVal<bits<2> val> {
bits<2> Value = val;
}
def None : ModRefVal<0>;
def Mod : ModRefVal<1>;
def Ref : ModRefVal<2>;
def ModRef : ModRefVal<3>;
class Value<ModRefVal MR> {
// Decode some information into a more convenient format, while providing
// a nice interface to the user of the "Value" class.
bit isMod = MR.Value{0};
bit isRef = MR.Value{1};
// other stuff...
}
// Example uses
def bork : Value<Mod>;
def zork : Value<Ref>;
def hork : Value<ModRef>;
This is obviously a contrived example, but it shows how template arguments can
be used to decouple the interface provided to the user of the class from the
actual internal data representation expected by the class. In this case,
running ``llvm-tblgen`` on the example prints the following definitions:
.. code-block:: llvm
def bork { // Value
bit isMod = 1;
bit isRef = 0;
}
def hork { // Value
bit isMod = 1;
bit isRef = 1;
}
def zork { // Value
bit isMod = 0;
bit isRef = 1;
}
This shows that TableGen was able to dig into the argument and extract a piece
of information that was requested by the designer of the "Value" class. For
more realistic examples, please see existing users of TableGen, such as the X86
backend.
Multiclass definitions and instances
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
While classes with template arguments are a good way to factor commonality
between two instances of a definition, multiclasses allow a convenient notation
for defining multiple definitions at once (instances of implicitly constructed
classes). For example, consider an 3-address instruction set whose instructions
come in two forms: "``reg = reg op reg``" and "``reg = reg op imm``"
(e.g. SPARC). In this case, you'd like to specify in one place that this
commonality exists, then in a separate place indicate what all the ops are.
Here is an example TableGen fragment that shows this idea:
.. code-block:: llvm
def ops;
def GPR;
def Imm;
class inst<int opc, string asmstr, dag operandlist>;
multiclass ri_inst<int opc, string asmstr> {
def _rr : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)>;
def _ri : inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)>;
}
// Instantiations of the ri_inst multiclass.
defm ADD : ri_inst<0b111, "add">;
defm SUB : ri_inst<0b101, "sub">;
defm MUL : ri_inst<0b100, "mul">;
...
The name of the resultant definitions has the multidef fragment names appended
to them, so this defines ``ADD_rr``, ``ADD_ri``, ``SUB_rr``, etc. A defm may
inherit from multiple multiclasses, instantiating definitions from each
multiclass. Using a multiclass this way is exactly equivalent to instantiating
the classes multiple times yourself, e.g. by writing:
.. code-block:: llvm
def ops;
def GPR;
def Imm;
class inst<int opc, string asmstr, dag operandlist>;
class rrinst<int opc, string asmstr>
: inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, GPR:$src2)>;
class riinst<int opc, string asmstr>
: inst<opc, !strconcat(asmstr, " $dst, $src1, $src2"),
(ops GPR:$dst, GPR:$src1, Imm:$src2)>;
// Instantiations of the ri_inst multiclass.
def ADD_rr : rrinst<0b111, "add">;
def ADD_ri : riinst<0b111, "add">;
def SUB_rr : rrinst<0b101, "sub">;
def SUB_ri : riinst<0b101, "sub">;
def MUL_rr : rrinst<0b100, "mul">;
def MUL_ri : riinst<0b100, "mul">;
...
A ``defm`` can also be used inside a multiclass providing several levels of
multiclass instantiations.
.. code-block:: llvm
class Instruction<bits<4> opc, string Name> {
bits<4> opcode = opc;
string name = Name;
}
multiclass basic_r<bits<4> opc> {
def rr : Instruction<opc, "rr">;
def rm : Instruction<opc, "rm">;
}
multiclass basic_s<bits<4> opc> {
defm SS : basic_r<opc>;
defm SD : basic_r<opc>;
def X : Instruction<opc, "x">;
}
multiclass basic_p<bits<4> opc> {
defm PS : basic_r<opc>;
defm PD : basic_r<opc>;
def Y : Instruction<opc, "y">;
}
defm ADD : basic_s<0xf>, basic_p<0xf>;
...
// Results
def ADDPDrm { ...
def ADDPDrr { ...
def ADDPSrm { ...
def ADDPSrr { ...
def ADDSDrm { ...
def ADDSDrr { ...
def ADDY { ...
def ADDX { ...
``defm`` declarations can inherit from classes too, the rule to follow is that
the class list must start after the last multiclass, and there must be at least
one multiclass before them.
.. code-block:: llvm
class XD { bits<4> Prefix = 11; }
class XS { bits<4> Prefix = 12; }
class I<bits<4> op> {
bits<4> opcode = op;
}
multiclass R {
def rr : I<4>;
def rm : I<2>;
}
multiclass Y {
defm SS : R, XD;
defm SD : R, XS;
}
defm Instr : Y;
// Results
def InstrSDrm {
bits<4> opcode = { 0, 0, 1, 0 };
bits<4> Prefix = { 1, 1, 0, 0 };
}
...
def InstrSSrr {
bits<4> opcode = { 0, 1, 0, 0 };
bits<4> Prefix = { 1, 0, 1, 1 };
}
File scope entities
-------------------
File inclusion
^^^^^^^^^^^^^^
TableGen supports the '``include``' token, which textually substitutes the
specified file in place of the include directive. The filename should be
specified as a double quoted string immediately after the '``include``' keyword.
Example:
.. code-block:: llvm
include "foo.td"
'let' expressions
^^^^^^^^^^^^^^^^^
"Let" expressions at file scope are similar to `"let" expressions within a
record`_, except they can specify a value binding for multiple records at a
time, and may be useful in certain other cases. File-scope let expressions are
really just another way that TableGen allows the end-user to factor out
commonality from the records.
File-scope "let" expressions take a comma-separated list of bindings to apply,
and one or more records to bind the values in. Here are some examples:
.. code-block:: llvm
let isTerminator = 1, isReturn = 1, isBarrier = 1, hasCtrlDep = 1 in
def RET : I<0xC3, RawFrm, (outs), (ins), "ret", [(X86retflag 0)]>;
let isCall = 1 in
// All calls clobber the non-callee saved registers...
let Defs = [EAX, ECX, EDX, FP0, FP1, FP2, FP3, FP4, FP5, FP6, ST0,
MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7, EFLAGS] in {
def CALLpcrel32 : Ii32<0xE8, RawFrm, (outs), (ins i32imm:$dst,variable_ops),
"call\t${dst:call}", []>;
def CALL32r : I<0xFF, MRM2r, (outs), (ins GR32:$dst, variable_ops),
"call\t{*}$dst", [(X86call GR32:$dst)]>;
def CALL32m : I<0xFF, MRM2m, (outs), (ins i32mem:$dst, variable_ops),
"call\t{*}$dst", []>;
}
File-scope "let" expressions are often useful when a couple of definitions need
to be added to several records, and the records do not otherwise need to be
opened, as in the case with the ``CALL*`` instructions above.
It's also possible to use "let" expressions inside multiclasses, providing more
ways to factor out commonality from the records, specially if using several
levels of multiclass instantiations. This also avoids the need of using "let"
expressions within subsequent records inside a multiclass.
def Foo {
int Bar = 5;
int Baz = Bar;
}
.. code-block:: llvm
multiclass basic_r<bits<4> opc> {
let Predicates = [HasSSE2] in {
def rr : Instruction<opc, "rr">;
def rm : Instruction<opc, "rm">;
}
let Predicates = [HasSSE3] in
def rx : Instruction<opc, "rx">;
}
* a template arg of a ``class``, such as the use of ``Bar`` in::
multiclass basic_ss<bits<4> opc> {
let IsDouble = 0 in
defm SS : basic_r<opc>;
class Foo<int Bar> {
int Baz = Bar;
}
let IsDouble = 1 in
defm SD : basic_r<opc>;
}
* value local to a ``multiclass``, such as the use of ``Bar`` in::
defm ADD : basic_ss<0xf>;
multiclass Foo {
int Bar = 5;
int Baz = Bar;
}
Looping
^^^^^^^
* a template arg to a ``multiclass``, such as the use of ``Bar`` in::
TableGen supports the '``foreach``' block, which textually replicates the loop
body, substituting iterator values for iterator references in the body.
Example:
multiclass Foo<int Bar> {
int Baz = Bar;
}
.. code-block:: llvm
.. productionlist::
SimpleValue: `TokInteger`
foreach i = [0, 1, 2, 3] in {
def R#i : Register<...>;
def F#i : Register<...>;
}
This represents the numeric value of the integer.
This will create objects ``R0``, ``R1``, ``R2`` and ``R3``. ``foreach`` blocks
may be nested. If there is only one item in the body the braces may be
elided:
.. productionlist::
SimpleValue: `TokString`+
.. code-block:: llvm
Multiple adjacent string literals are concatenated like in C/C++. The value
is the concatenation of the strings.
foreach i = [0, 1, 2, 3] in
def R#i : Register<...>;
.. productionlist::
SimpleValue: `TokCodeFragment`
Code Generator backend info
===========================
The value is the string value of the code fragment.
Expressions used by code generator to describe instructions and isel patterns:
.. productionlist::
SimpleValue: "?"
``(implicit a)``
an implicitly defined physical register. This tells the dag instruction
selection emitter the input pattern's extra definitions matches implicit
physical register definitions.
``?`` represents an "unset" initializer.
.. productionlist::
SimpleValue: "{" `ValueList` "}"
ValueList: [`ValueListNE`]
ValueListNE: `Value` ("," `Value`)*
This represents a sequence of bits, as would be used to initialize a
``bits<n>`` field (where ``n`` is the number of bits).
.. productionlist::
SimpleValue: `ClassID` "<" `ValueListNE` ">"
This generates a new anonymous record definition (as would be created by an
unnamed ``def`` inheriting from the given class with the given template
arguments) and the value is the value of that record definition.
.. productionlist::
SimpleValue: "[" `ValueList` "]" ["<" `Type` ">"]
A list initializer. The optional :token:`Type` can be used to indicate a
specific element type, otherwise the element type will be deduced from the
given values.
.. The initial `DagArg` of the dag must start with an identifier or
!cast, but this is more of an implementation detail and so for now just
leave it out.
.. productionlist::
SimpleValue: "(" `DagArg` `DagArgList` ")"
DagArgList: `DagArg` ("," `DagArg`)*
DagArg: `Value` [":" `TokVarName`] | `TokVarName`
The initial :token:`DagArg` is called the "operator" of the dag.
.. productionlist::
SimpleValue: `BangOperator` ["<" `Type` ">"] "(" `ValueListNE` ")"
Bodies
------
.. productionlist::
ObjectBody: `BaseClassList` `Body`
BaseClassList: [":" `BaseClassListNE`]
BaseClassListNE: `SubClassRef` ("," `SubClassRef`)*
SubClassRef: (`ClassID` | `MultiClassID`) ["<" `ValueList` ">"]
DefmID: `TokIdentifier`
The version with the :token:`MultiClassID` is only valid in the
:token:`BaseClassList` of a ``defm``.
The :token:`MultiClassID` should be the name of a ``multiclass``.
.. put this somewhere else
It is after parsing the base class list that the "let stack" is applied.
.. productionlist::
Body: ";" | "{" BodyList "}"
BodyList: BodyItem*
BodyItem: `Declaration` ";"
:| "let" `TokIdentifier` [`RangeList`] "=" `Value` ";"
The ``let`` form allows overriding the value of an inherited field.
``def``
-------
.. TODO::
There can be pastes in the names here, like ``#NAME#``. Look into that
and document it (it boils down to ParseIDValue with IDParseMode ==
ParseNameMode). ParseObjectName calls into the general ParseValue, with
the only different from "arbitrary expression parsing" being IDParseMode
== Mode.
.. productionlist::
Def: "def" `TokIdentifier` `ObjectBody`
Defines a record whose name is given by the :token:`TokIdentifier`. The
fields of the record are inherited from the base classes and defined in the
body.
Special handling occurs if this ``def`` appears inside a ``multiclass`` or
a ``foreach``.
``defm``
--------
.. productionlist::
Defm: "defm" `TokIdentifier` ":" `BaseClassListNE` ";"
Note that in the :token:`BaseClassList`, all of the ``multiclass``'s must
precede any ``class``'s that appear.
``foreach``
-----------
.. productionlist::
Foreach: "foreach" `Declaration` "in" "{" `Object`* "}"
:| "foreach" `Declaration` "in" `Object`
The value assigned to the variable in the declaration is iterated over and
the object or object list is reevaluated with the variable set at each
iterated value.
Top-Level ``let``
-----------------
.. productionlist::
Let: "let" `LetList` "in" "{" `Object`* "}"
:| "let" `LetList` "in" `Object`
LetList: `LetItem` ("," `LetItem`)*
LetItem: `TokIdentifier` [`RangeList`] "=" `Value`
This is effectively equivalent to ``let`` inside the body of a record
except that it applies to multiple records at a time. The bindings are
applied at the end of parsing the base classes of a record.
``multiclass``
--------------
.. productionlist::
MultiClass: "multiclass" `TokIdentifier` [`TemplateArgList`]
: [":" `BaseMultiClassList`] "{" `MultiClassObject`+ "}"
BaseMultiClassList: `MultiClassID` ("," `MultiClassID`)*
MultiClassID: `TokIdentifier`
MultiClassObject: `Def` | `Defm` | `Let` | `Foreach`

306
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@ -0,0 +1,306 @@
========
TableGen
========
.. contents::
:local:
.. toctree::
:hidden:
BackEnds
LangRef
Deficiencies
Introduction
============
TableGen's purpose is to help a human develop and maintain records of
domain-specific information. Because there may be a large number of these
records, it is specifically designed to allow writing flexible descriptions and
for common features of these records to be factored out. This reduces the
amount of duplication in the description, reduces the chance of error, and makes
it easier to structure domain specific information.
The core part of TableGen parses a file, instantiates the declarations, and
hands the result off to a domain-specific `backends`_ for processing.
The current major users of TableGen are :doc:`../CodeGenerator`
and the
`Clang diagnostics and attributes <http://clang.llvm.org/docs/UsersManual.html#controlling-errors-and-warnings>`_.
Note that if you work on TableGen much, and use emacs or vim, that you can find
an emacs "TableGen mode" and a vim language file in the ``llvm/utils/emacs`` and
``llvm/utils/vim`` directories of your LLVM distribution, respectively.
.. _intro:
The TableGen program
====================
TableGen files are interpreted by the TableGen program: `llvm-tblgen` available
on your build directory under `bin`. It is not installed in the system (or where
your sysroot is set to), since it has no use beyond LLVM's build process.
Running TableGen
----------------
TableGen runs just like any other LLVM tool. The first (optional) argument
specifies the file to read. If a filename is not specified, ``llvm-tblgen``
reads from standard input.
To be useful, one of the `backends`_ must be used. These backends are
selectable on the command line (type '``llvm-tblgen -help``' for a list). For
example, to get a list of all of the definitions that subclass a particular type
(which can be useful for building up an enum list of these records), use the
``-print-enums`` option:
.. code-block:: bash
$ llvm-tblgen X86.td -print-enums -class=Register
AH, AL, AX, BH, BL, BP, BPL, BX, CH, CL, CX, DH, DI, DIL, DL, DX, EAX, EBP, EBX,
ECX, EDI, EDX, EFLAGS, EIP, ESI, ESP, FP0, FP1, FP2, FP3, FP4, FP5, FP6, IP,
MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7, R10, R10B, R10D, R10W, R11, R11B, R11D,
R11W, R12, R12B, R12D, R12W, R13, R13B, R13D, R13W, R14, R14B, R14D, R14W, R15,
R15B, R15D, R15W, R8, R8B, R8D, R8W, R9, R9B, R9D, R9W, RAX, RBP, RBX, RCX, RDI,
RDX, RIP, RSI, RSP, SI, SIL, SP, SPL, ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
XMM0, XMM1, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, XMM2, XMM3, XMM4, XMM5,
XMM6, XMM7, XMM8, XMM9,
$ llvm-tblgen X86.td -print-enums -class=Instruction
ABS_F, ABS_Fp32, ABS_Fp64, ABS_Fp80, ADC32mi, ADC32mi8, ADC32mr, ADC32ri,
ADC32ri8, ADC32rm, ADC32rr, ADC64mi32, ADC64mi8, ADC64mr, ADC64ri32, ADC64ri8,
ADC64rm, ADC64rr, ADD16mi, ADD16mi8, ADD16mr, ADD16ri, ADD16ri8, ADD16rm,
ADD16rr, ADD32mi, ADD32mi8, ADD32mr, ADD32ri, ADD32ri8, ADD32rm, ADD32rr,
ADD64mi32, ADD64mi8, ADD64mr, ADD64ri32, ...
The default backend prints out all of the records.
If you plan to use TableGen, you will most likely have to write a `backend`_
that extracts the information specific to what you need and formats it in the
appropriate way.
Example
-------
With no other arguments, `llvm-tblgen` parses the specified file and prints out all
of the classes, then all of the definitions. This is a good way to see what the
various definitions expand to fully. Running this on the ``X86.td`` file prints
this (at the time of this writing):
.. code-block:: llvm
...
def ADD32rr { // Instruction X86Inst I
string Namespace = "X86";
dag OutOperandList = (outs GR32:$dst);
dag InOperandList = (ins GR32:$src1, GR32:$src2);
string AsmString = "add{l}\t{$src2, $dst|$dst, $src2}";
list<dag> Pattern = [(set GR32:$dst, (add GR32:$src1, GR32:$src2))];
list<Register> Uses = [];
list<Register> Defs = [EFLAGS];
list<Predicate> Predicates = [];
int CodeSize = 3;
int AddedComplexity = 0;
bit isReturn = 0;
bit isBranch = 0;
bit isIndirectBranch = 0;
bit isBarrier = 0;
bit isCall = 0;
bit canFoldAsLoad = 0;
bit mayLoad = 0;
bit mayStore = 0;
bit isImplicitDef = 0;
bit isConvertibleToThreeAddress = 1;
bit isCommutable = 1;
bit isTerminator = 0;
bit isReMaterializable = 0;
bit isPredicable = 0;
bit hasDelaySlot = 0;
bit usesCustomInserter = 0;
bit hasCtrlDep = 0;
bit isNotDuplicable = 0;
bit hasSideEffects = 0;
bit neverHasSideEffects = 0;
InstrItinClass Itinerary = NoItinerary;
string Constraints = "";
string DisableEncoding = "";
bits<8> Opcode = { 0, 0, 0, 0, 0, 0, 0, 1 };
Format Form = MRMDestReg;
bits<6> FormBits = { 0, 0, 0, 0, 1, 1 };
ImmType ImmT = NoImm;
bits<3> ImmTypeBits = { 0, 0, 0 };
bit hasOpSizePrefix = 0;
bit hasAdSizePrefix = 0;
bits<4> Prefix = { 0, 0, 0, 0 };
bit hasREX_WPrefix = 0;
FPFormat FPForm = ?;
bits<3> FPFormBits = { 0, 0, 0 };
}
...
This definition corresponds to the 32-bit register-register ``add`` instruction
of the x86 architecture. ``def ADD32rr`` defines a record named
``ADD32rr``, and the comment at the end of the line indicates the superclasses
of the definition. The body of the record contains all of the data that
TableGen assembled for the record, indicating that the instruction is part of
the "X86" namespace, the pattern indicating how the instruction should be
emitted into the assembly file, that it is a two-address instruction, has a
particular encoding, etc. The contents and semantics of the information in the
record are specific to the needs of the X86 backend, and are only shown as an
example.
As you can see, a lot of information is needed for every instruction supported
by the code generator, and specifying it all manually would be unmaintainable,
prone to bugs, and tiring to do in the first place. Because we are using
TableGen, all of the information was derived from the following definition:
.. code-block:: llvm
let Defs = [EFLAGS],
isCommutable = 1, // X = ADD Y,Z --> X = ADD Z,Y
isConvertibleToThreeAddress = 1 in // Can transform into LEA.
def ADD32rr : I<0x01, MRMDestReg, (outs GR32:$dst),
(ins GR32:$src1, GR32:$src2),
"add{l}\t{$src2, $dst|$dst, $src2}",
[(set GR32:$dst, (add GR32:$src1, GR32:$src2))]>;
This definition makes use of the custom class ``I`` (extended from the custom
class ``X86Inst``), which is defined in the X86-specific TableGen file, to
factor out the common features that instructions of its class share. A key
feature of TableGen is that it allows the end-user to define the abstractions
they prefer to use when describing their information.
Each ``def`` record has a special entry called "NAME". This is the name of the
record ("``ADD32rr``" above). In the general case ``def`` names can be formed
from various kinds of string processing expressions and ``NAME`` resolves to the
final value obtained after resolving all of those expressions. The user may
refer to ``NAME`` anywhere she desires to use the ultimate name of the ``def``.
``NAME`` should not be defined anywhere else in user code to avoid conflicts.
Syntax
======
TableGen has a syntax that is losely based on C++ templates, with built-in
types and specification. In addition, TableGen's syntax introduces some
automation concepts like multiclass, foreach, let, etc.
Basic concepts
--------------
TableGen files consist of two key parts: 'classes' and 'definitions', both of
which are considered 'records'.
**TableGen records** have a unique name, a list of values, and a list of
superclasses. The list of values is the main data that TableGen builds for each
record; it is this that holds the domain specific information for the
application. The interpretation of this data is left to a specific `backends`_,
but the structure and format rules are taken care of and are fixed by
TableGen.
**TableGen definitions** are the concrete form of 'records'. These generally do
not have any undefined values, and are marked with the '``def``' keyword.
.. code-block:: llvm
def FeatureFPARMv8 : SubtargetFeature<"fp-armv8", "HasFPARMv8", "true",
"Enable ARMv8 FP">;
In this example, FeatureFPARMv8 is ``SubtargetFeature`` record initialised
with some values. The names of the classes are defined via the
keyword `class` either on the same file or some other included. Most target
TableGen files include the generic ones in ``include/llvm/Target``.
**TableGen classes** are abstract records that are used to build and describe
other records. These classes allow the end-user to build abstractions for
either the domain they are targeting (such as "Register", "RegisterClass", and
"Instruction" in the LLVM code generator) or for the implementor to help factor
out common properties of records (such as "FPInst", which is used to represent
floating point instructions in the X86 backend). TableGen keeps track of all of
the classes that are used to build up a definition, so the backend can find all
definitions of a particular class, such as "Instruction".
.. code-block:: llvm
class ProcNoItin<string Name, list<SubtargetFeature> Features>
: Processor<Name, NoItineraries, Features>;
Here, the class ProcNoItin, receiving parameters `Name` of type `string` and
a list of target features is specializing the class Processor by passing the
arguments down as well as hard-coding NoItineraries.
**TableGen multiclasses** are groups of abstract records that are instantiated
all at once. Each instantiation can result in multiple TableGen definitions.
If a multiclass inherits from another multiclass, the definitions in the
sub-multiclass become part of the current multiclass, as if they were declared
in the current multiclass.
.. code-block:: llvm
multiclass ro_signed_pats<string T, string Rm, dag Base, dag Offset, dag Extend,
dag address, ValueType sty> {
def : Pat<(i32 (!cast<SDNode>("sextload" # sty) address)),
(!cast<Instruction>("LDRS" # T # "w_" # Rm # "_RegOffset")
Base, Offset, Extend)>;
def : Pat<(i64 (!cast<SDNode>("sextload" # sty) address)),
(!cast<Instruction>("LDRS" # T # "x_" # Rm # "_RegOffset")
Base, Offset, Extend)>;
}
defm : ro_signed_pats<"B", Rm, Base, Offset, Extend,
!foreach(decls.pattern, address,
!subst(SHIFT, imm_eq0, decls.pattern)),
i8>;
See the `TableGen Language Reference <LangRef.html>`_ for more information.
.. _backend:
.. _backends:
TableGen backends
=================
TableGen files have no real meaning without a back-end. The default operation
of running ``llvm-tblgen`` is to print the information in a textual format, but
that's only useful for debugging of the TableGen files themselves. The power
in TableGen is, however, to interpret the source files into an internal
representation that can be generated into anything you want.
Current usage of TableGen is to create include huge files with tables that you
can either include directly (if the output is in the language you're coding),
or be used in pre-processing via macros surrounding the include of the file.
Direct output can be used if the back-end already prints a table in C format
or if the output is just a list of strings (for error and warning messages).
Pre-processed output should be used if the same information needs to be used
in different contexts (like Instruction names), so your back-end should print
a meta-information list that can be shaped into different compile-time formats.
See the `TableGen BackEnds <BackEnds.html>`_ for more information.
TableGen Deficiencies
=====================
Despite being very generic, TableGen has some deficiencies that have been
pointed out numerous times. The common theme is that, while TableGen allows
you to build Domain-Specific-Languages, the final languages that you create
lack the power of other DSLs, which in turn increase considerably the size
and complecity of TableGen files.
At the same time, TableGen allows you to create virtually any meaning of
the basic concepts via custom-made back-ends, which can pervert the original
design and make it very hard for newcomers to understand the evil TableGen
file.
There are some in favour of extending the semantics even more, but makeing sure
back-ends adhere to strict rules. Others suggesting we should move to less,
more powerful DSLs designed with specific purposes, or even re-using existing
DSLs.
Either way, this is a discussion that is likely spanning across several years,
if not decades. You can read more in the `TableGen Deficiencies <Deficiencies.html>`_
document.

2
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LinkTimeOptimization
SegmentedStacks
TableGenFundamentals
TableGen/index
DebuggingJITedCode
GoldPlugin
MarkedUpDisassembly
@ -231,7 +232,6 @@ For API clients and LLVM developers.
WritingAnLLVMBackend
GarbageCollection
WritingAnLLVMPass
TableGen/LangRef
HowToUseAttributes
NVPTXUsage
StackMaps