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llvm-mirror/docs/AMDGPUOperandSyntax.rst
Dmitry Preobrazhensky ebbe05934d [AMDGPU][MC][DOC] Updated AMD GPU assembler description. 
Summary of changes:
- Updated to reflect recent changes in assembler;
- Minor bugfixing and improvements.

llvm-svn: 372857
2019-09-25 12:38:35 +00:00

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=====================================
Syntax of AMDGPU Instruction Operands
=====================================
.. contents::
:local:
Conventions
===========
The following notation is used throughout this document:
=================== =============================================================================
Notation Description
=================== =============================================================================
{0..N} Any integer value in the range from 0 to N (inclusive).
<x> Syntax and meaning of *x* is explained elsewhere.
=================== =============================================================================
.. _amdgpu_syn_operands:
Operands
========
.. _amdgpu_synid_v:
v
-
Vector registers. There are 256 32-bit vector registers.
A sequence of *vector* registers may be used to operate with more than 32 bits of data.
Assembler currently supports sequences of 1, 2, 3, 4, 8 and 16 *vector* registers.
=================================================== ====================================================================
Syntax Description
=================================================== ====================================================================
**v**\<N> A single 32-bit *vector* register.
*N* must be a decimal
:ref:`integer number<amdgpu_synid_integer_number>`.
**v[**\ <N>\ **]** A single 32-bit *vector* register.
*N* may be specified as an
:ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
**v[**\ <N>:<K>\ **]** A sequence of (\ *K-N+1*\ ) *vector* registers.
*N* and *K* may be specified as
:ref:`integer numbers<amdgpu_synid_integer_number>`
or :ref:`absolute expressions<amdgpu_synid_absolute_expression>`.
**[v**\ <N>, \ **v**\ <N+1>, ... **v**\ <K>\ **]** A sequence of (\ *K-N+1*\ ) *vector* registers.
Register indices must be specified as decimal
:ref:`integer numbers<amdgpu_synid_integer_number>`.
=================================================== ====================================================================
Note: *N* and *K* must satisfy the following conditions:
* *N* <= *K*.
* 0 <= *N* <= 255.
* 0 <= *K* <= 255.
* *K-N+1* must be equal to 1, 2, 3, 4, 8 or 16.
Examples:
.. parsed-literal::
v255
v[0]
v[0:1]
v[1:1]
v[0:3]
v[2*2]
v[1-1:2-1]
[v252]
[v252,v253,v254,v255]
.. _amdgpu_synid_nsa:
GFX10 *Image* instructions may use special *NSA* (Non-Sequential Address) syntax for *image addresses*:
===================================== =================================================
Syntax Description
===================================== =================================================
**[Vm**, \ **Vn**, ... **Vk**\ **]** A sequence of 32-bit *vector* registers.
Each register may be specified using a syntax
defined :ref:`above<amdgpu_synid_v>`.
In contrast with standard syntax, registers
in *NSA* sequence are not required to have
consecutive indices. Moreover, the same register
may appear in the list more than once.
===================================== =================================================
Examples:
.. parsed-literal::
[v32,v1,v[2]]
[v[32],v[1:1],[v2]]
[v4,v4,v4,v4]
.. _amdgpu_synid_s:
s
-
Scalar 32-bit registers. The number of available *scalar* registers depends on GPU:
======= ============================
GPU Number of *scalar* registers
======= ============================
GFX7 104
GFX8 102
GFX9 102
GFX10 106
======= ============================
A sequence of *scalar* registers may be used to operate with more than 32 bits of data.
Assembler currently supports sequences of 1, 2, 4, 8 and 16 *scalar* registers.
Pairs of *scalar* registers must be even-aligned (the first register must be even).
Sequences of 4 and more *scalar* registers must be quad-aligned.
======================================================== ====================================================================
Syntax Description
======================================================== ====================================================================
**s**\ <N> A single 32-bit *scalar* register.
*N* must be a decimal
:ref:`integer number<amdgpu_synid_integer_number>`.
**s[**\ <N>\ **]** A single 32-bit *scalar* register.
*N* may be specified as an
:ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
**s[**\ <N>:<K>\ **]** A sequence of (\ *K-N+1*\ ) *scalar* registers.
*N* and *K* may be specified as
:ref:`integer numbers<amdgpu_synid_integer_number>`
or :ref:`absolute expressions<amdgpu_synid_absolute_expression>`.
**[s**\ <N>, \ **s**\ <N+1>, ... **s**\ <K>\ **]** A sequence of (\ *K-N+1*\ ) *scalar* registers.
Register indices must be specified as decimal
:ref:`integer numbers<amdgpu_synid_integer_number>`.
======================================================== ====================================================================
Note: *N* and *K* must satisfy the following conditions:
* *N* must be properly aligned based on sequence size.
* *N* <= *K*.
* 0 <= *N* < *SMAX*\ , where *SMAX* is the number of available *scalar* registers.
* 0 <= *K* < *SMAX*\ , where *SMAX* is the number of available *scalar* registers.
* *K-N+1* must be equal to 1, 2, 4, 8 or 16.
Examples:
.. parsed-literal::
s0
s[0]
s[0:1]
s[1:1]
s[0:3]
s[2*2]
s[1-1:2-1]
[s4]
[s4,s5,s6,s7]
Examples of *scalar* registers with an invalid alignment:
.. parsed-literal::
s[1:2]
s[2:5]
.. _amdgpu_synid_trap:
trap
----
A set of trap handler registers:
* :ref:`ttmp<amdgpu_synid_ttmp>`
* :ref:`tba<amdgpu_synid_tba>`
* :ref:`tma<amdgpu_synid_tma>`
.. _amdgpu_synid_ttmp:
ttmp
----
Trap handler temporary scalar registers, 32-bits wide.
The number of available *ttmp* registers depends on GPU:
======= ===========================
GPU Number of *ttmp* registers
======= ===========================
GFX7 12
GFX8 12
GFX9 16
GFX10 16
======= ===========================
A sequence of *ttmp* registers may be used to operate with more than 32 bits of data.
Assembler currently supports sequences of 1, 2, 4, 8 and 16 *ttmp* registers.
Pairs of *ttmp* registers must be even-aligned (the first register must be even).
Sequences of 4 and more *ttmp* registers must be quad-aligned.
============================================================= ====================================================================
Syntax Description
============================================================= ====================================================================
**ttmp**\ <N> A single 32-bit *ttmp* register.
*N* must be a decimal
:ref:`integer number<amdgpu_synid_integer_number>`.
**ttmp[**\ <N>\ **]** A single 32-bit *ttmp* register.
*N* may be specified as an
:ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
**ttmp[**\ <N>:<K>\ **]** A sequence of (\ *K-N+1*\ ) *ttmp* registers.
*N* and *K* may be specified as
:ref:`integer numbers<amdgpu_synid_integer_number>`
or :ref:`absolute expressions<amdgpu_synid_absolute_expression>`.
**[ttmp**\ <N>, \ **ttmp**\ <N+1>, ... **ttmp**\ <K>\ **]** A sequence of (\ *K-N+1*\ ) *ttmp* registers.
Register indices must be specified as decimal
:ref:`integer numbers<amdgpu_synid_integer_number>`.
============================================================= ====================================================================
Note: *N* and *K* must satisfy the following conditions:
* *N* must be properly aligned based on sequence size.
* *N* <= *K*.
* 0 <= *N* < *TMAX*, where *TMAX* is the number of available *ttmp* registers.
* 0 <= *K* < *TMAX*, where *TMAX* is the number of available *ttmp* registers.
* *K-N+1* must be equal to 1, 2, 4, 8 or 16.
Examples:
.. parsed-literal::
ttmp0
ttmp[0]
ttmp[0:1]
ttmp[1:1]
ttmp[0:3]
ttmp[2*2]
ttmp[1-1:2-1]
[ttmp4]
[ttmp4,ttmp5,ttmp6,ttmp7]
Examples of *ttmp* registers with an invalid alignment:
.. parsed-literal::
ttmp[1:2]
ttmp[2:5]
.. _amdgpu_synid_tba:
tba
---
Trap base address, 64-bits wide. Holds the pointer to the current trap handler program.
================== ======================================================================= =============
Syntax Description Availability
================== ======================================================================= =============
tba 64-bit *trap base address* register. GFX7, GFX8
[tba] 64-bit *trap base address* register (an SP3 syntax). GFX7, GFX8
[tba_lo,tba_hi] 64-bit *trap base address* register (an SP3 syntax). GFX7, GFX8
================== ======================================================================= =============
High and low 32 bits of *trap base address* may be accessed as separate registers:
================== ======================================================================= =============
Syntax Description Availability
================== ======================================================================= =============
tba_lo Low 32 bits of *trap base address* register. GFX7, GFX8
tba_hi High 32 bits of *trap base address* register. GFX7, GFX8
[tba_lo] Low 32 bits of *trap base address* register (an SP3 syntax). GFX7, GFX8
[tba_hi] High 32 bits of *trap base address* register (an SP3 syntax). GFX7, GFX8
================== ======================================================================= =============
Note that *tba*, *tba_lo* and *tba_hi* are not accessible as assembler registers in GFX9 and GFX10,
but *tba* is readable/writable with the help of *s_get_reg* and *s_set_reg* instructions.
.. _amdgpu_synid_tma:
tma
---
Trap memory address, 64-bits wide.
================= ======================================================================= ==================
Syntax Description Availability
================= ======================================================================= ==================
tma 64-bit *trap memory address* register. GFX7, GFX8
[tma] 64-bit *trap memory address* register (an SP3 syntax). GFX7, GFX8
[tma_lo,tma_hi] 64-bit *trap memory address* register (an SP3 syntax). GFX7, GFX8
================= ======================================================================= ==================
High and low 32 bits of *trap memory address* may be accessed as separate registers:
================= ======================================================================= ==================
Syntax Description Availability
================= ======================================================================= ==================
tma_lo Low 32 bits of *trap memory address* register. GFX7, GFX8
tma_hi High 32 bits of *trap memory address* register. GFX7, GFX8
[tma_lo] Low 32 bits of *trap memory address* register (an SP3 syntax). GFX7, GFX8
[tma_hi] High 32 bits of *trap memory address* register (an SP3 syntax). GFX7, GFX8
================= ======================================================================= ==================
Note that *tma*, *tma_lo* and *tma_hi* are not accessible as assembler registers in GFX9 and GFX10,
but *tma* is readable/writable with the help of *s_get_reg* and *s_set_reg* instructions.
.. _amdgpu_synid_flat_scratch:
flat_scratch
------------
Flat scratch address, 64-bits wide. Holds the base address of scratch memory.
================================== ================================================================
Syntax Description
================================== ================================================================
flat_scratch 64-bit *flat scratch* address register.
[flat_scratch] 64-bit *flat scratch* address register (an SP3 syntax).
[flat_scratch_lo,flat_scratch_hi] 64-bit *flat scratch* address register (an SP3 syntax).
================================== ================================================================
High and low 32 bits of *flat scratch* address may be accessed as separate registers:
========================= =========================================================================
Syntax Description
========================= =========================================================================
flat_scratch_lo Low 32 bits of *flat scratch* address register.
flat_scratch_hi High 32 bits of *flat scratch* address register.
[flat_scratch_lo] Low 32 bits of *flat scratch* address register (an SP3 syntax).
[flat_scratch_hi] High 32 bits of *flat scratch* address register (an SP3 syntax).
========================= =========================================================================
.. _amdgpu_synid_xnack:
xnack
-----
Xnack mask, 64-bits wide. Holds a 64-bit mask of which threads
received an *XNACK* due to a vector memory operation.
.. WARNING:: GFX7 does not support *xnack* feature. For availability of this feature in other GPUs, refer :ref:`this table<amdgpu-processors>`.
\
============================== =====================================================
Syntax Description
============================== =====================================================
xnack_mask 64-bit *xnack mask* register.
[xnack_mask] 64-bit *xnack mask* register (an SP3 syntax).
[xnack_mask_lo,xnack_mask_hi] 64-bit *xnack mask* register (an SP3 syntax).
============================== =====================================================
High and low 32 bits of *xnack mask* may be accessed as separate registers:
===================== ==============================================================
Syntax Description
===================== ==============================================================
xnack_mask_lo Low 32 bits of *xnack mask* register.
xnack_mask_hi High 32 bits of *xnack mask* register.
[xnack_mask_lo] Low 32 bits of *xnack mask* register (an SP3 syntax).
[xnack_mask_hi] High 32 bits of *xnack mask* register (an SP3 syntax).
===================== ==============================================================
.. _amdgpu_synid_vcc:
.. _amdgpu_synid_vcc_lo:
vcc
---
Vector condition code, 64-bits wide. A bit mask with one bit per thread;
it holds the result of a vector compare operation.
Note that GFX10 H/W does not use high 32 bits of *vcc* in *wave32* mode.
================ =========================================================================
Syntax Description
================ =========================================================================
vcc 64-bit *vector condition code* register.
[vcc] 64-bit *vector condition code* register (an SP3 syntax).
[vcc_lo,vcc_hi] 64-bit *vector condition code* register (an SP3 syntax).
================ =========================================================================
High and low 32 bits of *vector condition code* may be accessed as separate registers:
================ =========================================================================
Syntax Description
================ =========================================================================
vcc_lo Low 32 bits of *vector condition code* register.
vcc_hi High 32 bits of *vector condition code* register.
[vcc_lo] Low 32 bits of *vector condition code* register (an SP3 syntax).
[vcc_hi] High 32 bits of *vector condition code* register (an SP3 syntax).
================ =========================================================================
.. _amdgpu_synid_m0:
m0
--
A 32-bit memory register. It has various uses,
including register indexing and bounds checking.
=========== ===================================================
Syntax Description
=========== ===================================================
m0 A 32-bit *memory* register.
[m0] A 32-bit *memory* register (an SP3 syntax).
=========== ===================================================
.. _amdgpu_synid_exec:
exec
----
Execute mask, 64-bits wide. A bit mask with one bit per thread,
which is applied to vector instructions and controls which threads execute
and which ignore the instruction.
Note that GFX10 H/W does not use high 32 bits of *exec* in *wave32* mode.
===================== =================================================================
Syntax Description
===================== =================================================================
exec 64-bit *execute mask* register.
[exec] 64-bit *execute mask* register (an SP3 syntax).
[exec_lo,exec_hi] 64-bit *execute mask* register (an SP3 syntax).
===================== =================================================================
High and low 32 bits of *execute mask* may be accessed as separate registers:
===================== =================================================================
Syntax Description
===================== =================================================================
exec_lo Low 32 bits of *execute mask* register.
exec_hi High 32 bits of *execute mask* register.
[exec_lo] Low 32 bits of *execute mask* register (an SP3 syntax).
[exec_hi] High 32 bits of *execute mask* register (an SP3 syntax).
===================== =================================================================
.. _amdgpu_synid_vccz:
vccz
----
A single bit flag indicating that the :ref:`vcc<amdgpu_synid_vcc>` is all zeros.
Note: when GFX10 operates in *wave32* mode, this register reflects state of :ref:`vcc_lo<amdgpu_synid_vcc_lo>`.
.. _amdgpu_synid_execz:
execz
-----
A single bit flag indicating that the :ref:`exec<amdgpu_synid_exec>` is all zeros.
Note: when GFX10 operates in *wave32* mode, this register reflects state of :ref:`exec_lo<amdgpu_synid_exec>`.
.. _amdgpu_synid_scc:
scc
---
A single bit flag indicating the result of a scalar compare operation.
.. _amdgpu_synid_lds_direct:
lds_direct
----------
A special operand which supplies a 32-bit value
fetched from *LDS* memory using :ref:`m0<amdgpu_synid_m0>` as an address.
.. _amdgpu_synid_null:
null
----
This is a special operand which may be used as a source or a destination.
When used as a destination, the result of the operation is discarded.
When used as a source, it supplies zero value.
GFX10 only.
.. WARNING:: Due to a H/W bug, this operand cannot be used with VALU instructions in first generation of GFX10.
.. _amdgpu_synid_constant:
inline constant
---------------
An *inline constant* is an integer or a floating-point value encoded as a part of an instruction.
Compare *inline constants* with :ref:`literals<amdgpu_synid_literal>`.
Inline constants include:
* :ref:`iconst<amdgpu_synid_iconst>`
* :ref:`fconst<amdgpu_synid_fconst>`
* :ref:`ival<amdgpu_synid_ival>`
If a number may be encoded as either
a :ref:`literal<amdgpu_synid_literal>` or
a :ref:`constant<amdgpu_synid_constant>`,
assembler selects the latter encoding as more efficient.
.. _amdgpu_synid_iconst:
iconst
~~~~~~
An :ref:`integer number<amdgpu_synid_integer_number>` or
an :ref:`absolute expression<amdgpu_synid_absolute_expression>`
encoded as an *inline constant*.
Only a small fraction of integer numbers may be encoded as *inline constants*.
They are enumerated in the table below.
Other integer numbers have to be encoded as :ref:`literals<amdgpu_synid_literal>`.
================================== ====================================
Value Note
================================== ====================================
{0..64} Positive integer inline constants.
{-16..-1} Negative integer inline constants.
================================== ====================================
.. WARNING:: GFX7 does not support inline constants for *f16* operands.
.. _amdgpu_synid_fconst:
fconst
~~~~~~
A :ref:`floating-point number<amdgpu_synid_floating-point_number>`
encoded as an *inline constant*.
Only a small fraction of floating-point numbers may be encoded as *inline constants*.
They are enumerated in the table below.
Other floating-point numbers have to be encoded as :ref:`literals<amdgpu_synid_literal>`.
===================== ===================================================== ==================
Value Note Availability
===================== ===================================================== ==================
0.0 The same as integer constant 0. All GPUs
0.5 Floating-point constant 0.5 All GPUs
1.0 Floating-point constant 1.0 All GPUs
2.0 Floating-point constant 2.0 All GPUs
4.0 Floating-point constant 4.0 All GPUs
-0.5 Floating-point constant -0.5 All GPUs
-1.0 Floating-point constant -1.0 All GPUs
-2.0 Floating-point constant -2.0 All GPUs
-4.0 Floating-point constant -4.0 All GPUs
0.1592 1.0/(2.0*pi). Use only for 16-bit operands. GFX8, GFX9, GFX10
0.15915494 1.0/(2.0*pi). Use only for 16- and 32-bit operands. GFX8, GFX9, GFX10
0.15915494309189532 1.0/(2.0*pi). GFX8, GFX9, GFX10
===================== ===================================================== ==================
.. WARNING:: GFX7 does not support inline constants for *f16* operands.
.. _amdgpu_synid_ival:
ival
~~~~
A symbolic operand encoded as an *inline constant*.
These operands provide read-only access to H/W registers.
======================== ================================================ =============
Syntax Note Availability
======================== ================================================ =============
shared_base Base address of shared memory region. GFX9, GFX10
shared_limit Address of the end of shared memory region. GFX9, GFX10
private_base Base address of private memory region. GFX9, GFX10
private_limit Address of the end of private memory region. GFX9, GFX10
pops_exiting_wave_id A dedicated counter for POPS. GFX9, GFX10
======================== ================================================ =============
.. _amdgpu_synid_literal:
literal
-------
A *literal* is a 64-bit value encoded as a separate 32-bit dword in the instruction stream.
Compare *literals* with :ref:`inline constants<amdgpu_synid_constant>`.
If a number may be encoded as either
a :ref:`literal<amdgpu_synid_literal>` or
an :ref:`inline constant<amdgpu_synid_constant>`,
assembler selects the latter encoding as more efficient.
Literals may be specified as :ref:`integer numbers<amdgpu_synid_integer_number>`,
:ref:`floating-point numbers<amdgpu_synid_floating-point_number>`,
:ref:`absolute expressions<amdgpu_synid_absolute_expression>` or
:ref:`relocatable expressions<amdgpu_synid_relocatable_expression>`.
An instruction may use only one literal but several operands may refer the same literal.
.. _amdgpu_synid_uimm8:
uimm8
-----
A 8-bit :ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
The value must be in the range 0..0xFF.
.. _amdgpu_synid_uimm32:
uimm32
------
A 32-bit :ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
The value must be in the range 0..0xFFFFFFFF.
.. _amdgpu_synid_uimm20:
uimm20
------
A 20-bit :ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
The value must be in the range 0..0xFFFFF.
.. _amdgpu_synid_uimm21:
uimm21
------
A 21-bit :ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
The value must be in the range 0..0x1FFFFF.
.. WARNING:: Assembler currently supports 20-bit offsets only. Use :ref:`uimm20<amdgpu_synid_uimm20>` as a replacement.
.. _amdgpu_synid_simm21:
simm21
------
A 21-bit :ref:`integer number<amdgpu_synid_integer_number>`
or an :ref:`absolute expression<amdgpu_synid_absolute_expression>`.
The value must be in the range -0x100000..0x0FFFFF.
.. WARNING:: Assembler currently supports 20-bit unsigned offsets only. Use :ref:`uimm20<amdgpu_synid_uimm20>` as a replacement.
.. _amdgpu_synid_off:
off
---
A special entity which indicates that the value of this operand is not used.
================================== ===================================================
Syntax Description
================================== ===================================================
off Indicates an unused operand.
================================== ===================================================
.. _amdgpu_synid_number:
Numbers
=======
.. _amdgpu_synid_integer_number:
Integer Numbers
---------------
Integer numbers are 64 bits wide.
They are converted to :ref:`expected operand type<amdgpu_syn_instruction_type>`
as described :ref:`here<amdgpu_synid_int_conv>`.
Integer numbers may be specified in binary, octal, hexadecimal and decimal formats:
============ =============================== ========
Format Syntax Example
============ =============================== ========
Decimal [-]?[1-9][0-9]* -1234
Binary [-]?0b[01]+ 0b1010
Octal [-]?0[0-7]+ 010
Hexadecimal [-]?0x[0-9a-fA-F]+ 0xff
\ [-]?[0x]?[0-9][0-9a-fA-F]*[hH] 0ffh
============ =============================== ========
.. _amdgpu_synid_floating-point_number:
Floating-Point Numbers
----------------------
All floating-point numbers are handled as double (64 bits wide).
They are converted to
:ref:`expected operand type<amdgpu_syn_instruction_type>`
as described :ref:`here<amdgpu_synid_fp_conv>`.
Floating-point numbers may be specified in hexadecimal and decimal formats:
============ ======================================================== ====================== ====================
Format Syntax Examples Note
============ ======================================================== ====================== ====================
Decimal [-]?[0-9]*[.][0-9]*([eE][+-]?[0-9]*)? -1.234, 234e2 Must include either
a decimal separator
or an exponent.
Hexadecimal [-]0x[0-9a-fA-F]*(.[0-9a-fA-F]*)?[pP][+-]?[0-9a-fA-F]+ -0x1afp-10, 0x.1afp10
============ ======================================================== ====================== ====================
.. _amdgpu_synid_expression:
Expressions
===========
An expression is evaluated to a 64-bit integer.
Note that floating-point expressions are not supported.
There are two kinds of expressions:
* :ref:`Absolute<amdgpu_synid_absolute_expression>`.
* :ref:`Relocatable<amdgpu_synid_relocatable_expression>`.
.. _amdgpu_synid_absolute_expression:
Absolute Expressions
--------------------
The value of an absolute expression does not change after program relocation.
Absolute expressions must not include unassigned and relocatable values
such as labels.
Absolute expressions are evaluated to 64-bit integer values and converted to
:ref:`expected operand type<amdgpu_syn_instruction_type>`
as described :ref:`here<amdgpu_synid_int_conv>`.
Examples:
.. parsed-literal::
x = -1
y = x + 10
.. _amdgpu_synid_relocatable_expression:
Relocatable Expressions
-----------------------
The value of a relocatable expression depends on program relocation.
Note that use of relocatable expressions is limited with branch targets
and 32-bit integer operands.
A relocatable expression is evaluated to a 64-bit integer value
which depends on operand kind and :ref:`relocation type<amdgpu-relocation-records>`
of symbol(s) used in the expression. For example, if an instruction refers a label,
this reference is evaluated to an offset from the address after the instruction
to the label address:
.. parsed-literal::
label:
v_add_co_u32_e32 v0, vcc, label, v1 // 'label' operand is evaluated to -4
Note that values of relocatable expressions are usually unknown at assembly time;
they are resolved later by a linker and converted to
:ref:`expected operand type<amdgpu_syn_instruction_type>`
as described :ref:`here<amdgpu_synid_rl_conv>`.
Operands and Operations
-----------------------
Expressions are composed of 64-bit integer operands and operations.
Operands include :ref:`integer numbers<amdgpu_synid_integer_number>`
and :ref:`symbols<amdgpu_synid_symbol>`.
Expressions may also use "." which is a reference to the current PC (program counter).
:ref:`Unary<amdgpu_synid_expression_un_op>` and :ref:`binary<amdgpu_synid_expression_bin_op>`
operations produce 64-bit integer results.
Syntax of Expressions
---------------------
The syntax of expressions is shown below::
expr ::= expr binop expr | primaryexpr ;
primaryexpr ::= '(' expr ')' | symbol | number | '.' | unop primaryexpr ;
binop ::= '&&'
| '||'
| '|'
| '^'
| '&'
| '!'
| '=='
| '!='
| '<>'
| '<'
| '<='
| '>'
| '>='
| '<<'
| '>>'
| '+'
| '-'
| '*'
| '/'
| '%' ;
unop ::= '~'
| '+'
| '-'
| '!' ;
.. _amdgpu_synid_expression_bin_op:
Binary Operators
----------------
Binary operators are described in the following table.
They operate on and produce 64-bit integers.
Operators with higher priority are performed first.
========== ========= ===============================================
Operator Priority Meaning
========== ========= ===============================================
\* 5 Integer multiplication.
/ 5 Integer division.
% 5 Integer signed remainder.
\+ 4 Integer addition.
\- 4 Integer subtraction.
<< 3 Integer shift left.
>> 3 Logical shift right.
== 2 Equality comparison.
!= 2 Inequality comparison.
<> 2 Inequality comparison.
< 2 Signed less than comparison.
<= 2 Signed less than or equal comparison.
> 2 Signed greater than comparison.
>= 2 Signed greater than or equal comparison.
\| 1 Bitwise or.
^ 1 Bitwise xor.
& 1 Bitwise and.
&& 0 Logical and.
|| 0 Logical or.
========== ========= ===============================================
.. _amdgpu_synid_expression_un_op:
Unary Operators
---------------
Unary operators are described in the following table.
They operate on and produce 64-bit integers.
========== ===============================================
Operator Meaning
========== ===============================================
! Logical negation.
~ Bitwise negation.
\+ Integer unary plus.
\- Integer unary minus.
========== ===============================================
.. _amdgpu_synid_symbol:
Symbols
-------
A symbol is a named 64-bit integer value, representing a relocatable
address or an absolute (non-relocatable) number.
Symbol names have the following syntax:
``[a-zA-Z_.][a-zA-Z0-9_$.@]*``
The table below provides several examples of syntax used for symbol definition.
================ ==========================================================
Syntax Meaning
================ ==========================================================
.globl <S> Declares a global symbol S without assigning it a value.
.set <S>, <E> Assigns the value of an expression E to a symbol S.
<S> = <E> Assigns the value of an expression E to a symbol S.
<S>: Declares a label S and assigns it the current PC value.
================ ==========================================================
A symbol may be used before it is declared or assigned;
unassigned symbols are assumed to be PC-relative.
Additional information about symbols may be found :ref:`here<amdgpu-symbols>`.
.. _amdgpu_synid_conv:
Type and Size Conversion
========================
This section describes what happens when a 64-bit
:ref:`integer number<amdgpu_synid_integer_number>`, a
:ref:`floating-point number<amdgpu_synid_floating-point_number>` or an
:ref:`expression<amdgpu_synid_expression>`
is used for an operand which has a different type or size.
.. _amdgpu_synid_int_conv:
Conversion of Integer Values
----------------------------
Instruction operands may be specified as 64-bit :ref:`integer numbers<amdgpu_synid_integer_number>` or
:ref:`absolute expressions<amdgpu_synid_absolute_expression>`. These values are converted to
the :ref:`expected operand type<amdgpu_syn_instruction_type>` using the following steps:
1. *Validation*. Assembler checks if the input value may be truncated without loss to the required *truncation width*
(see the table below). There are two cases when this operation is enabled:
* The truncated bits are all 0.
* The truncated bits are all 1 and the value after truncation has its MSB bit set.
In all other cases assembler triggers an error.
2. *Conversion*. The input value is converted to the expected type as described in the table below.
Depending on operand kind, this conversion is performed by either assembler or AMDGPU H/W (or both).
============== ================= =============== ====================================================================
Expected type Truncation Width Conversion Description
============== ================= =============== ====================================================================
i16, u16, b16 16 num.u16 Truncate to 16 bits.
i32, u32, b32 32 num.u32 Truncate to 32 bits.
i64 32 {-1,num.i32} Truncate to 32 bits and then sign-extend the result to 64 bits.
u64, b64 32 {0,num.u32} Truncate to 32 bits and then zero-extend the result to 64 bits.
f16 16 num.u16 Use low 16 bits as an f16 value.
f32 32 num.u32 Use low 32 bits as an f32 value.
f64 32 {num.u32,0} Use low 32 bits of the number as high 32 bits
of the result; low 32 bits of the result are zeroed.
============== ================= =============== ====================================================================
Examples of enabled conversions:
.. parsed-literal::
// GFX9
v_add_u16 v0, -1, 0 // src0 = 0xFFFF
v_add_f16 v0, -1, 0 // src0 = 0xFFFF (NaN)
//
v_add_u32 v0, -1, 0 // src0 = 0xFFFFFFFF
v_add_f32 v0, -1, 0 // src0 = 0xFFFFFFFF (NaN)
//
v_add_u16 v0, 0xff00, v0 // src0 = 0xff00
v_add_u16 v0, 0xffffffffffffff00, v0 // src0 = 0xff00
v_add_u16 v0, -256, v0 // src0 = 0xff00
//
s_bfe_i64 s[0:1], 0xffefffff, s3 // src0 = 0xffffffffffefffff
s_bfe_u64 s[0:1], 0xffefffff, s3 // src0 = 0x00000000ffefffff
v_ceil_f64_e32 v[0:1], 0xffefffff // src0 = 0xffefffff00000000 (-1.7976922776554302e308)
//
x = 0xffefffff //
s_bfe_i64 s[0:1], x, s3 // src0 = 0xffffffffffefffff
s_bfe_u64 s[0:1], x, s3 // src0 = 0x00000000ffefffff
v_ceil_f64_e32 v[0:1], x // src0 = 0xffefffff00000000 (-1.7976922776554302e308)
Examples of disabled conversions:
.. parsed-literal::
// GFX9
v_add_u16 v0, 0x1ff00, v0 // truncated bits are not all 0 or 1
v_add_u16 v0, 0xffffffffffff00ff, v0 // truncated bits do not match MSB of the result
.. _amdgpu_synid_fp_conv:
Conversion of Floating-Point Values
-----------------------------------
Instruction operands may be specified as 64-bit :ref:`floating-point numbers<amdgpu_synid_floating-point_number>`.
These values are converted to the :ref:`expected operand type<amdgpu_syn_instruction_type>` using the following steps:
1. *Validation*. Assembler checks if the input f64 number can be converted
to the *required floating-point type* (see the table below) without overflow or underflow.
Precision lost is allowed. If this conversion is not possible, assembler triggers an error.
2. *Conversion*. The input value is converted to the expected type as described in the table below.
Depending on operand kind, this is performed by either assembler or AMDGPU H/W (or both).
============== ================ ================= =================================================================
Expected type Required FP Type Conversion Description
============== ================ ================= =================================================================
i16, u16, b16 f16 f16(num) Convert to f16 and use bits of the result as an integer value.
i32, u32, b32 f32 f32(num) Convert to f32 and use bits of the result as an integer value.
i64, u64, b64 \- \- Conversion disabled.
f16 f16 f16(num) Convert to f16.
f32 f32 f32(num) Convert to f32.
f64 f64 {num.u32.hi,0} Use high 32 bits of the number as high 32 bits of the result;
zero-fill low 32 bits of the result.
Note that the result may differ from the original number.
============== ================ ================= =================================================================
Examples of enabled conversions:
.. parsed-literal::
// GFX9
v_add_f16 v0, 1.0, 0 // src0 = 0x3C00 (1.0)
v_add_u16 v0, 1.0, 0 // src0 = 0x3C00
//
v_add_f32 v0, 1.0, 0 // src0 = 0x3F800000 (1.0)
v_add_u32 v0, 1.0, 0 // src0 = 0x3F800000
// src0 before conversion:
// 1.7976931348623157e308 = 0x7fefffffffffffff
// src0 after conversion:
// 1.7976922776554302e308 = 0x7fefffff00000000
v_ceil_f64 v[0:1], 1.7976931348623157e308
v_add_f16 v1, 65500.0, v2 // ok for f16.
v_add_f32 v1, 65600.0, v2 // ok for f32, but would result in overflow for f16.
Examples of disabled conversions:
.. parsed-literal::
// GFX9
v_add_f16 v1, 65600.0, v2 // overflow
.. _amdgpu_synid_rl_conv:
Conversion of Relocatable Values
--------------------------------
:ref:`Relocatable expressions<amdgpu_synid_relocatable_expression>`
may be used with 32-bit integer operands and jump targets.
When the value of a relocatable expression is resolved by a linker, it is
converted as needed and truncated to the operand size. The conversion depends
on :ref:`relocation type<amdgpu-relocation-records>` and operand kind.
For example, when a 32-bit operand of an instruction refers a relocatable expression *expr*,
this reference is evaluated to a 64-bit offset from the address after the
instruction to the address being referenced, *counted in bytes*.
Then the value is truncated to 32 bits and encoded as a literal:
.. parsed-literal::
expr = .
v_add_co_u32_e32 v0, vcc, expr, v1 // 'expr' operand is evaluated to -4
// and then truncated to 0xFFFFFFFC
As another example, when a branch instruction refers a label,
this reference is evaluated to an offset from the address after the
instruction to the label address, *counted in dwords*.
Then the value is truncated to 16 bits:
.. parsed-literal::
label:
s_branch label // 'label' operand is evaluated to -1 and truncated to 0xFFFF
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