llvm-mirror/docs/AMDGPUInstructionSyntax.rst

=========================
AMDGPU Instruction Syntax
=========================

.. contents::
   :local:

.. _amdgpu_syn_instructions:

Instructions
============

Syntax
~~~~~~

An instruction has the following syntax:

    ``<``\ *opcode mnemonic*\ ``>    <``\ *operand0*\ ``>, <``\ *operand1*\ ``>,...    <``\ *modifier0*\ ``> <``\ *modifier1*\ ``>...``

:doc:`Operands<AMDGPUOperandSyntax>` are normally comma-separated while
:doc:`modifiers<AMDGPUModifierSyntax>` are space-separated.

The order of *operands* and *modifiers* is fixed.
Most *modifiers* are optional and may be omitted.

.. _amdgpu_syn_instruction_mnemo:

Opcode Mnemonic
~~~~~~~~~~~~~~~

Opcode mnemonic describes opcode semantics and may include one or more suffices in this order:

* :ref:`Destination operand type suffix<amdgpu_syn_instruction_type>`.
* :ref:`Source operand type suffix<amdgpu_syn_instruction_type>`.
* :ref:`Encoding suffix<amdgpu_syn_instruction_enc>`.

.. _amdgpu_syn_instruction_type:

Type and Size Suffices
~~~~~~~~~~~~~~~~~~~~~~

Instructions which operate with data have an implied type of *data* operands.
This data type is specified as a suffix of instruction mnemonic.

There are instructions which have 2 type suffices:
the first is the data type of the destination operand,
the second is the data type of source *data* operand(s).

Note that data type specified by an instruction does not apply
to other kinds of operands such as *addresses*, *offsets* and so on.

The following table enumerates the most frequently used type suffices.

    ============================================ ======================= =================
    Type Suffices                                Packed instruction?     Data Type
    ============================================ ======================= =================
    _b512, _b256, _b128, _b64, _b32, _b16, _b8   No                      Bits.
    _u64, _u32, _u16, _u8                        No                      Unsigned integer.
    _i64, _i32, _i16, _i8                        No                      Signed integer.
    _f64, _f32, _f16                             No                      Floating-point.
    _b16, _u16, _i16, _f16                       Yes                     Packed.
    ============================================ ======================= =================

Instructions which have no type suffices are assumed to operate with typeless data.
The size of data is specified by size suffices:

    ================= =================== =====================================
    Size Suffix       Implied data type   Required register size in dwords
    ================= =================== =====================================
    \-                b32                 1
    x2                b64                 2
    x3                b96                 3
    x4                b128                4
    x8                b256                8
    x16               b512                16
    x                 b32                 1
    xy                b64                 2
    xyz               b96                 3
    xyzw              b128                4
    d16_x             b16                 1
    d16_xy            b16x2               2 for GFX8.0, 1 for GFX8.1 and GFX9
    d16_xyz           b16x3               3 for GFX8.0, 2 for GFX8.1 and GFX9
    d16_xyzw          b16x4               4 for GFX8.0, 2 for GFX8.1 and GFX9
    ================= =================== =====================================

.. WARNING::
    There are exceptions from rules described above.
    Operands which have type different from type specified by the opcode are
    :ref:`tagged<amdgpu_syn_instruction_operand_tags>` in the description.

Examples of instructions with different types of source and destination operands:

.. parsed-literal::

    s_bcnt0_i32_b64
    v_cvt_f32_u32

Examples of instructions with one data type:

.. parsed-literal::

    v_max3_f32
    v_max3_i16

Examples of instructions which operate with packed data:

.. parsed-literal::

    v_pk_add_u16
    v_pk_add_i16
    v_pk_add_f16

Examples of typeless instructions which operate on b128 data:

.. parsed-literal::

    buffer_store_dwordx4
    flat_load_dwordx4

.. _amdgpu_syn_instruction_enc:

Encoding Suffices
~~~~~~~~~~~~~~~~~

Most *VOP1*, *VOP2* and *VOPC* instructions have several variants:
they may also be encoded in *VOP3*, *DPP* and *SDWA* formats.

The assembler will automatically use optimal encoding based on instruction operands.
To force specific encoding, one can add a suffix to the opcode of the instruction:

    =================================================== =================
    Encoding                                            Encoding Suffix
    =================================================== =================
    Native 32-bit encoding (*VOP1*, *VOP2* or *VOPC*)   _e32
    *VOP3* (64-bit) encoding                            _e64
    *DPP* encoding                                      _dpp
    *SDWA* encoding                                     _sdwa
    =================================================== =================

These suffices are used in this reference to indicate the assumed encoding.
When no suffix is specified, a native encoding is implied.

Operands
========

Syntax
~~~~~~

Syntax of most operands is described :doc:`in this document<AMDGPUOperandSyntax>`.

For detailed information about operands follow *operand links* in GPU-specific documents:

* :doc:`GFX7<AMDGPU/AMDGPUAsmGFX7>`
* :doc:`GFX8<AMDGPU/AMDGPUAsmGFX8>`
* :doc:`GFX9<AMDGPU/AMDGPUAsmGFX9>`

Modifiers
=========

Syntax
~~~~~~

Syntax of modifiers is described :doc:`in this document<AMDGPUModifierSyntax>`.

Information about modifiers supported for individual instructions may be found in GPU-specific documents:

* :doc:`GFX7<AMDGPU/AMDGPUAsmGFX7>`
* :doc:`GFX8<AMDGPU/AMDGPUAsmGFX8>`
* :doc:`GFX9<AMDGPU/AMDGPUAsmGFX9>`