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============================= User Guide for AMDGPU Backend ============================= .. contents:: :local: Introduction ============ The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the R600 family up until the current GCN families. It lives in the ``lib/Target/AMDGPU`` directory. LLVM ==== .. _amdgpu-target-triples: Target Triples -------------- Use the ``clang -target <Architecture>-<Vendor>-<OS>-<Environment>`` option to specify the target triple: .. table:: AMDGPU Target Triples :name: amdgpu-target-triples-table ============ ======== ========= =========== Architecture Vendor OS Environment ============ ======== ========= =========== r600 amd <empty> <empty> amdgcn amd <empty> <empty> amdgcn amd amdhsa <empty> amdgcn amd amdhsa opencl amdgcn amd amdhsa amdgizcl amdgcn amd amdhsa amdgiz amdgcn amd amdhsa hcc ============ ======== ========= =========== ``r600-amd--`` Supports AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders executed on the MESA runtime. ``amdgcn-amd--`` Supports AMD GPUs GCN GFX6 onwards for graphics and compute shaders executed on the MESA runtime. ``amdgcn-amd-amdhsa-`` Supports AMD GCN GPUs GFX6 onwards for compute kernels executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. ``amdgcn-amd-amdhsa-opencl`` Supports AMD GCN GPUs GFX6 onwards for OpenCL compute kernels executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. See :ref:`amdgpu-opencl`. ``amdgcn-amd-amdhsa-amdgizcl`` Same as ``amdgcn-amd-amdhsa-opencl`` except a different address space mapping is used (see :ref:`amdgpu-address-spaces`). ``amdgcn-amd-amdhsa-amdgiz`` Same as ``amdgcn-amd-amdhsa-`` except a different address space mapping is used (see :ref:`amdgpu-address-spaces`). ``amdgcn-amd-amdhsa-hcc`` Supports AMD GCN GPUs GFX6 onwards for AMD HC language compute kernels executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. See :ref:`amdgpu-hcc`. .. _amdgpu-processors: Processors ---------- Use the ``clang -mcpu <Processor>`` option to specify the AMD GPU processor. The names from both the *Processor* and *Alternative Processor* can be used. .. table:: AMDGPU Processors :name: amdgpu-processors-table ========== =========== ============ ===== ======= ================== Processor Alternative Target dGPU/ Runtime Example Processor Triple APU Support Products Architecture ========== =========== ============ ===== ======= ================== **Radeon HD 2000/3000 Series (R600)** [AMD-RADEON-HD-2000-3000]_ -------------------------------------------------------------------- r600 r600 dGPU r630 r600 dGPU rs880 r600 dGPU rv670 r600 dGPU **Radeon HD 4000 Series (R700)** [AMD-RADEON-HD-4000]_ -------------------------------------------------------------------- rv710 r600 dGPU rv730 r600 dGPU rv770 r600 dGPU **Radeon HD 5000 Series (Evergreen)** [AMD-RADEON-HD-5000]_ -------------------------------------------------------------------- cedar r600 dGPU redwood r600 dGPU sumo r600 dGPU juniper r600 dGPU cypress r600 dGPU **Radeon HD 6000 Series (Northern Islands)** [AMD-RADEON-HD-6000]_ -------------------------------------------------------------------- barts r600 dGPU turks r600 dGPU caicos r600 dGPU cayman r600 dGPU **GCN GFX6 (Southern Islands (SI))** [AMD-GCN-GFX6]_ -------------------------------------------------------------------- gfx600 - tahiti amdgcn dGPU gfx601 - pitcairn amdgcn dGPU - verde - oland - hainan **GCN GFX7 (Sea Islands (CI))** [AMD-GCN-GFX7]_ -------------------------------------------------------------------- gfx700 - bonaire amdgcn dGPU - Radeon HD 7790 - Radeon HD 8770 - R7 260 - R7 260X \ - kaveri amdgcn APU - A6-7000 - A6 Pro-7050B - A8-7100 - A8 Pro-7150B - A10-7300 - A10 Pro-7350B - FX-7500 - A8-7200P - A10-7400P - FX-7600P gfx701 - hawaii amdgcn dGPU ROCm - FirePro W8100 - FirePro W9100 - FirePro S9150 - FirePro S9170 gfx702 dGPU ROCm - Radeon R9 290 - Radeon R9 290x - Radeon R390 - Radeon R390x gfx703 - kabini amdgcn APU - E1-2100 - mullins - E1-2200 - E1-2500 - E2-3000 - E2-3800 - A4-5000 - A4-5100 - A6-5200 - A4 Pro-3340B **GCN GFX8 (Volcanic Islands (VI))** [AMD-GCN-GFX8]_ -------------------------------------------------------------------- gfx800 - iceland amdgcn dGPU - FirePro S7150 - FirePro S7100 - FirePro W7100 - Radeon R285 - Radeon R9 380 - Radeon R9 385 - Mobile FirePro M7170 gfx801 - carrizo amdgcn APU - A6-8500P - Pro A6-8500B - A8-8600P - Pro A8-8600B - FX-8800P - Pro A12-8800B \ amdgcn APU ROCm - A10-8700P - Pro A10-8700B - A10-8780P \ amdgcn APU - A10-9600P - A10-9630P - A12-9700P - A12-9730P - FX-9800P - FX-9830P \ amdgcn APU - E2-9010 - A6-9210 - A9-9410 gfx802 - tonga amdgcn dGPU ROCm Same as gfx800 gfx803 - fiji amdgcn dGPU ROCm - Radeon R9 Nano - Radeon R9 Fury - Radeon R9 FuryX - Radeon Pro Duo - FirePro S9300x2 - Radeon Instinct MI8 \ - polaris10 amdgcn dGPU ROCm - Radeon RX 470 - Radeon RX 480 - Radeon Instinct MI6 \ - polaris11 amdgcn dGPU ROCm - Radeon RX 460 gfx804 amdgcn dGPU Same as gfx803 gfx810 - stoney amdgcn APU **GCN GFX9** [AMD-GCN-GFX9]_ -------------------------------------------------------------------- gfx900 amdgcn dGPU - Radeon Vega Frontier Edition - Radeon RX Vega 56 - Radeon RX Vega 64 - Radeon RX Vega 64 Liquid - Radeon Instinct MI25 gfx901 amdgcn dGPU ROCm Same as gfx900 except XNACK is enabled gfx902 amdgcn APU *TBA* .. TODO Add product names. gfx903 amdgcn APU Same as gfx902 except XNACK is enabled ========== =========== ============ ===== ======= ================== .. _amdgpu-address-spaces: Address Spaces -------------- The AMDGPU backend uses the following address space mappings. The memory space names used in the table, aside from the region memory space, is from the OpenCL standard. LLVM Address Space number is used throughout LLVM (for example, in LLVM IR). .. table:: Address Space Mapping :name: amdgpu-address-space-mapping-table ================== ================= ================= ================= ================= LLVM Address Space Memory Space ------------------ ----------------------------------------------------------------------- \ Current Default amdgiz/amdgizcl hcc Future Default ================== ================= ================= ================= ================= 0 Private (Scratch) Generic (Flat) Generic (Flat) Generic (Flat) 1 Global Global Global Global 2 Constant Constant Constant Region (GDS) 3 Local (group/LDS) Local (group/LDS) Local (group/LDS) Local (group/LDS) 4 Generic (Flat) Region (GDS) Region (GDS) Constant 5 Region (GDS) Private (Scratch) Private (Scratch) Private (Scratch) ================== ================= ================= ================= ================= Current Default This is the current default address space mapping used for all languages except hcc. This will shortly be deprecated. amdgiz/amdgizcl This is the current address space mapping used when ``amdgiz`` or ``amdgizcl`` is specified as the target triple environment value. hcc This is the current address space mapping used when ``hcc`` is specified as the target triple environment value.This will shortly be deprecated. Future Default This will shortly be the only address space mapping for all languages using AMDGPU backend. .. _amdgpu-memory-scopes: Memory Scopes ------------- This section provides LLVM memory synchronization scopes supported by the AMDGPU backend memory model when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-amdhsa-memory-model` and :ref:`amdgpu-target-triples`). The memory model supported is based on the HSA memory model [HSA]_ which is based in turn on HRF-indirect with scope inclusion [HRF]_. The happens-before relation is transitive over the synchonizes-with relation independent of scope, and synchonizes-with allows the memory scope instances to be inclusive (see table :ref:`amdgpu-amdhsa-llvm-sync-scopes-amdhsa-table`). This is different to the OpenCL [OpenCL]_ memory model which does not have scope inclusion and requires the memory scopes to exactly match. However, this is conservatively correct for OpenCL. .. table:: AMDHSA LLVM Sync Scopes for AMDHSA :name: amdgpu-amdhsa-llvm-sync-scopes-amdhsa-table ================ ========================================================== LLVM Sync Scope Description ================ ========================================================== *none* The default: ``system``. Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation's sync scope is: - ``system``. - ``agent`` and executed by a thread on the same agent. - ``workgroup`` and executed by a thread in the same workgroup. - ``wavefront`` and executed by a thread in the same wavefront. ``agent`` Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation's sync scope is: - ``system`` or ``agent`` and executed by a thread on the same agent. - ``workgroup`` and executed by a thread in the same workgroup. - ``wavefront`` and executed by a thread in the same wavefront. ``workgroup`` Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation's sync scope is: - ``system``, ``agent`` or ``workgroup`` and executed by a thread in the same workgroup. - ``wavefront`` and executed by a thread in the same wavefront. ``wavefront`` Synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) for all address spaces (except private, or generic that accesses private) provided the other operation's sync scope is: - ``system``, ``agent``, ``workgroup`` or ``wavefront`` and executed by a thread in the same wavefront. ``singlethread`` Only synchronizes with, and participates in modification and seq_cst total orderings with, other operations (except image operations) running in the same thread for all address spaces (for example, in signal handlers). ================ ========================================================== AMDGPU Intrinsics ----------------- The AMDGPU backend implements the following intrinsics. *This section is WIP.* .. TODO List AMDGPU intrinsics Code Object =========== The AMDGPU backend generates a standard ELF [ELF]_ relocatable code object that can be linked by ``lld`` to produce a standard ELF shared code object which can be loaded and executed on an AMDGPU target. Header ------ The AMDGPU backend uses the following ELF header: .. table:: AMDGPU ELF Header :name: amdgpu-elf-header-table ========================== =============================== Field Value ========================== =============================== ``e_ident[EI_CLASS]`` ``ELFCLASS64`` ``e_ident[EI_DATA]`` ``ELFDATA2LSB`` ``e_ident[EI_OSABI]`` ``ELFOSABI_AMDGPU_HSA``, ``ELFOSABI_AMDGPU_PAL`` or ``ELFOSABI_AMDGPU_MESA3D`` ``e_ident[EI_ABIVERSION]`` ``ELFABIVERSION_AMDGPU_HSA``, ``ELFABIVERSION_AMDGPU_PAL`` or ``ELFABIVERSION_AMDGPU_MESA3D`` ``e_type`` ``ET_REL`` or ``ET_DYN`` ``e_machine`` ``EM_AMDGPU`` ``e_entry`` 0 ``e_flags`` 0 ========================== =============================== .. .. table:: AMDGPU ELF Header Enumeration Values :name: amdgpu-elf-header-enumeration-values-table =============================== ===== Name Value =============================== ===== ``EM_AMDGPU`` 224 ``ELFOSABI_AMDGPU_HSA`` 64 ``ELFOSABI_AMDGPU_PAL`` 65 ``ELFOSABI_AMDGPU_MESA3D`` 66 ``ELFABIVERSION_AMDGPU_HSA`` 1 ``ELFABIVERSION_AMDGPU_PAL`` 0 ``ELFABIVERSION_AMDGPU_MESA3D`` 0 =============================== ===== ``e_ident[EI_CLASS]`` The ELF class is always ``ELFCLASS64``. The AMDGPU backend only supports 64 bit applications. ``e_ident[EI_DATA]`` All AMDGPU targets use ELFDATA2LSB for little-endian byte ordering. ``e_ident[EI_OSABI]`` One of the following AMD GPU architecture specific OS ABIs: * ``ELFOSABI_AMDGPU_HSA`` is used to specify that the code object conforms to the AMD HSA runtime ABI [HSA]_. * ``ELFOSABI_AMDGPU_PAL`` is used to specify that the code object conforms to the AMD PAL runtime ABI. * ``ELFOSABI_AMDGPU_MESA3D`` is used to specify that the code object conforms to the AMD MESA runtime ABI. ``e_ident[EI_ABIVERSION]`` The ABI version of the AMD GPU architecture specific OS ABI to which the code object conforms: * ``ELFABIVERSION_AMDGPU_HSA`` is used to specify the version of AMD HSA runtime ABI. * ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL runtime ABI. * ``ELFABIVERSION_AMDGPU_MESA3D`` is used to specify the version of AMD MESA runtime ABI. ``e_type`` Can be one of the following values: ``ET_REL`` The type produced by the AMD GPU backend compiler as it is relocatable code object. ``ET_DYN`` The type produced by the linker as it is a shared code object. The AMD HSA runtime loader requires a ``ET_DYN`` code object. ``e_machine`` The value ``EM_AMDGPU`` is used for the machine for all members of the AMD GPU architecture family. The specific member is specified in the ``NT_AMD_AMDGPU_ISA`` entry in the ``.note`` section (see :ref:`amdgpu-note-records`). ``e_entry`` The entry point is 0 as the entry points for individual kernels must be selected in order to invoke them through AQL packets. ``e_flags`` The value is 0 as no flags are used. Sections -------- An AMDGPU target ELF code object has the standard ELF sections which include: .. table:: AMDGPU ELF Sections :name: amdgpu-elf-sections-table ================== ================ ================================= Name Type Attributes ================== ================ ================================= ``.bss`` ``SHT_NOBITS`` ``SHF_ALLOC`` + ``SHF_WRITE`` ``.data`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE`` ``.debug_``\ *\** ``SHT_PROGBITS`` *none* ``.dynamic`` ``SHT_DYNAMIC`` ``SHF_ALLOC`` ``.dynstr`` ``SHT_PROGBITS`` ``SHF_ALLOC`` ``.dynsym`` ``SHT_PROGBITS`` ``SHF_ALLOC`` ``.got`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE`` ``.hash`` ``SHT_HASH`` ``SHF_ALLOC`` ``.note`` ``SHT_NOTE`` *none* ``.rela``\ *name* ``SHT_RELA`` *none* ``.rela.dyn`` ``SHT_RELA`` *none* ``.rodata`` ``SHT_PROGBITS`` ``SHF_ALLOC`` ``.shstrtab`` ``SHT_STRTAB`` *none* ``.strtab`` ``SHT_STRTAB`` *none* ``.symtab`` ``SHT_SYMTAB`` *none* ``.text`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_EXECINSTR`` ================== ================ ================================= These sections have their standard meanings (see [ELF]_) and are only generated if needed. ``.debug``\ *\** The standard DWARF sections. See :ref:`amdgpu-dwarf` for information on the DWARF produced by the AMDGPU backend. ``.dynamic``, ``.dynstr``, ``.dynsym``, ``.hash`` The standard sections used by a dynamic loader. ``.note`` See :ref:`amdgpu-note-records` for the note records supported by the AMDGPU backend. ``.rela``\ *name*, ``.rela.dyn`` For relocatable code objects, *name* is the name of the section that the relocation records apply. For example, ``.rela.text`` is the section name for relocation records associated with the ``.text`` section. For linked shared code objects, ``.rela.dyn`` contains all the relocation records from each of the relocatable code object's ``.rela``\ *name* sections. See :ref:`amdgpu-relocation-records` for the relocation records supported by the AMDGPU backend. ``.text`` The executable machine code for the kernels and functions they call. Generated as position independent code. See :ref:`amdgpu-code-conventions` for information on conventions used in the isa generation. .. _amdgpu-note-records: Note Records ------------ As required by ``ELFCLASS64``, minimal zero byte padding must be generated after the ``name`` field to ensure the ``desc`` field is 4 byte aligned. In addition, minimal zero byte padding must be generated to ensure the ``desc`` field size is a multiple of 4 bytes. The ``sh_addralign`` field of the ``.note`` section must be at least 4 to indicate at least 8 byte alignment. The AMDGPU backend code object uses the following ELF note records in the ``.note`` section. The *Description* column specifies the layout of the note record's ``desc`` field. All fields are consecutive bytes. Note records with variable size strings have a corresponding ``*_size`` field that specifies the number of bytes, including the terminating null character, in the string. The string(s) come immediately after the preceding fields. Additional note records can be present. .. table:: AMDGPU ELF Note Records :name: amdgpu-elf-note-records-table ===== ============================== ====================================== Name Type Description ===== ============================== ====================================== "AMD" ``NT_AMD_AMDGPU_HSA_METADATA`` <metadata null terminated string> "AMD" ``NT_AMD_AMDGPU_ISA`` <isa name null terminated string> ===== ============================== ====================================== .. .. table:: AMDGPU ELF Note Record Enumeration Values :name: amdgpu-elf-note-record-enumeration-values-table ============================== ===== Name Value ============================== ===== *reserved* 0-9 ``NT_AMD_AMDGPU_HSA_METADATA`` 10 ``NT_AMD_AMDGPU_ISA`` 11 ============================== ===== ``NT_AMD_AMDGPU_ISA`` Specifies the instruction set architecture used by the machine code contained in the code object. This note record is required for code objects containing machine code for processors matching the ``amdgcn`` architecture in table :ref:`amdgpu-processors`. The null terminated string has the following syntax: *architecture*\ ``-``\ *vendor*\ ``-``\ *os*\ ``-``\ *environment*\ ``-``\ *processor* where: *architecture* The architecture from table :ref:`amdgpu-target-triples-table`. This is always ``amdgcn`` when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). *vendor* The vendor from table :ref:`amdgpu-target-triples-table`. For the AMDGPU backend this is always ``amd``. *os* The OS from table :ref:`amdgpu-target-triples-table`. *environment* An environment from table :ref:`amdgpu-target-triples-table`, or blank if the environment has no affect on the execution of the code object. For the AMDGPU backend this is currently always blank. *processor* The processor from table :ref:`amdgpu-processors-table`. For example: ``amdgcn-amd-amdhsa--gfx901`` ``NT_AMD_AMDGPU_HSA_METADATA`` Specifies extensible metadata associated with the code objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is required when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). See :ref:`amdgpu-amdhsa-hsa-code-object-metadata` for the syntax of the code object metadata string. .. _amdgpu-symbols: Symbols ------- Symbols include the following: .. table:: AMDGPU ELF Symbols :name: amdgpu-elf-symbols-table ===================== ============== ============= ================== Name Type Section Description ===================== ============== ============= ================== *link-name* ``STT_OBJECT`` - ``.data`` Global variable - ``.rodata`` - ``.bss`` *link-name*\ ``@kd`` ``STT_OBJECT`` - ``.rodata`` Kernel descriptor *link-name* ``STT_FUNC`` - ``.text`` Kernel entry point ===================== ============== ============= ================== Global variable Global variables both used and defined by the compilation unit. If the symbol is defined in the compilation unit then it is allocated in the appropriate section according to if it has initialized data or is readonly. If the symbol is external then its section is ``STN_UNDEF`` and the loader will resolve relocations using the definition provided by another code object or explicitly defined by the runtime. All global symbols, whether defined in the compilation unit or external, are accessed by the machine code indirectly through a GOT table entry. This allows them to be preemptable. The GOT table is only supported when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). .. TODO Add description of linked shared object symbols. Seems undefined symbols are marked as STT_NOTYPE. Kernel descriptor Every HSA kernel has an associated kernel descriptor. It is the address of the kernel descriptor that is used in the AQL dispatch packet used to invoke the kernel, not the kernel entry point. The layout of the HSA kernel descriptor is defined in :ref:`amdgpu-amdhsa-kernel-descriptor`. Kernel entry point Every HSA kernel also has a symbol for its machine code entry point. .. _amdgpu-relocation-records: Relocation Records ------------------ AMDGPU backend generates ``Elf64_Rela`` relocation records. Supported relocatable fields are: ``word32`` This specifies a 32-bit field occupying 4 bytes with arbitrary byte alignment. These values use the same byte order as other word values in the AMD GPU architecture. ``word64`` This specifies a 64-bit field occupying 8 bytes with arbitrary byte alignment. These values use the same byte order as other word values in the AMD GPU architecture. Following notations are used for specifying relocation calculations: **A** Represents the addend used to compute the value of the relocatable field. **G** Represents the offset into the global offset table at which the relocation entry's symbol will reside during execution. **GOT** Represents the address of the global offset table. **P** Represents the place (section offset for ``et_rel`` or address for ``et_dyn``) of the storage unit being relocated (computed using ``r_offset``). **S** Represents the value of the symbol whose index resides in the relocation entry. Relocations not using this must specify a symbol index of ``STN_UNDEF``. **B** Represents the base address of a loaded executable or shared object which is the difference between the ELF address and the actual load address. Relocations using this are only valid in executable or shared objects. The following relocation types are supported: .. table:: AMDGPU ELF Relocation Records :name: amdgpu-elf-relocation-records-table ========================== ===== ========== ============================== Relocation Type Value Field Calculation ========================== ===== ========== ============================== ``R_AMDGPU_NONE`` 0 *none* *none* ``R_AMDGPU_ABS32_LO`` 1 ``word32`` (S + A) & 0xFFFFFFFF ``R_AMDGPU_ABS32_HI`` 2 ``word32`` (S + A) >> 32 ``R_AMDGPU_ABS64`` 3 ``word64`` S + A ``R_AMDGPU_REL32`` 4 ``word32`` S + A - P ``R_AMDGPU_REL64`` 5 ``word64`` S + A - P ``R_AMDGPU_ABS32`` 6 ``word32`` S + A ``R_AMDGPU_GOTPCREL`` 7 ``word32`` G + GOT + A - P ``R_AMDGPU_GOTPCREL32_LO`` 8 ``word32`` (G + GOT + A - P) & 0xFFFFFFFF ``R_AMDGPU_GOTPCREL32_HI`` 9 ``word32`` (G + GOT + A - P) >> 32 ``R_AMDGPU_REL32_LO`` 10 ``word32`` (S + A - P) & 0xFFFFFFFF ``R_AMDGPU_REL32_HI`` 11 ``word32`` (S + A - P) >> 32 *reserved* 12 ``R_AMDGPU_RELATIVE64`` 13 ``word64`` B + A ========================== ===== ========== ============================== .. _amdgpu-dwarf: DWARF ----- Standard DWARF [DWARF]_ Version 2 sections can be generated. These contain information that maps the code object executable code and data to the source language constructs. It can be used by tools such as debuggers and profilers. Address Space Mapping ~~~~~~~~~~~~~~~~~~~~~ The following address space mapping is used: .. table:: AMDGPU DWARF Address Space Mapping :name: amdgpu-dwarf-address-space-mapping-table =================== ================= DWARF Address Space Memory Space =================== ================= 1 Private (Scratch) 2 Local (group/LDS) *omitted* Global *omitted* Constant *omitted* Generic (Flat) *not supported* Region (GDS) =================== ================= See :ref:`amdgpu-address-spaces` for information on the memory space terminology used in the table. An ``address_class`` attribute is generated on pointer type DIEs to specify the DWARF address space of the value of the pointer when it is in the *private* or *local* address space. Otherwise the attribute is omitted. An ``XDEREF`` operation is generated in location list expressions for variables that are allocated in the *private* and *local* address space. Otherwise no ``XDREF`` is omitted. Register Mapping ~~~~~~~~~~~~~~~~ *This section is WIP.* .. TODO Define DWARF register enumeration. If want to present a wavefront state then should expose vector registers as 64 wide (rather than per work-item view that LLVM uses). Either as separate registers, or a 64x4 byte single register. In either case use a new LANE op (akin to XDREF) to select the current lane usage in a location expression. This would also allow scalar register spilling to vector register lanes to be expressed (currently no debug information is being generated for spilling). If choose a wide single register approach then use LANE in conjunction with PIECE operation to select the dword part of the register for the current lane. If the separate register approach then use LANE to select the register. Source Text ~~~~~~~~~~~ *This section is WIP.* .. TODO DWARF extension to include runtime generated source text. .. _amdgpu-code-conventions: Code Conventions ================ This section provides code conventions used for each supported target triple OS (see :ref:`amdgpu-target-triples`). AMDHSA ------ This section provides code conventions used when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). .. _amdgpu-amdhsa-hsa-code-object-metadata: Code Object Metadata ~~~~~~~~~~~~~~~~~~~~ The code object metadata specifies extensible metadata associated with the code objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is specified by the ``NT_AMD_AMDGPU_HSA_METADATA`` note record (see :ref:`amdgpu-note-records`) and is required when the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). It must contain the minimum information necessary to support the ROCM kernel queries. For example, the segment sizes needed in a dispatch packet. In addition, a high level language runtime may require other information to be included. For example, the AMD OpenCL runtime records kernel argument information. The metadata is specified as a YAML formatted string (see [YAML]_ and :doc:`YamlIO`). .. TODO Is the string null terminated? It probably should not if YAML allows it to contain null characters, otherwise it should be. The metadata is represented as a single YAML document comprised of the mapping defined in table :ref:`amdgpu-amdhsa-code-object-metadata-mapping-table` and referenced tables. For boolean values, the string values of ``false`` and ``true`` are used for false and true respectively. Additional information can be added to the mappings. To avoid conflicts, any non-AMD key names should be prefixed by "*vendor-name*.". .. table:: AMDHSA Code Object Metadata Mapping :name: amdgpu-amdhsa-code-object-metadata-mapping-table ========== ============== ========= ======================================= String Key Value Type Required? Description ========== ============== ========= ======================================= "Version" sequence of Required - The first integer is the major 2 integers version. Currently 1. - The second integer is the minor version. Currently 0. "Printf" sequence of Each string is encoded information strings about a printf function call. The encoded information is organized as fields separated by colon (':'): ``ID:N:S[0]:S[1]:...:S[N-1]:FormatString`` where: ``ID`` A 32 bit integer as a unique id for each printf function call ``N`` A 32 bit integer equal to the number of arguments of printf function call minus 1 ``S[i]`` (where i = 0, 1, ... , N-1) 32 bit integers for the size in bytes of the i-th FormatString argument of the printf function call FormatString The format string passed to the printf function call. "Kernels" sequence of Required Sequence of the mappings for each mapping kernel in the code object. See :ref:`amdgpu-amdhsa-code-object-kernel-metadata-mapping-table` for the definition of the mapping. ========== ============== ========= ======================================= .. .. table:: AMDHSA Code Object Kernel Metadata Mapping :name: amdgpu-amdhsa-code-object-kernel-metadata-mapping-table ================= ============== ========= ================================ String Key Value Type Required? Description ================= ============== ========= ================================ "Name" string Required Source name of the kernel. "SymbolName" string Required Name of the kernel descriptor ELF symbol. "Language" string Source language of the kernel. Values include: - "OpenCL C" - "OpenCL C++" - "HCC" - "OpenMP" "LanguageVersion" sequence of - The first integer is the major 2 integers version. - The second integer is the minor version. "Attrs" mapping Mapping of kernel attributes. See :ref:`amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table` for the mapping definition. "Args" sequence of Sequence of mappings of the mapping kernel arguments. See :ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table` for the definition of the mapping. "CodeProps" mapping Mapping of properties related to the kernel code. See :ref:`amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table` for the mapping definition. "DebugProps" mapping Mapping of properties related to the kernel debugging. See :ref:`amdgpu-amdhsa-code-object-kernel-debug-properties-metadata-mapping-table` for the mapping definition. ================= ============== ========= ================================ .. .. table:: AMDHSA Code Object Kernel Attribute Metadata Mapping :name: amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table =================== ============== ========= ============================== String Key Value Type Required? Description =================== ============== ========= ============================== "ReqdWorkGroupSize" sequence of The dispatch work-group size 3 integers X, Y, Z must correspond to the specified values. Corresponds to the OpenCL ``reqd_work_group_size`` attribute. "WorkGroupSizeHint" sequence of The dispatch work-group size 3 integers X, Y, Z is likely to be the specified values. Corresponds to the OpenCL ``work_group_size_hint`` attribute. "VecTypeHint" string The name of a scalar or vector type. Corresponds to the OpenCL ``vec_type_hint`` attribute. "RuntimeHandle" string The external symbol name associated with a kernel. OpenCL runtime allocates a global buffer for the symbol and saves the kernel's address to it, which is used for device side enqueueing. Only available for device side enqueued kernels. =================== ============== ========= ============================== .. .. table:: AMDHSA Code Object Kernel Argument Metadata Mapping :name: amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table ================= ============== ========= ================================ String Key Value Type Required? Description ================= ============== ========= ================================ "Name" string Kernel argument name. "TypeName" string Kernel argument type name. "Size" integer Required Kernel argument size in bytes. "Align" integer Required Kernel argument alignment in bytes. Must be a power of two. "ValueKind" string Required Kernel argument kind that specifies how to set up the corresponding argument. Values include: "ByValue" The argument is copied directly into the kernarg. "GlobalBuffer" A global address space pointer to the buffer data is passed in the kernarg. "DynamicSharedPointer" A group address space pointer to dynamically allocated LDS is passed in the kernarg. "Sampler" A global address space pointer to a S# is passed in the kernarg. "Image" A global address space pointer to a T# is passed in the kernarg. "Pipe" A global address space pointer to an OpenCL pipe is passed in the kernarg. "Queue" A global address space pointer to an OpenCL device enqueue queue is passed in the kernarg. "HiddenGlobalOffsetX" The OpenCL grid dispatch global offset for the X dimension is passed in the kernarg. "HiddenGlobalOffsetY" The OpenCL grid dispatch global offset for the Y dimension is passed in the kernarg. "HiddenGlobalOffsetZ" The OpenCL grid dispatch global offset for the Z dimension is passed in the kernarg. "HiddenNone" An argument that is not used by the kernel. Space needs to be left for it, but it does not need to be set up. "HiddenPrintfBuffer" A global address space pointer to the runtime printf buffer is passed in kernarg. "HiddenDefaultQueue" A global address space pointer to the OpenCL device enqueue queue that should be used by the kernel by default is passed in the kernarg. "HiddenCompletionAction" *TBD* .. TODO Add description. "ValueType" string Required Kernel argument value type. Only present if "ValueKind" is "ByValue". For vector data types, the value is for the element type. Values include: - "Struct" - "I8" - "U8" - "I16" - "U16" - "F16" - "I32" - "U32" - "F32" - "I64" - "U64" - "F64" .. TODO How can it be determined if a vector type, and what size vector? "PointeeAlign" integer Alignment in bytes of pointee type for pointer type kernel argument. Must be a power of 2. Only present if "ValueKind" is "DynamicSharedPointer". "AddrSpaceQual" string Kernel argument address space qualifier. Only present if "ValueKind" is "GlobalBuffer" or "DynamicSharedPointer". Values are: - "Private" - "Global" - "Constant" - "Local" - "Generic" - "Region" .. TODO Is GlobalBuffer only Global or Constant? Is DynamicSharedPointer always Local? Can HCC allow Generic? How can Private or Region ever happen? "AccQual" string Kernel argument access qualifier. Only present if "ValueKind" is "Image" or "Pipe". Values are: - "ReadOnly" - "WriteOnly" - "ReadWrite" .. TODO Does this apply to GlobalBuffer? "ActualAccQual" string The actual memory accesses performed by the kernel on the kernel argument. Only present if "ValueKind" is "GlobalBuffer", "Image", or "Pipe". This may be more restrictive than indicated by "AccQual" to reflect what the kernel actual does. If not present then the runtime must assume what is implied by "AccQual" and "IsConst". Values are: - "ReadOnly" - "WriteOnly" - "ReadWrite" "IsConst" boolean Indicates if the kernel argument is const qualified. Only present if "ValueKind" is "GlobalBuffer". "IsRestrict" boolean Indicates if the kernel argument is restrict qualified. Only present if "ValueKind" is "GlobalBuffer". "IsVolatile" boolean Indicates if the kernel argument is volatile qualified. Only present if "ValueKind" is "GlobalBuffer". "IsPipe" boolean Indicates if the kernel argument is pipe qualified. Only present if "ValueKind" is "Pipe". .. TODO Can GlobalBuffer be pipe qualified? ================= ============== ========= ================================ .. .. table:: AMDHSA Code Object Kernel Code Properties Metadata Mapping :name: amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table ============================ ============== ========= ===================== String Key Value Type Required? Description ============================ ============== ========= ===================== "KernargSegmentSize" integer Required The size in bytes of the kernarg segment that holds the values of the arguments to the kernel. "GroupSegmentFixedSize" integer Required The amount of group segment memory required by a work-group in bytes. This does not include any dynamically allocated group segment memory that may be added when the kernel is dispatched. "PrivateSegmentFixedSize" integer Required The amount of fixed private address space memory required for a work-item in bytes. If IsDynamicCallstack is 1 then additional space must be added to this value for the call stack. "KernargSegmentAlign" integer Required The maximum byte alignment of arguments in the kernarg segment. Must be a power of 2. "WavefrontSize" integer Required Wavefront size. Must be a power of 2. "NumSGPRs" integer Number of scalar registers used by a wavefront for GFX6-GFX9. This includes the special SGPRs for VCC, Flat Scratch (GFX7-GFX9) and XNACK (for GFX8-GFX9). It does not include the 16 SGPR added if a trap handler is enabled. It is not rounded up to the allocation granularity. "NumVGPRs" integer Number of vector registers used by each work-item for GFX6-GFX9 "MaxFlatWorkGroupSize" integer Maximum flat work-group size supported by the kernel in work-items. "IsDynamicCallStack" boolean Indicates if the generated machine code is using a dynamically sized call stack. "IsXNACKEnabled" boolean Indicates if the generated machine code is capable of supporting XNACK. ============================ ============== ========= ===================== .. .. table:: AMDHSA Code Object Kernel Debug Properties Metadata Mapping :name: amdgpu-amdhsa-code-object-kernel-debug-properties-metadata-mapping-table =================================== ============== ========= ============== String Key Value Type Required? Description =================================== ============== ========= ============== "DebuggerABIVersion" sequence of 2 integers "ReservedNumVGPRs" integer "ReservedFirstVGPR" integer "PrivateSegmentBufferSGPR" integer "WavefrontPrivateSegmentOffsetSGPR" integer =================================== ============== ========= ============== .. TODO Plan to remove the debug properties metadata. Kernel Dispatch ~~~~~~~~~~~~~~~ The HSA architected queuing language (AQL) defines a user space memory interface that can be used to control the dispatch of kernels, in an agent independent way. An agent can have zero or more AQL queues created for it using the ROCm runtime, in which AQL packets (all of which are 64 bytes) can be placed. See the *HSA Platform System Architecture Specification* [HSA]_ for the AQL queue mechanics and packet layouts. The packet processor of a kernel agent is responsible for detecting and dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the packet processor is implemented by the hardware command processor (CP), asynchronous dispatch controller (ADC) and shader processor input controller (SPI). The ROCm runtime can be used to allocate an AQL queue object. It uses the kernel mode driver to initialize and register the AQL queue with CP. To dispatch a kernel the following actions are performed. This can occur in the CPU host program, or from an HSA kernel executing on a GPU. 1. A pointer to an AQL queue for the kernel agent on which the kernel is to be executed is obtained. 2. A pointer to the kernel descriptor (see :ref:`amdgpu-amdhsa-kernel-descriptor`) of the kernel to execute is obtained. It must be for a kernel that is contained in a code object that that was loaded by the ROCm runtime on the kernel agent with which the AQL queue is associated. 3. Space is allocated for the kernel arguments using the ROCm runtime allocator for a memory region with the kernarg property for the kernel agent that will execute the kernel. It must be at least 16 byte aligned. 4. Kernel argument values are assigned to the kernel argument memory allocation. The layout is defined in the *HSA Programmer's Language Reference* [HSA]_. For AMDGPU the kernel execution directly accesses the kernel argument memory in the same way constant memory is accessed. (Note that the HSA specification allows an implementation to copy the kernel argument contents to another location that is accessed by the kernel.) 5. An AQL kernel dispatch packet is created on the AQL queue. The ROCm runtime api uses 64 bit atomic operations to reserve space in the AQL queue for the packet. The packet must be set up, and the final write must use an atomic store release to set the packet kind to ensure the packet contents are visible to the kernel agent. AQL defines a doorbell signal mechanism to notify the kernel agent that the AQL queue has been updated. These rules, and the layout of the AQL queue and kernel dispatch packet is defined in the *HSA System Architecture Specification* [HSA]_. 6. A kernel dispatch packet includes information about the actual dispatch, such as grid and work-group size, together with information from the code object about the kernel, such as segment sizes. The ROCm runtime queries on the kernel symbol can be used to obtain the code object values which are recorded in the :ref:`amdgpu-amdhsa-hsa-code-object-metadata`. 7. CP executes micro-code and is responsible for detecting and setting up the GPU to execute the wavefronts of a kernel dispatch. 8. CP ensures that when the a wavefront starts executing the kernel machine code, the scalar general purpose registers (SGPR) and vector general purpose registers (VGPR) are set up as required by the machine code. The required setup is defined in the :ref:`amdgpu-amdhsa-kernel-descriptor`. The initial register state is defined in :ref:`amdgpu-amdhsa-initial-kernel-execution-state`. 9. The prolog of the kernel machine code (see :ref:`amdgpu-amdhsa-kernel-prolog`) sets up the machine state as necessary before continuing executing the machine code that corresponds to the kernel. 10. When the kernel dispatch has completed execution, CP signals the completion signal specified in the kernel dispatch packet if not 0. .. _amdgpu-amdhsa-memory-spaces: Memory Spaces ~~~~~~~~~~~~~ The memory space properties are: .. table:: AMDHSA Memory Spaces :name: amdgpu-amdhsa-memory-spaces-table ================= =========== ======== ======= ================== Memory Space Name HSA Segment Hardware Address NULL Value Name Name Size ================= =========== ======== ======= ================== Private private scratch 32 0x00000000 Local group LDS 32 0xFFFFFFFF Global global global 64 0x0000000000000000 Constant constant *same as 64 0x0000000000000000 global* Generic flat flat 64 0x0000000000000000 Region N/A GDS 32 *not implemented for AMDHSA* ================= =========== ======== ======= ================== The global and constant memory spaces both use global virtual addresses, which are the same virtual address space used by the CPU. However, some virtual addresses may only be accessible to the CPU, some only accessible by the GPU, and some by both. Using the constant memory space indicates that the data will not change during the execution of the kernel. This allows scalar read instructions to be used. The vector and scalar L1 caches are invalidated of volatile data before each kernel dispatch execution to allow constant memory to change values between kernel dispatches. The local memory space uses the hardware Local Data Store (LDS) which is automatically allocated when the hardware creates work-groups of wavefronts, and freed when all the wavefronts of a work-group have terminated. The data store (DS) instructions can be used to access it. The private memory space uses the hardware scratch memory support. If the kernel uses scratch, then the hardware allocates memory that is accessed using wavefront lane dword (4 byte) interleaving. The mapping used from private address to physical address is: ``wavefront-scratch-base + (private-address * wavefront-size * 4) + (wavefront-lane-id * 4)`` There are different ways that the wavefront scratch base address is determined by a wavefront (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). This memory can be accessed in an interleaved manner using buffer instruction with the scratch buffer descriptor and per wave scratch offset, by the scratch instructions, or by flat instructions. If each lane of a wavefront accesses the same private address, the interleaving results in adjacent dwords being accessed and hence requires fewer cache lines to be fetched. Multi-dword access is not supported except by flat and scratch instructions in GFX9. The generic address space uses the hardware flat address support available in GFX7-GFX9. This uses two fixed ranges of virtual addresses (the private and local appertures), that are outside the range of addressible global memory, to map from a flat address to a private or local address. FLAT instructions can take a flat address and access global, private (scratch) and group (LDS) memory depending in if the address is within one of the apperture ranges. Flat access to scratch requires hardware aperture setup and setup in the kernel prologue (see :ref:`amdgpu-amdhsa-flat-scratch`). Flat access to LDS requires hardware aperture setup and M0 (GFX7-GFX8) register setup (see :ref:`amdgpu-amdhsa-m0`). To convert between a segment address and a flat address the base address of the appertures address can be used. For GFX7-GFX8 these are available in the :ref:`amdgpu-amdhsa-hsa-aql-queue` the address of which can be obtained with Queue Ptr SGPR (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). For GFX9 the appature base addresses are directly available as inline constant registers ``SRC_SHARED_BASE/LIMIT`` and ``SRC_PRIVATE_BASE/LIMIT``. In 64 bit address mode the apperture sizes are 2^32 bytes and the base is aligned to 2^32 which makes it easier to convert from flat to segment or segment to flat. Image and Samplers ~~~~~~~~~~~~~~~~~~ Image and sample handles created by the ROCm runtime are 64 bit addresses of a hardware 32 byte V# and 48 byte S# object respectively. In order to support the HSA ``query_sampler`` operations two extra dwords are used to store the HSA BRIG enumeration values for the queries that are not trivially deducible from the S# representation. HSA Signals ~~~~~~~~~~~ HSA signal handles created by the ROCm runtime are 64 bit addresses of a structure allocated in memory accessible from both the CPU and GPU. The structure is defined by the ROCm runtime and subject to change between releases (see [AMD-ROCm-github]_). .. _amdgpu-amdhsa-hsa-aql-queue: HSA AQL Queue ~~~~~~~~~~~~~ The HSA AQL queue structure is defined by the ROCm runtime and subject to change between releases (see [AMD-ROCm-github]_). For some processors it contains fields needed to implement certain language features such as the flat address aperture bases. It also contains fields used by CP such as managing the allocation of scratch memory. .. _amdgpu-amdhsa-kernel-descriptor: Kernel Descriptor ~~~~~~~~~~~~~~~~~ A kernel descriptor consists of the information needed by CP to initiate the execution of a kernel, including the entry point address of the machine code that implements the kernel. Kernel Descriptor for GFX6-GFX9 +++++++++++++++++++++++++++++++ CP microcode requires the Kernel descritor to be allocated on 64 byte alignment. .. table:: Kernel Descriptor for GFX6-GFX9 :name: amdgpu-amdhsa-kernel-descriptor-gfx6-gfx9-table ======= ======= =============================== ============================ Bits Size Field Name Description ======= ======= =============================== ============================ 31:0 4 bytes GroupSegmentFixedSize The amount of fixed local address space memory required for a work-group in bytes. This does not include any dynamically allocated local address space memory that may be added when the kernel is dispatched. 63:32 4 bytes PrivateSegmentFixedSize The amount of fixed private address space memory required for a work-item in bytes. If is_dynamic_callstack is 1 then additional space must be added to this value for the call stack. 95:64 4 bytes MaxFlatWorkGroupSize Maximum flat work-group size supported by the kernel in work-items. 96 1 bit IsDynamicCallStack Indicates if the generated machine code is using a dynamically sized call stack. 97 1 bit IsXNACKEnabled Indicates if the generated machine code is capable of suppoting XNACK. 127:98 30 bits Reserved, must be 0. 191:128 8 bytes KernelCodeEntryByteOffset Byte offset (possibly negative) from base address of kernel descriptor to kernel's entry point instruction which must be 256 byte aligned. 383:192 24 Reserved, must be 0. bytes 415:384 4 bytes ComputePgmRsrc1 Compute Shader (CS) program settings used by CP to set up ``COMPUTE_PGM_RSRC1`` configuration register. See :ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table`. 447:416 4 bytes ComputePgmRsrc2 Compute Shader (CS) program settings used by CP to set up ``COMPUTE_PGM_RSRC2`` configuration register. See :ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table`. 448 1 bit EnableSGPRPrivateSegmentBuffer Enable the setup of the SGPR user data registers (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). The total number of SGPR user data registers requested must not exceed 16 and match value in ``compute_pgm_rsrc2.user_sgpr.user_sgpr_count``. Any requests beyond 16 will be ignored. 449 1 bit EnableSGPRDispatchPtr *see above* 450 1 bit EnableSGPRQueuePtr *see above* 451 1 bit EnableSGPRKernargSegmentPtr *see above* 452 1 bit EnableSGPRDispatchID *see above* 453 1 bit EnableSGPRFlatScratchInit *see above* 454 1 bit EnableSGPRPrivateSegmentSize *see above* 455 1 bit EnableSGPRGridWorkgroupCountX Not implemented in CP and should always be 0. 456 1 bit EnableSGPRGridWorkgroupCountY Not implemented in CP and should always be 0. 457 1 bit EnableSGPRGridWorkgroupCountZ Not implemented in CP and should always be 0. 463:458 6 bits Reserved, must be 0. 511:464 6 Reserved, must be 0. bytes 512 **Total size 64 bytes.** ======= ==================================================================== .. .. table:: compute_pgm_rsrc1 for GFX6-GFX9 :name: amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table ======= ======= =============================== =========================================================================== Bits Size Field Name Description ======= ======= =============================== =========================================================================== 5:0 6 bits GRANULATED_WORKITEM_VGPR_COUNT Number of vector registers used by each work-item, granularity is device specific: GFX6-9 - max_vgpr 1..256 - roundup((max_vgpg + 1) / 4) - 1 Used by CP to set up ``COMPUTE_PGM_RSRC1.VGPRS``. 9:6 4 bits GRANULATED_WAVEFRONT_SGPR_COUNT Number of scalar registers used by a wavefront, granularity is device specific: GFX6-8 - max_sgpr 1..112 - roundup((max_sgpg + 1) / 8) - 1 GFX9 - max_sgpr 1..112 - roundup((max_sgpg + 1) / 16) - 1 Includes the special SGPRs for VCC, Flat Scratch (for GFX7 onwards) and XNACK (for GFX8 onwards). It does not include the 16 SGPR added if a trap handler is enabled. Used by CP to set up ``COMPUTE_PGM_RSRC1.SGPRS``. 11:10 2 bits PRIORITY Must be 0. Start executing wavefront at the specified priority. CP is responsible for filling in ``COMPUTE_PGM_RSRC1.PRIORITY``. 13:12 2 bits FLOAT_ROUND_MODE_32 Wavefront starts execution with specified rounding mode for single (32 bit) floating point precision floating point operations. Floating point rounding mode values are defined in :ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`. Used by CP to set up ``COMPUTE_PGM_RSRC1.FLOAT_MODE``. 15:14 2 bits FLOAT_ROUND_MODE_16_64 Wavefront starts execution with specified rounding denorm mode for half/double (16 and 64 bit) floating point precision floating point operations. Floating point rounding mode values are defined in :ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`. Used by CP to set up ``COMPUTE_PGM_RSRC1.FLOAT_MODE``. 17:16 2 bits FLOAT_DENORM_MODE_32 Wavefront starts execution with specified denorm mode for single (32 bit) floating point precision floating point operations. Floating point denorm mode values are defined in :ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`. Used by CP to set up ``COMPUTE_PGM_RSRC1.FLOAT_MODE``. 19:18 2 bits FLOAT_DENORM_MODE_16_64 Wavefront starts execution with specified denorm mode for half/double (16 and 64 bit) floating point precision floating point operations. Floating point denorm mode values are defined in :ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`. Used by CP to set up ``COMPUTE_PGM_RSRC1.FLOAT_MODE``. 20 1 bit PRIV Must be 0. Start executing wavefront in privilege trap handler mode. CP is responsible for filling in ``COMPUTE_PGM_RSRC1.PRIV``. 21 1 bit ENABLE_DX10_CLAMP Wavefront starts execution with DX10 clamp mode enabled. Used by the vector ALU to force DX10 style treatment of NaN's (when set, clamp NaN to zero, otherwise pass NaN through). Used by CP to set up ``COMPUTE_PGM_RSRC1.DX10_CLAMP``. 22 1 bit DEBUG_MODE Must be 0. Start executing wavefront in single step mode. CP is responsible for filling in ``COMPUTE_PGM_RSRC1.DEBUG_MODE``. 23 1 bit ENABLE_IEEE_MODE Wavefront starts execution with IEEE mode enabled. Floating point opcodes that support exception flag gathering will quiet and propagate signaling-NaN inputs per IEEE 754-2008. Min_dx10 and max_dx10 become IEEE 754-2008 compliant due to signaling-NaN propagation and quieting. Used by CP to set up ``COMPUTE_PGM_RSRC1.IEEE_MODE``. 24 1 bit BULKY Must be 0. Only one work-group allowed to execute on a compute unit. CP is responsible for filling in ``COMPUTE_PGM_RSRC1.BULKY``. 25 1 bit CDBG_USER Must be 0. Flag that can be used to control debugging code. CP is responsible for filling in ``COMPUTE_PGM_RSRC1.CDBG_USER``. 26 1 bit FP16_OVFL GFX6-8 Reserved, must be 0. GFX9 Wavefront starts execution with specified fp16 overflow mode. - If 0, fp16 overflow generates +/-INF values. - If 1, fp16 overflow that is the result of an +/-INF input value or divide by 0 produces a +/-INF, otherwise clamps computed overflow to +/-MAX_FP16 as appropriate. Used by CP to set up ``COMPUTE_PGM_RSRC1.FP16_OVFL``. 31:27 5 bits Reserved, must be 0. 32 **Total size 4 bytes** ======= =================================================================================================================== .. .. table:: compute_pgm_rsrc2 for GFX6-GFX9 :name: amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table ======= ======= =============================== =========================================================================== Bits Size Field Name Description ======= ======= =============================== =========================================================================== 0 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the _WAVE_OFFSET SGPR wave scratch offset system register (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). Used by CP to set up ``COMPUTE_PGM_RSRC2.SCRATCH_EN``. 5:1 5 bits USER_SGPR_COUNT The total number of SGPR user data registers requested. This number must match the number of user data registers enabled. Used by CP to set up ``COMPUTE_PGM_RSRC2.USER_SGPR``. 6 1 bit ENABLE_TRAP_HANDLER Set to 1 if code contains a TRAP instruction which requires a trap handler to be enabled. CP sets ``COMPUTE_PGM_RSRC2.TRAP_PRESENT`` if the runtime has installed a trap handler regardless of the setting of this field. 7 1 bit ENABLE_SGPR_WORKGROUP_ID_X Enable the setup of the system SGPR register for the work-group id in the X dimension (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). Used by CP to set up ``COMPUTE_PGM_RSRC2.TGID_X_EN``. 8 1 bit ENABLE_SGPR_WORKGROUP_ID_Y Enable the setup of the system SGPR register for the work-group id in the Y dimension (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). Used by CP to set up ``COMPUTE_PGM_RSRC2.TGID_Y_EN``. 9 1 bit ENABLE_SGPR_WORKGROUP_ID_Z Enable the setup of the system SGPR register for the work-group id in the Z dimension (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). Used by CP to set up ``COMPUTE_PGM_RSRC2.TGID_Z_EN``. 10 1 bit ENABLE_SGPR_WORKGROUP_INFO Enable the setup of the system SGPR register for work-group information (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). Used by CP to set up ``COMPUTE_PGM_RSRC2.TGID_SIZE_EN``. 12:11 2 bits ENABLE_VGPR_WORKITEM_ID Enable the setup of the VGPR system registers used for the work-item ID. :ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table` defines the values. Used by CP to set up ``COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT``. 13 1 bit ENABLE_EXCEPTION_ADDRESS_WATCH Must be 0. Wavefront starts execution with address watch exceptions enabled which are generated when L1 has witnessed a thread access an *address of interest*. CP is responsible for filling in the address watch bit in ``COMPUTE_PGM_RSRC2.EXCP_EN_MSB`` according to what the runtime requests. 14 1 bit ENABLE_EXCEPTION_MEMORY Must be 0. Wavefront starts execution with memory violation exceptions exceptions enabled which are generated when a memory violation has occurred for this wave from L1 or LDS (write-to-read-only-memory, mis-aligned atomic, LDS address out of range, illegal address, etc.). CP sets the memory violation bit in ``COMPUTE_PGM_RSRC2.EXCP_EN_MSB`` according to what the runtime requests. 23:15 9 bits GRANULATED_LDS_SIZE Must be 0. CP uses the rounded value from the dispatch packet, not this value, as the dispatch may contain dynamically allocated group segment memory. CP writes directly to ``COMPUTE_PGM_RSRC2.LDS_SIZE``. Amount of group segment (LDS) to allocate for each work-group. Granularity is device specific: GFX6: roundup(lds-size / (64 * 4)) GFX7-GFX9: roundup(lds-size / (128 * 4)) 24 1 bit ENABLE_EXCEPTION_IEEE_754_FP Wavefront starts execution _INVALID_OPERATION with specified exceptions enabled. Used by CP to set up ``COMPUTE_PGM_RSRC2.EXCP_EN`` (set from bits 0..6). IEEE 754 FP Invalid Operation 25 1 bit ENABLE_EXCEPTION_FP_DENORMAL FP Denormal one or more _SOURCE input operands is a denormal number 26 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Division by _DIVISION_BY_ZERO Zero 27 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP FP Overflow _OVERFLOW 28 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Underflow _UNDERFLOW 29 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Inexact _INEXACT 30 1 bit ENABLE_EXCEPTION_INT_DIVIDE_BY Integer Division by Zero _ZERO (rcp_iflag_f32 instruction only) 31 1 bit Reserved, must be 0. 32 **Total size 4 bytes.** ======= =================================================================================================================== .. .. table:: Floating Point Rounding Mode Enumeration Values :name: amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table ====================================== ===== ============================== Enumeration Name Value Description ====================================== ===== ============================== AMDGPU_FLOAT_ROUND_MODE_NEAR_EVEN 0 Round Ties To Even AMDGPU_FLOAT_ROUND_MODE_PLUS_INFINITY 1 Round Toward +infinity AMDGPU_FLOAT_ROUND_MODE_MINUS_INFINITY 2 Round Toward -infinity AMDGPU_FLOAT_ROUND_MODE_ZERO 3 Round Toward 0 ====================================== ===== ============================== .. .. table:: Floating Point Denorm Mode Enumeration Values :name: amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table ====================================== ===== ============================== Enumeration Name Value Description ====================================== ===== ============================== AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC_DST 0 Flush Source and Destination Denorms AMDGPU_FLOAT_DENORM_MODE_FLUSH_DST 1 Flush Output Denorms AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC 2 Flush Source Denorms AMDGPU_FLOAT_DENORM_MODE_FLUSH_NONE 3 No Flush ====================================== ===== ============================== .. .. table:: System VGPR Work-Item ID Enumeration Values :name: amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table ======================================== ===== ============================ Enumeration Name Value Description ======================================== ===== ============================ AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X 0 Set work-item X dimension ID. AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y 1 Set work-item X and Y dimensions ID. AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y_Z 2 Set work-item X, Y and Z dimensions ID. AMDGPU_SYSTEM_VGPR_WORKITEM_ID_UNDEFINED 3 Undefined. ======================================== ===== ============================ .. _amdgpu-amdhsa-initial-kernel-execution-state: Initial Kernel Execution State ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This section defines the register state that will be set up by the packet processor prior to the start of execution of every wavefront. This is limited by the constraints of the hardware controllers of CP/ADC/SPI. The order of the SGPR registers is defined, but the compiler can specify which ones are actually setup in the kernel descriptor using the ``enable_sgpr_*`` bit fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used for enabled registers are dense starting at SGPR0: the first enabled register is SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have an SGPR number. The initial SGPRs comprise up to 16 User SRGPs that are set by CP and apply to all waves of the grid. It is possible to specify more than 16 User SGPRs using the ``enable_sgpr_*`` bit fields, in which case only the first 16 are actually initialized. These are then immediately followed by the System SGPRs that are set up by ADC/SPI and can have different values for each wave of the grid dispatch. SGPR register initial state is defined in :ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`. .. table:: SGPR Register Set Up Order :name: amdgpu-amdhsa-sgpr-register-set-up-order-table ========== ========================== ====== ============================== SGPR Order Name Number Description (kernel descriptor enable of field) SGPRs ========== ========================== ====== ============================== First Private Segment Buffer 4 V# that can be used, together (enable_sgpr_private with Scratch Wave Offset as an _segment_buffer) offset, to access the private memory space using a segment address. CP uses the value provided by the runtime. then Dispatch Ptr 2 64 bit address of AQL dispatch (enable_sgpr_dispatch_ptr) packet for kernel dispatch actually executing. then Queue Ptr 2 64 bit address of amd_queue_t (enable_sgpr_queue_ptr) object for AQL queue on which the dispatch packet was queued. then Kernarg Segment Ptr 2 64 bit address of Kernarg (enable_sgpr_kernarg segment. This is directly _segment_ptr) copied from the kernarg_address in the kernel dispatch packet. Having CP load it once avoids loading it at the beginning of every wavefront. then Dispatch Id 2 64 bit Dispatch ID of the (enable_sgpr_dispatch_id) dispatch packet being executed. then Flat Scratch Init 2 This is 2 SGPRs: (enable_sgpr_flat_scratch _init) GFX6 Not supported. GFX7-GFX8 The first SGPR is a 32 bit byte offset from ``SH_HIDDEN_PRIVATE_BASE_VIMID`` to per SPI base of memory for scratch for the queue executing the kernel dispatch. CP obtains this from the runtime. (The Scratch Segment Buffer base address is ``SH_HIDDEN_PRIVATE_BASE_VIMID`` plus this offset.) The value of Scratch Wave Offset must be added to this offset by the kernel machine code, right shifted by 8, and moved to the FLAT_SCRATCH_HI SGPR register. FLAT_SCRATCH_HI corresponds to SGPRn-4 on GFX7, and SGPRn-6 on GFX8 (where SGPRn is the highest numbered SGPR allocated to the wave). FLAT_SCRATCH_HI is multiplied by 256 (as it is in units of 256 bytes) and added to ``SH_HIDDEN_PRIVATE_BASE_VIMID`` to calculate the per wave FLAT SCRATCH BASE in flat memory instructions that access the scratch apperture. The second SGPR is 32 bit byte size of a single work-item's scratch memory usage. CP obtains this from the runtime, and it is always a multiple of DWORD. CP checks that the value in the kernel dispatch packet Private Segment Byte Size is not larger, and requests the runtime to increase the queue's scratch size if necessary. The kernel code must move it to FLAT_SCRATCH_LO which is SGPRn-3 on GFX7 and SGPRn-5 on GFX8. FLAT_SCRATCH_LO is used as the FLAT SCRATCH SIZE in flat memory instructions. Having CP load it once avoids loading it at the beginning of every wavefront. GFX9 This is the 64 bit base address of the per SPI scratch backing memory managed by SPI for the queue executing the kernel dispatch. CP obtains this from the runtime (and divides it if there are multiple Shader Arrays each with its own SPI). The value of Scratch Wave Offset must be added by the kernel machine code and the result moved to the FLAT_SCRATCH SGPR which is SGPRn-6 and SGPRn-5. It is used as the FLAT SCRATCH BASE in flat memory instructions. then Private Segment Size 1 The 32 bit byte size of a (enable_sgpr_private single work-item's scratch_segment_size) memory allocation. This is the value from the kernel dispatch packet Private Segment Byte Size rounded up by CP to a multiple of DWORD. Having CP load it once avoids loading it at the beginning of every wavefront. This is not used for GFX7-GFX8 since it is the same value as the second SGPR of Flat Scratch Init. However, it may be needed for GFX9 which changes the meaning of the Flat Scratch Init value. then Grid Work-Group Count X 1 32 bit count of the number of (enable_sgpr_grid work-groups in the X dimension _workgroup_count_X) for the grid being executed. Computed from the fields in the kernel dispatch packet as ((grid_size.x + workgroup_size.x - 1) / workgroup_size.x). then Grid Work-Group Count Y 1 32 bit count of the number of (enable_sgpr_grid work-groups in the Y dimension _workgroup_count_Y && for the grid being less than 16 previous executed. Computed from the SGPRs) fields in the kernel dispatch packet as ((grid_size.y + workgroup_size.y - 1) / workgroupSize.y). Only initialized if <16 previous SGPRs initialized. then Grid Work-Group Count Z 1 32 bit count of the number of (enable_sgpr_grid work-groups in the Z dimension _workgroup_count_Z && for the grid being less than 16 previous executed. Computed from the SGPRs) fields in the kernel dispatch packet as ((grid_size.z + workgroup_size.z - 1) / workgroupSize.z). Only initialized if <16 previous SGPRs initialized. then Work-Group Id X 1 32 bit work-group id in X (enable_sgpr_workgroup_id dimension of grid for _X) wavefront. then Work-Group Id Y 1 32 bit work-group id in Y (enable_sgpr_workgroup_id dimension of grid for _Y) wavefront. then Work-Group Id Z 1 32 bit work-group id in Z (enable_sgpr_workgroup_id dimension of grid for _Z) wavefront. then Work-Group Info 1 {first_wave, 14'b0000, (enable_sgpr_workgroup ordered_append_term[10:0], _info) threadgroup_size_in_waves[5:0]} then Scratch Wave Offset 1 32 bit byte offset from base (enable_sgpr_private of scratch base of queue _segment_wave_offset) executing the kernel dispatch. Must be used as an offset with Private segment address when using Scratch Segment Buffer. It must be used to set up FLAT SCRATCH for flat addressing (see :ref:`amdgpu-amdhsa-flat-scratch`). ========== ========================== ====== ============================== The order of the VGPR registers is defined, but the compiler can specify which ones are actually setup in the kernel descriptor using the ``enable_vgpr*`` bit fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used for enabled registers are dense starting at VGPR0: the first enabled register is VGPR0, the next enabled register is VGPR1 etc.; disabled registers do not have a VGPR number. VGPR register initial state is defined in :ref:`amdgpu-amdhsa-vgpr-register-set-up-order-table`. .. table:: VGPR Register Set Up Order :name: amdgpu-amdhsa-vgpr-register-set-up-order-table ========== ========================== ====== ============================== VGPR Order Name Number Description (kernel descriptor enable of field) VGPRs ========== ========================== ====== ============================== First Work-Item Id X 1 32 bit work item id in X (Always initialized) dimension of work-group for wavefront lane. then Work-Item Id Y 1 32 bit work item id in Y (enable_vgpr_workitem_id dimension of work-group for > 0) wavefront lane. then Work-Item Id Z 1 32 bit work item id in Z (enable_vgpr_workitem_id dimension of work-group for > 1) wavefront lane. ========== ========================== ====== ============================== The setting of registers is is done by GPU CP/ADC/SPI hardware as follows: 1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data registers. 2. Work-group Id registers X, Y, Z are set by ADC which supports any combination including none. 3. Scratch Wave Offset is set by SPI in a per wave basis which is why its value cannot included with the flat scratch init value which is per queue. 4. The VGPRs are set by SPI which only supports specifying either (X), (X, Y) or (X, Y, Z). Flat Scratch register pair are adjacent SGRRs so they can be moved as a 64 bit value to the hardware required SGPRn-3 and SGPRn-4 respectively. The global segment can be accessed either using buffer instructions (GFX6 which has V# 64 bit address support), flat instructions (GFX7-9), or global instructions (GFX9). If buffer operations are used then the compiler can generate a V# with the following properties: * base address of 0 * no swizzle * ATC: 1 if IOMMU present (such as APU) * ptr64: 1 * MTYPE set to support memory coherence that matches the runtime (such as CC for APU and NC for dGPU). .. _amdgpu-amdhsa-kernel-prolog: Kernel Prolog ~~~~~~~~~~~~~ .. _amdgpu-amdhsa-m0: M0 ++ GFX6-GFX8 The M0 register must be initialized with a value at least the total LDS size if the kernel may access LDS via DS or flat operations. Total LDS size is available in dispatch packet. For M0, it is also possible to use maximum possible value of LDS for given target (0x7FFF for GFX6 and 0xFFFF for GFX7-GFX8). GFX9 The M0 register is not used for range checking LDS accesses and so does not need to be initialized in the prolog. .. _amdgpu-amdhsa-flat-scratch: Flat Scratch ++++++++++++ If the kernel may use flat operations to access scratch memory, the prolog code must set up FLAT_SCRATCH register pair (FLAT_SCRATCH_LO/FLAT_SCRATCH_HI which are in SGPRn-4/SGPRn-3). Initialization uses Flat Scratch Init and Scratch Wave Offset SGPR registers (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`): GFX6 Flat scratch is not supported. GFX7-8 1. The low word of Flat Scratch Init is 32 bit byte offset from ``SH_HIDDEN_PRIVATE_BASE_VIMID`` to the base of scratch backing memory being managed by SPI for the queue executing the kernel dispatch. This is the same value used in the Scratch Segment Buffer V# base address. The prolog must add the value of Scratch Wave Offset to get the wave's byte scratch backing memory offset from ``SH_HIDDEN_PRIVATE_BASE_VIMID``. Since FLAT_SCRATCH_LO is in units of 256 bytes, the offset must be right shifted by 8 before moving into FLAT_SCRATCH_LO. 2. The second word of Flat Scratch Init is 32 bit byte size of a single work-items scratch memory usage. This is directly loaded from the kernel dispatch packet Private Segment Byte Size and rounded up to a multiple of DWORD. Having CP load it once avoids loading it at the beginning of every wavefront. The prolog must move it to FLAT_SCRATCH_LO for use as FLAT SCRATCH SIZE. GFX9 The Flat Scratch Init is the 64 bit address of the base of scratch backing memory being managed by SPI for the queue executing the kernel dispatch. The prolog must add the value of Scratch Wave Offset and moved to the FLAT_SCRATCH pair for use as the flat scratch base in flat memory instructions. .. _amdgpu-amdhsa-memory-model: Memory Model ~~~~~~~~~~~~ This section describes the mapping of LLVM memory model onto AMDGPU machine code (see :ref:`memmodel`). *The implementation is WIP.* .. TODO Update when implementation complete. The AMDGPU backend supports the memory synchronization scopes specified in :ref:`amdgpu-memory-scopes`. The code sequences used to implement the memory model are defined in table :ref:`amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table`. The sequences specify the order of instructions that a single thread must execute. The ``s_waitcnt`` and ``buffer_wbinvl1_vol`` are defined with respect to other memory instructions executed by the same thread. This allows them to be moved earlier or later which can allow them to be combined with other instances of the same instruction, or hoisted/sunk out of loops to improve performance. Only the instructions related to the memory model are given; additional ``s_waitcnt`` instructions are required to ensure registers are defined before being used. These may be able to be combined with the memory model ``s_waitcnt`` instructions as described above. The AMDGPU backend supports the following memory models: HSA Memory Model [HSA]_ The HSA memory model uses a single happens-before relation for all address spaces (see :ref:`amdgpu-address-spaces`). OpenCL Memory Model [OpenCL]_ The OpenCL memory model which has separate happens-before relations for the global and local address spaces. Only a fence specifying both global and local address space, and seq_cst instructions join the relationships. Since the LLVM ``memfence`` instruction does not allow an address space to be specified the OpenCL fence has to convervatively assume both local and global address space was specified. However, optimizations can often be done to eliminate the additional ``s_waitcnt`` instructions when there are no intervening memory instructions which access the corresponding address space. The code sequences in the table indicate what can be omitted for the OpenCL memory. The target triple environment is used to determine if the source language is OpenCL (see :ref:`amdgpu-opencl`). ``ds/flat_load/store/atomic`` instructions to local memory are termed LDS operations. ``buffer/global/flat_load/store/atomic`` instructions to global memory are termed vector memory operations. For GFX6-GFX9: * Each agent has multiple compute units (CU). * Each CU has multiple SIMDs that execute wavefronts. * The wavefronts for a single work-group are executed in the same CU but may be executed by different SIMDs. * Each CU has a single LDS memory shared by the wavefronts of the work-groups executing on it. * All LDS operations of a CU are performed as wavefront wide operations in a global order and involve no caching. Completion is reported to a wavefront in execution order. * The LDS memory has multiple request queues shared by the SIMDs of a CU. Therefore, the LDS operations performed by different waves of a work-group can be reordered relative to each other, which can result in reordering the visibility of vector memory operations with respect to LDS operations of other wavefronts in the same work-group. A ``s_waitcnt lgkmcnt(0)`` is required to ensure synchronization between LDS operations and vector memory operations between waves of a work-group, but not between operations performed by the same wavefront. * The vector memory operations are performed as wavefront wide operations and completion is reported to a wavefront in execution order. The exception is that for GFX7-9 ``flat_load/store/atomic`` instructions can report out of vector memory order if they access LDS memory, and out of LDS operation order if they access global memory. * The vector memory operations access a single vector L1 cache shared by all SIMDs a CU. Therefore, no special action is required for coherence between the lanes of a single wavefront, or for coherence between wavefronts in the same work-group. A ``buffer_wbinvl1_vol`` is required for coherence between waves executing in different work-groups as they may be executing on different CUs. * The scalar memory operations access a scalar L1 cache shared by all wavefronts on a group of CUs. The scalar and vector L1 caches are not coherent. However, scalar operations are used in a restricted way so do not impact the memory model. See :ref:`amdgpu-amdhsa-memory-spaces`. * The vector and scalar memory operations use an L2 cache shared by all CUs on the same agent. * The L2 cache has independent channels to service disjoint ranges of virtual addresses. * Each CU has a separate request queue per channel. Therefore, the vector and scalar memory operations performed by waves executing in different work-groups (which may be executing on different CUs) of an agent can be reordered relative to each other. A ``s_waitcnt vmcnt(0)`` is required to ensure synchronization between vector memory operations of different CUs. It ensures a previous vector memory operation has completed before executing a subsequent vector memory or LDS operation and so can be used to meet the requirements of acquire and release. * The L2 cache can be kept coherent with other agents on some targets, or ranges of virtual addresses can be set up to bypass it to ensure system coherence. Private address space uses ``buffer_load/store`` using the scratch V# (GFX6-8), or ``scratch_load/store`` (GFX9). Since only a single thread is accessing the memory, atomic memory orderings are not meaningful and all accesses are treated as non-atomic. Constant address space uses ``buffer/global_load`` instructions (or equivalent scalar memory instructions). Since the constant address space contents do not change during the execution of a kernel dispatch it is not legal to perform stores, and atomic memory orderings are not meaningful and all access are treated as non-atomic. A memory synchronization scope wider than work-group is not meaningful for the group (LDS) address space and is treated as work-group. The memory model does not support the region address space which is treated as non-atomic. Acquire memory ordering is not meaningful on store atomic instructions and is treated as non-atomic. Release memory ordering is not meaningful on load atomic instructions and is treated a non-atomic. Acquire-release memory ordering is not meaningful on load or store atomic instructions and is treated as acquire and release respectively. AMDGPU backend only uses scalar memory operations to access memory that is proven to not change during the execution of the kernel dispatch. This includes constant address space and global address space for program scope const variables. Therefore the kernel machine code does not have to maintain the scalar L1 cache to ensure it is coherent with the vector L1 cache. The scalar and vector L1 caches are invalidated between kernel dispatches by CP since constant address space data may change between kernel dispatch executions. See :ref:`amdgpu-amdhsa-memory-spaces`. The one execption is if scalar writes are used to spill SGPR registers. In this case the AMDGPU backend ensures the memory location used to spill is never accessed by vector memory operations at the same time. If scalar writes are used then a ``s_dcache_wb`` is inserted before the ``s_endpgm`` and before a function return since the locations may be used for vector memory instructions by a future wave that uses the same scratch area, or a function call that creates a frame at the same address, respectively. There is no need for a ``s_dcache_inv`` as all scalar writes are write-before-read in the same thread. Scratch backing memory (which is used for the private address space) is accessed with MTYPE NC_NV (non-coherenent non-volatile). Since the private address space is only accessed by a single thread, and is always write-before-read, there is never a need to invalidate these entries from the L1 cache. Hence all cache invalidates are done as ``*_vol`` to only invalidate the volatile cache lines. On dGPU the kernarg backing memory is accessed as UC (uncached) to avoid needing to invalidate the L2 cache. This also causes it to be treated as non-volatile and so is not invalidated by ``*_vol``. On APU it is accessed as CC (cache coherent) and so the L2 cache will coherent with the CPU and other agents. .. table:: AMDHSA Memory Model Code Sequences GFX6-GFX9 :name: amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table ============ ============ ============== ========== =============================== LLVM Instr LLVM Memory LLVM Memory AMDGPU AMDGPU Machine Code Ordering Sync Scope Address Space ============ ============ ============== ========== =============================== **Non-Atomic** ----------------------------------------------------------------------------------- load *none* *none* - global - !volatile & !nontemporal - generic - private 1. buffer/global/flat_load - constant - volatile & !nontemporal 1. buffer/global/flat_load glc=1 - nontemporal 1. buffer/global/flat_load glc=1 slc=1 load *none* *none* - local 1. ds_load store *none* *none* - global - !nontemporal - generic - private 1. buffer/global/flat_store - constant - nontemporal 1. buffer/global/flat_stote glc=1 slc=1 store *none* *none* - local 1. ds_store **Unordered Atomic** ----------------------------------------------------------------------------------- load atomic unordered *any* *any* *Same as non-atomic*. store atomic unordered *any* *any* *Same as non-atomic*. atomicrmw unordered *any* *any* *Same as monotonic atomic*. **Monotonic Atomic** ----------------------------------------------------------------------------------- load atomic monotonic - singlethread - global 1. buffer/global/flat_load - wavefront - generic - workgroup load atomic monotonic - singlethread - local 1. ds_load - wavefront - workgroup load atomic monotonic - agent - global 1. buffer/global/flat_load - system - generic glc=1 store atomic monotonic - singlethread - global 1. buffer/global/flat_store - wavefront - generic - workgroup - agent - system store atomic monotonic - singlethread - local 1. ds_store - wavefront - workgroup atomicrmw monotonic - singlethread - global 1. buffer/global/flat_atomic - wavefront - generic - workgroup - agent - system atomicrmw monotonic - singlethread - local 1. ds_atomic - wavefront - workgroup **Acquire Atomic** ----------------------------------------------------------------------------------- load atomic acquire - singlethread - global 1. buffer/global/ds/flat_load - wavefront - local - generic load atomic acquire - workgroup - global 1. buffer/global/flat_load load atomic acquire - workgroup - local 1. ds_load 2. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the load atomic value being acquired. load atomic acquire - workgroup - generic 1. flat_load 2. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the load atomic value being acquired. load atomic acquire - agent - global 1. buffer/global/flat_load - system glc=1 2. s_waitcnt vmcnt(0) - Must happen before following buffer_wbinvl1_vol. - Ensures the load has completed before invalidating the cache. 3. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. load atomic acquire - agent - generic 1. flat_load glc=1 - system 2. s_waitcnt vmcnt(0) & lgkmcnt(0) - If OpenCL omit lgkmcnt(0). - Must happen before following buffer_wbinvl1_vol. - Ensures the flat_load has completed before invalidating the cache. 3. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. atomicrmw acquire - singlethread - global 1. buffer/global/ds/flat_atomic - wavefront - local - generic atomicrmw acquire - workgroup - global 1. buffer/global/flat_atomic atomicrmw acquire - workgroup - local 1. ds_atomic 2. waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the atomicrmw value being acquired. atomicrmw acquire - workgroup - generic 1. flat_atomic 2. waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the atomicrmw value being acquired. atomicrmw acquire - agent - global 1. buffer/global/flat_atomic - system 2. s_waitcnt vmcnt(0) - Must happen before following buffer_wbinvl1_vol. - Ensures the atomicrmw has completed before invalidating the cache. 3. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. atomicrmw acquire - agent - generic 1. flat_atomic - system 2. s_waitcnt vmcnt(0) & lgkmcnt(0) - If OpenCL, omit lgkmcnt(0). - Must happen before following buffer_wbinvl1_vol. - Ensures the atomicrmw has completed before invalidating the cache. 3. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. fence acquire - singlethread *none* *none* - wavefront fence acquire - workgroup *none* 1. s_waitcnt lgkmcnt(0) - If OpenCL and address space is not generic, omit. - However, since LLVM currently has no address space on the fence need to conservatively always generate. If fence had an address space then set to address space of OpenCL fence flag, or to generic if both local and global flags are specified. - Must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic). - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the value read by the fence-paired-atomic. fence acquire - agent *none* 1. s_waitcnt lgkmcnt(0) & - system vmcnt(0) - If OpenCL and address space is not generic, omit lgkmcnt(0). - However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic). - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic). - Must happen before the following buffer_wbinvl1_vol. - Ensures that the fence-paired atomic has completed before invalidating the cache. Therefore any following locations read must be no older than the value read by the fence-paired-atomic. 2. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures that following loads will not see stale global data. **Release Atomic** ----------------------------------------------------------------------------------- store atomic release - singlethread - global 1. buffer/global/ds/flat_store - wavefront - local - generic store atomic release - workgroup - global 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following store. - Ensures that all memory operations to local have completed before performing the store that is being released. 2. buffer/global/flat_store store atomic release - workgroup - local 1. ds_store store atomic release - workgroup - generic 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following store. - Ensures that all memory operations to local have completed before performing the store that is being released. 2. flat_store store atomic release - agent - global 1. s_waitcnt lgkmcnt(0) & - system - generic vmcnt(0) - If OpenCL, omit lgkmcnt(0). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following store. - Ensures that all memory operations to memory have completed before performing the store that is being released. 2. buffer/global/ds/flat_store atomicrmw release - singlethread - global 1. buffer/global/ds/flat_atomic - wavefront - local - generic atomicrmw release - workgroup - global 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to local have completed before performing the atomicrmw that is being released. 2. buffer/global/flat_atomic atomicrmw release - workgroup - local 1. ds_atomic atomicrmw release - workgroup - generic 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to local have completed before performing the atomicrmw that is being released. 2. flat_atomic atomicrmw release - agent - global 1. s_waitcnt lgkmcnt(0) & - system - generic vmcnt(0) - If OpenCL, omit lgkmcnt(0). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to global and local have completed before performing the atomicrmw that is being released. 2. buffer/global/ds/flat_atomic fence release - singlethread *none* *none* - wavefront fence release - workgroup *none* 1. s_waitcnt lgkmcnt(0) - If OpenCL and address space is not generic, omit. - However, since LLVM currently has no address space on the fence need to conservatively always generate. If fence had an address space then set to address space of OpenCL fence flag, or to generic if both local and global flags are specified. - Must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw. - Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic). - Ensures that all memory operations to local have completed before performing the following fence-paired-atomic. fence release - agent *none* 1. s_waitcnt lgkmcnt(0) & - system vmcnt(0) - If OpenCL and address space is not generic, omit lgkmcnt(0). - If OpenCL and address space is local, omit vmcnt(0). - However, since LLVM currently has no address space on the fence need to conservatively always generate. If fence had an address space then set to address space of OpenCL fence flag, or to generic if both local and global flags are specified. - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before any following store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the fence-paired-atomic). - Ensures that all memory operations have completed before performing the following fence-paired-atomic. **Acquire-Release Atomic** ----------------------------------------------------------------------------------- atomicrmw acq_rel - singlethread - global 1. buffer/global/ds/flat_atomic - wavefront - local - generic atomicrmw acq_rel - workgroup - global 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to local have completed before performing the atomicrmw that is being released. 2. buffer/global/flat_atomic atomicrmw acq_rel - workgroup - local 1. ds_atomic 2. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the load atomic value being acquired. atomicrmw acq_rel - workgroup - generic 1. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to local have completed before performing the atomicrmw that is being released. 2. flat_atomic 3. s_waitcnt lgkmcnt(0) - If OpenCL, omit. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures any following global data read is no older than the load atomic value being acquired. atomicrmw acq_rel - agent - global 1. s_waitcnt lgkmcnt(0) & - system vmcnt(0) - If OpenCL, omit lgkmcnt(0). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to global have completed before performing the atomicrmw that is being released. 2. buffer/global/flat_atomic 3. s_waitcnt vmcnt(0) - Must happen before following buffer_wbinvl1_vol. - Ensures the atomicrmw has completed before invalidating the cache. 4. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. atomicrmw acq_rel - agent - generic 1. s_waitcnt lgkmcnt(0) & - system vmcnt(0) - If OpenCL, omit lgkmcnt(0). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following atomicrmw. - Ensures that all memory operations to global have completed before performing the atomicrmw that is being released. 2. flat_atomic 3. s_waitcnt vmcnt(0) & lgkmcnt(0) - If OpenCL, omit lgkmcnt(0). - Must happen before following buffer_wbinvl1_vol. - Ensures the atomicrmw has completed before invalidating the cache. 4. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/atomicrmw. - Ensures that following loads will not see stale global data. fence acq_rel - singlethread *none* *none* - wavefront fence acq_rel - workgroup *none* 1. s_waitcnt lgkmcnt(0) - If OpenCL and address space is not generic, omit. - However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence). - Must happen after any preceding local/generic load/load atomic/store/store atomic/atomicrmw. - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures that all memory operations to local have completed before performing any following global memory operations. - Ensures that the preceding local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic ) has completed before following global memory operations. This satisfies the requirements of acquire. - Ensures that all previous memory operations have completed before a following local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic ). This satisfies the requirements of release. fence acq_rel - agent *none* 1. s_waitcnt lgkmcnt(0) & - system vmcnt(0) - If OpenCL and address space is not generic, omit lgkmcnt(0). - However, since LLVM currently has no address space on the fence need to conservatively always generate (see comment for previous fence). - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - s_waitcnt vmcnt(0) must happen after any preceding global/generic load/store/load atomic/store atomic/atomicrmw. - s_waitcnt lgkmcnt(0) must happen after any preceding local/generic load/store/load atomic/store atomic/atomicrmw. - Must happen before the following buffer_wbinvl1_vol. - Ensures that the preceding global/local/generic load atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the acquire-fence-paired-atomic ) has completed before invalidating the cache. This satisfies the requirements of acquire. - Ensures that all previous memory operations have completed before a following global/local/generic store atomic/atomicrmw with an equal or wider sync scope and memory ordering stronger than unordered (this is termed the release-fence-paired-atomic ). This satisfies the requirements of release. 2. buffer_wbinvl1_vol - Must happen before any following global/generic load/load atomic/store/store atomic/atomicrmw. - Ensures that following loads will not see stale global data. This satisfies the requirements of acquire. **Sequential Consistent Atomic** ----------------------------------------------------------------------------------- load atomic seq_cst - singlethread - global *Same as corresponding - wavefront - local load atomic acquire, - generic except must generated all instructions even for OpenCL.* load atomic seq_cst - workgroup - global 1. s_waitcnt lgkmcnt(0) - generic - Must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.) - Ensures any preceding sequential consistent local memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the waitcnt of the release, but there is nothing preventing a store release followed by load acquire from competing out of order.) 2. *Following instructions same as corresponding load atomic acquire, except must generated all instructions even for OpenCL.* load atomic seq_cst - workgroup - local *Same as corresponding load atomic acquire, except must generated all instructions even for OpenCL.* load atomic seq_cst - agent - global 1. s_waitcnt lgkmcnt(0) & - system - generic vmcnt(0) - Could be split into separate s_waitcnt vmcnt(0) and s_waitcnt lgkmcnt(0) to allow them to be independently moved according to the following rules. - waitcnt lgkmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt lgkmcnt(0) and so do not need to be considered.) - waitcnt vmcnt(0) must happen after preceding global/generic load atomic/store atomic/atomicrmw with memory ordering of seq_cst and with equal or wider sync scope. (Note that seq_cst fences have their own s_waitcnt vmcnt(0) and so do not need to be considered.) - Ensures any preceding sequential consistent global memory instructions have completed before executing this sequentially consistent instruction. This prevents reordering a seq_cst store followed by a seq_cst load. (Note that seq_cst is stronger than acquire/release as the reordering of load acquire followed by a store release is prevented by the waitcnt of the release, but there is nothing preventing a store release followed by load acquire from competing out of order.) 2. *Following instructions same as corresponding load atomic acquire, except must generated all instructions even for OpenCL.* store atomic seq_cst - singlethread - global *Same as corresponding - wavefront - local store atomic release, - workgroup - generic except must generated all instructions even for OpenCL.* store atomic seq_cst - agent - global *Same as corresponding - system - generic store atomic release, except must generated all instructions even for OpenCL.* atomicrmw seq_cst - singlethread - global *Same as corresponding - wavefront - local atomicrmw acq_rel, - workgroup - generic except must generated all instructions even for OpenCL.* atomicrmw seq_cst - agent - global *Same as corresponding - system - generic atomicrmw acq_rel, except must generated all instructions even for OpenCL.* fence seq_cst - singlethread *none* *Same as corresponding - wavefront fence acq_rel, - workgroup except must generated - agent all instructions even - system for OpenCL.* ============ ============ ============== ========== =============================== The memory order also adds the single thread optimization constrains defined in table :ref:`amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table`. .. table:: AMDHSA Memory Model Single Thread Optimization Constraints GFX6-GFX9 :name: amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table ============ ============================================================== LLVM Memory Optimization Constraints Ordering ============ ============================================================== unordered *none* monotonic *none* acquire - If a load atomic/atomicrmw then no following load/load atomic/store/ store atomic/atomicrmw/fence instruction can be moved before the acquire. - If a fence then same as load atomic, plus no preceding associated fence-paired-atomic can be moved after the fence. release - If a store atomic/atomicrmw then no preceding load/load atomic/store/ store atomic/atomicrmw/fence instruction can be moved after the release. - If a fence then same as store atomic, plus no following associated fence-paired-atomic can be moved before the fence. acq_rel Same constraints as both acquire and release. seq_cst - If a load atomic then same constraints as acquire, plus no preceding sequentially consistent load atomic/store atomic/atomicrmw/fence instruction can be moved after the seq_cst. - If a store atomic then the same constraints as release, plus no following sequentially consistent load atomic/store atomic/atomicrmw/fence instruction can be moved before the seq_cst. - If an atomicrmw/fence then same constraints as acq_rel. ============ ============================================================== Trap Handler ABI ~~~~~~~~~~~~~~~~ For code objects generated by AMDGPU backend for HSA [HSA]_ compatible runtimes (such as ROCm [AMD-ROCm]_), the runtime installs a trap handler that supports the ``s_trap`` instruction with the following usage: .. table:: AMDGPU Trap Handler for AMDHSA OS :name: amdgpu-trap-handler-for-amdhsa-os-table =================== =============== =============== ======================= Usage Code Sequence Trap Handler Description Inputs =================== =============== =============== ======================= reserved ``s_trap 0x00`` Reserved by hardware. ``debugtrap(arg)`` ``s_trap 0x01`` ``SGPR0-1``: Reserved for HSA ``queue_ptr`` ``debugtrap`` ``VGPR0``: intrinsic (not ``arg`` implemented). ``llvm.trap`` ``s_trap 0x02`` ``SGPR0-1``: Causes dispatch to be ``queue_ptr`` terminated and its associated queue put into the error state. ``llvm.debugtrap`` ``s_trap 0x03`` ``SGPR0-1``: If debugger not ``queue_ptr`` installed handled same as ``llvm.trap``. debugger breakpoint ``s_trap 0x07`` Reserved for debugger breakpoints. debugger ``s_trap 0x08`` Reserved for debugger. debugger ``s_trap 0xfe`` Reserved for debugger. debugger ``s_trap 0xff`` Reserved for debugger. =================== =============== =============== ======================= Unspecified OS -------------- This section provides code conventions used when the target triple OS is empty (see :ref:`amdgpu-target-triples`). Trap Handler ABI ~~~~~~~~~~~~~~~~ For code objects generated by AMDGPU backend for non-amdhsa OS, the runtime does not install a trap handler. The ``llvm.trap`` and ``llvm.debugtrap`` instructions are handled as follows: .. table:: AMDGPU Trap Handler for Non-AMDHSA OS :name: amdgpu-trap-handler-for-non-amdhsa-os-table =============== =============== =========================================== Usage Code Sequence Description =============== =============== =========================================== llvm.trap s_endpgm Causes wavefront to be terminated. llvm.debugtrap *none* Compiler warning given that there is no trap handler installed. =============== =============== =========================================== Source Languages ================ .. _amdgpu-opencl: OpenCL ------ When generating code for the OpenCL language the target triple environment should be ``opencl`` or ``amdgizcl`` (see :ref:`amdgpu-target-triples`). When the language is OpenCL the following differences occur: 1. The OpenCL memory model is used (see :ref:`amdgpu-amdhsa-memory-model`). 2. The AMDGPU backend adds additional arguments to the kernel. 3. Additional metadata is generated (:ref:`amdgpu-amdhsa-hsa-code-object-metadata`). .. TODO Specify what affect this has. Hidden arguments added. Additional metadata generated. .. _amdgpu-hcc: HCC --- When generating code for the OpenCL language the target triple environment should be ``hcc`` (see :ref:`amdgpu-target-triples`). When the language is OpenCL the following differences occur: 1. The HSA memory model is used (see :ref:`amdgpu-amdhsa-memory-model`). .. TODO Specify what affect this has. Assembler --------- AMDGPU backend has LLVM-MC based assembler which is currently in development. It supports AMDGCN GFX6-GFX8. This section describes general syntax for instructions and operands. For more information about instructions, their semantics and supported combinations of operands, refer to one of instruction set architecture manuals [AMD-GCN-GFX6]_, [AMD-GCN-GFX7]_, [AMD-GCN-GFX8]_ and [AMD-GCN-GFX9]_. An instruction has the following syntax (register operands are normally comma-separated while extra operands are space-separated): *<opcode> <register_operand0>, ... <extra_operand0> ...* Operands ~~~~~~~~ The following syntax for register operands is supported: * SGPR registers: s0, ... or s[0], ... * VGPR registers: v0, ... or v[0], ... * TTMP registers: ttmp0, ... or ttmp[0], ... * Special registers: exec (exec_lo, exec_hi), vcc (vcc_lo, vcc_hi), flat_scratch (flat_scratch_lo, flat_scratch_hi) * Special trap registers: tba (tba_lo, tba_hi), tma (tma_lo, tma_hi) * Register pairs, quads, etc: s[2:3], v[10:11], ttmp[5:6], s[4:7], v[12:15], ttmp[4:7], s[8:15], ... * Register lists: [s0, s1], [ttmp0, ttmp1, ttmp2, ttmp3] * Register index expressions: v[2*2], s[1-1:2-1] * 'off' indicates that an operand is not enabled The following extra operands are supported: * offset, offset0, offset1 * idxen, offen bits * glc, slc, tfe bits * waitcnt: integer or combination of counter values * VOP3 modifiers: - abs (\| \|), neg (\-) * DPP modifiers: - row_shl, row_shr, row_ror, row_rol - row_mirror, row_half_mirror, row_bcast - wave_shl, wave_shr, wave_ror, wave_rol, quad_perm - row_mask, bank_mask, bound_ctrl * SDWA modifiers: - dst_sel, src0_sel, src1_sel (BYTE_N, WORD_M, DWORD) - dst_unused (UNUSED_PAD, UNUSED_SEXT, UNUSED_PRESERVE) - abs, neg, sext Instruction Examples ~~~~~~~~~~~~~~~~~~~~ DS ~~ .. code-block:: nasm ds_add_u32 v2, v4 offset:16 ds_write_src2_b64 v2 offset0:4 offset1:8 ds_cmpst_f32 v2, v4, v6 ds_min_rtn_f64 v[8:9], v2, v[4:5] For full list of supported instructions, refer to "LDS/GDS instructions" in ISA Manual. FLAT ++++ .. code-block:: nasm flat_load_dword v1, v[3:4] flat_store_dwordx3 v[3:4], v[5:7] flat_atomic_swap v1, v[3:4], v5 glc flat_atomic_cmpswap v1, v[3:4], v[5:6] glc slc flat_atomic_fmax_x2 v[1:2], v[3:4], v[5:6] glc For full list of supported instructions, refer to "FLAT instructions" in ISA Manual. MUBUF +++++ .. code-block:: nasm buffer_load_dword v1, off, s[4:7], s1 buffer_store_dwordx4 v[1:4], v2, ttmp[4:7], s1 offen offset:4 glc tfe buffer_store_format_xy v[1:2], off, s[4:7], s1 buffer_wbinvl1 buffer_atomic_inc v1, v2, s[8:11], s4 idxen offset:4 slc For full list of supported instructions, refer to "MUBUF Instructions" in ISA Manual. SMRD/SMEM +++++++++ .. code-block:: nasm s_load_dword s1, s[2:3], 0xfc s_load_dwordx8 s[8:15], s[2:3], s4 s_load_dwordx16 s[88:103], s[2:3], s4 s_dcache_inv_vol s_memtime s[4:5] For full list of supported instructions, refer to "Scalar Memory Operations" in ISA Manual. SOP1 ++++ .. code-block:: nasm s_mov_b32 s1, s2 s_mov_b64 s[0:1], 0x80000000 s_cmov_b32 s1, 200 s_wqm_b64 s[2:3], s[4:5] s_bcnt0_i32_b64 s1, s[2:3] s_swappc_b64 s[2:3], s[4:5] s_cbranch_join s[4:5] For full list of supported instructions, refer to "SOP1 Instructions" in ISA Manual. SOP2 ++++ .. code-block:: nasm s_add_u32 s1, s2, s3 s_and_b64 s[2:3], s[4:5], s[6:7] s_cselect_b32 s1, s2, s3 s_andn2_b32 s2, s4, s6 s_lshr_b64 s[2:3], s[4:5], s6 s_ashr_i32 s2, s4, s6 s_bfm_b64 s[2:3], s4, s6 s_bfe_i64 s[2:3], s[4:5], s6 s_cbranch_g_fork s[4:5], s[6:7] For full list of supported instructions, refer to "SOP2 Instructions" in ISA Manual. SOPC ++++ .. code-block:: nasm s_cmp_eq_i32 s1, s2 s_bitcmp1_b32 s1, s2 s_bitcmp0_b64 s[2:3], s4 s_setvskip s3, s5 For full list of supported instructions, refer to "SOPC Instructions" in ISA Manual. SOPP ++++ .. code-block:: nasm s_barrier s_nop 2 s_endpgm s_waitcnt 0 ; Wait for all counters to be 0 s_waitcnt vmcnt(0) & expcnt(0) & lgkmcnt(0) ; Equivalent to above s_waitcnt vmcnt(1) ; Wait for vmcnt counter to be 1. s_sethalt 9 s_sleep 10 s_sendmsg 0x1 s_sendmsg sendmsg(MSG_INTERRUPT) s_trap 1 For full list of supported instructions, refer to "SOPP Instructions" in ISA Manual. Unless otherwise mentioned, little verification is performed on the operands of SOPP Instructions, so it is up to the programmer to be familiar with the range or acceptable values. VALU ++++ For vector ALU instruction opcodes (VOP1, VOP2, VOP3, VOPC, VOP_DPP, VOP_SDWA), the assembler will automatically use optimal encoding based on its operands. To force specific encoding, one can add a suffix to the opcode of the instruction: * _e32 for 32-bit VOP1/VOP2/VOPC * _e64 for 64-bit VOP3 * _dpp for VOP_DPP * _sdwa for VOP_SDWA VOP1/VOP2/VOP3/VOPC examples: .. code-block:: nasm v_mov_b32 v1, v2 v_mov_b32_e32 v1, v2 v_nop v_cvt_f64_i32_e32 v[1:2], v2 v_floor_f32_e32 v1, v2 v_bfrev_b32_e32 v1, v2 v_add_f32_e32 v1, v2, v3 v_mul_i32_i24_e64 v1, v2, 3 v_mul_i32_i24_e32 v1, -3, v3 v_mul_i32_i24_e32 v1, -100, v3 v_addc_u32 v1, s[0:1], v2, v3, s[2:3] v_max_f16_e32 v1, v2, v3 VOP_DPP examples: .. code-block:: nasm v_mov_b32 v0, v0 quad_perm:[0,2,1,1] v_sin_f32 v0, v0 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0 v_mov_b32 v0, v0 wave_shl:1 v_mov_b32 v0, v0 row_mirror v_mov_b32 v0, v0 row_bcast:31 v_mov_b32 v0, v0 quad_perm:[1,3,0,1] row_mask:0xa bank_mask:0x1 bound_ctrl:0 v_add_f32 v0, v0, |v0| row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0 v_max_f16 v1, v2, v3 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0 VOP_SDWA examples: .. code-block:: nasm v_mov_b32 v1, v2 dst_sel:BYTE_0 dst_unused:UNUSED_PRESERVE src0_sel:DWORD v_min_u32 v200, v200, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD v_sin_f32 v0, v0 dst_unused:UNUSED_PAD src0_sel:WORD_1 v_fract_f32 v0, |v0| dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1 v_cmpx_le_u32 vcc, v1, v2 src0_sel:BYTE_2 src1_sel:WORD_0 For full list of supported instructions, refer to "Vector ALU instructions". HSA Code Object Directives ~~~~~~~~~~~~~~~~~~~~~~~~~~ AMDGPU ABI defines auxiliary data in output code object. In assembly source, one can specify them with assembler directives. .hsa_code_object_version major, minor +++++++++++++++++++++++++++++++++++++ *major* and *minor* are integers that specify the version of the HSA code object that will be generated by the assembler. .hsa_code_object_isa [major, minor, stepping, vendor, arch] +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ *major*, *minor*, and *stepping* are all integers that describe the instruction set architecture (ISA) version of the assembly program. *vendor* and *arch* are quoted strings. *vendor* should always be equal to "AMD" and *arch* should always be equal to "AMDGPU". By default, the assembler will derive the ISA version, *vendor*, and *arch* from the value of the -mcpu option that is passed to the assembler. .amdgpu_hsa_kernel (name) +++++++++++++++++++++++++ This directives specifies that the symbol with given name is a kernel entry point (label) and the object should contain corresponding symbol of type STT_AMDGPU_HSA_KERNEL. .amd_kernel_code_t ++++++++++++++++++ This directive marks the beginning of a list of key / value pairs that are used to specify the amd_kernel_code_t object that will be emitted by the assembler. The list must be terminated by the *.end_amd_kernel_code_t* directive. For any amd_kernel_code_t values that are unspecified a default value will be used. The default value for all keys is 0, with the following exceptions: - *kernel_code_version_major* defaults to 1. - *machine_kind* defaults to 1. - *machine_version_major*, *machine_version_minor*, and *machine_version_stepping* are derived from the value of the -mcpu option that is passed to the assembler. - *kernel_code_entry_byte_offset* defaults to 256. - *wavefront_size* defaults to 6. - *kernarg_segment_alignment*, *group_segment_alignment*, and *private_segment_alignment* default to 4. Note that alignments are specified as a power of two, so a value of **n** means an alignment of 2^ **n**. The *.amd_kernel_code_t* directive must be placed immediately after the function label and before any instructions. For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document, comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s. Here is an example of a minimal amd_kernel_code_t specification: .. code-block:: none .hsa_code_object_version 1,0 .hsa_code_object_isa .hsatext .globl hello_world .p2align 8 .amdgpu_hsa_kernel hello_world hello_world: .amd_kernel_code_t enable_sgpr_kernarg_segment_ptr = 1 is_ptr64 = 1 compute_pgm_rsrc1_vgprs = 0 compute_pgm_rsrc1_sgprs = 0 compute_pgm_rsrc2_user_sgpr = 2 kernarg_segment_byte_size = 8 wavefront_sgpr_count = 2 workitem_vgpr_count = 3 .end_amd_kernel_code_t s_load_dwordx2 s[0:1], s[0:1] 0x0 v_mov_b32 v0, 3.14159 s_waitcnt lgkmcnt(0) v_mov_b32 v1, s0 v_mov_b32 v2, s1 flat_store_dword v[1:2], v0 s_endpgm .Lfunc_end0: .size hello_world, .Lfunc_end0-hello_world Additional Documentation ======================== .. [AMD-RADEON-HD-2000-3000] `AMD R6xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R600_Instruction_Set_Architecture.pdf>`__ .. [AMD-RADEON-HD-4000] `AMD R7xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R700-Family_Instruction_Set_Architecture.pdf>`__ .. [AMD-RADEON-HD-5000] `AMD Evergreen shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_Evergreen-Family_Instruction_Set_Architecture.pdf>`__ .. [AMD-RADEON-HD-6000] `AMD Cayman/Trinity shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_HD_6900_Series_Instruction_Set_Architecture.pdf>`__ .. [AMD-GCN-GFX6] `AMD Southern Islands Series ISA <http://developer.amd.com/wordpress/media/2012/12/AMD_Southern_Islands_Instruction_Set_Architecture.pdf>`__ .. [AMD-GCN-GFX7] `AMD Sea Islands Series ISA <http://developer.amd.com/wordpress/media/2013/07/AMD_Sea_Islands_Instruction_Set_Architecture.pdf>`_ .. [AMD-GCN-GFX8] `AMD GCN3 Instruction Set Architecture <http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_GCN3_Instruction_Set_Architecture_rev1.1.pdf>`__ .. [AMD-GCN-GFX9] `AMD "Vega" Instruction Set Architecture <http://developer.amd.com/wordpress/media/2013/12/Vega_Shader_ISA_28July2017.pdf>`__ .. [AMD-OpenCL_Programming-Guide] `AMD Accelerated Parallel Processing OpenCL Programming Guide <http://developer.amd.com/download/AMD_Accelerated_Parallel_Processing_OpenCL_Programming_Guide.pdf>`_ .. [AMD-APP-SDK] `AMD Accelerated Parallel Processing APP SDK Documentation <http://developer.amd.com/tools/heterogeneous-computing/amd-accelerated-parallel-processing-app-sdk/documentation/>`__ .. [AMD-ROCm] `ROCm: Open Platform for Development, Discovery and Education Around GPU Computing <http://gpuopen.com/compute-product/rocm/>`__ .. [AMD-ROCm-github] `ROCm github <http://github.com/RadeonOpenCompute>`__ .. [HSA] `Heterogeneous System Architecture (HSA) Foundation <http://www.hsafoundation.com/>`__ .. [ELF] `Executable and Linkable Format (ELF) <http://www.sco.com/developers/gabi/>`__ .. [DWARF] `DWARF Debugging Information Format <http://dwarfstd.org/>`__ .. [YAML] `YAML Ain't Markup Language (YAML™) Version 1.2 <http://www.yaml.org/spec/1.2/spec.html>`__ .. [OpenCL] `The OpenCL Specification Version 2.0 <http://www.khronos.org/registry/cl/specs/opencl-2.0.pdf>`__ .. [HRF] `Heterogeneous-race-free Memory Models <http://benedictgaster.org/wp-content/uploads/2014/01/asplos269-FINAL.pdf>`__ .. [AMD-AMDGPU-Compute-Application-Binary-Interface] `AMDGPU Compute Application Binary Interface <https://github.com/RadeonOpenCompute/ROCm-ComputeABI-Doc/blob/master/AMDGPU-ABI.md>`__