[all-commits] [llvm/llvm-project] 7f5d59: [AMDGPU] ISel for @llvm.amdgcn.cs.chain intrinsic ...

[Diana via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 7f5d59b38dc4ea85bc47246340034b214b25e2ba
      https://github.com/llvm/llvm-project/commit/7f5d59b38dc4ea85bc47246340034b214b25e2ba
  Author: Diana <Diana-Magda.Picus at amd.com>
  Date:   2023-11-06 (Mon, 06 Nov 2023)

  Changed paths:
    M llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
    M llvm/lib/Target/AMDGPU/AMDGPUCallLowering.cpp
    M llvm/lib/Target/AMDGPU/AMDGPUCallLowering.h
    M llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
    M llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h
    M llvm/lib/Target/AMDGPU/AMDGPUInstrInfo.td
    M llvm/lib/Target/AMDGPU/SIISelLowering.cpp
    M llvm/lib/Target/AMDGPU/SIInstructions.td
    M llvm/lib/Target/AMDGPU/SILateBranchLowering.cpp
    M llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
    A llvm/test/CodeGen/AMDGPU/GlobalISel/irtranslator-amdgcn-cs-chain.ll
    M llvm/test/CodeGen/AMDGPU/amdgpu-cs-chain-cc.ll
    M llvm/test/CodeGen/AMDGPU/amdgpu-cs-chain-preserve-cc.ll
    A llvm/test/CodeGen/AMDGPU/isel-amdgcn-cs-chain-intrinsic-w32.ll
    A llvm/test/CodeGen/AMDGPU/isel-amdgcn-cs-chain-intrinsic-w64.ll

  Log Message:
  -----------
  [AMDGPU] ISel for @llvm.amdgcn.cs.chain intrinsic (#68186)

The @llvm.amdgcn.cs.chain intrinsic is essentially a call. The call
parameters are bundled up into 2 intrinsic arguments, one for those that
should go in the SGPRs (the 3rd intrinsic argument), and one for those
that should go in the VGPRs (the 4th intrinsic argument). Both will
often be some kind of aggregate.

Both instruction selection frameworks have some internal representation
for intrinsics (G_INTRINSIC[_WITH_SIDE_EFFECTS] for GlobalISel,
ISD::INTRINSIC_[VOID|WITH_CHAIN] for DAGISel), but we can't use those
because aggregates are dissolved very early on during ISel and we'd lose
the inreg information. Therefore, this patch shortcircuits both the
IRTranslator and SelectionDAGBuilder to lower this intrinsic as a call
from the very start. It tries to use the existing infrastructure as much
as possible, by calling into the code for lowering tail calls.

This has already gone through a few rounds of review in Phab:

Differential Revision: https://reviews.llvm.org/D153761