[all-commits] [llvm/llvm-project] 853b2a: [AMDGPU] Reserve SGPR pair when long branches are ...

[bcahoon via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 853b2a84cb9902725752e9603011041ebe33c7bf
      https://github.com/llvm/llvm-project/commit/853b2a84cb9902725752e9603011041ebe33c7bf
  Author: Brendon Cahoon <brendon.cahoon at amd.com>
  Date:   2023-06-29 (Thu, 29 Jun 2023)

  Changed paths:
    M llvm/lib/Target/AMDGPU/AMDGPU.h
    M llvm/lib/Target/AMDGPU/AMDGPUTargetMachine.cpp
    M llvm/lib/Target/AMDGPU/CMakeLists.txt
    A llvm/lib/Target/AMDGPU/GCNPreRALongBranchReg.cpp
    M llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
    M llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
    M llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp
    M llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
    M llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
    M llvm/test/CodeGen/AMDGPU/branch-relax-spill.ll
    M llvm/test/CodeGen/AMDGPU/branch-relaxation.ll
    M llvm/test/CodeGen/AMDGPU/literal-constant-like-operand-instruction-size.ll
    M llvm/test/CodeGen/AMDGPU/llc-pipeline.ll
    A llvm/test/CodeGen/AMDGPU/long-branch-reserve-register.ll
    A llvm/test/CodeGen/MIR/AMDGPU/long-branch-reg-all-sgpr-used.ll
    M llvm/test/CodeGen/MIR/AMDGPU/machine-function-info-after-pei.ll
    A llvm/test/CodeGen/MIR/AMDGPU/machine-function-info-long-branch-reg-debug.ll
    A llvm/test/CodeGen/MIR/AMDGPU/machine-function-info-long-branch-reg.ll
    M llvm/test/CodeGen/MIR/AMDGPU/machine-function-info-no-ir.mir
    M llvm/test/CodeGen/MIR/AMDGPU/machine-function-info.ll

  Log Message:
  -----------
  [AMDGPU] Reserve SGPR pair when long branches are present

Branch relaxation requires 2 additional SGPRs for AMDGPU to handle the
case when an indirect branch target is too far away. The register
scavanger may not find available registers, which causes a “did not find
scavenging index” assert to occur in assignRegToScavengingIndex.

In this patch, we estimate before register allocation whether an
indirect branch is likely to be needed, and reserve 2 SGPRs if the
branch distance is found to be above a threshold. The distance threshold
is an approximation as the exact code size and branch distance are
unknown prior to register allocation.

Patch by Corbin Robeck. Thanks!

Differential Review: https://reviews.llvm.org/D149775