[all-commits] [llvm/llvm-project] b3b3cb: [AMDGPU] Less aggressively break large PHIs

[Pierre van Houtryve via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b3b3cb2d2f7c650a63e19db12cccc9317a534b39
      https://github.com/llvm/llvm-project/commit/b3b3cb2d2f7c650a63e19db12cccc9317a534b39
  Author: pvanhout <pierre.vanhoutryve at amd.com>
  Date:   2023-04-14 (Fri, 14 Apr 2023)

  Changed paths:
    M llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp
    M llvm/test/CodeGen/AMDGPU/agpr-copy-no-free-registers.ll
    A llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-break-large-phis-heuristics.ll
    M llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-break-large-phis.ll
    M llvm/test/CodeGen/AMDGPU/extract-subvector-16bit.ll
    M llvm/test/CodeGen/AMDGPU/insert_vector_elt.ll
    M llvm/test/CodeGen/AMDGPU/loop-live-out-copy-undef-subrange.ll
    M llvm/test/CodeGen/AMDGPU/mfma-loop.ll
    M llvm/test/CodeGen/AMDGPU/wave32.ll
    M llvm/test/CodeGen/AMDGPU/wqm.ll

  Log Message:
  -----------
  [AMDGPU] Less aggressively break large PHIs

In some cases, breaking large PHIs can very negatively affect
performance (3x more instructions observed in a particular test case).

This patch adds some basic profitability heuristics to help with some of these issues without affecting the "good" cases.
e.g. avoid breaking PHIs if it causes back-and-forth between vector/scalar form for no good reason.

Fixes SWDEV-392803
Fixes SWDEV-393781
Fixes SWDEV-394228

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D147786