[all-commits] [llvm/llvm-project] 34d9a1: AMDGPU: Add option to expand 64-bit integer divisi...

[Matt Arsenault via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 34d9a16e54becbea4c790b19804d35453018a53f
      https://github.com/llvm/llvm-project/commit/34d9a16e54becbea4c790b19804d35453018a53f
  Author: Matt Arsenault <Matthew.Arsenault at amd.com>
  Date:   2020-02-14 (Fri, 14 Feb 2020)

  Changed paths:
    M llvm/lib/Target/AMDGPU/AMDGPUCodeGenPrepare.cpp
    M llvm/test/CodeGen/AMDGPU/amdgpu-codegenprepare-idiv.ll
    M llvm/test/CodeGen/AMDGPU/sdiv64.ll
    M llvm/test/CodeGen/AMDGPU/srem64.ll
    M llvm/test/CodeGen/AMDGPU/udiv64.ll
    M llvm/test/CodeGen/AMDGPU/urem64.ll

  Log Message:
  -----------
  AMDGPU: Add option to expand 64-bit integer division in IR

I didn't realize we were already expanding 24/32-bit division here
already. Use the available IntegerDivision utilities. This uses loops,
so produces significantly smaller code than the inline DAG expansion.

This now requires width reductions of 64-bit divisions before
introducing the expanded loops.

This helps work around missing legalization in GlobalISel for
division, which are the only remaining core instructions that didn't
work at all.

I think this is plausibly a better implementation than exists in the
DAG, although turning it on by default misses out on the constant
value optimizations and also needs benchmarking.