[all-commits] [llvm/llvm-project] 279166: [DAGCombiner] Check term use before applying aggre...

[Carl Ritson via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 2791667d2e3fb8c1f0abaff93fd8caaabb2b00b9
      https://github.com/llvm/llvm-project/commit/2791667d2e3fb8c1f0abaff93fd8caaabb2b00b9
  Author: Carl Ritson <carl.ritson at amd.com>
  Date:   2019-12-23 (Mon, 23 Dec 2019)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    M llvm/test/CodeGen/AMDGPU/fadd-fma-fmul-combine.ll

  Log Message:
  -----------
  [DAGCombiner] Check term use before applying aggressive FSUB optimisations

Summary:
Without this check unnecessary FMA instructions are generated when the FSUB terms are reused.
This also has the side-effect that the same value is computed to different levels of precision, which can create undesirable effects if the results are used together in subsequent computation.

Reviewers: arsenm, nhaehnle, foad, tpr, dstuttard, spatel

Reviewed By: arsenm

Subscribers: jvesely, wdng, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71656