[all-commits] [llvm/llvm-project] 9d3559: Reland "[LV] Use lookThroughAnd with logical reduc...

[kmclaughlin-arm via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9d355949937038c32c7608ebb558bbc3984f6340
      https://github.com/llvm/llvm-project/commit/9d355949937038c32c7608ebb558bbc3984f6340
  Author: Kerry McLaughlin <kerry.mclaughlin at arm.com>
  Date:   2021-07-30 (Fri, 30 Jul 2021)

  Changed paths:
    M llvm/lib/Analysis/IVDescriptors.cpp
    M llvm/test/Transforms/LoopVectorize/reduction-inloop-pred.ll
    M llvm/test/Transforms/LoopVectorize/reduction-inloop.ll
    A llvm/test/Transforms/LoopVectorize/trunc-reductions.ll

  Log Message:
  -----------
  Reland "[LV] Use lookThroughAnd with logical reductions"

If a reduction Phi has a single user which `AND`s the Phi with a type mask,
`lookThroughAnd` will return the user of the Phi and the narrower type represented
by the mask. Currently this is only used for arithmetic reductions, whereas loops
containing logical reductions will create a reduction intrinsic using the widened
type, for example:

  for.body:
    %phi = phi i32 [ %and, %for.body ], [ 255, %entry ]
    %mask = and i32 %phi, 255
    %gep = getelementptr inbounds i8, i8* %ptr, i32 %iv
    %load = load i8, i8* %gep
    %ext = zext i8 %load to i32
    %and = and i32 %mask, %ext
    ...

^ this will generate an and reduction intrinsic such as the following:
    call i32 @llvm.vector.reduce.and.v8i32(<8 x i32>...)

The same example for an add instruction would create an intrinsic of type i8:
    call i8 @llvm.vector.reduce.add.v8i8(<8 x i8>...)

This patch changes AddReductionVar to call lookThroughAnd for other integer
reductions, allowing loops similar to the example above with reductions such
as and, or & xor to vectorize.

Reviewed By: david-arm, dmgreen

Differential Revision: https://reviews.llvm.org/D105632