[PATCH] D49283: [InstCombine] fold icmp pred (sub 0, X) C for vector type

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: spatel, nemanjai.
Herald added a subscriber: hiraditya.

This is from https://reviews.llvm.org/D49238 code review comments.

Currently opt can fold scalar type for instruction pattern:

  define i32 @Op1Negated_Scalar(i32 %x) {
    %sub = sub nsw i32 0, %x
    %cmp = icmp sgt i32 %sub, -1
    %cond = select i1 %cmp, i32 %sub, i32 %x
    ret i32 %cond
  }

to

  define i32 @Op1Negated_Scalar(i32 %x) {
    %sub = sub nsw i32 0, %x
    %cmp = icmp slt i32 %x, 0
    %cond = select i1 %cmp, i32 %sub, i32 %x
    ret i32 %cond
  }

But it can not fold vector type for the same instruction pattern:

  define <2 x i32> @Op1Negated_Vec(<2 x i32> %x) {
    %sub = sub nsw <2 x i32> zeroinitializer, %x
    %cmp = icmp sgt <2 x i32> %sub, <i32 -1, i32 -1>
    %cond = select <2 x i1> %cmp, <2 x i32> %sub, <2 x i32> %x
    ret <2 x i32> %cond
  }

We should also fold %cmp = icmp sgt <2 x i32> %sub, <i32 -1, i32 -1> to %cmp = icmp slt <2 x i32> %x, zeroinitializer as what we do for scalar type.

Note: there must be two uses of %sub in case Op1Negated_Vec(), %cmp and %cond, otherwise if only one use %cmp, icmp is folded in earlier function in visitICmpInst() -> foldICmpWithConstant() -> foldICmpSubConstant().


https://reviews.llvm.org/D49283

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/abs_abs.ll
  llvm/test/Transforms/InstCombine/icmp.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D49283.155328.patch
Type: text/x-patch
Size: 5480 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20180713/c5614e3f/attachment.bin>