[PATCH] D66232: [InstCombine] Try to reuse constant from select in leading comparison

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: llvm/test/Transforms/InstCombine/unrecognized_three-way-comparison.ll:92-106
 define i32 @compare_against_two(i32 %x) {
 ; CHECK-LABEL: @compare_against_two(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = icmp sgt i32 [[X:%.*]], 2
-; CHECK-NEXT:    br i1 [[TMP0]], label [[CALLFOO:%.*]], label [[EXIT:%.*]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 [[X:%.*]], 2
+; CHECK-NEXT:    [[CMP2_INV:%.*]] = icmp sgt i32 [[X]], 1
+; CHECK-NEXT:    [[SELECT1:%.*]] = select i1 [[CMP2_INV]], i32 1, i32 -1
+; CHECK-NEXT:    [[SELECT2:%.*]] = select i1 [[CMP1]], i32 0, i32 [[SELECT1]]
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This is clearly a regression.
I suppose it means this fold happens before some other fold that used to happen,
and that fold does not know how to deal with the new pattern.
I'd prefer to look into this afterwards.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D66232/new/

https://reviews.llvm.org/D66232