[PATCH] D139275: [SimplifyCFG] `FoldBranchToCommonDest()`: deal with mismatched IV's in PHI's in common successor block

[Nikita Popov via Phabricator via llvm-commits]

nikic added inline comments.


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Comment at: llvm/test/Transforms/SimplifyCFG/X86/SpeculativeExec.ll:15
+; CHECK-NEXT:    [[T3:%.*]] = add i32 [[A]], 1
+; CHECK-NEXT:    [[T4:%.*]] = select i1 [[OR_COND]], i32 [[T3]], i32 [[T4_SEL]]
 ; CHECK-NEXT:    [[T5:%.*]] = sub i32 [[T4]], 1
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nikic wrote:
> Looks like this test, and many similar tests regress, where we go from two selects to three selects. And we never seem to recover from this in either the middle end or the back end: https://alive2.llvm.org/ce/z/GjCXkB
Filed https://github.com/llvm/llvm-project/issues/59393. We should at least add an InstCombine fold, but ideally we'd avoid regressing this in SimplifyCFG.


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https://reviews.llvm.org/D139275