From 9533407566c3bafa96d7000e460cf49919acbd38 Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Sun, 27 Sep 2015 20:34:31 +0000 Subject: [InstCombine] fold zexts and constants into a phi (PR24766) This is one step towards solving PR24766: https://llvm.org/bugs/show_bug.cgi?id=24766 We were not producing the same IR for these two C functions because the store to the temp bool causes extra zexts: #include bool switchy(char x1, char x2, char condition) { bool conditionMet = false; switch (condition) { case 0: conditionMet = (x1 == x2); break; case 1: conditionMet = (x1 <= x2); break; } return conditionMet; } bool switchy2(char x1, char x2, char condition) { switch (condition) { case 0: return (x1 == x2); case 1: return (x1 <= x2); } return false; } As noted in the code comments, this test case manages to avoid the more general existing phi optimizations where there are only 2 phi inputs or where there are no constant phi args mixed in with the casts ops. It seems like a corner case, but if we don't catch it, then I don't think we can get SimplifyCFG to further optimize towards the canonical form for this function shown in the bug report. Differential Revision: http://reviews.llvm.org/D12866 llvm-svn: 248689 --- llvm/lib/Transforms/InstCombine/InstCombineInternal.h | 1 + 1 file changed, 1 insertion(+) (limited to 'llvm/lib/Transforms/InstCombine/InstCombineInternal.h') diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h index dbaa5a88ee3..9e58c7428bd 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h +++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h @@ -545,6 +545,7 @@ private: Instruction *FoldPHIArgBinOpIntoPHI(PHINode &PN); Instruction *FoldPHIArgGEPIntoPHI(PHINode &PN); Instruction *FoldPHIArgLoadIntoPHI(PHINode &PN); + Instruction *FoldPHIArgZextsIntoPHI(PHINode &PN); Instruction *OptAndOp(Instruction *Op, ConstantInt *OpRHS, ConstantInt *AndRHS, BinaryOperator &TheAnd); -- cgit v1.2.3