diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineCompares.cpp | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp index bb1cbfa..274758c 100644 --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -1657,6 +1657,14 @@ static Instruction *ProcessUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B, CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth)) return 0; + // This is only really a signed overflow check if the inputs have been + // sign-extended; check for that condition. For example, if CI2 is 2^31 and + // the operands of the add are 64 bits wide, we need at least 33 sign bits. + unsigned NeededSignBits = CI1->getBitWidth() - NewWidth + 1; + if (IC.ComputeNumSignBits(A) < NeededSignBits || + IC.ComputeNumSignBits(B) < NeededSignBits) + return 0; + // In order to replace the original add with a narrower // llvm.sadd.with.overflow, the only uses allowed are the add-with-constant // and truncates that discard the high bits of the add. Verify that this is |