diff options
| -rw-r--r-- | llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp index eee1243338e..0d23ea0a948 100644 --- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -2041,6 +2041,13 @@ Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp, return Res; } + // If the comparison constant changes with the shift, the comparison cannot + // succeed (bits of the comparison constant cannot match the shifted value). + // This should be known by InstSimplify and already be folded to true/false. + assert(((IsAShr && C->shl(ShAmtVal).ashr(ShAmtVal) == *C) || + (!IsAShr && C->shl(ShAmtVal).lshr(ShAmtVal) == *C)) && + "Expected icmp+shr simplify did not occur."); + // Check if the bits shifted out are known to be zero. If so, we can compare // against the unshifted value: // (X & 4) >> 1 == 2 --> (X & 4) == 4. |
