diff options
| -rw-r--r-- | clang/lib/CodeGen/CGExprScalar.cpp | 17 |
1 files changed, 5 insertions, 12 deletions
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp index e761e9f3c7d..f8fae423015 100644 --- a/clang/lib/CodeGen/CGExprScalar.cpp +++ b/clang/lib/CodeGen/CGExprScalar.cpp @@ -1184,19 +1184,12 @@ Value *ScalarExprEmitter::EmitSub(const BinOpInfo &Ops) { // Optimize out the shift for element size of 1. if (ElementSize == 1) return BytesBetween; - - // HACK: LLVM doesn't have an divide instruction that 'knows' there is no - // remainder. As such, we handle common power-of-two cases here to generate - // better code. See PR2247. - if (llvm::isPowerOf2_64(ElementSize)) { - Value *ShAmt = - llvm::ConstantInt::get(ResultType, llvm::Log2_64(ElementSize)); - return Builder.CreateAShr(BytesBetween, ShAmt, "sub.ptr.shr"); - } - - // Otherwise, do a full sdiv. + + // Otherwise, do a full sdiv. This uses the "exact" form of sdiv, since + // pointer difference in C is only defined in the case where both + // operands are pointing to elements of an array. Value *BytesPerElt = llvm::ConstantInt::get(ResultType, ElementSize); - return Builder.CreateSDiv(BytesBetween, BytesPerElt, "sub.ptr.div"); + return Builder.CreateExactSDiv(BytesBetween, BytesPerElt, "sub.ptr.div"); } } |
