diff options
Diffstat (limited to 'lib/Transforms/InstCombine/InstCombineCompares.cpp')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineCompares.cpp | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp index 92cbc1b7f1..5ddf23ba8e 100644 --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -1097,7 +1097,23 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI, ConstantExpr::getZExt(RHS, Cast->getSrcTy())); } } - + + // If the LHS is an AND of a zext, and we have an equality compare, we can + // shrink the and/compare to the smaller type, eliminating the cast. + if (ZExtInst *Cast = dyn_cast<ZExtInst>(LHSI->getOperand(0))) { + const IntegerType *Ty = cast<IntegerType>(Cast->getSrcTy()); + // Make sure we don't compare the upper bits, SimplifyDemandedBits + // should fold the icmp to true/false in that case. + if (ICI.isEquality() && RHSV.getActiveBits() <= Ty->getBitWidth()) { + Value *NewAnd = + Builder->CreateAnd(Cast->getOperand(0), + ConstantExpr::getTrunc(AndCST, Ty)); + NewAnd->takeName(LHSI); + return new ICmpInst(ICI.getPredicate(), NewAnd, + ConstantExpr::getTrunc(RHS, Ty)); + } + } + // If this is: (X >> C1) & C2 != C3 (where any shift and any compare // could exist), turn it into (X & (C2 << C1)) != (C3 << C1). This // happens a LOT in code produced by the C front-end, for bitfield |