diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index f59874b1a5..c1a8eab95b 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -6343,6 +6343,28 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI, const APInt &RHSV = RHS->getValue(); switch (LHSI->getOpcode()) { + case Instruction::Trunc: + if (ICI.isEquality() && LHSI->hasOneUse()) { + // Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42|highbits if all + // of the high bits truncated out of x are known. + unsigned DstBits = LHSI->getType()->getPrimitiveSizeInBits(), + SrcBits = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits(); + APInt Mask(APInt::getHighBitsSet(SrcBits, SrcBits-DstBits)); + APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0); + ComputeMaskedBits(LHSI->getOperand(0), Mask, KnownZero, KnownOne); + + // If all the high bits are known, we can do this xform. + if ((KnownZero|KnownOne).countLeadingOnes() >= SrcBits-DstBits) { + // Pull in the high bits from known-ones set. + APInt NewRHS(RHS->getValue()); + NewRHS.zext(SrcBits); + NewRHS |= KnownOne; + return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0), + ConstantInt::get(NewRHS)); + } + } + break; + case Instruction::Xor: // (icmp pred (xor X, XorCST), CI) if (ConstantInt *XorCST = dyn_cast<ConstantInt>(LHSI->getOperand(1))) { // If this is a comparison that tests the signbit (X < 0) or (x > -1), |