diff options
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index d31e7e8333..6d39c50e3f 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -1475,6 +1475,41 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) { // integers at the end of their ranges... // if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) { + if (Instruction *LHSI = dyn_cast<Instruction>(Op0)) + if (LHSI->hasOneUse() && LHSI->getNumOperands() == 2 && + isa<ConstantInt>(LHSI->getOperand(1))) { + // 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 + // access. + if (LHSI->getOpcode() == Instruction::And && + LHSI->getOperand(0)->hasOneUse()) + if (ShiftInst *Shift = dyn_cast<ShiftInst>(LHSI->getOperand(0))) + if (ConstantUInt *ShAmt = + dyn_cast<ConstantUInt>(Shift->getOperand(1))) { + ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1)); + + // We can fold this as long as we can't shift unknown bits into + // the mask. This can only happen with signed shift rights, as + // they sign-extend. + const Type *Ty = Shift->getType(); + if (Shift->getOpcode() != Instruction::Shr || + Shift->getType()->isUnsigned() || + // To test for the bad case of the signed shr, see if any of + // the bits shifted in could be tested after the mask. + ConstantExpr::getAnd(ConstantExpr::getShl(ConstantInt::getAllOnesValue(Ty), ConstantUInt::get(Type::UByteTy, Ty->getPrimitiveSize()*8-ShAmt->getValue())), AndCST)->isNullValue()) { + unsigned ShiftOp = Shift->getOpcode() == Instruction::Shl + ? Instruction::Shr : Instruction::Shl; + I.setOperand(1, ConstantExpr::get(ShiftOp, CI, ShAmt)); + LHSI->setOperand(1, ConstantExpr::get(ShiftOp, AndCST, ShAmt)); + LHSI->setOperand(0, Shift->getOperand(0)); + WorkList.push_back(Shift); // Shift is probably dead. + AddUsesToWorkList(I); + return &I; + } + } + } + // Simplify seteq and setne instructions... if (I.getOpcode() == Instruction::SetEQ || I.getOpcode() == Instruction::SetNE) { |