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Implement InstCombine:shift.ll:test16, which turns (X >> C1) & C2 != C3
into (X & (C2 << C1)) != (C3 << C1), where the shift may be either left or right and the compare may be any one. This triggers 1546 times in 176.gcc alone, as it is a common pattern that occurs for bitfield accesses. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13740 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1475,6 +1475,41 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
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// integers at the end of their ranges...
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//
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if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
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if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
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if (LHSI->hasOneUse() && LHSI->getNumOperands() == 2 &&
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isa<ConstantInt>(LHSI->getOperand(1))) {
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// If this is: (X >> C1) & C2 != C3 (where any shift and any compare
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// could exist), turn it into (X & (C2 << C1)) != (C3 << C1). This
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// happens a LOT in code produced by the C front-end, for bitfield
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// access.
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if (LHSI->getOpcode() == Instruction::And &&
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LHSI->getOperand(0)->hasOneUse())
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if (ShiftInst *Shift = dyn_cast<ShiftInst>(LHSI->getOperand(0)))
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if (ConstantUInt *ShAmt =
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dyn_cast<ConstantUInt>(Shift->getOperand(1))) {
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ConstantInt *AndCST = cast<ConstantInt>(LHSI->getOperand(1));
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// We can fold this as long as we can't shift unknown bits into
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// the mask. This can only happen with signed shift rights, as
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// they sign-extend.
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const Type *Ty = Shift->getType();
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if (Shift->getOpcode() != Instruction::Shr ||
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Shift->getType()->isUnsigned() ||
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// To test for the bad case of the signed shr, see if any of
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// the bits shifted in could be tested after the mask.
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ConstantExpr::getAnd(ConstantExpr::getShl(ConstantInt::getAllOnesValue(Ty), ConstantUInt::get(Type::UByteTy, Ty->getPrimitiveSize()*8-ShAmt->getValue())), AndCST)->isNullValue()) {
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unsigned ShiftOp = Shift->getOpcode() == Instruction::Shl
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? Instruction::Shr : Instruction::Shl;
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I.setOperand(1, ConstantExpr::get(ShiftOp, CI, ShAmt));
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LHSI->setOperand(1, ConstantExpr::get(ShiftOp, AndCST, ShAmt));
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LHSI->setOperand(0, Shift->getOperand(0));
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WorkList.push_back(Shift); // Shift is probably dead.
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AddUsesToWorkList(I);
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return &I;
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}
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}
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}
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// Simplify seteq and setne instructions...
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if (I.getOpcode() == Instruction::SetEQ ||
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I.getOpcode() == Instruction::SetNE) {
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