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Instcombine: (A >> c1) << c2 for signed integers

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7295 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-07-24 18:38:56 +00:00
parent 709ad40dc8
commit 943c713c65
1 changed files with 12 additions and 10 deletions
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22
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -885,16 +885,10 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
(!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl)) (!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType())); return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
// Check to see if we are shifting left by 1. If so, turn it into an add
// instruction.
if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
// Convert 'shl int %X, 1' to 'add int %X, %X'
return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
// If this is a shift of a shift, see if we can fold the two together... // If this is a shift of a shift, see if we can fold the two together...
if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) { if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
if (isa<ConstantUInt>(Op1) && isa<Constant>(Op0SI->getOperand(1))) { if (ConstantUInt *ShiftAmt1C =
ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1)); dyn_cast<ConstantUInt>(Op0SI->getOperand(1))) {
unsigned ShiftAmt1 = ShiftAmt1C->getValue(); unsigned ShiftAmt1 = ShiftAmt1C->getValue();
unsigned ShiftAmt2 = CUI->getValue(); unsigned ShiftAmt2 = CUI->getValue();
@ -905,8 +899,10 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
ConstantUInt::get(Type::UByteTy, Amt)); ConstantUInt::get(Type::UByteTy, Amt));
} }
// Check for (A << c1) >> c2 or visaversa // Check for (A << c1) >> c2 or visaversa. If we are dealing with
if (I.getType()->isUnsigned()) { // signed types, we can only support the (A >> c1) << c2 configuration,
// because it can not turn an arbitrary bit of A into a sign bit.
if (I.getType()->isUnsigned() || I.getOpcode() == Instruction::Shl) {
// Calculate bitmask for what gets shifted off the edge... // Calculate bitmask for what gets shifted off the edge...
Constant *C = ConstantIntegral::getAllOnesValue(I.getType()); Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
if (I.getOpcode() == Instruction::Shr) if (I.getOpcode() == Instruction::Shr)
@ -932,6 +928,12 @@ Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
} }
} }
} }
// Check to see if we are shifting left by 1. If so, turn it into an add
// instruction.
if (I.getOpcode() == Instruction::Shl && CUI->equalsInt(1))
// Convert 'shl int %X, 1' to 'add int %X, %X'
return BinaryOperator::create(Instruction::Add, Op0, Op0, I.getName());
} }
// shr int -1, X = -1 (for any arithmetic shift rights of ~0) // shr int -1, X = -1 (for any arithmetic shift rights of ~0)