// We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't
// profitable unless we know the and'd out bits are already zero.
- if (CI->getZExtValue() > NumBits) {
+ if (CI->getValue().ult(TypeWidth) && CI->getZExtValue() > NumBits) {
unsigned LowBits = CI->getZExtValue() - NumBits;
if (MaskedValueIsZero(I->getOperand(0),
APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
IC.Worklist.Add(I);
switch (I->getOpcode()) {
- default: assert(0 && "Inconsistency with CanEvaluateShifted");
+ default: llvm_unreachable("Inconsistency with CanEvaluateShifted");
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
ShiftOp = 0;
if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) {
+
+ // This is a constant shift of a constant shift. Be careful about hiding
+ // shl instructions behind bit masks. They are used to represent multiplies
+ // by a constant, and it is important that simple arithmetic expressions
+ // are still recognizable by scalar evolution.
+ //
+ // The transforms applied to shl are very similar to the transforms applied
+ // to mul by constant. We can be more aggressive about optimizing right
+ // shifts.
+ //
+ // Combinations of right and left shifts will still be optimized in
+ // DAGCombine where scalar evolution no longer applies.
+
ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1));
uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits);
uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits);
if (ShiftAmt1 == 0) return 0; // Will be simplified in the future.
Value *X = ShiftOp->getOperand(0);
- uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
-
IntegerType *Ty = cast<IntegerType>(I.getType());
// Check for (X << c1) << c2 and (X >> c1) >> c2
if (I.getOpcode() == ShiftOp->getOpcode()) {
+ uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
// If this is oversized composite shift, then unsigned shifts get 0, ashr
// saturates.
if (AmtSum >= TypeBits) {
}
if (ShiftAmt1 == ShiftAmt2) {
- // If we have ((X >>? C) << C), turn this into X & (-1 << C).
- if (I.getOpcode() == Instruction::Shl &&
- ShiftOp->getOpcode() != Instruction::Shl) {
- APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1));
- return BinaryOperator::CreateAnd(X,
- ConstantInt::get(I.getContext(),Mask));
- }
// If we have ((X << C) >>u C), turn this into X & (-1 >>u C).
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
}
} else if (ShiftAmt1 < ShiftAmt2) {
uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1;
-
- // (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2)
+
+ // (X >>?,exact C1) << C2 --> X << (C2-C1)
+ // The inexact version is deferred to DAGCombine so we don't hide shl
+ // behind a bit mask.
if (I.getOpcode() == Instruction::Shl &&
- ShiftOp->getOpcode() != Instruction::Shl) {
+ ShiftOp->getOpcode() != Instruction::Shl &&
+ ShiftOp->isExact()) {
assert(ShiftOp->getOpcode() == Instruction::LShr ||
ShiftOp->getOpcode() == Instruction::AShr);
- Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
-
- APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
- return BinaryOperator::CreateAnd(Shift,
- ConstantInt::get(I.getContext(),Mask));
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
+ X, ShiftDiffCst);
+ NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
+ NewShl->setHasNoSignedWrap(I.hasNoSignedWrap());
+ return NewShl;
}
-
+
// (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2)
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
- assert(ShiftOp->getOpcode() == Instruction::Shl);
- Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff));
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ // (X <<nuw C1) >>u C2 --> X >>u (C2-C1)
+ if (ShiftOp->hasNoUnsignedWrap()) {
+ BinaryOperator *NewLShr = BinaryOperator::Create(Instruction::LShr,
+ X, ShiftDiffCst);
+ NewLShr->setIsExact(I.isExact());
+ return NewLShr;
+ }
+ Value *Shift = Builder->CreateLShr(X, ShiftDiffCst);
APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::CreateAnd(Shift,
ConstantInt::get(I.getContext(),Mask));
}
-
- // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in.
+
+ // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However,
+ // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
+ if (I.getOpcode() == Instruction::AShr &&
+ ShiftOp->getOpcode() == Instruction::Shl) {
+ if (ShiftOp->hasNoSignedWrap()) {
+ // (X <<nsw C1) >>s C2 --> X >>s (C2-C1)
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ BinaryOperator *NewAShr = BinaryOperator::Create(Instruction::AShr,
+ X, ShiftDiffCst);
+ NewAShr->setIsExact(I.isExact());
+ return NewAShr;
+ }
+ }
} else {
assert(ShiftAmt2 < ShiftAmt1);
uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2;
- // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2)
+ // (X >>?exact C1) << C2 --> X >>?exact (C1-C2)
+ // The inexact version is deferred to DAGCombine so we don't hide shl
+ // behind a bit mask.
if (I.getOpcode() == Instruction::Shl &&
- ShiftOp->getOpcode() != Instruction::Shl) {
- Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X,
- ConstantInt::get(Ty, ShiftDiff));
-
- APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2));
- return BinaryOperator::CreateAnd(Shift,
- ConstantInt::get(I.getContext(),Mask));
+ ShiftOp->getOpcode() != Instruction::Shl &&
+ ShiftOp->isExact()) {
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(),
+ X, ShiftDiffCst);
+ NewShr->setIsExact(true);
+ return NewShr;
}
-
+
// (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2)
if (I.getOpcode() == Instruction::LShr &&
ShiftOp->getOpcode() == Instruction::Shl) {
- Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff));
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ if (ShiftOp->hasNoUnsignedWrap()) {
+ // (X <<nuw C1) >>u C2 --> X <<nuw (C1-C2)
+ BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
+ X, ShiftDiffCst);
+ NewShl->setHasNoUnsignedWrap(true);
+ return NewShl;
+ }
+ Value *Shift = Builder->CreateShl(X, ShiftDiffCst);
APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2));
return BinaryOperator::CreateAnd(Shift,
ConstantInt::get(I.getContext(),Mask));
}
- // We can't handle (X << C1) >>a C2, it shifts arbitrary bits in.
+ // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However,
+ // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits.
+ if (I.getOpcode() == Instruction::AShr &&
+ ShiftOp->getOpcode() == Instruction::Shl) {
+ if (ShiftOp->hasNoSignedWrap()) {
+ // (X <<nsw C1) >>s C2 --> X <<nsw (C1-C2)
+ ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff);
+ BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl,
+ X, ShiftDiffCst);
+ NewShl->setHasNoSignedWrap(true);
+ return NewShl;
+ }
+ }
}
}
return 0;
projects / oota-llvm.git / blobdiff