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Enhance the shift-shift folding code to allow a no-op cast to occur in between

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the shifts.

This allows us to fold this (which is the 'integer add a constant' sequence
from cozmic's scheme compmiler):

int %x(uint %anf-temporary776) {
        %anf-temporary777 = shr uint %anf-temporary776, ubyte 1
        %anf-temporary800 = cast uint %anf-temporary777 to int
        %anf-temporary804 = shl int %anf-temporary800, ubyte 1
        %anf-temporary805 = add int %anf-temporary804, -2
        %anf-temporary806 = or int %anf-temporary805, 1
        ret int %anf-temporary806
}

into this:

int %x(uint %anf-temporary776) {
        %anf-temporary776 = cast uint %anf-temporary776 to int
        %anf-temporary776.mask1 = add int %anf-temporary776, -2
        %anf-temporary805 = or int %anf-temporary776.mask1, 1
        ret int %anf-temporary805
}

note that instcombine already knew how to eliminate the AND that the two
shifts fold into.  This is tested by InstCombine/shift.ll:test26

-Chris


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25128 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-01-06 07:52:12 +00:00
parent 6c7fbb8503
commit ad0124c188
1 changed files with 88 additions and 55 deletions
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143
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -3648,68 +3648,101 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantUInt *Op1,
}
}
// If this is a shift of a shift, see if we can fold the two together.
// Find out if this is a shift of a shift by a constant.
ShiftInst *ShiftOp = 0;
if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0))
if (ConstantUInt *ShiftAmt1C =
dyn_cast<ConstantUInt>(Op0SI->getOperand(1))) {
unsigned ShiftAmt1 = (unsigned)ShiftAmt1C->getValue();
unsigned ShiftAmt2 = (unsigned)Op1->getValue();
ShiftOp = Op0SI;
else if (CastInst *CI = dyn_cast<CastInst>(Op0)) {
// If this is a noop-integer case of a shift instruction, use the shift.
if (CI->getOperand(0)->getType()->isInteger() &&
CI->getOperand(0)->getType()->getPrimitiveSizeInBits() ==
CI->getType()->getPrimitiveSizeInBits() &&
isa<ShiftInst>(CI->getOperand(0))) {
ShiftOp = cast<ShiftInst>(CI->getOperand(0));
}
}
if (ShiftOp && isa<ConstantUInt>(ShiftOp->getOperand(1))) {
// Find the operands and properties of the input shift. Note that the
// signedness of the input shift may differ from the current shift if there
// is a noop cast between the two.
bool isShiftOfLeftShift = ShiftOp->getOpcode() == Instruction::Shl;
bool isShiftOfSignedShift = ShiftOp->getType()->isSigned();
bool isShiftOfUnsignedShift = !isSignedShift;
ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(ShiftOp->getOperand(1));
unsigned ShiftAmt1 = (unsigned)ShiftAmt1C->getValue();
unsigned ShiftAmt2 = (unsigned)Op1->getValue();
// Check for (A << c1) << c2 and (A >> c1) >> c2.
if (isLeftShift == isShiftOfLeftShift) {
// Do not fold these shifts if the first one is signed and the second one
// is unsigned and this is a right shift. Further, don't do any folding
// on them.
if (isShiftOfSignedShift && isUnsignedShift && !isLeftShift)
return 0;
// Check for (A << c1) << c2 and (A >> c1) >> c2
if (I.getOpcode() == Op0SI->getOpcode()) {
unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
if (Op0->getType()->getPrimitiveSizeInBits() < Amt)
Amt = Op0->getType()->getPrimitiveSizeInBits();
return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
ConstantUInt::get(Type::UByteTy, Amt));
}
unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift.
if (Amt > Op0->getType()->getPrimitiveSizeInBits())
Amt = Op0->getType()->getPrimitiveSizeInBits();
// Check for (A << c1) >> c2 or visaversa. If we are dealing with
// 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 (isUnsignedShift || isLeftShift) {
// Calculate bitmask for what gets shifted off the edge...
Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
if (isLeftShift)
C = ConstantExpr::getShl(C, ShiftAmt1C);
else
C = ConstantExpr::getShr(C, ShiftAmt1C);
Instruction *Mask =
BinaryOperator::createAnd(Op0SI->getOperand(0), C,
Op0SI->getOperand(0)->getName()+".mask");
InsertNewInstBefore(Mask, I);
// Figure out what flavor of shift we should use...
if (ShiftAmt1 == ShiftAmt2)
return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
else if (ShiftAmt1 < ShiftAmt2) {
return new ShiftInst(I.getOpcode(), Mask,
ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
} else {
return new ShiftInst(Op0SI->getOpcode(), Mask,
ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
}
Value *Op = ShiftOp->getOperand(0);
if (isShiftOfSignedShift != isSignedShift)
Op = InsertNewInstBefore(new CastInst(Op, I.getType(), "tmp"), I);
return new ShiftInst(I.getOpcode(), Op,
ConstantUInt::get(Type::UByteTy, Amt));
}
// Check for (A << c1) >> c2 or (A >> c1) << c2. If we are dealing with
// 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 (isUnsignedShift || isLeftShift) {
// Calculate bitmask for what gets shifted off the edge.
Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
if (isLeftShift)
C = ConstantExpr::getShl(C, ShiftAmt1C);
else
C = ConstantExpr::getShr(C, ShiftAmt1C); // must be an unsigned shr.
Value *Op = ShiftOp->getOperand(0);
if (isShiftOfSignedShift != isSignedShift)
Op = InsertNewInstBefore(new CastInst(Op, I.getType(),Op->getName()),I);
Instruction *Mask =
BinaryOperator::createAnd(Op, C, Op->getName()+".mask");
InsertNewInstBefore(Mask, I);
// Figure out what flavor of shift we should use...
if (ShiftAmt1 == ShiftAmt2)
return ReplaceInstUsesWith(I, Mask); // (A << c) >> c === A & c2
else if (ShiftAmt1 < ShiftAmt2) {
return new ShiftInst(I.getOpcode(), Mask,
ConstantUInt::get(Type::UByteTy, ShiftAmt2-ShiftAmt1));
} else {
// We can handle signed (X << C1) >> C2 if it's a sign extend. In
// this case, C1 == C2 and C1 is 8, 16, or 32.
if (ShiftAmt1 == ShiftAmt2) {
const Type *SExtType = 0;
switch (ShiftAmt1) {
case 8 : SExtType = Type::SByteTy; break;
case 16: SExtType = Type::ShortTy; break;
case 32: SExtType = Type::IntTy; break;
}
if (SExtType) {
Instruction *NewTrunc = new CastInst(Op0SI->getOperand(0),
SExtType, "sext");
InsertNewInstBefore(NewTrunc, I);
return new CastInst(NewTrunc, I.getType());
}
return new ShiftInst(ShiftOp->getOpcode(), Mask,
ConstantUInt::get(Type::UByteTy, ShiftAmt1-ShiftAmt2));
}
} else {
// We can handle signed (X << C1) >> C2 if it's a sign extend. In
// this case, C1 == C2 and C1 is 8, 16, or 32.
if (ShiftAmt1 == ShiftAmt2) {
const Type *SExtType = 0;
switch (ShiftAmt1) {
case 8 : SExtType = Type::SByteTy; break;
case 16: SExtType = Type::ShortTy; break;
case 32: SExtType = Type::IntTy; break;
}
if (SExtType) {
Instruction *NewTrunc = new CastInst(ShiftOp->getOperand(0),
SExtType, "sext");
InsertNewInstBefore(NewTrunc, I);
return new CastInst(NewTrunc, I.getType());
}
}
}
}
return 0;
}