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Fix bug: (x << 100) wasn't folded to 0, but (x >> 100) was (when x is unsigned)

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Implement new shift optimizations for shifting the result of a shift.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5729 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-03-10 19:16:08 +00:00
parent cb40a3749a
commit ea34005404
1 changed files with 48 additions and 7 deletions
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55
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -73,7 +73,7 @@ namespace {
Instruction *visitOr (BinaryOperator &I);
Instruction *visitXor(BinaryOperator &I);
Instruction *visitSetCondInst(BinaryOperator &I);
Instruction *visitShiftInst(Instruction &I);
Instruction *visitShiftInst(ShiftInst &I);
Instruction *visitCastInst(CastInst &CI);
Instruction *visitPHINode(PHINode &PN);
Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
@ -637,7 +637,7 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
Instruction *InstCombiner::visitShiftInst(Instruction &I) {
Instruction *InstCombiner::visitShiftInst(ShiftInst &I) {
assert(I.getOperand(1)->getType() == Type::UByteTy);
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -647,15 +647,56 @@ Instruction *InstCombiner::visitShiftInst(Instruction &I) {
Op0 == Constant::getNullValue(Op0->getType()))
return ReplaceInstUsesWith(I, Op0);
// If this is a shift of a shift, see if we can fold the two together...
if (ShiftInst *Op0SI = dyn_cast<ShiftInst>(Op0)) {
if (isa<Constant>(Op1) && isa<Constant>(Op0SI->getOperand(1))) {
ConstantUInt *ShiftAmt1C = cast<ConstantUInt>(Op0SI->getOperand(1));
unsigned ShiftAmt1 = ShiftAmt1C->getValue();
unsigned ShiftAmt2 = cast<ConstantUInt>(Op1)->getValue();
// Check for (A << c1) << c2 and (A >> c1) >> c2
if (I.getOpcode() == Op0SI->getOpcode()) {
unsigned Amt = ShiftAmt1+ShiftAmt2; // Fold into one big shift...
return new ShiftInst(I.getOpcode(), Op0SI->getOperand(0),
ConstantUInt::get(Type::UByteTy, Amt));
}
if (I.getType()->isUnsigned()) { // Check for (A << c1) >> c2 or visaversa
// Calculate bitmask for what gets shifted off the edge...
Constant *C = ConstantIntegral::getAllOnesValue(I.getType());
if (I.getOpcode() == Instruction::Shr)
C = *C >> *ShiftAmt1C;
else
C = *C << *ShiftAmt1C;
assert(C && "Couldn't constant fold shift expression?");
Instruction *Mask =
BinaryOperator::create(Instruction::And, Op0SI->getOperand(0),
C, Op0SI->getOperand(0)->getName()+".mask",&I);
WorkList.push_back(Mask);
// 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));
}
}
}
}
// shl uint X, 32 = 0 and shr ubyte Y, 9 = 0, ... just don't eliminate shr of
// a signed value.
//
if (ConstantUInt *CUI = dyn_cast<ConstantUInt>(Op1)) {
if (I.getOpcode() == Instruction::Shr) {
unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
if (CUI->getValue() >= TypeBits && !(Op0->getType()->isSigned()))
return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType()));
}
unsigned TypeBits = Op0->getType()->getPrimitiveSize()*8;
if (CUI->getValue() >= TypeBits &&
(!Op0->getType()->isSigned() || I.getOpcode() == Instruction::Shl))
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.