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Implement X / C1 / C2 folding

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Implement (setcc (shl X, C1), C2) folding.

The second one occurs several dozen times in spec.  The first was added
just in case.  :)

These are tested by shift.ll:test2[12], and div.ll:test5


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16549 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-09-28 18:22:15 +00:00
parent 46c4dcde44
commit 18d19ca6df
1 changed files with 54 additions and 8 deletions
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62
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -818,6 +818,15 @@ Instruction *InstCombiner::visitDiv(BinaryOperator &I) {
if (RHS->isAllOnesValue())
return BinaryOperator::createNeg(I.getOperand(0));
if (Instruction *LHS = dyn_cast<Instruction>(I.getOperand(0)))
if (LHS->getOpcode() == Instruction::Div)
if (ConstantInt *LHSRHS = dyn_cast<ConstantInt>(LHS->getOperand(1))) {
std::cerr << "DIV: " << *LHS << " : " << I;
// (X / C1) / C2 -> X / (C1*C2)
return BinaryOperator::createDiv(LHS->getOperand(0),
ConstantExpr::getMul(RHS, LHSRHS));
}
// Check to see if this is an unsigned division with an exact power of 2,
// if so, convert to a right shift.
if (ConstantUInt *C = dyn_cast<ConstantUInt>(RHS))
@ -1553,10 +1562,51 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
}
break;
case Instruction::Shl: // (setcc (shl X, ShAmt), CI)
if (ConstantUInt *ShAmt = dyn_cast<ConstantUInt>(LHSI->getOperand(1))) {
switch (I.getOpcode()) {
default: break;
case Instruction::SetEQ:
case Instruction::SetNE: {
// If we are comparing against bits always shifted out, the
// comparison cannot succeed.
Constant *Comp =
ConstantExpr::getShl(ConstantExpr::getShr(CI, ShAmt), ShAmt);
if (Comp != CI) {// Comparing against a bit that we know is zero.
bool IsSetNE = I.getOpcode() == Instruction::SetNE;
Constant *Cst = ConstantBool::get(IsSetNE);
return ReplaceInstUsesWith(I, Cst);
}
if (LHSI->hasOneUse()) {
// Otherwise strength reduce the shift into an and.
unsigned ShAmtVal = ShAmt->getValue();
unsigned TypeBits = CI->getType()->getPrimitiveSize()*8;
uint64_t Val = (1ULL << (TypeBits-ShAmtVal))-1;
Constant *Mask;
if (CI->getType()->isUnsigned()) {
Mask = ConstantUInt::get(CI->getType(), Val);
} else if (ShAmtVal != 0) {
Mask = ConstantSInt::get(CI->getType(), Val);
} else {
Mask = ConstantInt::getAllOnesValue(CI->getType());
}
Instruction *AndI =
BinaryOperator::createAnd(LHSI->getOperand(0),
Mask, LHSI->getName()+".mask");
Value *And = InsertNewInstBefore(AndI, I);
return new SetCondInst(I.getOpcode(), And,
ConstantExpr::getUShr(CI, ShAmt));
}
}
}
}
break;
case Instruction::Shr: // (setcc (shr X, ShAmt), CI)
if (ConstantUInt *ShAmt = dyn_cast<ConstantUInt>(LHSI->getOperand(1))) {
unsigned ShAmtVal = ShAmt->getValue();
switch (I.getOpcode()) {
default: break;
case Instruction::SetEQ:
@ -1573,6 +1623,8 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
}
if (LHSI->hasOneUse() || CI->isNullValue()) {
unsigned ShAmtVal = ShAmt->getValue();
// Otherwise strength reduce the shift into an and.
uint64_t Val = ~0ULL; // All ones.
Val <<= ShAmtVal; // Shift over to the right spot.
@ -1599,12 +1651,6 @@ Instruction *InstCombiner::visitSetCondInst(BinaryOperator &I) {
}
break;
case Instruction::Div:
if (0 && isa<ConstantInt>(LHSI->getOperand(1))) {
std::cerr << "COULD FOLD: " << *LHSI;
std::cerr << "COULD FOLD: " << I << "\n";
}
break;
case Instruction::Select:
// If either operand of the select is a constant, we can fold the
// comparison into the select arms, which will cause one to be