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rearrange some code, simplify handling of shifts.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@49995 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-04-20 18:24:14 +00:00
parent 9dd2ce46c5
commit 0e4b6c7551
1 changed files with 56 additions and 60 deletions
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116
lib/VMCore/ConstantFold.cpp
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@ -599,44 +599,12 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
}
}
if (isa<ConstantExpr>(C1)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
} else if (isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flop them around and fold the
// other way if possible.
switch (Opcode) {
case Instruction::Add:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// No change of opcode required.
return ConstantFoldBinaryInstruction(Opcode, C2, C1);
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::Sub:
case Instruction::SDiv:
case Instruction::UDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
default: // These instructions cannot be flopped around.
return 0;
}
}
// At this point we know neither constant is an UndefValue nor a ConstantExpr
// so look at directly computing the value.
// At this point we know neither constant is an UndefValue.
if (const ConstantInt *CI1 = dyn_cast<ConstantInt>(C1)) {
if (const ConstantInt *CI2 = dyn_cast<ConstantInt>(C2)) {
using namespace APIntOps;
APInt C1V = CI1->getValue();
APInt C2V = CI2->getValue();
const APInt &C1V = CI1->getValue();
const APInt &C2V = CI2->getValue();
switch (Opcode) {
default:
break;
@ -672,30 +640,27 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
return ConstantInt::get(C1V | C2V);
case Instruction::Xor:
return ConstantInt::get(C1V ^ C2V);
case Instruction::Shl:
if (uint32_t shiftAmt = C2V.getZExtValue()) {
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.shl(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
return const_cast<ConstantInt*>(CI1); // Zero shift is identity
case Instruction::LShr:
if (uint32_t shiftAmt = C2V.getZExtValue()) {
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.lshr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
return const_cast<ConstantInt*>(CI1); // Zero shift is identity
case Instruction::AShr:
if (uint32_t shiftAmt = C2V.getZExtValue()) {
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.ashr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
return const_cast<ConstantInt*>(CI1); // Zero shift is identity
case Instruction::Shl: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.shl(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
case Instruction::LShr: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.lshr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
case Instruction::AShr: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(C1V.ashr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
}
}
} else if (const ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) {
@ -769,7 +734,38 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
}
}
// We don't know how to fold this
if (isa<ConstantExpr>(C1)) {
// There are many possible foldings we could do here. We should probably
// at least fold add of a pointer with an integer into the appropriate
// getelementptr. This will improve alias analysis a bit.
} else if (isa<ConstantExpr>(C2)) {
// If C2 is a constant expr and C1 isn't, flop them around and fold the
// other way if possible.
switch (Opcode) {
case Instruction::Add:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// No change of opcode required.
return ConstantFoldBinaryInstruction(Opcode, C2, C1);
case Instruction::Shl:
case Instruction::LShr:
case Instruction::AShr:
case Instruction::Sub:
case Instruction::SDiv:
case Instruction::UDiv:
case Instruction::FDiv:
case Instruction::URem:
case Instruction::SRem:
case Instruction::FRem:
default: // These instructions cannot be flopped around.
break;
}
}
// We don't know how to fold this.
return 0;
}