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Move llvm::ConstantFoldInstruction from VMCore to here, next to ConstantFoldTerminator

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10785 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-01-12 18:25:22 +00:00
parent 28aabc34f7
commit 8f90b005d6
1 changed files with 58 additions and 0 deletions
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58
lib/Transforms/Utils/Local.cpp
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@ -39,6 +39,64 @@ bool llvm::doConstantPropagation(BasicBlock::iterator &II) {
return false;
}
/// ConstantFoldInstruction - Attempt to constant fold the specified
/// instruction. If successful, the constant result is returned, if not, null
/// is returned. Note that this function can only fail when attempting to fold
/// instructions like loads and stores, which have no constant expression form.
///
Constant *llvm::ConstantFoldInstruction(Instruction *I) {
if (PHINode *PN = dyn_cast<PHINode>(I)) {
if (PN->getNumIncomingValues() == 0)
return Constant::getNullValue(PN->getType());
Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
if (Result == 0) return 0;
// Handle PHI nodes specially here...
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
return 0; // Not all the same incoming constants...
// If we reach here, all incoming values are the same constant.
return Result;
}
Constant *Op0 = 0, *Op1 = 0;
switch (I->getNumOperands()) {
default:
case 2:
Op1 = dyn_cast<Constant>(I->getOperand(1));
if (Op1 == 0) return 0; // Not a constant?, can't fold
case 1:
Op0 = dyn_cast<Constant>(I->getOperand(0));
if (Op0 == 0) return 0; // Not a constant?, can't fold
break;
case 0: return 0;
}
if (isa<BinaryOperator>(I))
return ConstantExpr::get(I->getOpcode(), Op0, Op1);
switch (I->getOpcode()) {
default: return 0;
case Instruction::Cast:
return ConstantExpr::getCast(Op0, I->getType());
case Instruction::Shl:
case Instruction::Shr:
return ConstantExpr::getShift(I->getOpcode(), Op0, Op1);
case Instruction::GetElementPtr:
std::vector<Constant*> IdxList;
IdxList.reserve(I->getNumOperands()-1);
if (Op1) IdxList.push_back(Op1);
for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
IdxList.push_back(C);
else
return 0; // Non-constant operand
return ConstantExpr::getGetElementPtr(Op0, IdxList);
}
}
// ConstantFoldTerminator - If a terminator instruction is predicated on a
// constant value, convert it into an unconditional branch to the constant
// destination.