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Implement constant folding of undef values.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@17070 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-10-16 23:31:32 +00:00
parent 79a564caa7
commit 71d3778c0b
1 changed files with 54 additions and 4 deletions
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58
lib/VMCore/ConstantFold.cpp
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@ -486,7 +486,8 @@ ConstRules &ConstRules::get(const Constant *V1, const Constant *V2) {
static DirectFPRules <ConstantFP , double , &Type::DoubleTy> DoubleR;
if (isa<ConstantExpr>(V1) || isa<ConstantExpr>(V2) ||
isa<GlobalValue>(V1) || isa<GlobalValue>(V2))
isa<GlobalValue>(V1) || isa<GlobalValue>(V2) ||
isa<UndefValue>(V1) || isa<UndefValue>(V2))
return EmptyR;
switch (V1->getType()->getTypeID()) {
@ -525,15 +526,14 @@ Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
if (V->getType() == DestTy) return (Constant*)V;
// Cast of a global address to boolean is always true.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
if (DestTy == Type::BoolTy)
// FIXME: When we support 'external weak' references, we have to prevent
// this transformation from happening. In the meantime we avoid folding
// any cast of an external symbol.
if (!GV->isExternal())
return ConstantBool::True;
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (CE->getOpcode() == Instruction::Cast) {
Constant *Op = const_cast<Constant*>(CE->getOperand(0));
// Try to not produce a cast of a cast, which is almost always redundant.
@ -561,6 +561,9 @@ Constant *llvm::ConstantFoldCastInstruction(const Constant *V,
if (isAllNull)
return ConstantExpr::getCast(CE->getOperand(0), DestTy);
}
} else if (isa<UndefValue>(V)) {
return UndefValue::get(DestTy);
}
// Check to see if we are casting an array of X to a pointer to X. If so, use
// a GEP to get to the first element of the array instead of a cast!
@ -600,6 +603,10 @@ Constant *llvm::ConstantFoldSelectInstruction(const Constant *Cond,
return const_cast<Constant*>(V1);
else if (Cond == ConstantBool::False)
return const_cast<Constant*>(V2);
if (isa<UndefValue>(V1)) return const_cast<Constant*>(V2);
if (isa<UndefValue>(V2)) return const_cast<Constant*>(V1);
if (isa<UndefValue>(Cond)) return const_cast<Constant*>(V1);
return 0;
}
@ -865,6 +872,49 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
break;
}
if (isa<UndefValue>(V1) || isa<UndefValue>(V2)) {
switch (Opcode) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::SetEQ:
case Instruction::SetNE:
case Instruction::SetLT:
case Instruction::SetLE:
case Instruction::SetGT:
case Instruction::SetGE:
case Instruction::Xor:
return UndefValue::get(V1->getType());
case Instruction::Mul:
case Instruction::And:
return Constant::getNullValue(V1->getType());
case Instruction::Div:
case Instruction::Rem:
if (!isa<UndefValue>(V2)) // undef/X -> 0
return Constant::getNullValue(V1->getType());
return const_cast<Constant*>(V2); // X/undef -> undef
case Instruction::Or: // X|undef -> -1
return ConstantInt::getAllOnesValue(V1->getType());
case Instruction::Shr:
if (!isa<UndefValue>(V2)) {
if (V1->getType()->isSigned())
return const_cast<Constant*>(V1); // undef >>s X -> undef
// undef >>u X -> 0
} else if (isa<UndefValue>(V1)) {
return const_cast<Constant*>(V1); // undef >> undef -> undef
} else {
if (V1->getType()->isSigned())
return const_cast<Constant*>(V1); // X >>s undef -> X
// X >>u undef -> 0
}
return Constant::getNullValue(V1->getType());
case Instruction::Shl:
// undef << X -> 0 X << undef -> 0
return Constant::getNullValue(V1->getType());
}
}
if (const ConstantExpr *CE1 = dyn_cast<ConstantExpr>(V1)) {
if (const ConstantExpr *CE2 = dyn_cast<ConstantExpr>(V2)) {
// There are many possible foldings we could do here. We should probably