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Teach instsimplify how to simplify comparisons of pointers which are

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constant-offsets of a common base using the generic GEP-walking logic
I added for computing pointer differences in the same situation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153419 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2012-03-25 21:28:14 +00:00
parent 9d9e29b4a8
commit 58725a66c0
2 changed files with 107 additions and 1 deletions
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46
lib/Analysis/InstructionSimplify.cpp
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@ -1591,6 +1591,45 @@ static Value *ExtractEquivalentCondition(Value *V, CmpInst::Predicate Pred,
return 0;
}
static Constant *computePointerICmp(const TargetData &TD,
CmpInst::Predicate Pred,
Value *LHS, Value *RHS) {
// We can only fold certain predicates on pointer comparisons.
switch (Pred) {
default:
return 0;
// Equality comaprisons are easy to fold.
case CmpInst::ICMP_EQ:
case CmpInst::ICMP_NE:
break;
// We can only handle unsigned relational comparisons because 'inbounds' on
// a GEP only protects against unsigned wrapping.
case CmpInst::ICMP_UGT:
case CmpInst::ICMP_UGE:
case CmpInst::ICMP_ULT:
case CmpInst::ICMP_ULE:
// However, we have to switch them to their signed variants to handle
// negative indices from the base pointer.
Pred = ICmpInst::getSignedPredicate(Pred);
break;
}
Constant *LHSOffset = stripAndComputeConstantOffsets(TD, LHS);
if (!LHSOffset)
return 0;
Constant *RHSOffset = stripAndComputeConstantOffsets(TD, RHS);
if (!RHSOffset)
return 0;
// If LHS and RHS are not related via constant offsets to the same base
// value, there is nothing we can do here.
if (LHS != RHS)
return 0;
return ConstantExpr::getICmp(Pred, LHSOffset, RHSOffset);
}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
@ -2311,7 +2350,12 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
return getFalse(ITy);
}
// Simplify comparisons of GEPs.
// Simplify comparisons of related pointers using a powerful, recursive
// GEP-walk when we have target data available..
if (Q.TD && LHS->getType()->isPointerTy() && RHS->getType()->isPointerTy())
if (Constant *C = computePointerICmp(*Q.TD, Pred, LHS, RHS))
return C;
if (GetElementPtrInst *GLHS = dyn_cast<GetElementPtrInst>(LHS)) {
if (GEPOperator *GRHS = dyn_cast<GEPOperator>(RHS)) {
if (GLHS->getPointerOperand() == GRHS->getPointerOperand() &&