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IR: Fold away compares between GV GEPs and GVs

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A GEP of a non-weak global variable will not be equivalent to another
non-weak global variable or a GEP of such a variable.

Differential Revision: http://reviews.llvm.org/D4238

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212360 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-07-04 22:05:26 +00:00
parent 483d89bcd4
commit 76735fbd2e
5 changed files with 44 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

29
lib/IR/ConstantFold.cpp
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@ -1334,6 +1334,15 @@ static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
return FCmpInst::BAD_FCMP_PREDICATE;
}
static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!GV1->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}
/// evaluateICmpRelation - This function determines if there is anything we can
/// decide about the two constants provided. This doesn't need to handle simple
/// things like integer comparisons, but should instead handle ConstantExprs
@ -1395,10 +1404,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
// constant (which, since the types must match, means that it's a
// ConstantPointerNull).
if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV) && !isa<GlobalAlias>(GV2))
if (!GV->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
return ICmpInst::ICMP_NE;
return areGlobalsPotentiallyEqual(GV, GV2);
} else if (isa<BlockAddress>(V2)) {
return ICmpInst::ICMP_NE; // Globals never equal labels.
} else {
@ -1463,7 +1469,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
}
break;
case Instruction::GetElementPtr:
case Instruction::GetElementPtr: {
GEPOperator *CE1GEP = cast<GEPOperator>(CE1);
// Ok, since this is a getelementptr, we know that the constant has a
// pointer type. Check the various cases.
if (isa<ConstantPointerNull>(V2)) {
@ -1510,7 +1517,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
"Surprising getelementptr!");
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
} else {
// If they are different globals, we don't know what the value is.
if (CE1GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(GV, GV2);
return ICmpInst::BAD_ICMP_PREDICATE;
}
}
@ -1526,8 +1534,14 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
// By far the most common case to handle is when the base pointers are
// obviously to the same global.
if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) {
if (CE1Op0 != CE2Op0) // Don't know relative ordering.
// Don't know relative ordering, but check for inequality.
if (CE1Op0 != CE2Op0) {
GEPOperator *CE2GEP = cast<GEPOperator>(CE2);
if (CE1GEP->hasAllZeroIndices() && CE2GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(cast<GlobalValue>(CE1Op0),
cast<GlobalValue>(CE2Op0));
return ICmpInst::BAD_ICMP_PREDICATE;
}
// Ok, we know that both getelementptr instructions are based on the
// same global. From this, we can precisely determine the relative
// ordering of the resultant pointers.
@ -1573,6 +1587,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
}
}
}
}
default:
break;
}