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A store or load cannot alias a global if the accessed amount is larger then

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the global.

This implements Regression/Analysis/BasicAA/global-size.ll

llvm-svn: 18261
This commit is contained in:
Chris Lattner 2004-11-26 19:20:01 +00:00
parent e750683dc2
commit e076e608d8
1 changed files with 49 additions and 20 deletions
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43
lib/Analysis/BasicAliasAnalysis.cpp
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@ -265,7 +265,8 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *O2 = getUnderlyingObject(V2);
// Pointing at a discernible object?
if (O1 && O2) {
if (O1) {
if (O2) {
if (isa<Argument>(O1)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O2)) return NoAlias;
@ -274,19 +275,47 @@ BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O1)) return NoAlias;
// Otherwise, nothing is known...
} else {
} else if (O1 != O2) {
// If they are two different objects, we know that we have no alias...
if (O1 != O2) return NoAlias;
return NoAlias;
}
// If they are the same object, they we can look at the indexes. If they
// index off of the object is the same for both pointers, they must alias.
// If they are provably different, they must not alias. Otherwise, we can't
// tell anything.
} else if (O1 && !isa<Argument>(O1) && isa<ConstantPointerNull>(V2)) {
// If they are provably different, they must not alias. Otherwise, we
// can't tell anything.
}
if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
return NoAlias; // Unique values don't alias null
} else if (O2 && !isa<Argument>(O2) && isa<ConstantPointerNull>(V1)) {
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(O1))
if (GV->getType()->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global, it cannot be accessing the global (it's undefined to load or
// store bytes after the global).
unsigned GlobalSize =
getTargetData().getTypeSize(GV->getType()->getElementType());
if (GlobalSize < V2Size)
return NoAlias;
}
}
if (O2) {
if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
return NoAlias; // Unique values don't alias null
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(O2))
if (GV->getType()->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global, it cannot be accessing the global (it's undefined to load or
// store bytes after the global).
unsigned GlobalSize =
getTargetData().getTypeSize(GV->getType()->getElementType());
if (GlobalSize < V1Size)
return NoAlias;
}
}
// If we have two gep instructions with must-alias'ing base pointers, figure