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Teach steens-aa two things about mod/ref information:

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1. If memory never escapes the program, it cannot be mod/ref'd by external
     functions.
  2. If memory is global never mod/ref'd in the program, it cannot be mod/ref'd
     by any call.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20867 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-03-26 22:43:20 +00:00
parent 0772e78789
commit b7523418b0
1 changed files with 33 additions and 3 deletions
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36
lib/Analysis/DataStructure/Steensgaard.cpp
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@ -62,10 +62,11 @@ namespace {
// Implement the AliasAnalysis API
//
// alias - This is the only method here that does anything interesting...
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
private:
void ResolveFunctionCall(Function *F, const DSCallSite &Call,
DSNodeHandle &RetVal);
@ -183,7 +184,6 @@ bool Steens::runOnModule(Module &M) {
return false;
}
// alias - This is the only method here that does anything interesting...
AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
assert(ResultGraph && "Result graph has not been computed yet!");
@ -224,3 +224,33 @@ AliasAnalysis::AliasResult Steens::alias(const Value *V1, unsigned V1Size,
//
return AliasAnalysis::alias(V1, V1Size, V2, V2Size);
}
AliasAnalysis::ModRefResult
Steens::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
AliasAnalysis::ModRefResult Result = ModRef;
// Find the node in question.
DSGraph::ScalarMapTy &GSM = ResultGraph->getScalarMap();
DSGraph::ScalarMapTy::iterator I = GSM.find(P);
if (I != GSM.end() && !I->second.isNull()) {
DSNode *N = I->second.getNode();
if (N->isComplete()) {
// If this is a direct call to an external function, and if the pointer
// points to a complete node, the external function cannot modify or read
// the value (we know it's not passed out of the program!).
if (Function *F = CS.getCalledFunction())
if (F->isExternal())
return NoModRef;
// Otherwise, if the node is complete, but it is only M or R, return this.
// This can be useful for globals that should be marked const but are not.
if (!N->isModified())
Result = (ModRefResult)(Result & ~Mod);
if (!N->isRead())
Result = (ModRefResult)(Result & ~Ref);
}
}
return (ModRefResult)(Result & AliasAnalysis::getModRefInfo(CS, P, Size));
}