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Re-introduce the MaxLookup limit to BasicAliasAnalysis'

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pointsToConstantMemory code to guard against possible
compile time slowdowns.

llvm-svn: 118440
This commit is contained in:
Dan Gohman 2010-11-08 20:26:19 +00:00
parent cee4cb4b0a
commit 9f78edd2a7
1 changed files with 8 additions and 2 deletions
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10
lib/Analysis/BasicAliasAnalysis.cpp
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@ -524,6 +524,7 @@ bool
BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
assert(Visited.empty() && "Visited must be cleared after use!");
unsigned MaxLookup = 8;
SmallVector<const Value *, 16> Worklist;
Worklist.push_back(Loc.Ptr);
do {
@ -559,6 +560,11 @@ BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
// If all values incoming to a phi node point to local memory, then so does
// the phi.
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
// Don't bother inspecting phi nodes with many operands.
if (PN->getNumIncomingValues() > MaxLookup) {
Visited.clear();
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
}
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
Worklist.push_back(PN->getIncomingValue(i));
continue;
@ -568,10 +574,10 @@ BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
Visited.clear();
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
} while (!Worklist.empty());
} while (!Worklist.empty() && --MaxLookup);
Visited.clear();
return true;
return Worklist.empty();
}
/// getModRefBehavior - Return the behavior when calling the given call site.