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Duncan convinced me that it's not possible to transform control-based escapes into 

data-based ones.  Just be conservative when analyzing control-based escapes.

llvm-svn: 57400
This commit is contained in:
Owen Anderson 2008-10-12 03:59:45 +00:00
parent 924efdf623
commit 36b48de43c
1 changed files with 10 additions and 13 deletions
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23
llvm/lib/Analysis/EscapeAnalysis.cpp
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@ -78,6 +78,11 @@ bool EscapeAnalysis::runOnFunction(Function& F) {
// for malloc to alloca promotion.
} else if (isa<ReturnInst>(I)) {
EscapePoints.insert(I);
// Branching on the value of a pointer may allow the value to escape through
// methods not discoverable via def-use chaining.
} else if(isa<BranchInst>(I) || isa<SwitchInst>(I)) {
EscapePoints.insert(I);
}
// FIXME: Are there any other possible escape points?
@ -93,19 +98,18 @@ bool EscapeAnalysis::runOnFunction(Function& F) {
/// FIXME: Once we've discovered a path, it would be a good idea to memoize it,
/// and all of its subpaths, to amortize the cost of future queries.
bool EscapeAnalysis::escapes(AllocationInst* A) {
std::vector<Value*> worklist;
std::vector<Instruction*> worklist;
worklist.push_back(A);
SmallPtrSet<Value*, 8> visited;
SmallPtrSet<Instruction*, 8> visited;
while (!worklist.empty()) {
Value* curr = worklist.back();
Instruction* curr = worklist.back();
worklist.pop_back();
visited.insert(curr);
if (Instruction* CurrInst = dyn_cast<Instruction>(curr))
if (EscapePoints.count(CurrInst))
return true;
if (EscapePoints.count(curr))
return true;
for (Instruction::use_iterator UI = curr->use_begin(), UE = curr->use_end();
UI != UE; ++UI)
@ -116,13 +120,6 @@ bool EscapeAnalysis::escapes(AllocationInst* A) {
// have been found to alias a global, so stores to them would have
// been in EscapePoints.
worklist.push_back(cast<Instruction>(S->getPointerOperand()));
} else if (isa<BranchInst>(U) || isa<SwitchInst>(U)) {
// Because branches on the pointer value can hide data dependencies,
// we need to track values that were generated by branching on the
// pointer (or some derived value). To do that, we push the block,
// whose uses will be the PHINodes that generate information based
// one it.
worklist.push_back(U->getParent());
} else
worklist.push_back(U);
}