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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@57400 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/EscapeAnalysis.cpp b/lib/Analysis/EscapeAnalysis.cpp
index 07f4761..a2579ab 100644
--- a/lib/Analysis/EscapeAnalysis.cpp
+++ b/lib/Analysis/EscapeAnalysis.cpp
@@ -78,6 +78,11 @@
// 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 @@
/// 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 @@
// 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);
}