fix PR6414, a nondeterminism issue in IPSCCP which was because
of a subtle interation in a loop operating in densemap order.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97288 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 8d06690..5a0f620 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1918,6 +1918,14 @@
// all call uses with the inferred value. This means we don't need to bother
// actually returning anything from the function. Replace all return
// instructions with return undef.
+ //
+ // Do this in two stages: first identify the functions we should process, then
+ // actually zap their returns. This is important because we can only do this
+ // the address of the function isn't taken. In cases where a return is the
+ // last use of a function, the order of processing functions would affect
+ // whether we other functions are optimizable.
+ SmallVector<ReturnInst*, 8> ReturnsToZap;
+
// TODO: Process multiple value ret instructions also.
const DenseMap<Function*, LatticeVal> &RV = Solver.getTrackedRetVals();
for (DenseMap<Function*, LatticeVal>::const_iterator I = RV.begin(),
@@ -1933,7 +1941,13 @@
for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB)
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator()))
if (!isa<UndefValue>(RI->getOperand(0)))
- RI->setOperand(0, UndefValue::get(F->getReturnType()));
+ ReturnsToZap.push_back(RI);
+ }
+
+ // Zap all returns which we've identified as zap to change.
+ for (unsigned i = 0, e = ReturnsToZap.size(); i != e; ++i) {
+ Function *F = ReturnsToZap[i]->getParent()->getParent();
+ ReturnsToZap[i]->setOperand(0, UndefValue::get(F->getReturnType()));
}
// If we infered constant or undef values for globals variables, we can delete