Fix EscapeAnalysis iterator invalidation.

Noticed by code inspection during debugging.

Iterator invalidaton could occur because two types of edges, which are
handled independently, actually share the same phyical list.

Fix the visitor utility that iterates over defer edges to be robust
for visitors that change the pointsTo edge. Use a temporary vector to
be safe.

Author: atrick

lib/SILOptimizer/Analysis/EscapeAnalysis.cpp

@@ -363,7 +363,10 @@ bool EscapeAnalysis::CGNode::visitSuccessors(Visitor &&visitor) const {
 
 template <typename Visitor>
 bool EscapeAnalysis::CGNode::visitDefers(Visitor &&visitor) const {
-  for (Predecessor pred : Preds) {
+  // Save predecessors before calling `visitor` which may assign pointsTo edges
+  // which invalidates the predecessor iterator.
+  SmallVector<Predecessor, 4> predVector(Preds.begin(), Preds.end());
+  for (Predecessor pred : predVector) {
     if (!pred.is(EdgeType::Defer))
       continue;
     if (!visitor(pred.getPredNode(), false))