Add EH support for CodeFolding (#2665)

This does two things:
- Treats the target branch of `br_on_exn` as unoptimizables, because it
  is a conditional branch.
- Makes sure we don't move expressions that contain `exnref.pop`, which
  should follow right after `catch`.
- Adds `containsChild` utility function, which can search all children,
  optionally with limited depth. This was actually added to be used in
  CodeFolding but ended up not being used, but wasn't removed in case
  there will be uses later.

1 files changed, 24 insertions, 0 deletions

diff --git a/src/ir/iteration.h b/src/ir/iteration.h
index 289e5fa01..fd275f749 100644
--- a/src/ir/iteration.h
+++ b/src/ir/iteration.h
@@ -82,6 +82,30 @@ public:
   Iterator end() const { return Iterator(*this, children.size()); }
 };
 
+// Returns true if the current expression contains a certain kind of expression,
+// within the given depth of BFS. If depth is -1, this searches all children.
+template<typename T> bool containsChild(Expression* parent, int depth = -1) {
+  std::vector<Expression*> exprs;
+  std::vector<Expression*> nextExprs;
+  exprs.push_back(parent);
+  while (!exprs.empty() && depth > 0) {
+    for (auto* expr : exprs) {
+      for (auto* child : ChildIterator(expr)) {
+        if (child->is<T>()) {
+          return true;
+        }
+        nextExprs.push_back(child);
+      }
+    }
+    exprs.swap(nextExprs);
+    nextExprs.clear();
+    if (depth > 0) {
+      depth--;
+    }
+  }
+  return false;
+}
+
 } // namespace wasm
 
 #endif // wasm_ir_iteration_h