1 files changed, 71 insertions, 0 deletions
diff --git a/src/ir/eh-utils.cpp b/src/ir/eh-utils.cpp
new file mode 100644
index 000000000..de85478a2
--- /dev/null
+++ b/src/ir/eh-utils.cpp
@@ -0,0 +1,71 @@
+/*
+ * Copyright 2021 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "ir/eh-utils.h"
+#include "ir/branch-utils.h"
+
+namespace wasm {
+
+namespace EHUtils {
+
+bool isPopValid(Expression* catchBody) {
+  Expression* firstChild = nullptr;
+  auto* block = catchBody->dynCast<Block>();
+  if (!block) {
+    firstChild = catchBody;
+  } else {
+    // When there are multiple expressions within a catch body, an implicit
+    // block is created within it for convenience purposes, and if there are no
+    // branches that targets the block, it will be omitted when written back.
+    // But if there is a branch targetting this block, this block cannot be
+    // removed, and 'pop''s location will be like
+    // (catch $e
+    //   (block $l0
+    //     (pop i32) ;; within a block!
+    //     (br $l0)
+    //     ...
+    //   )
+    // )
+    // which is invalid.
+    if (BranchUtils::BranchSeeker::has(block, block->name)) {
+      return false;
+    }
+    // There should be a pop somewhere
+    if (block->list.empty()) {
+      return false;
+    }
+    firstChild = *block->list.begin();
+  }
+
+  // Go down the line for the first child until we reach a leaf. A pop should be
+  // in that first-decendent line.
+  while (true) {
+    if (firstChild->is<Pop>()) {
+      return true;
+    }
+    // We use ValueChildIterator in order not to go into block/loop/try/if
+    // bodies, because a pop cannot be in those control flow expressions.
+    ValueChildIterator it(firstChild);
+    if (it.begin() == it.end()) {
+      return false;
+    }
+    firstChild = *it.begin();
+  }
+}
+
+} // namespace EHUtils
+
+} // namespace wasm