2 files changed, 57 insertions, 0 deletions
diff --git a/src/asm2wasm.h b/src/asm2wasm.h
index e91a9344e..0320b7924 100644
--- a/src/asm2wasm.h
+++ b/src/asm2wasm.h
@@ -1573,6 +1573,7 @@ void Asm2WasmBuilder::optimize() {
   PassRunner passRunner(&allocator);
   passRunner.add("remove-unused-brs");
   passRunner.add("remove-unused-names");
+  passRunner.add("merge-blocks");
   passRunner.run(&wasm);
 }
 
diff --git a/src/passes/MergeBlocks.cpp b/src/passes/MergeBlocks.cpp
new file mode 100644
index 000000000..3d7afc4cb
--- /dev/null
+++ b/src/passes/MergeBlocks.cpp
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2015 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.
+ */
+
+//
+// Merges blocks to their parents.
+//
+
+#include <wasm.h>
+#include <pass.h>
+
+namespace wasm {
+
+struct MergeBlocks : public Pass {
+  void visitBlock(Block *curr) override {
+    bool more = true;
+    while (more) {
+      more = false;
+      for (size_t i = 0; i < curr->list.size(); i++) {
+        Block* child = curr->list[i]->dyn_cast<Block>();
+        if (!child) continue;
+        if (child->name.is()) continue; // named blocks can have breaks to them (and certainly do, if we ran RemoveUnusedNames and RemoveUnusedBrs)
+        ExpressionList merged;
+        for (size_t j = 0; j < i; j++) {
+          merged.push_back(curr->list[j]);
+        }
+        for (auto item : child->list) {
+          merged.push_back(item);
+        }
+        for (size_t j = i + 1; j < curr->list.size(); j++) {
+          merged.push_back(curr->list[j]);
+        }
+        curr->list = merged;
+        more = true;
+        break;
+      }
+    }
+  }
+};
+
+static RegisterPass<MergeBlocks> registerPass("merge-blocks", "merges blocks to their parents");
+
+} // namespace wasm
+