Untee pass (#1053)

1 files changed, 61 insertions, 0 deletions

diff --git a/src/passes/Untee.cpp b/src/passes/Untee.cpp
new file mode 100644
index 000000000..b61875243
--- /dev/null
+++ b/src/passes/Untee.cpp
@@ -0,0 +1,61 @@
+/*
+ * Copyright 2017 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.
+ */
+
+//
+// Removes tee_locals, replacing them with gets and sets.
+//
+// This makes the code "flatter", with less nested side
+// effects. That can make some passes, like CodePushing,
+// more effective.
+//
+
+#include <wasm.h>
+#include <pass.h>
+#include <wasm-builder.h>
+
+namespace wasm {
+
+struct Untee : public WalkerPass<PostWalker<Untee>> {
+  bool isFunctionParallel() override { return true; }
+
+  Pass* create() override { return new Untee; }
+
+  void visitSetLocal(SetLocal *curr) {
+    if (curr->isTee()) {
+      if (curr->value->type == unreachable) {
+        // we don't reach the tee, just remove it
+        replaceCurrent(curr->value);
+      } else {
+        // a normal tee. replace with set and get
+        Builder builder(*getModule());
+        replaceCurrent(
+          builder.makeSequence(
+            curr,
+            builder.makeGetLocal(curr->index, curr->value->type)
+          )
+        );
+        curr->setTee(false);
+      }
+    }
+  }
+};
+
+Pass *createUnteePass() {
+  return new Untee();
+}
+
+} // namespace wasm
+