Add a pass to order functions by their use frequency. (#452)

2 files changed, 63 insertions, 0 deletions

diff --git a/src/passes/CMakeLists.txt b/src/passes/CMakeLists.txt
index 460910978..5c9983dfd 100644
--- a/src/passes/CMakeLists.txt
+++ b/src/passes/CMakeLists.txt
@@ -11,6 +11,7 @@ SET(passes_SOURCES
   RemoveUnusedBrs.cpp
   RemoveUnusedNames.cpp
   ReorderLocals.cpp
+  ReorderFunctions.cpp
   SimplifyLocals.cpp
   Vacuum.cpp
 )
diff --git a/src/passes/ReorderFunctions.cpp b/src/passes/ReorderFunctions.cpp
new file mode 100644
index 000000000..0991155e0
--- /dev/null
+++ b/src/passes/ReorderFunctions.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2016 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.
+ */
+
+//
+// Sorts functions by their static use count. This helps reduce the size of wasm
+// binaries because fewer bytes are needed to encode references to frequently
+// used functions.
+//
+
+
+#include <memory>
+
+#include <wasm.h>
+#include <pass.h>
+
+namespace wasm {
+
+struct ReorderFunctions : public WalkerPass<PostWalker<ReorderFunctions, Visitor<ReorderFunctions>>> {
+  std::map<Name, uint32_t> counts;
+
+  void visitModule(Module *module) {
+    if (module->start.is()) {
+      counts[module->start]++;
+    }
+    for (auto& curr : module->exports) {
+      counts[curr->value]++;
+    }
+    for (auto& curr : module->table.names) {
+      counts[curr]++;
+    }
+    sort(module->functions.begin(), module->functions.end(), [this](
+      std::unique_ptr<Function>& a,
+      std::unique_ptr<Function>& b) -> bool {
+      if (this->counts[a->name] == this->counts[b->name]) {
+        return strcmp(a->name.str, b->name.str) > 0;
+      }
+      return this->counts[a->name] > this->counts[b->name];
+    });
+    counts.clear();
+  }
+
+  void visitCall(Call *curr) {
+    counts[curr->target]++;
+  }
+};
+
+static RegisterPass<ReorderFunctions> registerPass("reorder-functions", "sorts functions by access frequency");
+
+} // namespace wasm