1 files changed, 155 insertions, 0 deletions
diff --git a/src/passes/RemoveUnusedModuleElements.cpp b/src/passes/RemoveUnusedModuleElements.cpp
new file mode 100644
index 000000000..cf9741961
--- /dev/null
+++ b/src/passes/RemoveUnusedModuleElements.cpp
@@ -0,0 +1,155 @@
+/*
+ * 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.
+ */
+
+//
+// Removes module elements that are are never used: functions and globals,
+// which may be imported or not.
+//
+
+
+#include <memory>
+
+#include "wasm.h"
+#include "pass.h"
+#include "ast_utils.h"
+
+namespace wasm {
+
+enum class ModuleElementKind {
+  Function,
+  Global
+};
+
+typedef std::pair<ModuleElementKind, Name> ModuleElement;
+
+// Finds reachabilities
+
+struct ReachabilityAnalyzer : public PostWalker<ReachabilityAnalyzer, Visitor<ReachabilityAnalyzer>> {
+  Module* module;
+  std::vector<ModuleElement> queue;
+  std::set<ModuleElement> reachable;
+
+  ReachabilityAnalyzer(Module* module, const std::vector<ModuleElement>& roots) : module(module) {
+    queue = roots;
+    // Globals used in memory/table init expressions are also roots
+    for (auto& segment : module->memory.segments) {
+      walk(segment.offset);
+    }
+    for (auto& segment : module->table.segments) {
+      walk(segment.offset);
+    }
+    // main loop
+    while (queue.size()) {
+      auto& curr = queue.back();
+      queue.pop_back();
+      if (reachable.count(curr) == 0) {
+        reachable.insert(curr);
+        if (curr.first == ModuleElementKind::Function) {
+          // if not an import, walk it
+          auto* func = module->checkFunction(curr.second);
+          if (func) {
+            walk(func->body);
+          }
+        } else {
+          // if not imported, it has an init expression we need to walk
+          auto* glob = module->checkGlobal(curr.second);
+          if (glob) {
+            walk(glob->init);
+          }
+        }
+      }
+    }
+  }
+
+  void visitCall(Call* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
+      queue.emplace_back(ModuleElementKind::Function, curr->target);
+    }
+  }
+  void visitCallImport(CallImport* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
+      queue.emplace_back(ModuleElementKind::Function, curr->target);
+    }
+  }
+
+  void visitGetGlobal(GetGlobal* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
+      queue.emplace_back(ModuleElementKind::Global, curr->name);
+    }
+  }
+  void visitSetGlobal(SetGlobal* curr) {
+    if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
+      queue.emplace_back(ModuleElementKind::Global, curr->name);
+    }
+  }
+};
+
+struct RemoveUnusedModuleElements : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    std::vector<ModuleElement> roots;
+    // Module start is a root.
+    if (module->start.is()) {
+      roots.emplace_back(ModuleElementKind::Function, module->start);
+    }
+    // Exports are roots.
+    for (auto& curr : module->exports) {
+      if (curr->kind == ExternalKind::Function) {
+        roots.emplace_back(ModuleElementKind::Function, curr->value);
+      } else if (curr->kind == ExternalKind::Global) {
+        roots.emplace_back(ModuleElementKind::Global, curr->value);
+      }
+    }
+    // For now, all functions that can be called indirectly are marked as roots.
+    for (auto& segment : module->table.segments) {
+      for (auto& curr : segment.data) {
+        roots.emplace_back(ModuleElementKind::Function, curr);
+      }
+    }
+    // Compute reachability starting from the root set.
+    ReachabilityAnalyzer analyzer(module, roots);
+    // Remove unreachable elements.
+    {
+      auto& v = module->functions;
+      v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Function>& curr) {
+        return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
+      }), v.end());
+    }
+    {
+      auto& v = module->globals;
+      v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Global>& curr) {
+        return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
+      }), v.end());
+    }
+    {
+      auto& v = module->imports;
+      v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Import>& curr) {
+        if (curr->kind == ExternalKind::Function) {
+          return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
+        } else if (curr->kind == ExternalKind::Global) {
+          return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
+        }
+        return false;
+      }), v.end());
+    }
+    module->updateMaps();
+  }
+};
+
+Pass* createRemoveUnusedModuleElementsPass() {
+  return new RemoveUnusedModuleElements();
+}
+
+} // namespace wasm