ensure we create the OptimizeInstructions database on demand, avoiding global ctors

3 files changed, 43 insertions, 3 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 9fa059327..2a5e7b8c4 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -23,6 +23,7 @@
 #include <wasm.h>
 #include <pass.h>
 #include <wasm-s-parser.h>
+#include <support/threads.h>
 
 namespace wasm {
 
@@ -71,7 +72,16 @@ struct PatternDatabase {
   };
 };
 
-static PatternDatabase database;
+static PatternDatabase* database = nullptr;
+
+static void ensureDatabase() {
+  if (!database) {
+    // we must only ever create one database
+    static OnlyOnce onlyOnce;
+    onlyOnce.verify();
+    database = new PatternDatabase;
+  }
+}
 
 // Check for matches and apply them
 struct Match {
@@ -151,11 +161,15 @@ struct OptimizeInstructions : public WalkerPass<PostWalker<OptimizeInstructions,
 
   Pass* create() override { return new OptimizeInstructions; }
 
+  OptimizeInstructions() {
+    ensureDatabase();
+  }
+
   void visitExpression(Expression* curr) {
     // we may be able to apply multiple patterns, one may open opportunities that look deeper NB: patterns must not have cycles
     while (1) {
-      auto iter = database.patternMap.find(curr->_id);
-      if (iter == database.patternMap.end()) return;
+      auto iter = database->patternMap.find(curr->_id);
+      if (iter == database->patternMap.end()) return;
       auto& patterns = iter->second;
       bool more = false;
       for (auto& pattern : patterns) {
diff --git a/src/support/threads.h b/src/support/threads.h
index ea9e53c13..45c09e602 100644
--- a/src/support/threads.h
+++ b/src/support/threads.h
@@ -105,6 +105,24 @@ private:
   bool areThreadsReady();
 };
 
+// Verify a code segment is only entered once. Usage:
+//    static OnlyOnce onlyOnce;
+//    onlyOnce.verify();
+
+class OnlyOnce {
+  std::atomic<int> created;
+
+public:
+  OnlyOnce() {
+    created.store(0);
+  }
+
+  void verify() {
+    auto before = created.fetch_add(1);
+    assert(before == 0);
+  }
+};
+
 } // namespace wasm
 
 #endif  // wasm_support_threads_h
diff --git a/src/wasm-module-building.h b/src/wasm-module-building.h
index 43cc493d1..52a4e7536 100644
--- a/src/wasm-module-building.h
+++ b/src/wasm-module-building.h
@@ -96,6 +96,14 @@ public:
       return;
     }
 
+    // Before parallelism, create all passes on the main thread here, to ensure
+    // constructors run at least once on the main thread, for one-time init things.
+    {
+      PassRunner passRunner(wasm);
+      addPrePasses(passRunner);
+      passRunner.addDefaultFunctionOptimizationPasses();
+    }
+
     // prepare work list
     endMarker = new Function();
     list = new std::atomic<Function*>[numFunctions];