Fix global effect computation with -O flags (#6211)

We tested --generate-global-effects --vacuum and such, but not
--generate-global-effects -O3 or the other -O flags. Unfortunately, our
targeted testing missed a bug because of that. Specifically, we have special
logic for -O flags to make sure the passes they expand into run with the
proper opt and shrink levels, but that logic happened to also interfere with
global effect computation. It would also interfere with allowing GUFA info
or other things to be stored on the side, which we've proposed. This PR
fixes that + future issues.

The fix is to just allow a pass runner to execute more than once. We thought
to avoid that and assert against it to keep the model "hermetic" (you create
a pass runner, you run the passes, and you throw it out), which feels nice in
a way, but it led to the bug here, and I'm not sure it would prevent any other
ones really. It is also more code. It is simpler to allow a runner to execute more
than once, and add a method to clear it. With that, the logic for -O3 execution
is both simpler and does not interfere with anything but the opt and shrink
level flags: we create a single runner, give it the proper options, and then keep
using that runner + those options as we go, normally.

3 files changed, 31 insertions, 29 deletions

diff --git a/src/pass.h b/src/pass.h
index 83f53c23a..2c2fa0619 100644
--- a/src/pass.h
+++ b/src/pass.h
@@ -235,8 +235,9 @@ struct PassOptions {
   // other passes later can benefit from it. It is up to the sequence of passes
   // to update or discard this when necessary - in particular, when new effects
   // are added to a function this must be changed or we may optimize
-  // incorrectly (however, it is extremely rare for a pass to *add* effects;
-  // passes normally only remove effects).
+  // incorrectly. However, it is extremely rare for a pass to *add* effects;
+  // passes normally only remove effects. Passes that do add effects must set
+  // addsEffects() so the pass runner is aware of them.
   std::shared_ptr<FuncEffectsMap> funcEffectsMap;
 
   // -Os is our default
@@ -318,6 +319,9 @@ struct PassRunner {
   // Add a pass given an instance.
   void add(std::unique_ptr<Pass> pass) { doAdd(std::move(pass)); }
 
+  // Clears away all passes that have been added.
+  void clear();
+
   // Adds the pass if there are no DWARF-related issues. There is an issue if
   // there is DWARF and if the pass does not support DWARF (as defined by the
   // pass returning true from invalidatesDWARF); otherwise, if there is no
@@ -387,9 +391,6 @@ private:
   // yet) have removed DWARF.
   bool addedPassesRemovedDWARF = false;
 
-  // Whether this pass runner has run. A pass runner should only be run once.
-  bool ran = false;
-
   void runPass(Pass* pass);
   void runPassOnFunction(Pass* pass, Function* func);
 
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index d7391a390..62b3683fa 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -739,9 +739,6 @@ static void dumpWasm(Name name, Module* wasm) {
 }
 
 void PassRunner::run() {
-  assert(!ran);
-  ran = true;
-
   static const int passDebug = getPassDebug();
   // Emit logging information when asked for. At passDebug level 1+ we log
   // the main passes, while in 2 we also log nested ones. Note that for
@@ -885,6 +882,8 @@ void PassRunner::doAdd(std::unique_ptr<Pass> pass) {
   passes.emplace_back(std::move(pass));
 }
 
+void PassRunner::clear() { passes.clear(); }
+
 // Checks that the state is valid before and after a
 // pass runs on a function. We run these extra checks when
 // pass-debug mode is enabled.
diff --git a/src/tools/optimization-options.h b/src/tools/optimization-options.h
index 045542ac2..0a47d9f70 100644
--- a/src/tools/optimization-options.h
+++ b/src/tools/optimization-options.h
@@ -328,44 +328,46 @@ struct OptimizationOptions : public ToolOptions {
   bool runningPasses() { return passes.size() > 0; }
 
   void runPasses(Module& wasm) {
-    std::unique_ptr<PassRunner> passRunner;
+    PassRunner passRunner(&wasm, passOptions);
+    if (debug) {
+      passRunner.setDebug(true);
+    }
 
     // Flush anything in the current pass runner, and then reset it to a fresh
     // state so it is ready for new things.
-    auto flushAndReset = [&]() {
-      if (passRunner) {
-        passRunner->run();
-      }
-      passRunner = std::make_unique<PassRunner>(&wasm, passOptions);
-      if (debug) {
-        passRunner->setDebug(true);
-      }
+    auto flush = [&]() {
+      passRunner.run();
+      passRunner.clear();
     };
 
-    flushAndReset();
-
     for (auto& pass : passes) {
       if (pass.name == DEFAULT_OPT_PASSES) {
         // This is something like -O3 or -Oz. We must run this now, in order to
         // set the proper opt and shrink levels. To do that, first reset the
         // runner so that anything already queued is run (since we can only run
         // after those things).
-        flushAndReset();
+        flush();
 
         // -O3/-Oz etc. always set their own optimize/shrinkLevels.
         assert(pass.optimizeLevel);
         assert(pass.shrinkLevel);
-        passRunner->options.optimizeLevel = *pass.optimizeLevel;
-        passRunner->options.shrinkLevel = *pass.shrinkLevel;
 
-        // Run our optimizations now, and reset the runner so that the default
-        // pass options are used later (and not the temporary optimize/
-        // shrinkLevels we just set).
-        passRunner->addDefaultOptimizationPasses();
-        flushAndReset();
+        // Temporarily override the default levels.
+        assert(passRunner.options.optimizeLevel == passOptions.optimizeLevel);
+        assert(passRunner.options.shrinkLevel == passOptions.shrinkLevel);
+        passRunner.options.optimizeLevel = *pass.optimizeLevel;
+        passRunner.options.shrinkLevel = *pass.shrinkLevel;
+
+        // Run our optimizations now with the custom levels.
+        passRunner.addDefaultOptimizationPasses();
+        flush();
+
+        // Restore the default optimize/shrinkLevels.
+        passRunner.options.optimizeLevel = passOptions.optimizeLevel;
+        passRunner.options.shrinkLevel = passOptions.shrinkLevel;
       } else {
         // This is a normal pass. Add it to the queue for execution.
-        passRunner->add(pass.name);
+        passRunner.add(pass.name);
 
         // Normal passes do not set their own optimize/shrinkLevels.
         assert(!pass.optimizeLevel);
@@ -373,7 +375,7 @@ struct OptimizationOptions : public ToolOptions {
       }
     }
 
-    flushAndReset();
+    flush();
   }
 };