Add partial support for -fwasm-exceptions in Asyncify (#5343) (#5475)

This supports Try in general, but not unwinding from a Catch. In
asserts mode we error on an unwind nested in a Catch.

Author: caiiiycuk

src/passes/Asyncify.cpp

@@ -96,6 +96,13 @@
 // Overall, this should allow good performance with small overhead that is
 // mostly noticed at rewind time.
 //
+// Exceptions handling (-fwasm-exceptions) is partially supported, everything
+// except for handling unwinding from within a catch block. If assertions mode
+// is enabled then this pass will check for that problem, and if so, throw an
+// unreachable exception. (If "ignore unwind from catch" mode is enabled then
+// Asyncify will silently skip any unwind call from within catch blocks, see
+// below.)
+//
 // After this pass is run a new i32 global "__asyncify_state" is added, which
 // has the following values:
 //
@@ -239,6 +246,12 @@
 //      an unwind/rewind in an invalid place (this can be helpful for manual
 //      tweaking of the only-list / remove-list, see later).
 //
+//   --pass-arg=asyncify-ignore-unwind-from-catch
+//
+//      When an unwind operation is triggered from inside a wasm-exceptions
+//      catch block, which is not supported, silently ignore it rather than
+//      fail during rewinding later. (This is unsafe in general.)
+//
 //   --pass-arg=asyncify-verbose
 //
 //      Logs out instrumentation decisions to the console. This can help figure
@@ -1138,6 +1151,18 @@ struct AsyncifyFlow : public Pass {
         // here as well.
         results.push_back(makeCallSupport(curr));
         continue;
+      } else if (auto* try_ = curr->dynCast<Try>()) {
+        if (item.phase == Work::Scan) {
+          work.push_back(Work{curr, Work::Finish});
+          work.push_back(Work{try_->body, Work::Scan});
+          // catchBodies are ignored because we assume that pause/resume will
+          // not happen inside them
+          continue;
+        }
+        try_->body = results.back();
+        results.pop_back();
+        results.push_back(try_);
+        continue;
       }
       // We must handle all control flow above, and all things that can change
       // the state, so there should be nothing that can reach here - add it
@@ -1316,6 +1341,93 @@ struct AsyncifyAssertInNonInstrumented : public Pass {
   Module* module;
 };
 
+struct AsyncifyUnwindWalker
+  : WalkerPass<ExpressionStackWalker<AsyncifyUnwindWalker>> {
+  Function* function;
+  Module* module;
+
+  // Adds a check for Call that is inside a Catch block (we do not handle
+  // unwinding there).
+  template<typename T> void replaceCallWithCheck(T* call) {
+    auto builder = std::make_unique<Builder>(*module);
+    auto check = builder->makeIf(
+      builder->makeBinary(NeInt32,
+                          builder->makeGlobalGet(ASYNCIFY_STATE, Type::i32),
+                          builder->makeConst(int32_t(State::Normal))),
+      builder->makeUnreachable());
+    if (call->type.isConcrete()) {
+      auto temp = builder->addVar(function, call->type);
+      replaceCurrent(builder->makeBlock(
+        {
+          builder->makeLocalSet(temp, call),
+          check,
+          builder->makeLocalGet(temp, call->type),
+        },
+        call->type));
+    } else {
+      replaceCurrent(builder->makeBlock(
+        {
+          call,
+          check,
+        },
+        call->type));
+    }
+  }
+
+  template<typename T> void visitCallLike(T* curr) {
+    assert(!expressionStack.empty());
+    // A return_call (curr->isReturn) can be ignored here: It returns first,
+    // leaving the Catch, before calling.
+    if (curr->isReturn) {
+      return;
+    }
+    // Go up the stack and see if we are in a Catch.
+    Index i = expressionStack.size() - 1;
+    while (i > 0) {
+      auto* expr = expressionStack[i];
+      if (Try* aTry = expr->template dynCast<Try>()) {
+        // check if curr is inside body of aTry (which is safe),
+        // otherwise do replace a call
+        assert(i + 1 < expressionStack.size());
+        if (expressionStack[i + 1] != aTry->body) {
+          replaceCallWithCheck(curr);
+        }
+        break;
+      }
+      i--;
+    }
+  }
+
+  void visitCall(Call* curr) { visitCallLike(curr); }
+
+  void visitCallRef(CallRef* curr) { visitCallLike(curr); }
+
+  void visitCallIndirect(CallIndirect* curr) { visitCallLike(curr); }
+};
+
+struct AsyncifyAssertUnwindCorrectness : Pass {
+  bool isFunctionParallel() override { return true; }
+
+  ModuleAnalyzer* analyzer;
+  Module* module;
+
+  AsyncifyAssertUnwindCorrectness(ModuleAnalyzer* analyzer, Module* module) {
+    this->analyzer = analyzer;
+    this->module = module;
+  }
+
+  std::unique_ptr<Pass> create() override {
+    return std::make_unique<AsyncifyAssertUnwindCorrectness>(analyzer, module);
+  }
+
+  void runOnFunction(Module* module_, Function* function) override {
+    AsyncifyUnwindWalker walker;
+    walker.function = function;
+    walker.module = module_;
+    walker.walk(function->body);
+  }
+};
+
 // Instrument local saving/restoring.
 struct AsyncifyLocals : public WalkerPass<PostWalker<AsyncifyLocals>> {
   bool isFunctionParallel() override { return true; }
@@ -1761,6 +1873,8 @@ struct Asyncify : public Pass {
       PassRunner runner(module);
       runner.add(std::make_unique<AsyncifyAssertInNonInstrumented>(
         &analyzer, pointerType, asyncifyMemory));
+      runner.add(
+        std::make_unique<AsyncifyAssertUnwindCorrectness>(&analyzer, module));
       runner.setIsNested(true);
       runner.setValidateGlobally(false);
       runner.run();