3 files changed, 90 insertions, 0 deletions

diff --git a/src/passes/LegalizeJSInterface.cpp b/src/passes/LegalizeJSInterface.cpp
index 3ca6b7095..0082ba7ab 100644
--- a/src/passes/LegalizeJSInterface.cpp
+++ b/src/passes/LegalizeJSInterface.cpp
@@ -29,6 +29,12 @@
 // across modules, we still want to legalize dynCalls so JS can call into the
 // tables even to a signature that is not legal.
 //
+// Another variation also "prunes" imports and exports that we cannot yet
+// legalize, like exports and imports with SIMD or multivalue. Until we write
+// the logic to legalize them, removing those imports/exports still allows us to
+// fuzz all the legal imports/exports. (Note that multivalue is supported in
+// exports in newer VMs - node 16+ - so that part is only needed for older VMs.)
+//
 
 #include "asmjs/shared-constants.h"
 #include "ir/element-utils.h"
@@ -43,6 +49,8 @@
 
 namespace wasm {
 
+namespace {
+
 // These are aliases for getTempRet0/setTempRet0 which emscripten defines in
 // compiler-rt and exports under these names.
 static Name GET_TEMP_RET_EXPORT("__get_temp_ret");
@@ -358,10 +366,88 @@ private:
   }
 };
 
+struct LegalizeAndPruneJSInterface : public LegalizeJSInterface {
+  // Legalize fully (true) and add pruning on top.
+  LegalizeAndPruneJSInterface() : LegalizeJSInterface(true) {}
+
+  void run(Module* module) override {
+    LegalizeJSInterface::run(module);
+
+    prune(module);
+  }
+
+  void prune(Module* module) {
+    // For each function name, the exported id it is exported with. For
+    // example,
+    //
+    //   (func $foo (export "bar")
+    //
+    // Would have exportedFunctions["foo"] = "bar";
+    std::unordered_map<Name, Name> exportedFunctions;
+    for (auto& exp : module->exports) {
+      if (exp->kind == ExternalKind::Function) {
+        exportedFunctions[exp->value] = exp->name;
+      }
+    }
+
+    for (auto& func : module->functions) {
+      // If the function is neither exported nor imported, no problem.
+      auto imported = func->imported();
+      auto exported = exportedFunctions.count(func->name);
+      if (!imported && !exported) {
+        continue;
+      }
+
+      // The params are allowed to be multivalue, but not the results. Otherwise
+      // look for SIMD.
+      auto sig = func->type.getSignature();
+      auto illegal = isIllegal(sig.results);
+      illegal =
+        illegal || std::any_of(sig.params.begin(),
+                               sig.params.end(),
+                               [&](const Type& t) { return isIllegal(t); });
+      if (!illegal) {
+        continue;
+      }
+
+      // Prune an import by implementing it in a trivial manner.
+      if (imported) {
+        func->module = func->base = Name();
+
+        Builder builder(*module);
+        if (sig.results == Type::none) {
+          func->body = builder.makeNop();
+        } else {
+          func->body =
+            builder.makeConstantExpression(Literal::makeZeros(sig.results));
+        }
+      }
+
+      // Prune an export by just removing it.
+      if (exported) {
+        module->removeExport(exportedFunctions[func->name]);
+      }
+    }
+
+    // TODO: globals etc.
+  }
+
+  bool isIllegal(Type type) {
+    auto features = type.getFeatures();
+    return features.hasSIMD() || features.hasMultivalue();
+  }
+};
+
+} // anonymous namespace
+
 Pass* createLegalizeJSInterfacePass() { return new LegalizeJSInterface(true); }
 
 Pass* createLegalizeJSInterfaceMinimallyPass() {
   return new LegalizeJSInterface(false);
 }
 
+Pass* createLegalizeAndPruneJSInterfacePass() {
+  return new LegalizeAndPruneJSInterface();
+}
+
 } // namespace wasm
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 1fe81cbfc..6faf77276 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -221,6 +221,9 @@ void PassRegistry::registerPasses() {
                "legalizes i64 types on the import/export boundary in a minimal "
                "manner, only on things only JS will call",
                createLegalizeJSInterfaceMinimallyPass);
+  registerPass("legalize-and-prune-js-interface",
+               "legalizes the import/export boundary and prunes when needed",
+               createLegalizeAndPruneJSInterfacePass);
   registerPass("local-cse",
                "common subexpression elimination inside basic blocks",
                createLocalCSEPass);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index c3ab7773f..2f188a689 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -67,6 +67,7 @@ Pass* createInliningPass();
 Pass* createInliningOptimizingPass();
 Pass* createJSPIPass();
 Pass* createJ2CLOptsPass();
+Pass* createLegalizeAndPruneJSInterfacePass();
 Pass* createLegalizeJSInterfacePass();
 Pass* createLegalizeJSInterfaceMinimallyPass();
 Pass* createLimitSegmentsPass();