StubUnsupportedJSOps: Remove global exports (#8436)

This pass removes things we can't handle in wasm2js, and globals are
such a feature: wasm2js emits them in a partial way (it emits simple
fake objects, which are not actually WebAssembly.Global instances, and can
mix up the fuzzer).

Note that this pass is only used in the fuzzer - it is not part of
wasm2js's normal pipeline, so this does not affect any production workload. Also,
this PR makes the pass non-parallel (it is just easier), but that also is not
a problem for this reason.

Doing this will allow fuzzing more global things (this will avoid
breakage in wasm2js).

Author: kripken

src/passes/RemoveNonJSOps.cpp

@@ -337,11 +337,6 @@ struct RemoveNonJSOpsPass : public WalkerPass<PostWalker<RemoveNonJSOpsPass>> {
 
 struct StubUnsupportedJSOpsPass
   : public WalkerPass<PostWalker<StubUnsupportedJSOpsPass>> {
-  bool isFunctionParallel() override { return true; }
-
-  std::unique_ptr<Pass> create() override {
-    return std::make_unique<StubUnsupportedJSOpsPass>();
-  }
 
   void visitUnary(Unary* curr) {
     switch (curr->op) {
@@ -386,6 +381,21 @@ struct StubUnsupportedJSOpsPass
     }
     replaceCurrent(replacement);
   }
+
+  void visitModule(Module* module) {
+    // We remove global exports, as wasm2js doesn't emit them in a fully
+    // compatible form yet (they aren't instances of WebAssembly.Global).
+    // Globals.
+    std::vector<Name> badExports;
+    for (auto& exp : module->exports) {
+      if (exp->kind == ExternalKind::Global) {
+        badExports.push_back(exp->name);
+      }
+    }
+    for (auto name : badExports) {
+      module->removeExport(name);
+    }
+  }
 };
 
 Pass* createRemoveNonJSOpsPass() { return new RemoveNonJSOpsPass(); }

test/lit/passes/stub-unsupported-js-globals.wast

@@ -0,0 +1,30 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; RUN: foreach %s %t wasm-opt -all --stub-unsupported-js -S -o - | filecheck %s
+
+;; We should remove global exports, as wasm2js doesn't emit them in a fully
+;; compatible form yet (they aren't instances of WebAssembly.Global). All the
+;; global exports below should vanish, but not the function export.
+
+(module
+ ;; CHECK:      (type $0 (func))
+
+ ;; CHECK:      (global $i32 i32 (i32.const 42))
+ (global $i32 i32 (i32.const 42))
+
+ ;; CHECK:      (global $v128 v128 (v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000))
+ (global $v128 v128 (v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000))
+
+ (export "bad1" (global $v128))
+
+ (export "bad2" (global $i32))
+
+ ;; CHECK:      (export "good" (func $func))
+ (export "good" (func $func))
+
+ ;; CHECK:      (func $func (type $0)
+ ;; CHECK-NEXT: )
+ (func $func
+ )
+)
+