Fix RefFunc type updating in I64ToI32Lowering (WebAssembly#7390)

We recently started updating RefFunc types in I64ToI32Lowering to ensure
that their types matched the updated types of their functions. But the
way we updated the types of RefFunc expressions and Functions were not
the same. When updating Functions that return i64, we replace the result
type with i32 and use a global to propagate the remaining bits to the
caller. Previously when updating RefFunc result types, we would instead
split i64s into pairs of i32s, depending on multivalue to lower the
type. Update the logic for updating RefFunc results to match the
existing logic for updating Functions.

Author: tlively

src/passes/I64ToI32Lowering.cpp

@@ -300,33 +300,35 @@ struct I64ToI32Lowering : public WalkerPass<PostWalker<I64ToI32Lowering>> {
   void visitRefFunc(RefFunc* curr) {
     auto sig = curr->type.getHeapType().getSignature();
 
-    auto lowerTypes = [](Type types) {
-      bool hasI64 = false;
-      for (auto t : types) {
-        if (t == Type::i64) {
-          hasI64 = true;
-          break;
-        }
-      }
-      if (!hasI64) {
-        return types;
+    bool hasI64Param = false;
+    for (auto t : sig.params) {
+      if (t == Type::i64) {
+        hasI64Param = true;
+        break;
       }
-      std::vector<Type> newTypes;
-      for (auto t : types) {
+    }
+    auto params = sig.params;
+    if (hasI64Param) {
+      std::vector<Type> newParams;
+      for (auto t : sig.params) {
         if (t == Type::i64) {
-          newTypes.push_back(Type::i32);
-          newTypes.push_back(Type::i32);
+          newParams.push_back(Type::i32);
+          newParams.push_back(Type::i32);
         } else {
-          newTypes.push_back(t);
+          newParams.push_back(t);
         }
       }
-      return Type(newTypes);
+      params = Type(newParams);
     };
+    auto results = sig.results;
+    // Update the results the same way we do when visiting functions. We use a
+    // global rather than multivalue to lower i64 results.
+    if (results == Type::i64) {
+      results = Type::i32;
+    }
 
-    auto newParams = lowerTypes(sig.params);
-    auto newResults = lowerTypes(sig.results);
-    if (newParams != sig.params || newResults != sig.results) {
-      curr->type = curr->type.with(HeapType(Signature(newParams, newResults)));
+    if (params != sig.params || results != sig.results) {
+      curr->type = curr->type.with(HeapType(Signature(params, results)));
     }
   }
 

test/lit/passes/flatten_i64-to-i32-lowering.wast

@@ -665,3 +665,26 @@
   )
  )
 )
+
+;; Make sure we update the ref.func in the table with the correct return type.
+(module
+ (table 1 1 funcref)
+
+ (elem (i32.const 0) $f)
+
+ ;; CHECK:      (type $0 (func (result i32)))
+
+ ;; CHECK:      (global $i64toi32_i32$HIGH_BITS (mut i32) (i32.const 0))
+
+ ;; CHECK:      (table $0 1 1 funcref)
+
+ ;; CHECK:      (elem $0 (i32.const 0) $f)
+
+ ;; CHECK:      (func $f (type $0) (result i32)
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT: )
+ (func $f (result i64)
+  (unreachable)
+ )
+)