Add anyref feature and type (#3109)

Adds `anyref` type, which is enabled by a new feature `--enable-anyref`. This type is primarily used for testing that passes correctly handle subtype relationships so that the codebase will continue to be prepared for future subtyping. Since `--enable-anyref` is meaningless without also using `--enable-reference-types`, this PR also makes it a validation error to pass only the former (and similarly makes it a validation error to enable exception handling without enabling reference types).

28 files changed, 203 insertions, 31 deletions

diff --git a/src/asmjs/asm_v_wasm.cpp b/src/asmjs/asm_v_wasm.cpp
index ddcb27d3d..8d2894f13 100644
--- a/src/asmjs/asm_v_wasm.cpp
+++ b/src/asmjs/asm_v_wasm.cpp
@@ -57,6 +57,7 @@ AsmType wasmToAsmType(Type type) {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
       assert(false && "reference types are not supported by asm2wasm");
     case Type::none:
       return ASM_NONE;
@@ -85,6 +86,8 @@ char getSig(Type type) {
       return 'X';
     case Type::exnref:
       return 'E';
+    case Type::anyref:
+      return 'A';
     case Type::none:
       return 'v';
     case Type::unreachable:
diff --git a/src/binaryen-c.cpp b/src/binaryen-c.cpp
index 9b2da350d..e11b762dd 100644
--- a/src/binaryen-c.cpp
+++ b/src/binaryen-c.cpp
@@ -73,6 +73,7 @@ BinaryenLiteral toBinaryenLiteral(Literal x) {
       break;
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
       assert(x.isNull());
       break;
     case Type::none:
@@ -98,6 +99,7 @@ Literal fromBinaryenLiteral(BinaryenLiteral x) {
       return Literal::makeFunc(x.func);
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
       return Literal::makeNull(Type(x.type));
     case Type::none:
     case Type::unreachable:
@@ -133,6 +135,7 @@ BinaryenType BinaryenTypeVec128(void) { return Type::v128; }
 BinaryenType BinaryenTypeFuncref(void) { return Type::funcref; }
 BinaryenType BinaryenTypeExternref(void) { return Type::externref; }
 BinaryenType BinaryenTypeExnref(void) { return Type::exnref; }
+BinaryenType BinaryenTypeAnyref(void) { return Type::anyref; }
 BinaryenType BinaryenTypeUnreachable(void) { return Type::unreachable; }
 BinaryenType BinaryenTypeAuto(void) { return uintptr_t(-1); }
 
@@ -324,6 +327,9 @@ BinaryenFeatures BinaryenFeatureReferenceTypes(void) {
 BinaryenFeatures BinaryenFeatureMultivalue(void) {
   return static_cast<BinaryenFeatures>(FeatureSet::Multivalue);
 }
+BinaryenFeatures BinaryenFeatureAnyref(void) {
+  return static_cast<BinaryenFeatures>(FeatureSet::Anyref);
+}
 BinaryenFeatures BinaryenFeatureAll(void) {
   return static_cast<BinaryenFeatures>(FeatureSet::All);
 }
diff --git a/src/binaryen-c.h b/src/binaryen-c.h
index beaf72499..e622419ac 100644
--- a/src/binaryen-c.h
+++ b/src/binaryen-c.h
@@ -101,6 +101,7 @@ BINARYEN_API BinaryenType BinaryenTypeVec128(void);
 BINARYEN_API BinaryenType BinaryenTypeFuncref(void);
 BINARYEN_API BinaryenType BinaryenTypeExternref(void);
 BINARYEN_API BinaryenType BinaryenTypeExnref(void);
+BINARYEN_API BinaryenType BinaryenTypeAnyref(void);
 BINARYEN_API BinaryenType BinaryenTypeUnreachable(void);
 // Not a real type. Used as the last parameter to BinaryenBlock to let
 // the API figure out the type instead of providing one.
@@ -196,6 +197,7 @@ BINARYEN_API BinaryenFeatures BinaryenFeatureExceptionHandling(void);
 BINARYEN_API BinaryenFeatures BinaryenFeatureTailCall(void);
 BINARYEN_API BinaryenFeatures BinaryenFeatureReferenceTypes(void);
 BINARYEN_API BinaryenFeatures BinaryenFeatureMultivalue(void);
+BINARYEN_API BinaryenFeatures BinaryenFeatureAnyref(void);
 BINARYEN_API BinaryenFeatures BinaryenFeatureAll(void);
 
 // Modules
diff --git a/src/gen-s-parser.inc b/src/gen-s-parser.inc
index 97ba15c32..4b02b09c2 100644
--- a/src/gen-s-parser.inc
+++ b/src/gen-s-parser.inc
@@ -8,13 +8,21 @@ char op[27] = {'\0'};
 strncpy(op, s[0]->c_str(), 26);
 switch (op[0]) {
   case 'a': {
-    switch (op[7]) {
-      case 'f':
-        if (strcmp(op, "atomic.fence") == 0) { return makeAtomicFence(s); }
-        goto parse_error;
+    switch (op[1]) {
       case 'n':
-        if (strcmp(op, "atomic.notify") == 0) { return makeAtomicNotify(s); }
+        if (strcmp(op, "anyref.pop") == 0) { return makePop(Type::anyref); }
         goto parse_error;
+      case 't': {
+        switch (op[7]) {
+          case 'f':
+            if (strcmp(op, "atomic.fence") == 0) { return makeAtomicFence(s); }
+            goto parse_error;
+          case 'n':
+            if (strcmp(op, "atomic.notify") == 0) { return makeAtomicNotify(s); }
+            goto parse_error;
+          default: goto parse_error;
+        }
+      }
       default: goto parse_error;
     }
   }
diff --git a/src/ir/abstract.h b/src/ir/abstract.h
index b00537bf5..5f1fd393e 100644
--- a/src/ir/abstract.h
+++ b/src/ir/abstract.h
@@ -104,6 +104,7 @@ inline UnaryOp getUnary(Type type, Op op) {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable: {
       return InvalidUnary;
@@ -268,6 +269,7 @@ inline BinaryOp getBinary(Type type, Op op) {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable: {
       return InvalidBinary;
diff --git a/src/js/binaryen.js-post.js b/src/js/binaryen.js-post.js
index 66de10848..fd121b8af 100644
--- a/src/js/binaryen.js-post.js
+++ b/src/js/binaryen.js-post.js
@@ -36,6 +36,7 @@ function initializeConstants() {
     ['funcref', 'Funcref'],
     ['externref', 'Externref'],
     ['exnref', 'Exnref'],
+    ['anyref', 'Anyref'],
     ['unreachable', 'Unreachable'],
     ['auto', 'Auto']
   ].forEach(entry => {
@@ -120,6 +121,7 @@ function initializeConstants() {
     'TailCall',
     'ReferenceTypes',
     'Multivalue',
+    'Anyref',
     'All'
   ].forEach(name => {
     Module['Features'][name] = Module['_BinaryenFeature' + name]();
@@ -2063,6 +2065,12 @@ function wrapModule(module, self = {}) {
     }
   };
 
+  self['anyref'] = {
+    'pop'() {
+      return Module['_BinaryenPop'](module, Module['anyref']);
+    }
+  };
+
   self['ref'] = {
     'null'(type) {
       return Module['_BinaryenRefNull'](module, type);
diff --git a/src/literal.h b/src/literal.h
index 1b3949d21..981f5b6d4 100644
--- a/src/literal.h
+++ b/src/literal.h
@@ -579,6 +579,7 @@ template<> struct less<wasm::Literal> {
       case wasm::Type::funcref:
       case wasm::Type::externref:
       case wasm::Type::exnref:
+      case wasm::Type::anyref:
       case wasm::Type::none:
       case wasm::Type::unreachable:
         return false;
diff --git a/src/parsing.h b/src/parsing.h
index 663b901fd..d809cbedd 100644
--- a/src/parsing.h
+++ b/src/parsing.h
@@ -266,6 +266,7 @@ parseConst(cashew::IString s, Type type, MixedArena& allocator) {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
       WASM_UNREACHABLE("unexpected const type");
     case Type::none:
     case Type::unreachable: {
diff --git a/src/passes/ConstHoisting.cpp b/src/passes/ConstHoisting.cpp
index e3583d3bb..3b34751ff 100644
--- a/src/passes/ConstHoisting.cpp
+++ b/src/passes/ConstHoisting.cpp
@@ -96,7 +96,8 @@ private:
       case Type::v128:
       case Type::funcref:
       case Type::externref:
-      case Type::exnref: {
+      case Type::exnref:
+      case Type::anyref: {
         return false;
       }
       case Type::none:
diff --git a/src/passes/FuncCastEmulation.cpp b/src/passes/FuncCastEmulation.cpp
index 160895f23..101834790 100644
--- a/src/passes/FuncCastEmulation.cpp
+++ b/src/passes/FuncCastEmulation.cpp
@@ -67,7 +67,8 @@ static Expression* toABI(Expression* value, Module* module) {
     }
     case Type::funcref:
     case Type::externref:
-    case Type::exnref: {
+    case Type::exnref:
+    case Type::anyref: {
       WASM_UNREACHABLE("reference types cannot be converted to i64");
     }
     case Type::none: {
@@ -110,7 +111,8 @@ static Expression* fromABI(Expression* value, Type type, Module* module) {
     }
     case Type::funcref:
     case Type::externref:
-    case Type::exnref: {
+    case Type::exnref:
+    case Type::anyref: {
       WASM_UNREACHABLE("reference types cannot be converted from i64");
     }
     case Type::none: {
diff --git a/src/passes/InstrumentLocals.cpp b/src/passes/InstrumentLocals.cpp
index ee288c103..b1ce5f05e 100644
--- a/src/passes/InstrumentLocals.cpp
+++ b/src/passes/InstrumentLocals.cpp
@@ -59,6 +59,7 @@ Name get_f64("get_f64");
 Name get_funcref("get_funcref");
 Name get_externref("get_externref");
 Name get_exnref("get_exnref");
+Name get_anyref("get_anyref");
 Name get_v128("get_v128");
 
 Name set_i32("set_i32");
@@ -68,6 +69,7 @@ Name set_f64("set_f64");
 Name set_funcref("set_funcref");
 Name set_externref("set_externref");
 Name set_exnref("set_exnref");
+Name set_anyref("set_anyref");
 Name set_v128("set_v128");
 
 struct InstrumentLocals : public WalkerPass<PostWalker<InstrumentLocals>> {
@@ -99,6 +101,9 @@ struct InstrumentLocals : public WalkerPass<PostWalker<InstrumentLocals>> {
       case Type::exnref:
         import = get_exnref;
         break;
+      case Type::anyref:
+        import = get_anyref;
+        break;
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("unexpected type");
@@ -145,6 +150,9 @@ struct InstrumentLocals : public WalkerPass<PostWalker<InstrumentLocals>> {
       case Type::exnref:
         import = set_exnref;
         break;
+      case Type::anyref:
+        import = set_anyref;
+        break;
       case Type::unreachable:
         return; // nothing to do here
       case Type::none:
@@ -184,12 +192,18 @@ struct InstrumentLocals : public WalkerPass<PostWalker<InstrumentLocals>> {
                 set_externref,
                 {Type::i32, Type::i32, Type::externref},
                 Type::externref);
-    }
-    if (curr->features.hasExceptionHandling()) {
-      addImport(
-        curr, get_exnref, {Type::i32, Type::i32, Type::exnref}, Type::exnref);
-      addImport(
-        curr, set_exnref, {Type::i32, Type::i32, Type::exnref}, Type::exnref);
+      if (curr->features.hasExceptionHandling()) {
+        addImport(
+          curr, get_exnref, {Type::i32, Type::i32, Type::exnref}, Type::exnref);
+        addImport(
+          curr, set_exnref, {Type::i32, Type::i32, Type::exnref}, Type::exnref);
+      }
+      if (curr->features.hasAnyref()) {
+        addImport(
+          curr, get_anyref, {Type::i32, Type::i32, Type::anyref}, Type::anyref);
+        addImport(
+          curr, set_anyref, {Type::i32, Type::i32, Type::anyref}, Type::anyref);
+      }
     }
     if (curr->features.hasSIMD()) {
       addImport(curr, get_v128, {Type::i32, Type::i32, Type::v128}, Type::v128);
diff --git a/src/shell-interface.h b/src/shell-interface.h
index 92f562b48..ae86d13ec 100644
--- a/src/shell-interface.h
+++ b/src/shell-interface.h
@@ -118,6 +118,7 @@ struct ShellExternalInterface : ModuleInstance::ExternalInterface {
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
             globals[import->name] = {Literal::makeNull(import->type)};
             break;
           case Type::none:
diff --git a/src/tools/fuzzing.h b/src/tools/fuzzing.h
index ef7844c60..9768b63c4 100644
--- a/src/tools/fuzzing.h
+++ b/src/tools/fuzzing.h
@@ -315,7 +315,20 @@ private:
     }
     SmallVector<Type, 2> options;
     options.push_back(type); // includes itself
-    // TODO (GC): subtyping
+    TODO_SINGLE_COMPOUND(type);
+    switch (type.getBasic()) {
+      case Type::anyref:
+        if (wasm.features.hasReferenceTypes()) {
+          options.push_back(Type::funcref);
+          options.push_back(Type::externref);
+          if (wasm.features.hasExceptionHandling()) {
+            options.push_back(Type::exnref);
+          }
+        }
+        break;
+      default:
+        break;
+    }
     return pick(options);
   }
 
@@ -1349,6 +1362,7 @@ private:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("invalid type");
@@ -1452,6 +1466,7 @@ private:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("invalid type");
@@ -1580,6 +1595,7 @@ private:
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
           case Type::none:
           case Type::unreachable:
             WASM_UNREACHABLE("invalid type");
@@ -1624,6 +1640,7 @@ private:
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
           case Type::none:
           case Type::unreachable:
             WASM_UNREACHABLE("unexpected type");
@@ -1691,6 +1708,7 @@ private:
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
           case Type::none:
           case Type::unreachable:
             WASM_UNREACHABLE("unexpected type");
@@ -1717,6 +1735,7 @@ private:
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
           case Type::none:
           case Type::unreachable:
             WASM_UNREACHABLE("unexpected type");
@@ -1826,6 +1845,7 @@ private:
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
             return makeTrivial(type);
           case Type::none:
           case Type::unreachable:
@@ -1970,6 +1990,7 @@ private:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("unexpected type");
@@ -2206,6 +2227,7 @@ private:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("unexpected type");
@@ -2412,6 +2434,7 @@ private:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("unexpected type");
@@ -2592,6 +2615,9 @@ private:
     if (wasm.features.hasExceptionHandling()) {
       options.push_back(Type::exnref);
     }
+    if (wasm.features.hasAnyref()) {
+      options.push_back(Type::anyref);
+    }
     return builder.makeRefIsNull(make(pick(options)));
   }
 
@@ -2657,7 +2683,8 @@ private:
         .add(FeatureSet::SIMD, Type::v128)
         .add(FeatureSet::ReferenceTypes, Type::funcref, Type::externref)
         .add(FeatureSet::ReferenceTypes | FeatureSet::ExceptionHandling,
-             Type::exnref));
+             Type::exnref)
+        .add(FeatureSet::ReferenceTypes | FeatureSet::Anyref, Type::anyref));
   }
 
   Type getSingleConcreteType() { return pick(getSingleConcreteTypes()); }
@@ -2697,7 +2724,7 @@ private:
 
   // - funcref cannot be logged because referenced functions can be inlined or
   // removed during optimization
-  // - there's no point in logging externref because it is opaque
+  // - there's no point in logging externref or anyref because these are opaque
   // - don't bother logging tuples
   std::vector<Type> getLoggableTypes() {
     return items(
diff --git a/src/tools/spec-wrapper.h b/src/tools/spec-wrapper.h
index c073a994c..200571fd0 100644
--- a/src/tools/spec-wrapper.h
+++ b/src/tools/spec-wrapper.h
@@ -58,6 +58,9 @@ static std::string generateSpecWrapper(Module& wasm) {
         case Type::exnref:
           ret += "(ref.null exn)";
           break;
+        case Type::anyref:
+          ret += "(ref.null any)";
+          break;
         case Type::none:
         case Type::unreachable:
           WASM_UNREACHABLE("unexpected type");
diff --git a/src/tools/tool-options.h b/src/tools/tool-options.h
index f04b95304..082e95549 100644
--- a/src/tools/tool-options.h
+++ b/src/tools/tool-options.h
@@ -87,6 +87,7 @@ struct ToolOptions : public Options {
       .addFeature(FeatureSet::TailCall, "tail call operations")
       .addFeature(FeatureSet::ReferenceTypes, "reference types")
       .addFeature(FeatureSet::Multivalue, "multivalue functions")
+      .addFeature(FeatureSet::Anyref, "anyref type (without GC)")
       .add("--no-validation",
            "-n",
            "Disables validation, assumes inputs are correct",
diff --git a/src/tools/wasm-reduce.cpp b/src/tools/wasm-reduce.cpp
index 1a7c3544d..7410ff91e 100644
--- a/src/tools/wasm-reduce.cpp
+++ b/src/tools/wasm-reduce.cpp
@@ -598,6 +598,7 @@ struct Reducer
               case Type::funcref:
               case Type::externref:
               case Type::exnref:
+              case Type::anyref:
                 continue; // not implemented yet
               case Type::none:
               case Type::unreachable:
@@ -623,6 +624,7 @@ struct Reducer
               case Type::funcref:
               case Type::externref:
               case Type::exnref:
+              case Type::anyref:
                 continue; // not implemented yet
               case Type::none:
               case Type::unreachable:
@@ -648,6 +650,7 @@ struct Reducer
               case Type::funcref:
               case Type::externref:
               case Type::exnref:
+              case Type::anyref:
                 continue; // not implemented yet
               case Type::none:
               case Type::unreachable:
@@ -673,6 +676,7 @@ struct Reducer
               case Type::funcref:
               case Type::externref:
               case Type::exnref:
+              case Type::anyref:
                 continue; // not implemented yet
               case Type::none:
               case Type::unreachable:
@@ -684,6 +688,7 @@ struct Reducer
           case Type::funcref:
           case Type::externref:
           case Type::exnref:
+          case Type::anyref:
             continue; // not implemented yet
           case Type::none:
           case Type::unreachable:
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index 865a882df..33f78ce7f 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -347,6 +347,8 @@ enum EncodedType {
   funcref = -0x10, // 0x70
   // opaque host reference type
   externref = -0x11, // 0x6f
+  // any reference type
+  anyref = -0x12, // 0x6e
   // exception reference type
   exnref = -0x18, // 0x68
   // func_type form
@@ -358,6 +360,7 @@ enum EncodedType {
 enum EncodedHeapType {
   func = -0x10,    // 0x70
   extern_ = -0x11, // 0x6f
+  any = -0x12,     // 0x6e
   exn = -0x18,     // 0x68
 };
 
@@ -380,6 +383,7 @@ extern const char* ExceptionHandlingFeature;
 extern const char* TailCallFeature;
 extern const char* ReferenceTypesFeature;
 extern const char* MultivalueFeature;
+extern const char* AnyrefFeature;
 
 enum Subsection {
   NameFunction = 1,
@@ -975,6 +979,9 @@ inline S32LEB binaryType(Type type) {
     case Type::exnref:
       ret = BinaryConsts::EncodedType::exnref;
       break;
+    case Type::anyref:
+      ret = BinaryConsts::EncodedType::anyref;
+      break;
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
   }
@@ -994,6 +1001,8 @@ inline S32LEB binaryHeapType(HeapType type) {
       ret = BinaryConsts::EncodedHeapType::exn;
       break;
     case HeapType::AnyKind:
+      ret = BinaryConsts::EncodedHeapType::any;
+      break;
     case HeapType::EqKind:
     case HeapType::I31Kind:
     case HeapType::SignatureKind:
diff --git a/src/wasm-builder.h b/src/wasm-builder.h
index 1ce3a507c..6c1923482 100644
--- a/src/wasm-builder.h
+++ b/src/wasm-builder.h
@@ -631,6 +631,7 @@ public:
         return makeRefNull(value.type);
       case Type::externref:
       case Type::exnref: // TODO: ExceptionPackage?
+      case Type::anyref:
         assert(value.isNull());
         return makeRefNull(value.type);
       default:
@@ -825,6 +826,7 @@ public:
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
         return ExpressionManipulator::refNull(curr, curr->type);
       case Type::none:
         return ExpressionManipulator::nop(curr);
diff --git a/src/wasm-features.h b/src/wasm-features.h
index c35ff0442..5d05b6284 100644
--- a/src/wasm-features.h
+++ b/src/wasm-features.h
@@ -36,7 +36,8 @@ struct FeatureSet {
     TailCall = 1 << 7,
     ReferenceTypes = 1 << 8,
     Multivalue = 1 << 9,
-    All = (1 << 10) - 1
+    Anyref = 1 << 10,
+    All = (1 << 11) - 1
   };
 
   static std::string toString(Feature f) {
@@ -61,6 +62,8 @@ struct FeatureSet {
         return "reference-types";
       case Multivalue:
         return "multivalue";
+      case Anyref:
+        return "anyref";
       default:
         WASM_UNREACHABLE("unexpected feature");
     }
@@ -84,6 +87,7 @@ struct FeatureSet {
   bool hasTailCall() const { return (features & TailCall) != 0; }
   bool hasReferenceTypes() const { return (features & ReferenceTypes) != 0; }
   bool hasMultivalue() const { return (features & Multivalue) != 0; }
+  bool hasAnyref() const { return (features & Anyref) != 0; }
   bool hasAll() const { return (features & All) != 0; }
 
   void makeMVP() { features = MVP; }
@@ -100,6 +104,7 @@ struct FeatureSet {
   void setTailCall(bool v = true) { set(TailCall, v); }
   void setReferenceTypes(bool v = true) { set(ReferenceTypes, v); }
   void setMultivalue(bool v = true) { set(Multivalue, v); }
+  void setAnyref(bool v = true) { set(Anyref, v); }
   void setAll(bool v = true) { features = v ? All : MVP; }
 
   void enable(const FeatureSet& other) { features |= other.features; }
diff --git a/src/wasm-interpreter.h b/src/wasm-interpreter.h
index 44cac9d49..361545a2c 100644
--- a/src/wasm-interpreter.h
+++ b/src/wasm-interpreter.h
@@ -1647,6 +1647,7 @@ public:
         case Type::funcref:
         case Type::externref:
         case Type::exnref:
+        case Type::anyref:
         case Type::none:
         case Type::unreachable:
           WASM_UNREACHABLE("unexpected type");
@@ -1703,6 +1704,7 @@ public:
         case Type::funcref:
         case Type::externref:
         case Type::exnref:
+        case Type::anyref:
         case Type::none:
         case Type::unreachable:
           WASM_UNREACHABLE("unexpected type");
diff --git a/src/wasm-type.h b/src/wasm-type.h
index 384cc589f..f3973068f 100644
--- a/src/wasm-type.h
+++ b/src/wasm-type.h
@@ -50,7 +50,8 @@ public:
     funcref,
     externref,
     exnref,
-    _last_basic_id = exnref
+    anyref,
+    _last_basic_id = anyref
   };
 
   Type() = default;
@@ -88,11 +89,11 @@ public:
   // │ v128        ║ x │   │ x │ x │     V │ ┘
   // ├─ Aliases ───╫───┼───┼───┼───┤───────┤
   // │ funcref     ║ x │   │ x │ x │ f  n  │ ┐ Ref
-  // │ externref   ║ x │   │ x │ x │ f? n  │ │  f_unc, n_ullable
-  // │ anyref      ║ x │   │ x │ x │ f? n  │ │ ┐
-  // │ eqref       ║ x │   │ x │ x │    n  │ │ │ TODO (GC)
+  // │ externref   ║ x │   │ x │ x │ f? n  │ │  f_unc
+  // │ exnref      ║ x │   │ x │ x │    n  │ │  n_ullable
+  // │ anyref      ║ x │   │ x │ x │ f? n  │ │
+  // │ eqref       ║ x │   │ x │ x │    n  │ │ ┐ TODO (GC)
   // │ i31ref      ║ x │   │ x │ x │       │ │ ┘
-  // │ exnref      ║ x │   │ x │ x │    n  │ │
   // ├─ Compound ──╫───┼───┼───┼───┤───────┤ │
   // │ Ref         ║   │ x │ x │ x │ f? n? │◄┘
   // │ Tuple       ║   │ x │   │ x │       │
@@ -330,11 +331,11 @@ struct HeapType {
   enum Kind {
     FuncKind,
     ExternKind,
+    ExnKind,
     AnyKind,
     EqKind,
     I31Kind,
-    ExnKind,
-    _last_basic_kind = ExnKind,
+    _last_basic_kind = I31Kind,
     SignatureKind,
     StructKind,
     ArrayKind,
diff --git a/src/wasm/literal.cpp b/src/wasm/literal.cpp
index ffb98abe4..39a4cea3c 100644
--- a/src/wasm/literal.cpp
+++ b/src/wasm/literal.cpp
@@ -69,6 +69,7 @@ Literal::Literal(const Literal& other) : type(other.type) {
       case Type::none:
         break;
       case Type::externref:
+      case Type::anyref:
         break; // null
       case Type::funcref:
       case Type::exnref:
@@ -221,6 +222,7 @@ void Literal::getBits(uint8_t (&buf)[16]) const {
       break;
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
       if (isNull()) {
         break;
       }
@@ -384,6 +386,10 @@ std::ostream& operator<<(std::ostream& o, Literal literal) {
         o << "exnref(" << literal.getExceptionPackage() << ")";
       }
       break;
+    case Type::anyref:
+      assert(literal.isNull() && "TODO: non-null anyref values");
+      o << "anyref(null)";
+      break;
     case Type::externref:
       assert(literal.isNull() && "TODO: non-null externref values");
       o << "externref(null)";
@@ -612,6 +618,7 @@ Literal Literal::eqz() const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -633,6 +640,7 @@ Literal Literal::neg() const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -654,6 +662,7 @@ Literal Literal::abs() const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -758,6 +767,7 @@ Literal Literal::add(const Literal& other) const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -779,6 +789,7 @@ Literal Literal::sub(const Literal& other) const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -896,6 +907,7 @@ Literal Literal::mul(const Literal& other) const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -1141,6 +1153,7 @@ Literal Literal::eq(const Literal& other) const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
@@ -1162,6 +1175,7 @@ Literal Literal::ne(const Literal& other) const {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index b78d6b86b..de82f0656 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -691,6 +691,8 @@ void WasmBinaryWriter::writeFeaturesSection() {
         return BinaryConsts::UserSections::ReferenceTypesFeature;
       case FeatureSet::Multivalue:
         return BinaryConsts::UserSections::MultivalueFeature;
+      case FeatureSet::Anyref:
+        return BinaryConsts::UserSections::AnyrefFeature;
       default:
         WASM_UNREACHABLE("unexpected feature flag");
     }
@@ -1138,6 +1140,8 @@ Type WasmBinaryBuilder::getType() {
       return Type::externref;
     case BinaryConsts::EncodedType::exnref:
       return Type::exnref;
+    case BinaryConsts::EncodedType::anyref:
+      return Type::anyref;
     default:
       throwError("invalid wasm type: " + std::to_string(type));
   }
@@ -1160,6 +1164,8 @@ HeapType WasmBinaryBuilder::getHeapType() {
       return HeapType::ExternKind;
     case BinaryConsts::EncodedHeapType::exn:
       return HeapType::ExnKind;
+    case BinaryConsts::EncodedHeapType::any:
+      return HeapType::AnyKind;
     default:
       throwError("invalid wasm heap type: " + std::to_string(type));
   }
@@ -2203,6 +2209,8 @@ void WasmBinaryBuilder::readFeatures(size_t payloadLen) {
         wasm.features.setReferenceTypes();
       } else if (name == BinaryConsts::UserSections::MultivalueFeature) {
         wasm.features.setMultivalue();
+      } else if (name == BinaryConsts::UserSections::AnyrefFeature) {
+        wasm.features.setAnyref();
       }
     }
   }
diff --git a/src/wasm/wasm-s-parser.cpp b/src/wasm/wasm-s-parser.cpp
index bac5f958c..e4a33c034 100644
--- a/src/wasm/wasm-s-parser.cpp
+++ b/src/wasm/wasm-s-parser.cpp
@@ -874,6 +874,9 @@ Type SExpressionWasmBuilder::stringToType(const char* str,
   if (strncmp(str, "exnref", 6) == 0 && (prefix || str[6] == 0)) {
     return Type::exnref;
   }
+  if (strncmp(str, "anyref", 6) == 0 && (prefix || str[6] == 0)) {
+    return Type::anyref;
+  }
   if (allowError) {
     return Type::none;
   }
diff --git a/src/wasm/wasm-stack.cpp b/src/wasm/wasm-stack.cpp
index aee5079c2..64622e814 100644
--- a/src/wasm/wasm-stack.cpp
+++ b/src/wasm/wasm-stack.cpp
@@ -191,6 +191,7 @@ void BinaryInstWriter::visitLoad(Load* curr) {
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
         WASM_UNREACHABLE("unexpected type");
     }
@@ -292,6 +293,7 @@ void BinaryInstWriter::visitStore(Store* curr) {
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         WASM_UNREACHABLE("unexpected type");
@@ -694,6 +696,7 @@ void BinaryInstWriter::visitConst(Const* curr) {
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
     case Type::unreachable:
       WASM_UNREACHABLE("unexpected type");
diff --git a/src/wasm/wasm-type.cpp b/src/wasm/wasm-type.cpp
index 729cc88f5..0c49e8dcc 100644
--- a/src/wasm/wasm-type.cpp
+++ b/src/wasm/wasm-type.cpp
@@ -256,12 +256,13 @@ std::unordered_map<TypeInfo, uintptr_t> indices = {
   {TypeInfo(HeapType(HeapType::FuncKind), true), Type::funcref},
   {TypeInfo({Type::externref}), Type::externref},
   {TypeInfo(HeapType(HeapType::ExternKind), true), Type::externref},
+  {TypeInfo({Type::exnref}), Type::exnref},
+  {TypeInfo(HeapType(HeapType::ExnKind), true), Type::exnref},
+  {TypeInfo({Type::anyref}), Type::anyref},
+  {TypeInfo(HeapType(HeapType::AnyKind), true), Type::anyref},
   // TODO (GC): Add canonical ids
-  // * `(ref null any) == anyref`
   // * `(ref null eq) == eqref`
   // * `(ref i31) == i31ref`
-  {TypeInfo({Type::exnref}), Type::exnref},
-  {TypeInfo(HeapType(HeapType::ExnKind), true), Type::exnref},
 };
 
 } // anonymous namespace
@@ -340,7 +341,7 @@ bool Type::isTuple() const {
 
 bool Type::isRef() const {
   if (isBasic()) {
-    return id >= funcref && id <= exnref;
+    return id >= funcref && id <= anyref;
   } else {
     return getTypeInfo(*this)->isRef();
   }
@@ -366,7 +367,7 @@ bool Type::isException() const {
 
 bool Type::isNullable() const {
   if (isBasic()) {
-    return id >= funcref && id <= exnref;
+    return id >= funcref && id <= anyref;
   } else {
     return getTypeInfo(*this)->isNullable();
   }
@@ -407,6 +408,7 @@ unsigned Type::getByteSize() const {
       case Type::funcref:
       case Type::externref:
       case Type::exnref:
+      case Type::anyref:
       case Type::none:
       case Type::unreachable:
         break;
@@ -451,6 +453,8 @@ FeatureSet Type::getFeatures() const {
         return FeatureSet::ReferenceTypes;
       case Type::exnref:
         return FeatureSet::ReferenceTypes | FeatureSet::ExceptionHandling;
+      case Type::anyref:
+        return FeatureSet::ReferenceTypes | FeatureSet::Anyref;
       default:
         return FeatureSet::MVP;
     }
@@ -478,6 +482,8 @@ HeapType Type::getHeapType() const {
         return HeapType::ExternKind;
       case exnref:
         return HeapType::ExnKind;
+      case anyref:
+        return HeapType::AnyKind;
       default:
         break;
     }
@@ -502,10 +508,12 @@ Type Type::get(unsigned byteSize, bool float_) {
 }
 
 bool Type::isSubType(Type left, Type right) {
-  // TODO (GC): subtyping, currently checks for equality only
   if (left == right) {
     return true;
   }
+  if (left.isRef() && right.isRef()) {
+    return right == Type::anyref;
+  }
   if (left.isTuple() && right.isTuple()) {
     if (left.size() != right.size()) {
       return false;
@@ -533,6 +541,17 @@ Type Type::getLeastUpperBound(Type a, Type b) {
   if (a.size() != b.size()) {
     return Type::none; // a poison value that must not be consumed
   }
+  if (a.isRef()) {
+    if (b.isRef()) {
+      // The LUB of two different reference types is anyref, which may or may
+      // not be a valid type depending on whether the anyref feature is enabled.
+      // When anyref is disabled, it is possible for the finalization of invalid
+      // code to introduce a use of anyref via this function, but that is not a
+      // problem because it will be caught and rejected by validation.
+      return Type::anyref;
+    }
+    return Type::none;
+  }
   if (a.isTuple()) {
     TypeList types;
     types.resize(a.size());
@@ -732,6 +751,9 @@ std::ostream& operator<<(std::ostream& os, Type type) {
       case Type::exnref:
         os << "exnref";
         break;
+      case Type::anyref:
+        os << "anyref";
+        break;
     }
   } else {
     os << *getTypeInfo(type);
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index c6d679a24..80c54abed 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -1363,6 +1363,7 @@ void FunctionValidator::validateMemBytes(uint8_t bytes,
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
       WASM_UNREACHABLE("unexpected type");
   }
@@ -2176,6 +2177,7 @@ void FunctionValidator::validateAlignment(
     case Type::funcref:
     case Type::externref:
     case Type::exnref:
+    case Type::anyref:
     case Type::none:
       WASM_UNREACHABLE("invalid type");
   }
@@ -2475,6 +2477,20 @@ static void validateModule(Module& module, ValidationInfo& info) {
   }
 }
 
+static void validateFeatures(Module& module, ValidationInfo& info) {
+  if (module.features.hasAnyref()) {
+    info.shouldBeTrue(module.features.hasReferenceTypes(),
+                      module.features,
+                      "--enable-anyref requires --enable-reference-types");
+  }
+  if (module.features.hasExceptionHandling()) { // implies exnref
+    info.shouldBeTrue(
+      module.features.hasReferenceTypes(),
+      module.features,
+      "--enable-exception-handling requires --enable-reference-types");
+  }
+}
+
 // TODO: If we want the validator to be part of libwasm rather than libpasses,
 // then Using PassRunner::getPassDebug causes a circular dependence. We should
 // fix that, perhaps by moving some of the pass infrastructure into libsupport.
@@ -2495,6 +2511,7 @@ bool WasmValidator::validate(Module& module, Flags flags) {
     validateTable(module, info);
     validateEvents(module, info);
     validateModule(module, info);
+    validateFeatures(module, info);
   }
   // validate additional internal IR details when in pass-debug mode
   if (PassRunner::getPassDebug()) {
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index fe7c1b229..31e05f42e 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -45,6 +45,7 @@ const char* SIMD128Feature = "simd128";
 const char* TailCallFeature = "tail-call";
 const char* ReferenceTypesFeature = "reference-types";
 const char* MultivalueFeature = "multivalue";
+const char* AnyrefFeature = "anyref";
 } // namespace UserSections
 } // namespace BinaryConsts