Implement `extern.externalize` and `extern.internalize` (#4975)

These new GC instructions infallibly convert between `extern` and `any`
references now that those types are not in the same hierarchy.

14 files changed, 171 insertions, 11 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 049652cfe..7e005f6e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,7 @@ Current Trunk
 - HeapType::ext has been restored but is no longer a subtype of HeapType::any to
   match the latest updates in the GC spec. (#4898)
 - `i31ref` and `dataref` are now nullable to match the latest GC spec. (#4843)
+- Add support for `extern.externalize` and `extern.internalize`. (#4975)
 
 v109
 ----
diff --git a/scripts/fuzz_opt.py b/scripts/fuzz_opt.py
index 3ff1cb554..d287bee97 100755
--- a/scripts/fuzz_opt.py
+++ b/scripts/fuzz_opt.py
@@ -270,8 +270,10 @@ def init_important_initial_contents():
 INITIAL_CONTENTS_IGNORE = [
     # not all relaxed SIMD instructions are implemented in the interpreter
     'relaxed-simd.wast',
-    # TODO fuzzer and interpreter support for strings
+    # TODO: fuzzer and interpreter support for strings
     'strings.wast',
+    # TODO: fuzzer and interpreter support for extern conversions
+    'extern-conversions.wast',
     # ignore DWARF because it is incompatible with multivalue atm
     'zlib.wasm',
     'cubescript.wasm',
diff --git a/scripts/gen-s-parser.py b/scripts/gen-s-parser.py
index bb56b76e3..93fc676e4 100755
--- a/scripts/gen-s-parser.py
+++ b/scripts/gen-s-parser.py
@@ -604,6 +604,8 @@ instructions = [
     ("ref.as_func",          "makeRefAs(s, RefAsFunc)"),
     ("ref.as_data",          "makeRefAs(s, RefAsData)"),
     ("ref.as_i31",           "makeRefAs(s, RefAsI31)"),
+    ("extern.internalize",   "makeRefAs(s, ExternInternalize)"),
+    ("extern.externalize",   "makeRefAs(s, ExternExternalize)"),
     ("string.new_wtf8",      "makeStringNew(s, StringNewWTF8)"),
     ("string.new_wtf16",     "makeStringNew(s, StringNewWTF16)"),
     ("string.new_wtf8_array",  "makeStringNew(s, StringNewWTF8Array)"),
diff --git a/src/gen-s-parser.inc b/src/gen-s-parser.inc
index caf4f5578..4803f60b5 100644
--- a/src/gen-s-parser.inc
+++ b/src/gen-s-parser.inc
@@ -185,9 +185,25 @@ switch (op[0]) {
       default: goto parse_error;
     }
   }
-  case 'e':
-    if (strcmp(op, "else") == 0) { return makeThenOrElse(s); }
-    goto parse_error;
+  case 'e': {
+    switch (op[1]) {
+      case 'l':
+        if (strcmp(op, "else") == 0) { return makeThenOrElse(s); }
+        goto parse_error;
+      case 'x': {
+        switch (op[7]) {
+          case 'e':
+            if (strcmp(op, "extern.externalize") == 0) { return makeRefAs(s, ExternExternalize); }
+            goto parse_error;
+          case 'i':
+            if (strcmp(op, "extern.internalize") == 0) { return makeRefAs(s, ExternInternalize); }
+            goto parse_error;
+          default: goto parse_error;
+        }
+      }
+      default: goto parse_error;
+    }
+  }
   case 'f': {
     switch (op[1]) {
       case '3': {
@@ -3816,13 +3832,37 @@ switch (op[0]) {
       default: goto parse_error;
     }
   }
-  case 'e':
-    if (op == "else"sv) {
-      auto ret = makeThenOrElse(ctx, in);
-      CHECK_ERR(ret);
-      return *ret;
+  case 'e': {
+    switch (op[1]) {
+      case 'l':
+        if (op == "else"sv) {
+          auto ret = makeThenOrElse(ctx, in);
+          CHECK_ERR(ret);
+          return *ret;
+        }
+        goto parse_error;
+      case 'x': {
+        switch (op[7]) {
+          case 'e':
+            if (op == "extern.externalize"sv) {
+              auto ret = makeRefAs(ctx, in, ExternExternalize);
+              CHECK_ERR(ret);
+              return *ret;
+            }
+            goto parse_error;
+          case 'i':
+            if (op == "extern.internalize"sv) {
+              auto ret = makeRefAs(ctx, in, ExternInternalize);
+              CHECK_ERR(ret);
+              return *ret;
+            }
+            goto parse_error;
+          default: goto parse_error;
+        }
+      }
+      default: goto parse_error;
     }
-    goto parse_error;
+  }
   case 'f': {
     switch (op[1]) {
       case '3': {
diff --git a/src/ir/effects.h b/src/ir/effects.h
index 5e50441ac..f5fdc5184 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -726,6 +726,10 @@ private:
       parent.implicitTrap = true;
     }
     void visitRefAs(RefAs* curr) {
+      if (curr->op == ExternInternalize || curr->op == ExternExternalize) {
+        // These conversions are infallible.
+        return;
+      }
       // traps when the arg is not valid
       parent.implicitTrap = true;
       // Note: We could be more precise here and report the lack of a possible
diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 5fb17af76..dc247c737 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -2214,6 +2214,12 @@ struct PrintExpressionContents
       case RefAsI31:
         printMedium(o, "ref.as_i31");
         break;
+      case ExternInternalize:
+        printMedium(o, "extern.internalize");
+        break;
+      case ExternExternalize:
+        printMedium(o, "extern.externalize");
+        break;
       default:
         WASM_UNREACHABLE("invalid ref.is_*");
     }
diff --git a/src/wasm-binary.h b/src/wasm-binary.h
index e150915a0..562196580 100644
--- a/src/wasm-binary.h
+++ b/src/wasm-binary.h
@@ -1125,6 +1125,8 @@ enum ASTNodes {
   BrOnNonFunc = 0x63,
   BrOnNonData = 0x64,
   BrOnNonI31 = 0x65,
+  ExternInternalize = 0x70,
+  ExternExternalize = 0x71,
   StringNewWTF8 = 0x80,
   StringNewWTF16 = 0x81,
   StringConst = 0x82,
diff --git a/src/wasm-interpreter.h b/src/wasm-interpreter.h
index fec560e35..56336b237 100644
--- a/src/wasm-interpreter.h
+++ b/src/wasm-interpreter.h
@@ -1874,6 +1874,9 @@ public:
           trap("not an i31");
         }
         break;
+      case ExternInternalize:
+      case ExternExternalize:
+        WASM_UNREACHABLE("unimplemented extern conversion");
       default:
         WASM_UNREACHABLE("unimplemented ref.as_*");
     }
@@ -2226,6 +2229,13 @@ public:
   Flow visitStringSliceIter(StringSliceIter* curr) {
     return Flow(NONCONSTANT_FLOW);
   }
+  Flow visitRefAs(RefAs* curr) {
+    // TODO: Remove this once interpretation is implemented.
+    if (curr->op == ExternInternalize || curr->op == ExternExternalize) {
+      return Flow(NONCONSTANT_FLOW);
+    }
+    return ExpressionRunner<SubType>::visitRefAs(curr);
+  }
 
   void trap(const char* why) override { throw NonconstantException(); }
 
diff --git a/src/wasm.h b/src/wasm.h
index 62a63e493..7b895a0cf 100644
--- a/src/wasm.h
+++ b/src/wasm.h
@@ -568,6 +568,8 @@ enum RefAsOp {
   RefAsFunc,
   RefAsData,
   RefAsI31,
+  ExternInternalize,
+  ExternExternalize,
 };
 
 enum BrOnOp {
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index df99fabb9..d449d4bdb 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -3978,7 +3978,9 @@ BinaryConsts::ASTNodes WasmBinaryBuilder::readExpression(Expression*& curr) {
       }
       if (opcode == BinaryConsts::RefAsFunc ||
           opcode == BinaryConsts::RefAsData ||
-          opcode == BinaryConsts::RefAsI31) {
+          opcode == BinaryConsts::RefAsI31 ||
+          opcode == BinaryConsts::ExternInternalize ||
+          opcode == BinaryConsts::ExternExternalize) {
         visitRefAs((curr = allocator.alloc<RefAs>())->cast<RefAs>(), opcode);
         break;
       }
@@ -7347,6 +7349,12 @@ void WasmBinaryBuilder::visitRefAs(RefAs* curr, uint8_t code) {
     case BinaryConsts::RefAsI31:
       curr->op = RefAsI31;
       break;
+    case BinaryConsts::ExternInternalize:
+      curr->op = ExternInternalize;
+      break;
+    case BinaryConsts::ExternExternalize:
+      curr->op = ExternExternalize;
+      break;
     default:
       WASM_UNREACHABLE("invalid code for ref.as_*");
   }
@@ -7356,6 +7364,7 @@ void WasmBinaryBuilder::visitRefAs(RefAs* curr, uint8_t code) {
   }
   curr->finalize();
 }
+
 void WasmBinaryBuilder::throwError(std::string text) {
   throw ParseException(text, 0, pos);
 }
diff --git a/src/wasm/wasm-stack.cpp b/src/wasm/wasm-stack.cpp
index 13bd09927..fddb7e41c 100644
--- a/src/wasm/wasm-stack.cpp
+++ b/src/wasm/wasm-stack.cpp
@@ -2170,6 +2170,14 @@ void BinaryInstWriter::visitRefAs(RefAs* curr) {
     case RefAsI31:
       o << int8_t(BinaryConsts::GCPrefix) << U32LEB(BinaryConsts::RefAsI31);
       break;
+    case ExternInternalize:
+      o << int8_t(BinaryConsts::GCPrefix)
+        << U32LEB(BinaryConsts::ExternInternalize);
+      break;
+    case ExternExternalize:
+      o << int8_t(BinaryConsts::GCPrefix)
+        << U32LEB(BinaryConsts::ExternExternalize);
+      break;
     default:
       WASM_UNREACHABLE("invalid ref.as_*");
   }
diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index 532529d2a..75cbcf53a 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -424,6 +424,7 @@ public:
   void visitMemoryGrow(MemoryGrow* curr);
   void visitRefNull(RefNull* curr);
   void visitRefIs(RefIs* curr);
+  void visitRefAs(RefAs* curr);
   void visitRefFunc(RefFunc* curr);
   void visitRefEq(RefEq* curr);
   void visitTableGet(TableGet* curr);
@@ -2125,6 +2126,40 @@ void FunctionValidator::visitRefIs(RefIs* curr) {
                "ref.is_*'s argument should be a reference type");
 }
 
+void FunctionValidator::visitRefAs(RefAs* curr) {
+  switch (curr->op) {
+    default:
+      // TODO: validate all the other ref.as_*
+      break;
+    case ExternInternalize: {
+      shouldBeTrue(getModule()->features.hasGC(),
+                   curr,
+                   "extern.internalize requries GC to be enabled");
+      if (curr->type == Type::unreachable) {
+        return;
+      }
+      shouldBeSubType(curr->value->type,
+                      Type(HeapType::ext, Nullable),
+                      curr->value,
+                      "extern.internalize value should be an externref");
+      break;
+    }
+    case ExternExternalize: {
+      shouldBeTrue(getModule()->features.hasGC(),
+                   curr,
+                   "extern.externalize requries GC to be enabled");
+      if (curr->type == Type::unreachable) {
+        return;
+      }
+      shouldBeSubType(curr->value->type,
+                      Type(HeapType::any, Nullable),
+                      curr->value,
+                      "extern.externalize value should be an anyref");
+      break;
+    }
+  }
+}
+
 void FunctionValidator::visitRefFunc(RefFunc* curr) {
   // If we are not in a function, this is a global location like a table. We
   // allow RefFunc there as we represent tables that way regardless of what
diff --git a/src/wasm/wasm.cpp b/src/wasm/wasm.cpp
index 8226e9079..56db8d7a9 100644
--- a/src/wasm/wasm.cpp
+++ b/src/wasm/wasm.cpp
@@ -1122,6 +1122,12 @@ void RefAs::finalize() {
     case RefAsI31:
       type = Type(HeapType::i31, NonNullable);
       break;
+    case ExternInternalize:
+      type = Type(HeapType::any, value->type.getNullability());
+      break;
+    case ExternExternalize:
+      type = Type(HeapType::ext, value->type.getNullability());
+      break;
     default:
       WASM_UNREACHABLE("invalid ref.as_*");
   }
diff --git a/test/lit/extern-conversions.wast b/test/lit/extern-conversions.wast
new file mode 100644
index 000000000..403b558f6
--- /dev/null
+++ b/test/lit/extern-conversions.wast
@@ -0,0 +1,33 @@
+;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.
+
+;; Check that extern conversion instructions are emitted properly in the binary format.
+
+;; RUN: wasm-opt %s -all --roundtrip -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (type $ref|any|_=>_ref|extern| (func (param (ref any)) (result (ref extern))))
+
+ ;; CHECK:      (type $externref_=>_anyref (func (param externref) (result anyref)))
+
+ ;; CHECK:      (func $extern.externalize (param $x (ref any)) (result (ref extern))
+ ;; CHECK-NEXT:  (extern.externalize
+ ;; CHECK-NEXT:   (local.get $x)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $extern.externalize (param $x (ref any)) (result (ref extern))
+  (extern.externalize
+   (local.get $x)
+  )
+ )
+
+ ;; CHECK:      (func $extern.internalize (param $x externref) (result anyref)
+ ;; CHECK-NEXT:  (extern.internalize
+ ;; CHECK-NEXT:   (local.get $x)
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $extern.internalize (param $x (ref null extern)) (result (ref null any))
+  (extern.internalize
+   (local.get $x)
+  )
+ )
+)