[WebAssembly] Add support for externalref to MC and wasm-ld

This allows code for handling externref values to be processed by the
assembler and linker.

Differential Revision: https://reviews.llvm.org/D81977

lld/test/wasm/externref.s

@@ -0,0 +1,44 @@
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -o %t.o %s
+# RUN: wasm-ld %t.o -o %t.wasm
+# RUN: obj2yaml %t.wasm | FileCheck %s
+
+# Tests use of externref type, including storing it in a global
+
+.globaltype my_global, externref
+
+.globl read_externref
+read_externref:
+  .functype read_externref () -> (externref)
+  global.get my_global
+  end_function
+
+.globl write_externref
+write_externref:
+  .functype write_externref (externref) -> ()
+  local.get 0
+  global.set my_global
+  end_function
+
+my_global:
+
+.globl _start
+_start:
+  .functype _start () -> ()
+  call read_externref
+  call write_externref
+  end_function
+
+#      CHECK:  - Type:            GLOBAL
+# CHECK-NEXT:    Globals:
+# CHECK-NEXT:      - Index:           0
+# CHECK-NEXT:        Type:            I32
+# CHECK-NEXT:        Mutable:         true
+# CHECK-NEXT:        InitExpr:
+# CHECK-NEXT:          Opcode:          I32_CONST
+# CHECK-NEXT:          Value:           66560
+# CHECK-NEXT:      - Index:           1
+# CHECK-NEXT:        Type:            EXTERNREF
+# CHECK-NEXT:        Mutable:         true
+# CHECK-NEXT:        InitExpr:
+# CHECK-NEXT:          Opcode:          REF_NULL
+# CHECK-NEXT:          Type:            EXTERNREF

lld/wasm/WriterUtils.cpp

@@ -32,6 +32,8 @@ std::string toString(ValType type) {
     return "v128";
   case ValType::EXNREF:
     return "exnref";
+  case ValType::EXTERNREF:
+    return "externref";
   }
   llvm_unreachable("Invalid wasm::ValType");
 }
@@ -155,6 +157,9 @@ void writeInitExpr(raw_ostream &os, const WasmInitExpr &initExpr) {
   case WASM_OPCODE_GLOBAL_GET:
     writeUleb128(os, initExpr.Value.Global, "literal (global index)");
     break;
+  case WASM_OPCODE_REF_NULL:
+    writeValueType(os, ValType::EXTERNREF, "literal (externref type)");
+    break;
   default:
     fatal("unknown opcode in init expr: " + Twine(initExpr.Opcode));
   }

llvm/include/llvm/BinaryFormat/Wasm.h

@@ -232,6 +232,7 @@ enum : unsigned {
   WASM_TYPE_V128 = 0x7B,
   WASM_TYPE_FUNCREF = 0x70,
   WASM_TYPE_EXNREF = 0x68,
+  WASM_TYPE_EXTERNREF = 0x6F,
   WASM_TYPE_FUNC = 0x60,
   WASM_TYPE_NORESULT = 0x40, // for blocks with no result values
 };
@@ -258,6 +259,7 @@ enum : unsigned {
   WASM_OPCODE_F32_CONST = 0x43,
   WASM_OPCODE_F64_CONST = 0x44,
   WASM_OPCODE_I32_ADD = 0x6a,
+  WASM_OPCODE_REF_NULL = 0xd0,
 };
 
 // Opcodes used in synthetic functions.
@@ -355,6 +357,7 @@ enum class ValType {
   F64 = WASM_TYPE_F64,
   V128 = WASM_TYPE_V128,
   EXNREF = WASM_TYPE_EXNREF,
+  EXTERNREF = WASM_TYPE_EXTERNREF,
 };
 
 struct WasmSignature {

llvm/lib/MC/WasmObjectWriter.cpp

@@ -833,6 +833,9 @@ void WasmObjectWriter::writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals) {
     case wasm::WASM_TYPE_F64:
       writeI64(0);
       break;
+    case wasm::WASM_TYPE_EXTERNREF:
+      writeValueType(wasm::ValType::EXTERNREF);
+      break;
     default:
       llvm_unreachable("unexpected type");
     }
@@ -1462,6 +1465,9 @@ uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
         case wasm::WASM_TYPE_F64:
           Global.InitExpr.Opcode = wasm::WASM_OPCODE_F64_CONST;
           break;
+        case wasm::WASM_TYPE_EXTERNREF:
+          Global.InitExpr.Opcode = wasm::WASM_OPCODE_REF_NULL;
+          break;
         default:
           llvm_unreachable("unexpected type");
         }

llvm/lib/Object/WasmObjectFile.cpp

@@ -184,6 +184,14 @@ static Error readInitExpr(wasm::WasmInitExpr &Expr,
   case wasm::WASM_OPCODE_GLOBAL_GET:
     Expr.Value.Global = readULEB128(Ctx);
     break;
+  case wasm::WASM_OPCODE_REF_NULL: {
+    wasm::ValType Ty = static_cast<wasm::ValType>(readULEB128(Ctx));
+    if (Ty != wasm::ValType::EXTERNREF) {
+      return make_error<GenericBinaryError>("Invalid type for ref.null",
+                                            object_error::parse_failed);
+    }
+    break;
+  }
   default:
     return make_error<GenericBinaryError>("Invalid opcode in init_expr",
                                           object_error::parse_failed);

llvm/lib/ObjectYAML/WasmYAML.cpp

@@ -433,6 +433,11 @@ void MappingTraits<wasm::WasmInitExpr>::mapping(IO &IO,
   case wasm::WASM_OPCODE_GLOBAL_GET:
     IO.mapRequired("Index", Expr.Value.Global);
     break;
+  case wasm::WASM_OPCODE_REF_NULL: {
+    WasmYAML::ValueType Ty = wasm::WASM_TYPE_EXTERNREF;
+    IO.mapRequired("Type", Ty);
+    break;
+  }
   }
 }
 
@@ -559,6 +564,8 @@ void ScalarEnumerationTraits<WasmYAML::ValueType>::enumeration(
   ECase(F64);
   ECase(V128);
   ECase(FUNCREF);
+  ECase(EXNREF);
+  ECase(EXTERNREF);
   ECase(FUNC);
 #undef ECase
 }
@@ -583,6 +590,7 @@ void ScalarEnumerationTraits<WasmYAML::Opcode>::enumeration(
   ECase(F64_CONST);
   ECase(F32_CONST);
   ECase(GLOBAL_GET);
+  ECase(REF_NULL);
 #undef ECase
 }
 

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

@@ -322,6 +322,8 @@ public:
       return wasm::ValType::V128;
     if (Type == "exnref")
       return wasm::ValType::EXNREF;
+    if (Type == "externref")
+      return wasm::ValType::EXTERNREF;
     return Optional<wasm::ValType>();
   }
 

llvm/test/MC/WebAssembly/externref.s

@@ -0,0 +1,36 @@
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj < %s | obj2yaml | FileCheck %s
+
+# Tests use of externref type, including storing it in a global
+
+.globaltype my_global, externref
+
+.globl read_externref
+read_externref:
+  .functype read_externref () -> (externref)
+  global.get my_global
+  end_function
+
+.globl write_externref
+write_externref:
+  .functype write_externref (externref) -> ()
+  local.get 0
+  global.set my_global
+  end_function
+
+.globl call_with_ref
+call_with_ref:
+  .functype call_with_ref () -> ()
+  call read_externref
+  call write_externref
+  end_function
+
+my_global:
+
+#      CHECK:  - Type:            GLOBAL
+# CHECK-NEXT:    Globals:
+# CHECK-NEXT:      - Index:           0
+# CHECK-NEXT:        Type:            EXTERNREF
+# CHECK-NEXT:        Mutable:         true
+# CHECK-NEXT:        InitExpr:
+# CHECK-NEXT:          Opcode:          REF_NULL
+# CHECK-NEXT:          Type:            EXTERNREF