[wasm-gc] Support immutable arrays

Since we introduced `array.init` as a way to create fully initialized
arrays, immutable arrays are no longer useless, and they enable certain
static optimizations, so this patch allows them.

Bug: v8:7748
Change-Id: I404aab60099826f4bd83cf54e5e1acbc38a3ca9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3221151
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77397}

src/wasm/module-decoder.cc

@@ -1926,9 +1926,6 @@ class ModuleDecoderImpl : public Decoder {
     ValueType field = consume_storage_type();
     if (failed()) return nullptr;
     bool mutability = consume_mutability();
-    if (!V8_LIKELY(mutability)) {
-      error(this->pc() - 1, "immutable arrays are not supported yet");
-    }
     return zone->New<ArrayType>(field, mutability);
   }
 

test/cctest/wasm/test-gc.cc

@@ -918,6 +918,7 @@ WASM_COMPILED_EXEC_TEST(WasmBasicArray) {
 
   const byte type_index = tester.DefineArray(wasm::kWasmI32, true);
   const byte fp_type_index = tester.DefineArray(wasm::kWasmF64, true);
+  const byte immut_type_index = tester.DefineArray(wasm::kWasmI32, false);
   ValueType kRefTypes[] = {ref(type_index)};
   FunctionSig sig_q_v(1, 0, kRefTypes);
   ValueType kOptRefType = optref(type_index);
@@ -961,6 +962,15 @@ WASM_COMPILED_EXEC_TEST(WasmBasicArray) {
                        WASM_I32V(30), WASM_RTT_CANON(type_index)),
        kExprEnd});
 
+  const byte kImmutable = tester.DefineFunction(
+      tester.sigs.i_v(), {},
+      {WASM_ARRAY_GET(
+           immut_type_index,
+           WASM_ARRAY_INIT(immut_type_index, 2, WASM_I32V(42), WASM_I32V(43),
+                           WASM_RTT_CANON(immut_type_index)),
+           WASM_I32V(0)),
+       kExprEnd});
+
   const uint32_t kLongLength = 1u << 16;
   const byte kAllocateLarge = tester.DefineFunction(
       &sig_q_v, {},
@@ -998,6 +1008,7 @@ WASM_COMPILED_EXEC_TEST(WasmBasicArray) {
   tester.CheckHasThrown(kGetElem, 3);
   tester.CheckHasThrown(kGetElem, -1);
   tester.CheckResult(kGetLength, 42);
+  tester.CheckResult(kImmutable, 42);
   tester.CheckResult(kTestFpArray, static_cast<int32_t>(result_value));
 
   Handle<Object> h_result = tester.GetResultObject(kAllocate).ToHandleChecked();

test/mjsunit/wasm/wasm-module-builder.js

@@ -1291,7 +1291,6 @@ class WasmStructSubtype extends WasmStruct {
 class WasmArray {
   constructor(type, mutability) {
     this.type = type;
-    if (!mutability) throw new Error("Immutable arrays are not supported yet");
     this.mutability = mutability;
     this.type_form = kWasmArrayTypeForm;
   }

test/unittests/wasm/function-body-decoder-unittest.cc

@@ -4131,13 +4131,17 @@ TEST_F(FunctionBodyDecoderTest, GCArray) {
 
   byte array_type_index = builder.AddArray(kWasmFuncRef, true);
   byte struct_type_index = builder.AddStruct({F(kWasmI32, false)});
+  byte immutable_array_type_index = builder.AddArray(kWasmI32, false);
 
   ValueType array_type = ValueType::Ref(array_type_index, kNonNullable);
+  ValueType immutable_array_type =
+      ValueType::Ref(immutable_array_type_index, kNonNullable);
   ValueType reps_c_r[] = {kWasmFuncRef, array_type};
   ValueType reps_f_r[] = {kWasmF32, array_type};
   ValueType reps_i_r[] = {kWasmI32, array_type};
   const FunctionSig sig_c_r(1, 1, reps_c_r);
   const FunctionSig sig_v_r(0, 1, &array_type);
+  const FunctionSig sig_v_r2(0, 1, &immutable_array_type);
   const FunctionSig sig_r_v(1, 0, &array_type);
   const FunctionSig sig_f_r(1, 1, reps_f_r);
   const FunctionSig sig_v_cr(0, 2, reps_c_r);
@@ -4260,6 +4264,21 @@ TEST_F(FunctionBodyDecoderTest, GCArray) {
   ExpectFailure(&sig_i_r,
                 {WASM_ARRAY_LEN(struct_type_index, WASM_LOCAL_GET(0))},
                 kAppendEnd, "invalid array index: 1");
+
+  // Immutable array.
+  // Allocating and reading is OK:
+  ExpectValidates(
+      sigs.i_v(),
+      {WASM_ARRAY_GET(
+          immutable_array_type_index,
+          WASM_ARRAY_INIT(immutable_array_type_index, 1, WASM_I32V(42),
+                          WASM_RTT_CANON(immutable_array_type_index)),
+          WASM_I32V(0))});
+  // Writing fails:
+  ExpectFailure(&sig_v_r2,
+                {WASM_ARRAY_SET(immutable_array_type_index, WASM_LOCAL_GET(0),
+                                WASM_I32V(0), WASM_I32V(42))},
+                kAppendEnd, "array.set: immediate array type 2 is immutable");
 }
 
 TEST_F(FunctionBodyDecoderTest, PackedFields) {

test/unittests/wasm/module-decoder-unittest.cc

@@ -1118,6 +1118,7 @@ TEST_F(WasmModuleVerifyTest, ArrayInitInitExpr) {
               WASM_INIT_EXPR_ARRAY_INIT(0, 3, WASM_I32V(10), WASM_I32V(20),
                                         WASM_I32V(30), WASM_RTT_CANON(0)))};
   EXPECT_VERIFIES(basic);
+
   static const byte basic_nominal[] = {
       SECTION(Type, ENTRY_COUNT(1), WASM_ARRAY_DEF(kI16Code, true)),
       SECTION(Global, ENTRY_COUNT(1),  // --
@@ -1126,6 +1127,14 @@ TEST_F(WasmModuleVerifyTest, ArrayInitInitExpr) {
                                                WASM_I32V(20), WASM_I32V(30)))};
   EXPECT_VERIFIES(basic_nominal);
 
+  static const byte basic_immutable[] = {
+      SECTION(Type, ENTRY_COUNT(1), WASM_ARRAY_DEF(kI32Code, false)),
+      SECTION(Global, ENTRY_COUNT(1),  // --
+              kRefCode, 0, 0,          // type, mutability
+              WASM_INIT_EXPR_ARRAY_INIT(0, 3, WASM_I32V(10), WASM_I32V(20),
+                                        WASM_I32V(30), WASM_RTT_CANON(0)))};
+  EXPECT_VERIFIES(basic_immutable);
+
   static const byte type_error[] = {
       SECTION(Type, ENTRY_COUNT(2),  // --
               WASM_ARRAY_DEF(kI32Code, true),
@@ -1421,14 +1430,12 @@ TEST_F(WasmModuleVerifyTest, InvalidArrayTypeDef) {
               2)};                   // invalid mutability value
   EXPECT_FAILURE_WITH_MSG(invalid_mutability, "invalid mutability");
 
-  static const byte invalid_mutability2[] = {
-      SECTION(Type,
+  static const byte immutable[] = {SECTION(Type,
                                            ENTRY_COUNT(1),      // --
                                            kWasmArrayTypeCode,  // --
                                            kI32Code,            // field type
-              0)};                 // immmutability (disallowed in MVP)
-  EXPECT_FAILURE_WITH_MSG(invalid_mutability2,
-                          "immutable arrays are not supported");
+                                           0)};                 // immmutability
+  EXPECT_VERIFIES(immutable);
 }
 
 TEST_F(WasmModuleVerifyTest, ZeroExceptions) {