[stringrefs] Implement string.as_wtf16, stringview_wtf16.length

Bug: v8:12868
Change-Id: I19190dc8163de42964fb3911f82e8aeabaf48524
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695585Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andy Wingo <wingo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81046}

src/compiler/wasm-typer.cc

@@ -212,8 +212,12 @@ Reduction WasmTyper::Reduce(Node* node) {
           m.Is(wasm::ObjectAccess::ToTagged(WasmArray::kLengthOffset))) {
         return NoChange();
       }
-      // Do not modify if we are retrieving anything from a string.
-      if (object_type.type.is_reference_to(wasm::HeapType::kString)) {
+      // Do not modify if we are retrieving anything from a string or a view on
+      // a string.
+      if (object_type.type.is_reference_to(wasm::HeapType::kString) ||
+          object_type.type.is_reference_to(wasm::HeapType::kStringViewWtf8) ||
+          object_type.type.is_reference_to(wasm::HeapType::kStringViewWtf16) ||
+          object_type.type.is_reference_to(wasm::HeapType::kStringViewIter)) {
         return NoChange();
       }
       uint32_t ref_index = object_type.type.ref_index();

src/wasm/baseline/liftoff-compiler.cc

@@ -6176,15 +6176,6 @@ class LiftoffCompiler {
     UNIMPLEMENTED();
   }
 
-  void StringAsWtf16(FullDecoder* decoder, const Value& str, Value* result) {
-    UNIMPLEMENTED();
-  }
-
-  void StringViewWtf16Length(FullDecoder* decoder, const Value& view,
-                             Value* result) {
-    UNIMPLEMENTED();
-  }
-
   void StringViewWtf16GetCodeUnit(FullDecoder* decoder, const Value& view,
                                   const Value& pos, Value* result) {
     UNIMPLEMENTED();

src/wasm/function-body-decoder-impl.h

@@ -1153,8 +1153,6 @@ struct ControlBase : public PcForErrors<validate> {
     const Value& bytes, Value* next_pos, Value* bytes_written)                 \
   F(StringViewWtf8Slice, const Value& view, const Value& start,                \
     const Value& end, Value* result)                                           \
-  F(StringAsWtf16, const Value& str, Value* result)                            \
-  F(StringViewWtf16Length, const Value& view, Value* result)                   \
   F(StringViewWtf16GetCodeUnit, const Value& view, const Value& pos,           \
     Value* result)                                                             \
   F(StringViewWtf16Encode, const MemoryIndexImmediate<validate>& memory,       \
@@ -5300,7 +5298,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         NON_CONST_ONLY
         Value str = Peek(0, 0, kWasmStringRef);
         Value result = CreateValue(kWasmStringViewWtf16);
-        CALL_INTERFACE_IF_OK_AND_REACHABLE(StringAsWtf16, str, &result);
+        CALL_INTERFACE_IF_OK_AND_REACHABLE(Forward, str, &result);
         Drop(str);
         Push(result);
         return opcode_length;
@@ -5309,8 +5307,7 @@ class WasmFullDecoder : public WasmDecoder<validate, decoding_mode> {
         NON_CONST_ONLY
         Value view = Peek(0, 0, kWasmStringViewWtf16);
         Value result = CreateValue(kWasmI32);
-        CALL_INTERFACE_IF_OK_AND_REACHABLE(StringViewWtf16Length, view,
-                                           &result);
+        CALL_INTERFACE_IF_OK_AND_REACHABLE(StringMeasureWtf16, view, &result);
         Drop(view);
         Push(result);
         return opcode_length;

src/wasm/graph-builder-interface.cc

@@ -1475,15 +1475,6 @@ class WasmGraphBuildingInterface {
     UNIMPLEMENTED();
   }
 
-  void StringAsWtf16(FullDecoder* decoder, const Value& str, Value* result) {
-    UNIMPLEMENTED();
-  }
-
-  void StringViewWtf16Length(FullDecoder* decoder, const Value& view,
-                             Value* result) {
-    UNIMPLEMENTED();
-  }
-
   void StringViewWtf16GetCodeUnit(FullDecoder* decoder, const Value& view,
                                   const Value& pos, Value* result) {
     UNIMPLEMENTED();

test/mjsunit/wasm/stringrefs-exec.js

@@ -241,3 +241,30 @@ function makeWtf16TestDataSegment() {
   assertThrows(() => instance.exports.string_measure_wtf16_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();
+
+(function TestStringViewWtf16() {
+  let builder = new WasmModuleBuilder();
+
+  builder.addFunction("string_measure_wtf16", kSig_i_w)
+    .exportFunc()
+    .addBody([
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringAsWtf16,
+      kGCPrefix, kExprStringViewWtf16Length
+    ]);
+
+  builder.addFunction("string_measure_wtf16_null", kSig_i_v)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringViewWtf16Code,
+      kGCPrefix, kExprStringViewWtf16Length
+    ]);
+
+  let instance = builder.instantiate();
+  for (let str of interestingStrings) {
+    assertEquals(str.length, instance.exports.string_measure_wtf16(str));
+  }
+
+  assertThrows(() => instance.exports.string_measure_wtf16_null(),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
+})();