[stringrefs] Implement string.measure_wtf16

Bug: v8:12868
Change-Id: I717326b27ce783710ffd141370648dde7e0d74a1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695561
Commit-Queue: Andy Wingo <wingo@igalia.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81035}

src/compiler/wasm-compiler.cc

@@ -5775,6 +5775,17 @@ Node* WasmGraphBuilder::StringMeasureWtf8(Node* string, CheckForNull null_check,
                             string);
 }
 
+Node* WasmGraphBuilder::StringMeasureWtf16(Node* string,
+                                           CheckForNull null_check,
+                                           wasm::WasmCodePosition position) {
+  if (null_check == kWithNullCheck) {
+    string = AssertNotNull(string, position);
+  }
+  return gasm_->LoadImmutableFromObject(
+      MachineType::Int32(), string,
+      wasm::ObjectAccess::ToTagged(String::kLengthOffset));
+}
+
 // 1 bit V8 Smi tag, 31 bits V8 Smi shift, 1 bit i31ref high-bit truncation.
 constexpr int kI31To32BitSmiShift = 33;
 

src/compiler/wasm-compiler.h

@@ -545,6 +545,8 @@ class WasmGraphBuilder {
                           wasm::WasmCodePosition position);
   Node* StringMeasureWtf8(Node* string, CheckForNull null_check,
                           wasm::WasmCodePosition position);
+  Node* StringMeasureWtf16(Node* string, CheckForNull null_check,
+                           wasm::WasmCodePosition position);
   Node* IsNull(Node* object);
   Node* TypeGuard(Node* value, wasm::ValueType type);
 

src/compiler/wasm-typer.cc

@@ -212,6 +212,10 @@ 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)) {
+        return NoChange();
+      }
       uint32_t ref_index = object_type.type.ref_index();
       DCHECK(object_type.module->has_type(ref_index));
       wasm::TypeDefinition type_def = object_type.module->types[ref_index];

src/wasm/baseline/liftoff-compiler.cc

@@ -6120,7 +6120,14 @@ class LiftoffCompiler {
 
   void StringMeasureWtf16(FullDecoder* decoder, const Value& str,
                           Value* result) {
-    UNIMPLEMENTED();
+    LiftoffRegList pinned;
+    LiftoffRegister string_reg = pinned.set(__ PopToRegister(pinned));
+    MaybeEmitNullCheck(decoder, string_reg.gp(), pinned, str.type);
+    LiftoffRegister value = __ GetUnusedRegister(kGpReg, pinned);
+    LoadObjectField(value, string_reg.gp(), no_reg,
+                    wasm::ObjectAccess::ToTagged(String::kLengthOffset),
+                    ValueKind::kI32, false /* is_signed */, pinned);
+    __ PushRegister(kI32, value);
   }
 
   void StringEncodeWtf8(FullDecoder* decoder,

src/wasm/graph-builder-interface.cc

@@ -1425,7 +1425,8 @@ class WasmGraphBuildingInterface {
 
   void StringMeasureWtf16(FullDecoder* decoder, const Value& str,
                           Value* result) {
-    UNIMPLEMENTED();
+    result->node = builder_->StringMeasureWtf16(
+        str.node, NullCheckFor(str.type), decoder->position());
   }
 
   void StringEncodeWtf8(FullDecoder* decoder,

test/mjsunit/wasm/stringrefs-exec.js

@@ -215,3 +215,29 @@ function makeWtf16TestDataSegment() {
   assertThrows(() => instance.exports.string_measure_wtf8_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();
+
+(function TestStringMeasureWtf16() {
+  let builder = new WasmModuleBuilder();
+
+  builder.addFunction("string_measure_wtf16", kSig_i_w)
+    .exportFunc()
+    .addBody([
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringMeasureWtf16
+    ]);
+
+  builder.addFunction("string_measure_wtf16_null", kSig_i_v)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringRefCode,
+      kGCPrefix, kExprStringMeasureWtf16
+    ]);
+
+  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");
+})();