[stringrefs] Implement stringview_wtf16.slice

Bug: v8:12868
Change-Id: Ib92cbf7eae8e4b7bc76bc918011be747254d931f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3700075
Commit-Queue: Andy Wingo <wingo@igalia.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81087}

src/builtins/wasm.tq

@@ -823,4 +823,12 @@ transitioning builtin WasmStringViewWtf16GetCodeUnit(
     unreachable;
   }
 }
+transitioning builtin WasmStringViewWtf16Slice(
+    string: String, start: uint32, end: uint32): String {
+  const length = Unsigned(string.length);
+  if (start >= length) return kEmptyString;
+  if (end < start) return kEmptyString;
+  const clampedEnd = Convert<uintptr>(end < length ? end + 1 : length);
+  return string::SubString(string, Convert<uintptr>(start), clampedEnd);
+}
 }

src/compiler/wasm-compiler.cc

@@ -5796,6 +5796,17 @@ Node* WasmGraphBuilder::StringViewWtf16GetCodeUnit(
                             Operator::kNoDeopt, string, offset);
 }
 
+Node* WasmGraphBuilder::StringViewWtf16Slice(Node* string,
+                                             CheckForNull null_check,
+                                             Node* start, Node* end,
+                                             wasm::WasmCodePosition position) {
+  if (null_check == kWithNullCheck) {
+    string = AssertNotNull(string, position);
+  }
+  return gasm_->CallBuiltin(Builtin::kWasmStringViewWtf16Slice,
+                            Operator::kNoDeopt, string, start, end);
+}
+
 // 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

@@ -550,6 +550,8 @@ class WasmGraphBuilder {
   Node* StringViewWtf16GetCodeUnit(Node* string, CheckForNull null_check,
                                    Node* offset,
                                    wasm::WasmCodePosition position);
+  Node* StringViewWtf16Slice(Node* string, CheckForNull null_check, Node* start,
+                             Node* end, wasm::WasmCodePosition position);
   Node* IsNull(Node* object);
   Node* TypeGuard(Node* value, wasm::ValueType type);
 

src/wasm/baseline/liftoff-compiler.cc

@@ -6208,7 +6208,27 @@ class LiftoffCompiler {
   void StringViewWtf16Slice(FullDecoder* decoder, const Value& view,
                             const Value& start, const Value& end,
                             Value* result) {
-    UNIMPLEMENTED();
+    LiftoffRegList pinned;
+    LiftoffRegister end_reg = pinned.set(__ PopToRegister(pinned));
+    LiftoffRegister start_reg = pinned.set(__ PopToRegister(pinned));
+    LiftoffRegister view_reg = pinned.set(__ PopToRegister(pinned));
+    MaybeEmitNullCheck(decoder, view_reg.gp(), pinned, view.type);
+    LiftoffAssembler::VarState view_var(kRef, view_reg, 0);
+    LiftoffAssembler::VarState start_var(kI32, start_reg, 0);
+    LiftoffAssembler::VarState end_var(kI32, end_reg, 0);
+
+    CallRuntimeStub(WasmCode::kWasmStringViewWtf16Slice,
+                    MakeSig::Returns(kRef).Params(kRef, kI32, kI32),
+                    {
+                        view_var,
+                        start_var,
+                        end_var,
+                    },
+                    decoder->position());
+    RegisterDebugSideTableEntry(decoder, DebugSideTableBuilder::kDidSpill);
+
+    LiftoffRegister result_reg(kReturnRegister0);
+    __ PushRegister(kRef, result_reg);
   }
 
   void StringAsIter(FullDecoder* decoder, const Value& str, Value* result) {

src/wasm/graph-builder-interface.cc

@@ -1493,7 +1493,9 @@ class WasmGraphBuildingInterface {
   void StringViewWtf16Slice(FullDecoder* decoder, const Value& view,
                             const Value& start, const Value& end,
                             Value* result) {
-    UNIMPLEMENTED();
+    result->node = builder_->StringViewWtf16Slice(
+        view.node, NullCheckFor(view.type), start.node, end.node,
+        decoder->position());
   }
 
   void StringAsIter(FullDecoder* decoder, const Value& str, Value* result) {

src/wasm/wasm-code-manager.h

@@ -128,7 +128,8 @@ struct WasmModule;
   V(WasmStringConst)                     \
   V(WasmStringMeasureUtf8)               \
   V(WasmStringMeasureWtf8)               \
-  V(WasmStringViewWtf16GetCodeUnit)
+  V(WasmStringViewWtf16GetCodeUnit)      \
+  V(WasmStringViewWtf16Slice)
 
 // Sorted, disjoint and non-overlapping memory regions. A region is of the
 // form [start, end). So there's no [start, end), [end, other_end),

test/mjsunit/wasm/stringrefs-exec.js

@@ -10,6 +10,8 @@ let kSig_w_ii = makeSig([kWasmI32, kWasmI32], [kWasmStringRef]);
 let kSig_w_v = makeSig([], [kWasmStringRef]);
 let kSig_i_w = makeSig([kWasmStringRef], [kWasmI32]);
 let kSig_i_wi = makeSig([kWasmStringRef, kWasmI32], [kWasmI32]);
+let kSig_w_wii = makeSig([kWasmStringRef, kWasmI32, kWasmI32],
+                         [kWasmStringRef]);
 
 function encodeWtf8(str) {
   // String iterator coalesces surrogate pairs.
@@ -278,6 +280,25 @@ function makeWtf16TestDataSegment() {
       kGCPrefix, kExprStringViewWtf16GetCodeunit
     ]);
 
+  builder.addFunction("string_view_wtf16_slice", kSig_w_wii)
+    .exportFunc()
+    .addBody([
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringAsWtf16,
+      kExprLocalGet, 1,
+      kExprLocalGet, 2,
+      kGCPrefix, kExprStringViewWtf16Slice
+    ]);
+
+  builder.addFunction("string_view_wtf16_slice_null", kSig_w_v)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringViewWtf16Code,
+      kExprI32Const, 0,
+      kExprI32Const, 0,
+      kGCPrefix, kExprStringViewWtf16Slice
+    ]);
+
   let instance = builder.instantiate();
   for (let str of interestingStrings) {
     assertEquals(str.length, instance.exports.string_view_wtf16_length(str));
@@ -285,12 +306,22 @@ function makeWtf16TestDataSegment() {
       assertEquals(str.charCodeAt(i),
                    instance.exports.string_view_wtf16_get_codeunit(str, i));
     }
+    assertEquals(str, instance.exports.string_view_wtf16_slice(str, 0, -1));
   }
 
+  assertEquals("f", instance.exports.string_view_wtf16_slice("foo", 0, 0));
+  assertEquals("fo", instance.exports.string_view_wtf16_slice("foo", 0, 1));
+  assertEquals("foo", instance.exports.string_view_wtf16_slice("foo", 0, 2));
+  assertEquals("oo", instance.exports.string_view_wtf16_slice("foo", 1, 2));
+  assertEquals("oo", instance.exports.string_view_wtf16_slice("foo", 1, 100));
+  assertEquals("", instance.exports.string_view_wtf16_slice("foo", 1, 0));
+
   assertThrows(() => instance.exports.string_view_wtf16_length_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
   assertThrows(() => instance.exports.string_view_wtf16_get_codeunit_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
   assertThrows(() => instance.exports.string_view_wtf16_get_codeunit("", 0),
                WebAssembly.RuntimeError, "string offset out of bounds");
+  assertThrows(() => instance.exports.string_view_wtf16_slice_null(),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();