[stringrefs] Implement stringview_iter.slice

Feature complete!

Bug: v8:12868
Change-Id: I7727071bdd062a6dae26206a65080f675ef7ee93
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3758226
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andy Wingo <wingo@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81694}

src/builtins/wasm.tq

@@ -1133,4 +1133,25 @@ builtin WasmStringViewIterRewind(
   view.offset = offset;
   return rewound;
 }
+builtin WasmStringViewIterSlice(
+    view: WasmStringViewIter, codepoints: uint32): String {
+  const string = view.string;
+  const start = view.offset;
+  let end = view.offset;
+  let advanced: uint32 = 0;
+  while (advanced < codepoints) {
+    if (end == Unsigned(string.length)) break;
+    advanced = advanced + 1;
+    if (end + 1 < Unsigned(string.length) &&
+        IsLeadSurrogate(StringCharCodeAt(string, Convert<uintptr>(end))) &&
+        IsTrailSurrogate(StringCharCodeAt(string, Convert<uintptr>(end + 1)))) {
+      end = end + 2;
+    } else {
+      end = end + 1;
+    }
+  }
+  return (start == end) ?
+      kEmptyString :
+      string::SubString(string, Convert<uintptr>(start), Convert<uintptr>(end));
+}
 }

src/compiler/wasm-compiler.cc

@@ -6007,6 +6007,15 @@ Node* WasmGraphBuilder::StringViewIterRewind(Node* view,
                             Operator::kNoDeopt, view, codepoints);
 }
 
+Node* WasmGraphBuilder::StringViewIterSlice(Node* view, CheckForNull null_check,
+                                            Node* codepoints,
+                                            wasm::WasmCodePosition position) {
+  if (null_check == kWithNullCheck) view = AssertNotNull(view, position);
+
+  return gasm_->CallBuiltin(Builtin::kWasmStringViewIterSlice,
+                            Operator::kNoDeopt, view, codepoints);
+}
+
 // 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

@@ -596,6 +596,8 @@ class WasmGraphBuilder {
                               wasm::WasmCodePosition position);
   Node* StringViewIterRewind(Node* view, CheckForNull null_check,
                              Node* codepoints, wasm::WasmCodePosition position);
+  Node* StringViewIterSlice(Node* view, CheckForNull null_check,
+                            Node* codepoints, wasm::WasmCodePosition position);
   Node* IsNull(Node* object);
   Node* TypeGuard(Node* value, wasm::ValueType type);
 

src/wasm/baseline/liftoff-compiler.cc

@@ -6918,7 +6918,27 @@ class LiftoffCompiler {
 
   void StringViewIterSlice(FullDecoder* decoder, const Value& view,
                            const Value& codepoints, Value* result) {
-    UNIMPLEMENTED();
+    LiftoffRegList pinned;
+
+    LiftoffAssembler::VarState& codepoints_var =
+        __ cache_state()->stack_state.end()[-1];
+
+    LiftoffRegister view_reg = pinned.set(
+        __ LoadToRegister(__ cache_state()->stack_state.end()[-2], pinned));
+    MaybeEmitNullCheck(decoder, view_reg.gp(), pinned, view.type);
+    LiftoffAssembler::VarState view_var(kRef, view_reg, 0);
+
+    CallRuntimeStub(WasmCode::kWasmStringViewIterSlice,
+                    MakeSig::Returns(kRef).Params(kRef, kI32),
+                    {
+                        view_var,
+                        codepoints_var,
+                    },
+                    decoder->position());
+    RegisterDebugSideTableEntry(decoder, DebugSideTableBuilder::kDidSpill);
+
+    LiftoffRegister result_reg(kReturnRegister0);
+    __ PushRegister(kRef, result_reg);
   }
 
   void Forward(FullDecoder* decoder, const Value& from, Value* to) {

src/wasm/graph-builder-interface.cc

@@ -1575,7 +1575,9 @@ class WasmGraphBuildingInterface {
 
   void StringViewIterSlice(FullDecoder* decoder, const Value& view,
                            const Value& codepoints, Value* result) {
-    UNIMPLEMENTED();
+    SetAndTypeNode(result, builder_->StringViewIterSlice(
+                               view.node, NullCheckFor(view.type),
+                               codepoints.node, decoder->position()));
   }
 
   void Forward(FullDecoder* decoder, const Value& from, Value* to) {

src/wasm/wasm-code-manager.h

@@ -147,7 +147,8 @@ struct WasmModule;
   V(WasmStringAsIter)                    \
   V(WasmStringViewIterNext)              \
   V(WasmStringViewIterAdvance)           \
-  V(WasmStringViewIterRewind)
+  V(WasmStringViewIterRewind)            \
+  V(WasmStringViewIterSlice)
 
 // 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

@@ -17,6 +17,7 @@ let kSig_i_wiii = makeSig([kWasmStringRef, kWasmI32, kWasmI32, kWasmI32],
 let kSig_ii_wiii = makeSig([kWasmStringRef, kWasmI32, kWasmI32, kWasmI32],
                            [kWasmI32, kWasmI32]);
 let kSig_v_w = makeSig([kWasmStringRef], []);
+let kSig_w_i = makeSig([kWasmI32], [kWasmStringRef]);
 let kSig_w_wii = makeSig([kWasmStringRef, kWasmI32, kWasmI32],
                          [kWasmStringRef]);
 let kSig_w_ww = makeSig([kWasmStringRef, kWasmStringRef], [kWasmStringRef]);
@@ -1101,6 +1102,22 @@ function makeWtf16TestDataSegment() {
       kGCPrefix, kExprStringViewIterRewind
     ]);
 
+  builder.addFunction("slice", kSig_w_i)
+    .exportFunc()
+    .addBody([
+      kExprGlobalGet, global.index,
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringViewIterSlice
+    ]);
+
+  builder.addFunction("slice_null", kSig_w_i)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringViewIterCode,
+      kExprI32Const, 0,
+      kGCPrefix, kExprStringViewIterSlice
+    ]);
+
   let instance = builder.instantiate();
 
   for (let str of interestingStrings) {
@@ -1131,6 +1148,22 @@ function makeWtf16TestDataSegment() {
     assertEquals(0, instance.exports.rewind(-1));
     assertEquals(codepoints.length, instance.exports.advance(-1));
     assertEquals(0, instance.exports.advance(-1));
+
+    for (let start = 0; start <= codepoints.length; start++) {
+      for (let end = start; end <= codepoints.length; end++) {
+        let expected_slice =
+            String.fromCodePoint(...codepoints.slice(start, end));
+        instance.exports.iterate(str);
+        assertEquals(start, instance.exports.advance(start));
+        assertEquals(expected_slice, instance.exports.slice(end - start));
+      }
+    }
+    instance.exports.iterate(str);
+    assertEquals(str, instance.exports.slice(codepoints.length));
+    assertEquals(str, instance.exports.slice(-1));
+    assertEquals("", instance.exports.slice(0));
+    assertEquals(codepoints.length, instance.exports.advance(-1));
+    assertEquals("", instance.exports.slice(-1));
   }
 
   assertThrows(() => instance.exports.iterate_null(),
@@ -1141,4 +1174,6 @@ function makeWtf16TestDataSegment() {
                WebAssembly.RuntimeError, "dereferencing a null pointer");
   assertThrows(() => instance.exports.rewind_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
+  assertThrows(() => instance.exports.slice_null(),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();