[stringrefs] Implement stringview_iter.advance, stringview_iter.rewind

Bug: v8:12868
Change-Id: I2e4a1733876a817dca36e0134ba4b7549f0cf4b8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3757886
Commit-Queue: Andy Wingo <wingo@igalia.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81693}

src/builtins/wasm.tq

@@ -1091,4 +1091,46 @@ builtin WasmStringViewIterNext(view: WasmStringViewIter): int32 {
   view.offset = offset + 1;
   return Signed(Convert<uint32>(code));
 }
+builtin WasmStringViewIterAdvance(
+    view: WasmStringViewIter, codepoints: uint32): uint32 {
+  const string = view.string;
+  let offset = view.offset;
+  let advanced: uint32 = 0;
+  while (advanced < codepoints) {
+    if (offset == Unsigned(string.length)) break;
+    advanced = advanced + 1;
+    if (offset + 1 < Unsigned(string.length) &&
+        IsLeadSurrogate(StringCharCodeAt(string, Convert<uintptr>(offset))) &&
+        IsTrailSurrogate(
+            StringCharCodeAt(string, Convert<uintptr>(offset + 1)))) {
+      offset = offset + 2;
+    } else {
+      offset = offset + 1;
+    }
+  }
+  view.offset = offset;
+  return advanced;
+}
+builtin WasmStringViewIterRewind(
+    view: WasmStringViewIter, codepoints: uint32): uint32 {
+  const string = view.string;
+  let offset = view.offset;
+  let rewound: uint32 = 0;
+  if (string.length == 0) return 0;
+  while (rewound < codepoints) {
+    if (offset == 0) break;
+    rewound = rewound + 1;
+    if (offset >= 2 &&
+        IsTrailSurrogate(
+            StringCharCodeAt(string, Convert<uintptr>(offset - 1))) &&
+        IsLeadSurrogate(
+            StringCharCodeAt(string, Convert<uintptr>(offset - 2)))) {
+      offset = offset - 2;
+    } else {
+      offset = offset - 1;
+    }
+  }
+  view.offset = offset;
+  return rewound;
+}
 }

src/compiler/wasm-compiler.cc

@@ -5987,6 +5987,26 @@ Node* WasmGraphBuilder::StringViewIterNext(Node* view, CheckForNull null_check,
                             Operator::kNoDeopt, view);
 }
 
+Node* WasmGraphBuilder::StringViewIterAdvance(Node* view,
+                                              CheckForNull null_check,
+                                              Node* codepoints,
+                                              wasm::WasmCodePosition position) {
+  if (null_check == kWithNullCheck) view = AssertNotNull(view, position);
+
+  return gasm_->CallBuiltin(Builtin::kWasmStringViewIterAdvance,
+                            Operator::kNoDeopt, view, codepoints);
+}
+
+Node* WasmGraphBuilder::StringViewIterRewind(Node* view,
+                                             CheckForNull null_check,
+                                             Node* codepoints,
+                                             wasm::WasmCodePosition position) {
+  if (null_check == kWithNullCheck) view = AssertNotNull(view, position);
+
+  return gasm_->CallBuiltin(Builtin::kWasmStringViewIterRewind,
+                            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

@@ -591,6 +591,11 @@ class WasmGraphBuilder {
                      wasm::WasmCodePosition position);
   Node* StringViewIterNext(Node* view, CheckForNull null_check,
                            wasm::WasmCodePosition position);
+  Node* StringViewIterAdvance(Node* view, CheckForNull null_check,
+                              Node* codepoints,
+                              wasm::WasmCodePosition position);
+  Node* StringViewIterRewind(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

@@ -6868,12 +6868,52 @@ class LiftoffCompiler {
 
   void StringViewIterAdvance(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::kWasmStringViewIterAdvance,
+                    MakeSig::Returns(kI32).Params(kRef, kI32),
+                    {
+                        view_var,
+                        codepoints_var,
+                    },
+                    decoder->position());
+    RegisterDebugSideTableEntry(decoder, DebugSideTableBuilder::kDidSpill);
+
+    LiftoffRegister result_reg(kReturnRegister0);
+    __ PushRegister(kI32, result_reg);
   }
 
   void StringViewIterRewind(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::kWasmStringViewIterRewind,
+                    MakeSig::Returns(kI32).Params(kRef, kI32),
+                    {
+                        view_var,
+                        codepoints_var,
+                    },
+                    decoder->position());
+    RegisterDebugSideTableEntry(decoder, DebugSideTableBuilder::kDidSpill);
+
+    LiftoffRegister result_reg(kReturnRegister0);
+    __ PushRegister(kI32, result_reg);
   }
 
   void StringViewIterSlice(FullDecoder* decoder, const Value& view,

src/wasm/graph-builder-interface.cc

@@ -1561,12 +1561,16 @@ class WasmGraphBuildingInterface {
 
   void StringViewIterAdvance(FullDecoder* decoder, const Value& view,
                              const Value& codepoints, Value* result) {
-    UNIMPLEMENTED();
+    result->node =
+        builder_->StringViewIterAdvance(view.node, NullCheckFor(view.type),
+                                        codepoints.node, decoder->position());
   }
 
   void StringViewIterRewind(FullDecoder* decoder, const Value& view,
                             const Value& codepoints, Value* result) {
-    UNIMPLEMENTED();
+    result->node =
+        builder_->StringViewIterRewind(view.node, NullCheckFor(view.type),
+                                       codepoints.node, decoder->position());
   }
 
   void StringViewIterSlice(FullDecoder* decoder, const Value& view,

src/wasm/wasm-code-manager.h

@@ -145,7 +145,9 @@ struct WasmModule;
   V(WasmStringViewWtf8Encode)            \
   V(WasmStringViewWtf8Slice)             \
   V(WasmStringAsIter)                    \
-  V(WasmStringViewIterNext)
+  V(WasmStringViewIterNext)              \
+  V(WasmStringViewIterAdvance)           \
+  V(WasmStringViewIterRewind)
 
 // 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

@@ -1069,19 +1069,76 @@ function makeWtf16TestDataSegment() {
       kGCPrefix, kExprStringViewIterNext
     ]);
 
+  builder.addFunction("advance", kSig_i_i)
+    .exportFunc()
+    .addBody([
+      kExprGlobalGet, global.index,
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringViewIterAdvance
+    ]);
+
+  builder.addFunction("advance_null", kSig_i_v)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringViewIterCode,
+      kExprI32Const, 0,
+      kGCPrefix, kExprStringViewIterAdvance
+    ]);
+
+  builder.addFunction("rewind", kSig_i_i)
+    .exportFunc()
+    .addBody([
+      kExprGlobalGet, global.index,
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringViewIterRewind
+    ]);
+
+  builder.addFunction("rewind_null", kSig_i_v)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringViewIterCode,
+      kExprI32Const, 0,
+      kGCPrefix, kExprStringViewIterRewind
+    ]);
+
   let instance = builder.instantiate();
 
   for (let str of interestingStrings) {
-    instance.exports.iterate(str);
+    let codepoints = [];
     for (let codepoint of str) {
-      assertEquals(codepoint.codePointAt(0), instance.exports.next());
+      codepoints.push(codepoint.codePointAt(0));
+    }
+
+    instance.exports.iterate(str);
+    for (let codepoint of codepoints) {
+      assertEquals(codepoint, instance.exports.next());
     }
     assertEquals(-1, instance.exports.next());
     assertEquals(-1, instance.exports.next());
+
+    for (let i = 1; i <= codepoints.length; i++) {
+      assertEquals(i, instance.exports.rewind(i));
+      assertEquals(codepoints[codepoints.length - i], instance.exports.next());
+      assertEquals(i - 1, instance.exports.advance(-1));
+    }
+    for (let i = 0; i < codepoints.length; i++) {
+      instance.exports.rewind(-1);
+      assertEquals(i, instance.exports.advance(i));
+      assertEquals(codepoints[i], instance.exports.next());
+    }
+
+    assertEquals(codepoints.length, instance.exports.rewind(-1));
+    assertEquals(0, instance.exports.rewind(-1));
+    assertEquals(codepoints.length, instance.exports.advance(-1));
+    assertEquals(0, instance.exports.advance(-1));
   }
 
   assertThrows(() => instance.exports.iterate_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
   assertThrows(() => instance.exports.next_null(),
                WebAssembly.RuntimeError, "dereferencing a null pointer");
+  assertThrows(() => instance.exports.advance_null(),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
+  assertThrows(() => instance.exports.rewind_null(),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();