[stringrefs] Implement string.eq

Bug: v8:12868
Change-Id: I56ccab1a0cfacfae236c4f87c31a84d3afecafc8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3702437
Commit-Queue: Andy Wingo <wingo@igalia.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81153}

src/builtins/wasm.tq

@@ -833,6 +833,13 @@ builtin WasmStringConcat(a: String, b: String): String {
   const context = LoadContextFromFrame();
   return a + b;
 }
+builtin WasmStringEqual(a: String, b: String): int32 {
+  if (TaggedEqual(a, b)) return 1;
+  if (a.length != b.length) return 0;
+  const context = LoadContextFromFrame();
+  if (StringEqual(context, a, b) == True) return 1;
+  return 0;
+}
 transitioning builtin WasmStringViewWtf16GetCodeUnit(
     string: String, offset: uint32): uint32 {
   try {

src/compiler/wasm-compiler.cc

@@ -5818,6 +5818,20 @@ Node* WasmGraphBuilder::StringConcat(Node* head, CheckForNull head_null_check,
                             head, tail);
 }
 
+Node* WasmGraphBuilder::StringEqual(Node* a, CheckForNull a_null_check, Node* b,
+                                    CheckForNull b_null_check,
+                                    wasm::WasmCodePosition position) {
+  if (a_null_check == kWithNullCheck) a = AssertNotNull(a, position);
+  if (b_null_check == kWithNullCheck) b = AssertNotNull(b, position);
+
+  auto done = gasm_->MakeLabel(MachineRepresentation::kWord32);
+  gasm_->GotoIf(gasm_->TaggedEqual(a, b), &done, Int32Constant(1));
+  gasm_->Goto(&done, gasm_->CallBuiltin(Builtin::kWasmStringEqual,
+                                        Operator::kNoDeopt, a, b));
+  gasm_->Bind(&done);
+  return done.PhiAt(0);
+}
+
 Node* WasmGraphBuilder::StringViewWtf16GetCodeUnit(
     Node* string, CheckForNull null_check, Node* offset,
     wasm::WasmCodePosition position) {

src/compiler/wasm-compiler.h

@@ -556,6 +556,8 @@ class WasmGraphBuilder {
   Node* StringConcat(Node* head, CheckForNull head_null_check, Node* tail,
                      CheckForNull tail_null_check,
                      wasm::WasmCodePosition position);
+  Node* StringEqual(Node* a, CheckForNull a_null_check, Node* b,
+                    CheckForNull b_null_check, wasm::WasmCodePosition position);
   Node* StringViewWtf16GetCodeUnit(Node* string, CheckForNull null_check,
                                    Node* offset,
                                    wasm::WasmCodePosition position);

src/wasm/baseline/liftoff-compiler.cc

@@ -6223,7 +6223,27 @@ class LiftoffCompiler {
 
   void StringEq(FullDecoder* decoder, const Value& a, const Value& b,
                 Value* result) {
-    UNIMPLEMENTED();
+    LiftoffRegList pinned;
+
+    LiftoffRegister b_reg = pinned.set(__ PopToRegister(pinned));
+    MaybeEmitNullCheck(decoder, b_reg.gp(), pinned, b.type);
+    LiftoffAssembler::VarState b_var(kRef, b_reg, 0);
+
+    LiftoffRegister a_reg = pinned.set(__ PopToRegister(pinned));
+    MaybeEmitNullCheck(decoder, a_reg.gp(), pinned, a.type);
+    LiftoffAssembler::VarState a_var(kRef, a_reg, 0);
+
+    CallRuntimeStub(WasmCode::kWasmStringEqual,
+                    MakeSig::Returns(kI32).Params(kRef, kRef),
+                    {
+                        a_var,
+                        b_var,
+                    },
+                    decoder->position());
+    RegisterDebugSideTableEntry(decoder, DebugSideTableBuilder::kDidSpill);
+
+    LiftoffRegister result_reg(kReturnRegister0);
+    __ PushRegister(kI32, result_reg);
   }
 
   void StringAsWtf8(FullDecoder* decoder, const Value& str, Value* result) {

src/wasm/graph-builder-interface.cc

@@ -1455,7 +1455,9 @@ class WasmGraphBuildingInterface {
 
   void StringEq(FullDecoder* decoder, const Value& a, const Value& b,
                 Value* result) {
-    UNIMPLEMENTED();
+    result->node =
+        builder_->StringEqual(a.node, NullCheckFor(a.type), b.node,
+                              NullCheckFor(b.type), decoder->position());
   }
 
   void StringAsWtf8(FullDecoder* decoder, const Value& str, Value* result) {

src/wasm/wasm-code-manager.h

@@ -131,6 +131,7 @@ struct WasmModule;
   V(WasmStringEncodeWtf8)                \
   V(WasmStringEncodeWtf16)               \
   V(WasmStringConcat)                    \
+  V(WasmStringEqual)                     \
   V(WasmStringViewWtf16GetCodeUnit)      \
   V(WasmStringViewWtf16Encode)           \
   V(WasmStringViewWtf16Slice)

test/mjsunit/wasm/stringrefs-exec.js

@@ -10,6 +10,7 @@ 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_i_ww = makeSig([kWasmStringRef, kWasmStringRef], [kWasmI32]);
 let kSig_w_wii = makeSig([kWasmStringRef, kWasmI32, kWasmI32],
                          [kWasmStringRef]);
 let kSig_v_wi = makeSig([kWasmStringRef, kWasmI32], []);
@@ -475,6 +476,48 @@ function HasIsolatedSurrogate(str) {
                WebAssembly.RuntimeError, "dereferencing a null pointer");
 })();
 
+(function TestStringEq() {
+  let builder = new WasmModuleBuilder();
+
+  builder.addFunction("eq", kSig_i_ww)
+    .exportFunc()
+    .addBody([
+      kExprLocalGet, 0,
+      kExprLocalGet, 1,
+      kGCPrefix, kExprStringEq
+    ]);
+
+  builder.addFunction("eq_null_a", kSig_i_w)
+    .exportFunc()
+    .addBody([
+      kExprRefNull, kStringRefCode,
+      kExprLocalGet, 0,
+      kGCPrefix, kExprStringEq
+    ]);
+  builder.addFunction("eq_null_b", kSig_i_w)
+    .exportFunc()
+    .addBody([
+      kExprLocalGet, 0,
+      kExprRefNull, kStringRefCode,
+      kGCPrefix, kExprStringEq
+    ]);
+
+  let instance = builder.instantiate();
+
+  for (let head of interestingStrings) {
+    for (let tail of interestingStrings) {
+      let result = (head == tail)|0;
+      assertEquals(result, instance.exports.eq(head, tail));
+      assertEquals(result, instance.exports.eq(head + head, tail + tail));
+    }
+  }
+
+  assertThrows(() => instance.exports.eq_null_a("hey"),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
+  assertThrows(() => instance.exports.eq_null_b("hey"),
+               WebAssembly.RuntimeError, "dereferencing a null pointer");
+})();
+
 (function TestStringViewWtf16() {
   let builder = new WasmModuleBuilder();