[compiler] Introduce StringEqualStub and StringNotEqualStub.

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index d0f40f0440f422f3fac51698add42b6604d6a1c4..3814986e438fd3493566a8b023e5782e071b4d75 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -7,6 +7,7 @@
 #include <sstream>
 
 #include "src/bootstrapper.h"
+#include "src/code-factory.h"
 #include "src/compiler/code-stub-assembler.h"
 #include "src/factory.h"
 #include "src/gdb-jit.h"
@@ -500,12 +501,12 @@ void StringLengthStub::GenerateAssembly(
 
 namespace {
 
-enum StrictEqualMode { kStrictEqual, kStrictNotEqual };
+enum ResultMode { kDontNegateResult, kNegateResult };
 
 void GenerateStrictEqual(compiler::CodeStubAssembler* assembler,
-                         StrictEqualMode mode) {
-  // Here's pseudo-code for the algorithm below in case of kStrictEqual mode;
-  // for kStrictNotEqual mode we properly negate the result.
+                         Isolate* isolate, ResultMode mode) {
+  // Here's pseudo-code for the algorithm below in case of kDontNegateResult
+  // mode; for kNegateResult mode we properly negate the result.
   //
   // if (lhs == rhs) {
   //   if (lhs->IsHeapNumber()) return HeapNumber::cast(lhs)->value() != NaN;
@@ -705,12 +706,10 @@ void GenerateStrictEqual(compiler::CodeStubAssembler* assembler,
 
             assembler->Bind(&if_rhsisstring);
             {
-              // TODO(bmeurer): Optimize this further once the StringEqual
-              // functionality is available in TurboFan land.
-              Runtime::FunctionId function_id = (mode == kStrictEqual)
-                                                    ? Runtime::kStringEqual
-                                                    : Runtime::kStringNotEqual;
-              assembler->TailCallRuntime(function_id, context, lhs, rhs);
+              Callable callable = (mode == kDontNegateResult)
+                                      ? CodeFactory::StringEqual(isolate)
+                                      : CodeFactory::StringNotEqual(isolate);
+              assembler->TailCallStub(callable, context, lhs, rhs);
             }
 
             assembler->Bind(&if_rhsisnotstring);
@@ -730,7 +729,7 @@ void GenerateStrictEqual(compiler::CodeStubAssembler* assembler,
             assembler->Bind(&if_lhsissimd128value);
             {
               // TODO(bmeurer): Inline the Simd128Value equality check.
-              Runtime::FunctionId function_id = (mode == kStrictEqual)
+              Runtime::FunctionId function_id = (mode == kDontNegateResult)
                                                     ? Runtime::kStrictEqual
                                                     : Runtime::kStrictNotEqual;
               assembler->TailCallRuntime(function_id, context, lhs, rhs);
@@ -785,22 +784,209 @@ void GenerateStrictEqual(compiler::CodeStubAssembler* assembler,
   }
 
   assembler->Bind(&if_equal);
-  assembler->Return(assembler->BooleanConstant(mode == kStrictEqual));
+  assembler->Return(assembler->BooleanConstant(mode == kDontNegateResult));
+
+  assembler->Bind(&if_notequal);
+  assembler->Return(assembler->BooleanConstant(mode == kNegateResult));
+}
+
+void GenerateStringEqual(compiler::CodeStubAssembler* assembler,
+                         ResultMode mode) {
+  // Here's pseudo-code for the algorithm below in case of kDontNegateResult
+  // mode; for kNegateResult mode we properly negate the result.
+  //
+  // if (lhs == rhs) return true;
+  // if (lhs->length() != rhs->length()) return false;
+  // if (lhs->IsInternalizedString() && rhs->IsInternalizedString()) {
+  //   return false;
+  // }
+  // if (lhs->IsSeqOneByteString() && rhs->IsSeqOneByteString()) {
+  //   for (i = 0; i != lhs->length(); ++i) {
+  //     if (lhs[i] != rhs[i]) return false;
+  //   }
+  //   return true;
+  // }
+  // return %StringEqual(lhs, rhs);
+
+  typedef compiler::CodeStubAssembler::Label Label;
+  typedef compiler::Node Node;
+  typedef compiler::CodeStubAssembler::Variable Variable;
+
+  Node* lhs = assembler->Parameter(0);
+  Node* rhs = assembler->Parameter(1);
+  Node* context = assembler->Parameter(2);
+
+  Label if_equal(assembler), if_notequal(assembler);
+
+  // Fast check to see if {lhs} and {rhs} refer to the same String object.
+  Label if_same(assembler), if_notsame(assembler);
+  assembler->Branch(assembler->WordEqual(lhs, rhs), &if_same, &if_notsame);
+
+  assembler->Bind(&if_same);
+  assembler->Goto(&if_equal);
+
+  assembler->Bind(&if_notsame);
+  {
+    // The {lhs} and {rhs} don't refer to the exact same String object.
+
+    // Load the length of {lhs} and {rhs}.
+    Node* lhs_length = assembler->LoadObjectField(lhs, String::kLengthOffset);
+    Node* rhs_length = assembler->LoadObjectField(rhs, String::kLengthOffset);
+
+    // Check if the lengths of {lhs} and {rhs} are equal.
+    Label if_lengthisequal(assembler), if_lengthisnotequal(assembler);
+    assembler->Branch(assembler->WordEqual(lhs_length, rhs_length),
+                      &if_lengthisequal, &if_lengthisnotequal);
+
+    assembler->Bind(&if_lengthisequal);
+    {
+      // Load instance types of {lhs} and {rhs}.
+      Node* lhs_instance_type = assembler->LoadInstanceType(lhs);
+      Node* rhs_instance_type = assembler->LoadInstanceType(rhs);
+
+      // Combine the instance types into a single 16-bit value, so we can check
+      // both of them at once.
+      Node* both_instance_types = assembler->Word32Or(
+          lhs_instance_type,
+          assembler->Word32Shl(rhs_instance_type, assembler->Int32Constant(8)));
+
+      // Check if both {lhs} and {rhs} are internalized.
+      int const kBothInternalizedMask =
+          kIsNotInternalizedMask | (kIsNotInternalizedMask << 8);
+      int const kBothInternalizedTag =
+          kInternalizedTag | (kInternalizedTag << 8);
+      Label if_bothinternalized(assembler), if_notbothinternalized(assembler);
+      assembler->Branch(assembler->Word32Equal(
+                            assembler->Word32And(both_instance_types,
+                                                 assembler->Int32Constant(
+                                                     kBothInternalizedMask)),
+                            assembler->Int32Constant(kBothInternalizedTag)),
+                        &if_bothinternalized, &if_notbothinternalized);
+
+      assembler->Bind(&if_bothinternalized);
+      {
+        // Fast negative check for internalized-to-internalized equality.
+        assembler->Goto(&if_notequal);
+      }
+
+      assembler->Bind(&if_notbothinternalized);
+      {
+        // Check that both {lhs} and {rhs} are flat one-byte strings.
+        int const kBothSeqOneByteStringMask =
+            kStringEncodingMask | kStringRepresentationMask |
+            ((kStringEncodingMask | kStringRepresentationMask) << 8);
+        int const kBothSeqOneByteStringTag =
+            kOneByteStringTag | kSeqStringTag |
+            ((kOneByteStringTag | kSeqStringTag) << 8);
+        Label if_bothonebyteseqstrings(assembler),
+            if_notbothonebyteseqstrings(assembler);
+        assembler->Branch(
+            assembler->Word32Equal(
+                assembler->Word32And(
+                    both_instance_types,
+                    assembler->Int32Constant(kBothSeqOneByteStringMask)),
+                assembler->Int32Constant(kBothSeqOneByteStringTag)),
+            &if_bothonebyteseqstrings, &if_notbothonebyteseqstrings);
+
+        assembler->Bind(&if_bothonebyteseqstrings);
+        {
+          // Compute the effective offset of the first character.
+          Node* begin = assembler->IntPtrConstant(
+              SeqOneByteString::kHeaderSize - kHeapObjectTag);
+
+          // Compute the first offset after the string from the length.
+          Node* end =
+              assembler->IntPtrAdd(begin, assembler->SmiUntag(lhs_length));
+
+          // Loop over the {lhs} and {rhs} strings to see if they are equal.
+          Variable var_offset(assembler, MachineType::PointerRepresentation());
+          Label loop(assembler, &var_offset);
+          var_offset.Bind(begin);
+          assembler->Goto(&loop);
+          assembler->Bind(&loop);
+          {
+            // Check if {offset} equals {end}.
+            Node* offset = var_offset.value();
+            Label if_done(assembler), if_notdone(assembler);
+            assembler->Branch(assembler->WordEqual(offset, end), &if_done,
+                              &if_notdone);
+
+            assembler->Bind(&if_notdone);
+            {
+              // Load the next characters from {lhs} and {rhs}.
+              Node* lhs_value =
+                  assembler->Load(MachineType::Uint8(), lhs, offset);
+              Node* rhs_value =
+                  assembler->Load(MachineType::Uint8(), rhs, offset);
+
+              // Check if the characters match.
+              Label if_valueissame(assembler), if_valueisnotsame(assembler);
+              assembler->Branch(assembler->Word32Equal(lhs_value, rhs_value),
+                                &if_valueissame, &if_valueisnotsame);
+
+              assembler->Bind(&if_valueissame);
+              {
+                // Advance to next character.
+                var_offset.Bind(
+                    assembler->IntPtrAdd(offset, assembler->IntPtrConstant(1)));
+              }
+              assembler->Goto(&loop);
+
+              assembler->Bind(&if_valueisnotsame);
+              assembler->Goto(&if_notequal);
+            }
+
+            assembler->Bind(&if_done);
+            assembler->Goto(&if_equal);
+          }
+        }
+
+        assembler->Bind(&if_notbothonebyteseqstrings);
+        {
+          // TODO(bmeurer): Add fast case support for flattened cons strings;
+          // also add support for two byte string equality checks.
+          Runtime::FunctionId function_id = (mode == kDontNegateResult)
+                                                ? Runtime::kStringEqual
+                                                : Runtime::kStringNotEqual;
+          assembler->TailCallRuntime(function_id, context, lhs, rhs);
+        }
+      }
+    }
+
+    assembler->Bind(&if_lengthisnotequal);
+    {
+      // Mismatch in length of {lhs} and {rhs}, cannot be equal.
+      assembler->Goto(&if_notequal);
+    }
+  }
+
+  assembler->Bind(&if_equal);
+  assembler->Return(assembler->BooleanConstant(mode == kDontNegateResult));
 
   assembler->Bind(&if_notequal);
-  assembler->Return(assembler->BooleanConstant(mode == kStrictNotEqual));
+  assembler->Return(assembler->BooleanConstant(mode == kNegateResult));
 }
 
 }  // namespace
 
 void StrictEqualStub::GenerateAssembly(
     compiler::CodeStubAssembler* assembler) const {
-  GenerateStrictEqual(assembler, kStrictEqual);
+  GenerateStrictEqual(assembler, isolate(), kDontNegateResult);
 }
 
 void StrictNotEqualStub::GenerateAssembly(
     compiler::CodeStubAssembler* assembler) const {
-  GenerateStrictEqual(assembler, kStrictNotEqual);
+  GenerateStrictEqual(assembler, isolate(), kNegateResult);
+}
+
+void StringEqualStub::GenerateAssembly(
+    compiler::CodeStubAssembler* assembler) const {
+  GenerateStringEqual(assembler, kDontNegateResult);
+}
+
+void StringNotEqualStub::GenerateAssembly(
+    compiler::CodeStubAssembler* assembler) const {
+  GenerateStringEqual(assembler, kNegateResult);
 }
 
 void ToBooleanStub::GenerateAssembly(