Faster string equals in generated code.

In my previous change I mixed up "compare" and "equals". This made us
miss the fast length check before comparing strings for equality.

Now we have a separate helper for "equals". It shares some of the
inner loop details with "compare". I'll see if this can be cleaned up
without making it unreadable.

Review URL: http://codereview.chromium.org/6928020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7794 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/code-stubs-arm.cc

@@ -1568,13 +1568,22 @@ void CompareStub::Generate(MacroAssembler* masm) {
   __ JumpIfNonSmisNotBothSequentialAsciiStrings(lhs_, rhs_, r2, r3, &slow);
 
   __ IncrementCounter(isolate->counters()->string_compare_native(), 1, r2, r3);
-  StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+  if (cc_ == eq) {
+    StringCompareStub::GenerateFlatAsciiStringEquals(masm,
                                                      lhs_,
                                                      rhs_,
                                                      r2,
                                                      r3,
-                                                     r4,
-                                                     r5);
+                                                     r4);
+  } else {
+    StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+                                                       lhs_,
+                                                       rhs_,
+                                                       r2,
+                                                       r3,
+                                                       r4,
+                                                       r5);
+  }
   // Never falls through to here.
 
   __ bind(&slow);
@@ -5392,6 +5401,63 @@ void SubStringStub::Generate(MacroAssembler* masm) {
 }
 
 
+void StringCompareStub::GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                                      Register left,
+                                                      Register right,
+                                                      Register scratch1,
+                                                      Register scratch2,
+                                                      Register scratch3) {
+  Register length = scratch1;
+
+  // Compare lengths.
+  Label strings_not_equal, check_zero_length;
+  __ ldr(length, FieldMemOperand(left, String::kLengthOffset));
+  __ ldr(scratch2, FieldMemOperand(right, String::kLengthOffset));
+  __ cmp(length, scratch2);
+  __ b(eq, &check_zero_length);
+  __ bind(&strings_not_equal);
+  __ mov(r0, Operand(Smi::FromInt(NOT_EQUAL)));
+  __ Ret();
+
+  // Check if the length is zero.
+  Label compare_chars;
+  __ bind(&check_zero_length);
+  STATIC_ASSERT(kSmiTag == 0);
+  __ tst(length, Operand(length));
+  __ b(ne, &compare_chars);
+  __ mov(r0, Operand(Smi::FromInt(EQUAL)));
+  __ Ret();
+
+  // Compare characters.
+  __ bind(&compare_chars);
+
+  // Change index to run from -length to -1 by adding length to string
+  // start. This means that loop ends when index reaches zero, which
+  // doesn't need an additional compare.
+  __ SmiUntag(length);
+  __ add(scratch2, length,
+         Operand(SeqAsciiString::kHeaderSize - kHeapObjectTag));
+  __ add(left, left, Operand(scratch2));
+  __ add(right, right, Operand(scratch2));
+  __ rsb(length, length, Operand(0));
+  Register index = length;  // index = -length;
+
+  // Compare loop.
+  Label loop;
+  __ bind(&loop);
+  __ ldrb(scratch2, MemOperand(left, index));
+  __ ldrb(scratch3, MemOperand(right, index));
+  __ cmp(scratch2, scratch3);
+  __ b(ne, &strings_not_equal);
+  __ add(index, index, Operand(1), SetCC);
+  __ b(ne, &loop);
+
+  // Characters are equal.
+  __ mov(r0, Operand(Smi::FromInt(EQUAL)));
+  __ Ret();
+}
+
+
 void StringCompareStub::GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                                         Register left,
                                                         Register right,
@@ -5955,13 +6021,13 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
                                                   &runtime);
 
   // Compare flat ASCII strings. Returns when done.
-  StringCompareStub::GenerateCompareFlatAsciiStrings(
-      masm, left, right, tmp1, tmp2, tmp3, tmp4);
+  StringCompareStub::GenerateFlatAsciiStringEquals(
+      masm, left, right, tmp1, tmp2, tmp3);
 
   // Handle more complex cases in runtime.
   __ bind(&runtime);
   __ Push(left, right);
-  __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
+  __ TailCallRuntime(Runtime::kStringEquals, 2, 1);
 
   __ bind(&miss);
   GenerateMiss(masm);

src/arm/code-stubs-arm.h

@@ -327,8 +327,7 @@ class StringCompareStub: public CodeStub {
  public:
   StringCompareStub() { }
 
-  // Compare two flat ASCII strings and returns result in r0.
-  // Does not use the stack.
+  // Compares two flat ASCII strings and returns result in r0.
   static void GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                               Register left,
                                               Register right,
@@ -337,6 +336,15 @@ class StringCompareStub: public CodeStub {
                                               Register scratch3,
                                               Register scratch4);
 
+  // Compares two flat ASCII strings for equality and returns result
+  // in r0.
+  static void GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                            Register left,
+                                            Register right,
+                                            Register scratch1,
+                                            Register scratch2,
+                                            Register scratch3);
+
  private:
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }

src/ia32/code-stubs-ia32.cc

@@ -3901,12 +3901,20 @@ void CompareStub::Generate(MacroAssembler* masm) {
                                          &check_unequal_objects);
 
   // Inline comparison of ascii strings.
-  StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+  if (cc_ == equal) {
+    StringCompareStub::GenerateFlatAsciiStringEquals(masm,
                                                      edx,
                                                      eax,
                                                      ecx,
-                                                     ebx,
-                                                     edi);
+                                                     ebx);
+  } else {
+    StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+                                                       edx,
+                                                       eax,
+                                                       ecx,
+                                                       ebx,
+                                                       edi);
+  }
 #ifdef DEBUG
   __ Abort("Unexpected fall-through from string comparison");
 #endif
@@ -5602,6 +5610,60 @@ void SubStringStub::Generate(MacroAssembler* masm) {
 }
 
 
+void StringCompareStub::GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                                      Register left,
+                                                      Register right,
+                                                      Register scratch1,
+                                                      Register scratch2) {
+  Register length = scratch1;
+
+  // Compare lengths.
+  NearLabel strings_not_equal, check_zero_length;
+  __ mov(length, FieldOperand(left, String::kLengthOffset));
+  __ cmp(length, FieldOperand(right, String::kLengthOffset));
+  __ j(equal, &check_zero_length);
+  __ bind(&strings_not_equal);
+  __ Set(eax, Immediate(Smi::FromInt(NOT_EQUAL)));
+  __ ret(0);
+
+  // Check if the length is zero.
+  NearLabel compare_chars;
+  __ bind(&check_zero_length);
+  STATIC_ASSERT(kSmiTag == 0);
+  __ test(length, Operand(length));
+  __ j(not_zero, &compare_chars);
+  __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+  __ ret(0);
+
+  // Compare characters.
+  __ bind(&compare_chars);
+
+  // Change index to run from -length to -1 by adding length to string
+  // start. This means that loop ends when index reaches zero, which
+  // doesn't need an additional compare.
+  __ SmiUntag(length);
+  __ lea(left,
+         FieldOperand(left, length, times_1, SeqAsciiString::kHeaderSize));
+  __ lea(right,
+         FieldOperand(right, length, times_1, SeqAsciiString::kHeaderSize));
+  __ neg(length);
+  Register index = length;  // index = -length;
+
+  // Compare loop.
+  NearLabel loop;
+  __ bind(&loop);
+  __ mov_b(scratch2, Operand(left, index, times_1, 0));
+  __ cmpb(scratch2, Operand(right, index, times_1, 0));
+  __ j(not_equal, &strings_not_equal);
+  __ add(Operand(index), Immediate(1));
+  __ j(not_zero, &loop);
+
+  // Characters are equal.
+  __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
+  __ ret(0);
+}
+
+
 void StringCompareStub::GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                                         Register left,
                                                         Register right,
@@ -5808,6 +5870,7 @@ void ICCompareStub::GenerateHeapNumbers(MacroAssembler* masm) {
 
 void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   ASSERT(state_ == CompareIC::STRINGS);
+  ASSERT(GetCondition() == equal);
   Label miss;
 
   // Registers containing left and right operands respectively.
@@ -5851,7 +5914,6 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   // Check that both strings are symbols. If they are, we're done
   // because we already know they are not identical.
   NearLabel do_compare;
-  ASSERT(GetCondition() == equal);
   STATIC_ASSERT(kSymbolTag != 0);
   __ and_(tmp1, Operand(tmp2));
   __ test(tmp1, Immediate(kIsSymbolMask));
@@ -5867,8 +5929,8 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   __ JumpIfNotBothSequentialAsciiStrings(left, right, tmp1, tmp2, &runtime);
 
   // Compare flat ASCII strings. Returns when done.
-  StringCompareStub::GenerateCompareFlatAsciiStrings(
-      masm, left, right, tmp1, tmp2, tmp3);
+  StringCompareStub::GenerateFlatAsciiStringEquals(
+      masm, left, right, tmp1, tmp2);
 
   // Handle more complex cases in runtime.
   __ bind(&runtime);
@@ -5876,7 +5938,7 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   __ push(left);
   __ push(right);
   __ push(tmp1);
-  __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
+  __ TailCallRuntime(Runtime::kStringEquals, 2, 1);
 
   __ bind(&miss);
   GenerateMiss(masm);

src/ia32/code-stubs-ia32.h

@@ -372,11 +372,9 @@ class SubStringStub: public CodeStub {
 
 class StringCompareStub: public CodeStub {
  public:
-  explicit StringCompareStub() {
-  }
+  StringCompareStub() { }
 
-  // Compare two flat ascii strings and returns result in eax after popping two
-  // arguments from the stack.
+  // Compares two flat ASCII strings and returns result in eax.
   static void GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                               Register left,
                                               Register right,
@@ -384,6 +382,14 @@ class StringCompareStub: public CodeStub {
                                               Register scratch2,
                                               Register scratch3);
 
+  // Compares two flat ASCII strings for equality and returns result
+  // in eax.
+  static void GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                            Register left,
+                                            Register right,
+                                            Register scratch1,
+                                            Register scratch2);
+
  private:
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }

src/x64/code-stubs-x64.cc

@@ -2835,13 +2835,21 @@ void CompareStub::Generate(MacroAssembler* masm) {
       rdx, rax, rcx, rbx, &check_unequal_objects);
 
   // Inline comparison of ascii strings.
-  StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+  if (cc_ == equal) {
+    StringCompareStub::GenerateFlatAsciiStringEquals(masm,
                                                      rdx,
                                                      rax,
                                                      rcx,
-                                                     rbx,
-                                                     rdi,
-                                                     r8);
+                                                     rbx);
+  } else {
+    StringCompareStub::GenerateCompareFlatAsciiStrings(masm,
+                                                       rdx,
+                                                       rax,
+                                                       rcx,
+                                                       rbx,
+                                                       rdi,
+                                                       r8);
+  }
 
 #ifdef DEBUG
   __ Abort("Unexpected fall-through from string comparison");
@@ -4489,6 +4497,64 @@ void SubStringStub::Generate(MacroAssembler* masm) {
 }
 
 
+void StringCompareStub::GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                                      Register left,
+                                                      Register right,
+                                                      Register scratch1,
+                                                      Register scratch2) {
+  Register length = scratch1;
+
+  // Compare lengths.
+  NearLabel check_zero_length;
+  __ movq(length, FieldOperand(left, String::kLengthOffset));
+  __ SmiCompare(length, FieldOperand(right, String::kLengthOffset));
+  __ j(equal, &check_zero_length);
+  __ Move(rax, Smi::FromInt(NOT_EQUAL));
+  __ ret(0);
+
+  // Check if the length is zero.
+  NearLabel compare_chars;
+  __ bind(&check_zero_length);
+  STATIC_ASSERT(kSmiTag == 0);
+  __ SmiTest(length);
+  __ j(not_zero, &compare_chars);
+  __ Move(rax, Smi::FromInt(EQUAL));
+  __ ret(0);
+
+  // Compare characters.
+  __ bind(&compare_chars);
+
+  // Change index to run from -length to -1 by adding length to string
+  // start. This means that loop ends when index reaches zero, which
+  // doesn't need an additional compare.
+  __ SmiToInteger32(length, length);
+  __ lea(left,
+         FieldOperand(left, length, times_1, SeqAsciiString::kHeaderSize));
+  __ lea(right,
+         FieldOperand(right, length, times_1, SeqAsciiString::kHeaderSize));
+  __ neg(length);
+  Register index = length;  // index = -length;
+
+  // Compare loop.
+  NearLabel strings_not_equal, loop;
+  __ bind(&loop);
+  __ movb(scratch2, Operand(left, index, times_1, 0));
+  __ cmpb(scratch2, Operand(right, index, times_1, 0));
+  __ j(not_equal, &strings_not_equal);
+  __ addq(index, Immediate(1));
+  __ j(not_zero, &loop);
+
+  // Characters are equal.
+  __ Move(rax, Smi::FromInt(EQUAL));
+  __ ret(0);
+
+  // Characters are not equal.
+  __ bind(&strings_not_equal);
+  __ Move(rax, Smi::FromInt(NOT_EQUAL));
+  __ ret(0);
+}
+
+
 void StringCompareStub::GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                                         Register left,
                                                         Register right,
@@ -4687,6 +4753,7 @@ void ICCompareStub::GenerateHeapNumbers(MacroAssembler* masm) {
 
 void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   ASSERT(state_ == CompareIC::STRINGS);
+  ASSERT(GetCondition() == equal);
   Label miss;
 
   // Registers containing left and right operands respectively.
@@ -4695,7 +4762,6 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   Register tmp1 = rcx;
   Register tmp2 = rbx;
   Register tmp3 = rdi;
-  Register tmp4 = r8;
 
   // Check that both operands are heap objects.
   Condition cond = masm->CheckEitherSmi(left, right, tmp1);
@@ -4728,7 +4794,6 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   // Check that both strings are symbols. If they are, we're done
   // because we already know they are not identical.
   NearLabel do_compare;
-  ASSERT(GetCondition() == equal);
   STATIC_ASSERT(kSymbolTag != 0);
   __ and_(tmp1, tmp2);
   __ testl(tmp1, Immediate(kIsSymbolMask));
@@ -4744,8 +4809,8 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   __ JumpIfNotBothSequentialAsciiStrings(left, right, tmp1, tmp2, &runtime);
 
   // Compare flat ASCII strings. Returns when done.
-  StringCompareStub::GenerateCompareFlatAsciiStrings(
-      masm, left, right, tmp1, tmp2, tmp3, tmp4);
+  StringCompareStub::GenerateFlatAsciiStringEquals(
+      masm, left, right, tmp1, tmp2);
 
   // Handle more complex cases in runtime.
   __ bind(&runtime);
@@ -4753,7 +4818,7 @@ void ICCompareStub::GenerateStrings(MacroAssembler* masm) {
   __ push(left);
   __ push(right);
   __ push(tmp1);
-  __ TailCallRuntime(Runtime::kStringCompare, 2, 1);
+  __ TailCallRuntime(Runtime::kStringEquals, 2, 1);
 
   __ bind(&miss);
   GenerateMiss(masm);

src/x64/code-stubs-x64.h

@@ -364,10 +364,9 @@ class SubStringStub: public CodeStub {
 
 class StringCompareStub: public CodeStub {
  public:
-  explicit StringCompareStub() {}
+  StringCompareStub() {}
 
-  // Compare two flat ascii strings and returns result in rax after popping two
-  // arguments from the stack.
+  // Compares two flat ASCII strings and returns result in rax.
   static void GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                               Register left,
                                               Register right,
@@ -376,6 +375,14 @@ class StringCompareStub: public CodeStub {
                                               Register scratch3,
                                               Register scratch4);
 
+  // Compares two flat ASCII strings for equality and returns result
+  // in rax.
+  static void GenerateFlatAsciiStringEquals(MacroAssembler* masm,
+                                            Register left,
+                                            Register right,
+                                            Register scratch1,
+                                            Register scratch2);
+
  private:
   Major MajorKey() { return StringCompare; }
   int MinorKey() { return 0; }