Extract common code in string compare loops.

src/ia32/code-stubs-ia32.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5619 matching lines @@
   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);
+  GenerateAsciiCharsCompareLoop(masm, left, right, length, scratch2,
+                                &strings_not_equal);
 
   // Characters are equal.
   __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
   __ ret(0);
 }
 
 
 void StringCompareStub::GenerateCompareFlatAsciiStrings(MacroAssembler* masm,
                                                         Register left,
                                                         Register right,
                                                         Register scratch1,
                                                         Register scratch2,
                                                         Register scratch3) {
-  Label result_not_equal;
-  Label result_greater;
-  Label compare_lengths;
-
   Counters* counters = masm->isolate()->counters();
   __ IncrementCounter(counters->string_compare_native(), 1);
 
   // Find minimum length.
   NearLabel left_shorter;
   __ mov(scratch1, FieldOperand(left, String::kLengthOffset));
   __ mov(scratch3, scratch1);
   __ sub(scratch3, FieldOperand(right, String::kLengthOffset));
 
   Register length_delta = scratch3;
 
   __ j(less_equal, &left_shorter);
   // Right string is shorter. Change scratch1 to be length of right string.
   __ sub(scratch1, Operand(length_delta));
   __ bind(&left_shorter);
 
   Register min_length = scratch1;
 
   // If either length is zero, just compare lengths.
+  NearLabel compare_lengths;
   __ test(min_length, Operand(min_length));
   __ j(zero, &compare_lengths);
 
-  // Change index to run from -min_length to -1 by adding min_length
-  // to string start. This means that loop ends when index reaches zero,
-  // which doesn't need an additional compare.
-  __ SmiUntag(min_length);
-  __ lea(left,
-         FieldOperand(left,
-                      min_length, times_1,
-                      SeqAsciiString::kHeaderSize));
-  __ lea(right,
-         FieldOperand(right,
-                      min_length, times_1,
-                      SeqAsciiString::kHeaderSize));
-  __ neg(min_length);
-
-  Register index = min_length;  // index = -min_length;
-
-  {
-    // Compare loop.
-    NearLabel loop;
-    __ bind(&loop);
-    // Compare characters.
-    __ mov_b(scratch2, Operand(left, index, times_1, 0));
-    __ cmpb(scratch2, Operand(right, index, times_1, 0));
-    __ j(not_equal, &result_not_equal);
-    __ add(Operand(index), Immediate(1));
-    __ j(not_zero, &loop);
-  }
+  // Compare characters.
+  NearLabel result_not_equal;
+  GenerateAsciiCharsCompareLoop(masm, left, right, min_length, scratch2,
+                                &result_not_equal);
 
   // Compare lengths -  strings up to min-length are equal.
   __ bind(&compare_lengths);
   __ test(length_delta, Operand(length_delta));
   __ j(not_zero, &result_not_equal);
 
   // Result is EQUAL.
   STATIC_ASSERT(EQUAL == 0);
   STATIC_ASSERT(kSmiTag == 0);
   __ Set(eax, Immediate(Smi::FromInt(EQUAL)));
   __ ret(0);
 
+  NearLabel result_greater;
   __ bind(&result_not_equal);
   __ j(greater, &result_greater);
 
   // Result is LESS.
   __ Set(eax, Immediate(Smi::FromInt(LESS)));
   __ ret(0);
 
   // Result is GREATER.
   __ bind(&result_greater);
   __ Set(eax, Immediate(Smi::FromInt(GREATER)));
   __ ret(0);
 }
 
 
+void StringCompareStub::GenerateAsciiCharsCompareLoop(
+    MacroAssembler* masm,
+    Register left,
+    Register right,
+    Register length,
+    Register scratch,
+    NearLabel* chars_not_equal) {
+  // 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(scratch, Operand(left, index, times_1, 0));
+  __ cmpb(scratch, Operand(right, index, times_1, 0));
+  __ j(not_equal, chars_not_equal);
+  __ add(Operand(index), Immediate(1));
+  __ j(not_zero, &loop);
+}
+
+
 void StringCompareStub::Generate(MacroAssembler* masm) {
   Label runtime;
 
   // Stack frame on entry.
   //  esp[0]: return address
   //  esp[4]: right string
   //  esp[8]: left string
 
   __ mov(edx, Operand(esp, 2 * kPointerSize));  // left
   __ mov(eax, Operand(esp, 1 * kPointerSize));  // right
@@ skipping 234 matching lines @@
   // Do a tail call to the rewritten stub.
   __ jmp(Operand(edi));
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32