Combine %_SubString and %_StringCharAt.

src/arm/code-stubs-arm.cc

 // Copyright 2012 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 5864 matching lines @@
   __ push(code_);
   __ CallRuntime(Runtime::kCharFromCode, 1);
   __ Move(result_, r0);
   call_helper.AfterCall(masm);
   __ jmp(&exit_);
 
   __ Abort("Unexpected fallthrough from CharFromCode slow case");
 }
 
 
-// -------------------------------------------------------------------------
-// StringCharAtGenerator
-
-void StringCharAtGenerator::GenerateFast(MacroAssembler* masm) {
-  char_code_at_generator_.GenerateFast(masm);
-  char_from_code_generator_.GenerateFast(masm);
-}
-
-
-void StringCharAtGenerator::GenerateSlow(
-    MacroAssembler* masm,
-    const RuntimeCallHelper& call_helper) {
-  char_code_at_generator_.GenerateSlow(masm, call_helper);
-  char_from_code_generator_.GenerateSlow(masm, call_helper);
-}
-
-
 void StringHelper::GenerateCopyCharacters(MacroAssembler* masm,
                                           Register dest,
                                           Register src,
                                           Register count,
                                           Register scratch,
                                           bool ascii) {
   Label loop;
   Label done;
   // This loop just copies one character at a time, as it is only used for very
   // short strings.
@@ skipping 387 matching lines @@
 
   // Make sure first argument is a string.
   __ ldr(r0, MemOperand(sp, kStringOffset));
   STATIC_ASSERT(kSmiTag == 0);
   // Do a JumpIfSmi, but fold its jump into the subsequent string test.
   __ tst(r0, Operand(kSmiTagMask));
   Condition is_string = masm->IsObjectStringType(r0, r1, ne);
   ASSERT(is_string == eq);
   __ b(NegateCondition(is_string), &runtime);
 
+  Label single_char;
+  __ cmp(r2, Operand(1));
+  __ b(eq, &single_char);
+
   // Short-cut for the case of trivial substring.
   Label return_r0;
   // r0: original string
   // r2: result string length
   __ ldr(r4, FieldMemOperand(r0, String::kLengthOffset));
   __ cmp(r2, Operand(r4, ASR, 1));
   // Return original string.
   __ b(eq, &return_r0);
   // Longer than original string's length or negative: unsafe arguments.
   __ b(hi, &runtime);
@@ skipping 133 matching lines @@
   // r1: first character of result.
   // r2: result length.
   // r5: first character of substring to copy.
   STATIC_ASSERT((SeqTwoByteString::kHeaderSize & kObjectAlignmentMask) == 0);
   StringHelper::GenerateCopyCharactersLong(
       masm, r1, r5, r2, r3, r4, r6, r7, r9, DEST_ALWAYS_ALIGNED);
 
   __ bind(&return_r0);
   Counters* counters = masm->isolate()->counters();
   __ IncrementCounter(counters->sub_string_native(), 1, r3, r4);
-  __ add(sp, sp, Operand(3 * kPointerSize));
+  __ Drop(3);
   __ Ret();
 
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kSubString, 3, 1);
+
+  __ bind(&single_char);
+  // r0: original string
+  // r1: instance type
+  // r2: length
+  // r3: from index (untagged)
+  __ SmiTag(r3, r3);
+  StringCharAtGenerator generator(
+      r0, r3, r2, r0, &runtime, &runtime, &runtime, STRING_INDEX_IS_NUMBER);
+  generator.GenerateFast(masm);
+  __ Drop(3);
+  __ Ret();
+  generator.SkipSlow(masm, &runtime);
 }
 
 
 void StringCompareStub::GenerateFlatAsciiStringEquals(MacroAssembler* masm,
                                                       Register left,
                                                       Register right,
                                                       Register scratch1,
                                                       Register scratch2,
                                                       Register scratch3) {
   Register length = scratch1;
@@ skipping 1468 matching lines @@
 
   __ Pop(lr, r5, r1);
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM