Combine %_SubString and %_StringCharAt.

src/x64/code-stubs-x64.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 4740 matching lines @@
   if (!result_.is(rax)) {
     __ movq(result_, rax);
   }
   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 StringAddStub::Generate(MacroAssembler* masm) {
   Label call_runtime, call_builtin;
   Builtins::JavaScript builtin_id = Builtins::ADD;
 
   // Load the two arguments.
   __ movq(rax, Operand(rsp, 2 * kPointerSize));  // First argument (left).
   __ movq(rdx, Operand(rsp, 1 * kPointerSize));  // Second argument (right).
 
   // Make sure that both arguments are strings if not known in advance.
   if (flags_ == NO_STRING_ADD_FLAGS) {
@@ skipping 600 matching lines @@
   Label not_original_string;
   // Shorter than original string's length: an actual substring.
   __ j(below, &not_original_string, Label::kNear);
   // Longer than original string's length or negative: unsafe arguments.
   __ j(above, &runtime);
   // Return original string.
   Counters* counters = masm->isolate()->counters();
   __ IncrementCounter(counters->sub_string_native(), 1);
   __ ret(kArgumentsSize);
   __ bind(&not_original_string);
+
+  Label single_char;
+  __ SmiCompare(rcx, Smi::FromInt(1));
+  __ j(equal, &single_char);
+
   __ SmiToInteger32(rcx, rcx);
 
   // rax: string
   // rbx: instance type
   // rcx: sub string length
   // rdx: from index (smi)
   // Deal with different string types: update the index if necessary
   // and put the underlying string into edi.
   Label underlying_unpacked, sliced_string, seq_or_external_string;
   // If the string is not indirect, it can only be sequential or external.
@@ skipping 140 matching lines @@
   // rsi: character of sub string start
   // r14: original value of rsi
   StringHelper::GenerateCopyCharactersREP(masm, rdi, rsi, rcx, false);
   __ movq(rsi, r14);  // Restore esi.
   __ IncrementCounter(counters->sub_string_native(), 1);
   __ ret(kArgumentsSize);
 
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kSubString, 3, 1);
+
+  __ bind(&single_char);
+  // rax: string
+  // rbx: instance type
+  // rcx: sub string length (smi)
+  // rdx: from index (smi)
+  StringCharAtGenerator generator(
+      rax, rdx, rcx, rax, &runtime, &runtime, &runtime, STRING_INDEX_IS_NUMBER);
+  generator.GenerateFast(masm);
+  __ ret(kArgumentsSize);
+  generator.SkipSlow(masm, &runtime);
 }
 
 
 void StringCompareStub::GenerateFlatAsciiStringEquals(MacroAssembler* masm,
                                                       Register left,
                                                       Register right,
                                                       Register scratch1,
                                                       Register scratch2) {
   Register length = scratch1;
 
@@ skipping 1144 matching lines @@
 #endif
 
   __ Ret();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64