Improve keyed loads on strings by using a new stub

src/ia32/ic-ia32.cc

 // Copyright 2006-2008 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 373 matching lines @@
   ASSERT(TenToThe(String::kMaxCachedArrayIndexLength) <
          (1 << String::kArrayIndexValueBits));
   __ bind(&index_string);
   __ mov(eax, Operand(ebx));
   __ and_(eax, String::kArrayIndexHashMask);
   __ shr(eax, String::kHashShift);
   __ jmp(&index_int);
 }
 
 
+void KeyedLoadIC::GenerateString(MacroAssembler* masm) {
+  // ----------- S t a t e -------------
+  //  -- esp[0] : return address
+  //  -- esp[4] : key
+  //  -- esp[8] : receiver
+  // -----------------------------------
+  Label miss, index_ok;
+
+  // Pop return address.
+  // Performing the load early is better in the common case.
+  __ pop(eax);
+
+  __ mov(ebx, Operand(esp, 1 * kPointerSize));
+  __ test(ebx, Immediate(kSmiTagMask));
+  __ j(zero, &miss);
+  __ mov(ecx, FieldOperand(ebx, HeapObject::kMapOffset));
+  __ movzx_b(ecx, FieldOperand(ecx, Map::kInstanceTypeOffset));
+  __ test(ecx, Immediate(kIsNotStringMask));
+  __ j(not_zero, &miss);
+
+  // Check if key is a smi or a heap number.
+  __ mov(edx, Operand(esp, 0));
+  __ test(edx, Immediate(kSmiTagMask));
+  __ j(zero, &index_ok);
+  __ mov(ecx, FieldOperand(ebx, HeapObject::kMapOffset));
+  __ cmp(ecx, Factory::heap_number_map());
+  __ j(not_equal, &miss);
+
+  __ bind(&index_ok);
+  // Duplicate receiver and key since they are expected on the stack after
+  // the KeyedLoadIC call.
+  __ push(ebx);  // receiver
+  __ push(edx);  // key
+  __ push(eax);  // return address
+  __ InvokeBuiltin(Builtins::STRING_CHAR_AT, JUMP_FUNCTION);
+
+  __ bind(&miss);
+  __ push(eax);
+  GenerateMiss(masm);
+}
+
+
 void KeyedLoadIC::GenerateExternalArray(MacroAssembler* masm,
                                         ExternalArrayType array_type) {
   // ----------- S t a t e -------------
   //  -- esp[0] : return address
   //  -- esp[4] : key
   //  -- esp[8] : receiver
   // -----------------------------------
   Label slow, failed_allocation;
 
   // Load name and receiver.
@@ skipping 1035 matching lines @@
 
   // Do tail-call to runtime routine.
   __ TailCallRuntime(
       ExternalReference(IC_Utility(kSharedStoreIC_ExtendStorage)), 3, 1);
 }
 
 #undef __
 
 
 } }  // namespace v8::internal