Pretenure ASCII cons string in high promotion mode.

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 4906 matching lines @@
   __ testl(rcx, Immediate(kStringEncodingMask));
   __ j(zero, &non_ascii);
   __ bind(&ascii_data);
   // Allocate an ASCII cons string.
   __ AllocateAsciiConsString(rcx, rdi, no_reg, &call_runtime);
   __ bind(&allocated);
   // Fill the fields of the cons string.
   __ movq(FieldOperand(rcx, ConsString::kLengthOffset), rbx);
   __ movq(FieldOperand(rcx, ConsString::kHashFieldOffset),
           Immediate(String::kEmptyHashField));
+
+  Label skip_write_barrier, after_writing;
+  ExternalReference high_promotion_mode = ExternalReference::
+      new_space_high_promotion_mode_active_address(masm->isolate());
+  __ Load(rbx, high_promotion_mode);
+  __ testb(rbx, Immediate(1));
+  __ j(zero, &skip_write_barrier);
+
+  __ movq(FieldOperand(rcx, ConsString::kFirstOffset), rax);
+  __ RecordWriteField(rcx,
+                      ConsString::kFirstOffset,
+                      rax,
+                      rbx,
+                      kDontSaveFPRegs);
+  __ movq(FieldOperand(rcx, ConsString::kSecondOffset), rdx);
+  __ RecordWriteField(rcx,
+                      ConsString::kSecondOffset,
+                      rdx,
+                      rbx,
+                      kDontSaveFPRegs);
+  __ jmp(&after_writing);
+
+  __ bind(&skip_write_barrier);
   __ movq(FieldOperand(rcx, ConsString::kFirstOffset), rax);
   __ movq(FieldOperand(rcx, ConsString::kSecondOffset), rdx);
+
+  __ bind(&after_writing);
+
   __ movq(rax, rcx);
   __ IncrementCounter(counters->string_add_native(), 1);
   __ ret(2 * kPointerSize);
   __ bind(&non_ascii);
   // At least one of the strings is two-byte. Check whether it happens
   // to contain only one byte characters.
   // rcx: first instance type AND second instance type.
   // r8: first instance type.
   // r9: second instance type.
   __ testb(rcx, Immediate(kOneByteDataHintMask));
@@ skipping 1418 matching lines @@
   // and ElementsTransitionGenerator::GenerateDoubleToObject
   { REG(rdx), REG(rbx), REG(rdi), EMIT_REMEMBERED_SET},
   { REG(rdx), REG(rbx), REG(rdi), OMIT_REMEMBERED_SET},
   // ElementsTransitionGenerator::GenerateSmiToDouble
   // and ElementsTransitionGenerator::GenerateDoubleToObject
   { REG(rdx), REG(r11), REG(r15), EMIT_REMEMBERED_SET},
   // ElementsTransitionGenerator::GenerateDoubleToObject
   { REG(r11), REG(rax), REG(r15), EMIT_REMEMBERED_SET},
   // StoreArrayLiteralElementStub::Generate
   { REG(rbx), REG(rax), REG(rcx), EMIT_REMEMBERED_SET},
-  // FastNewClosureStub::Generate
+  // FastNewClosureStub::Generate and
+  // StringAddStub::Generate
   { REG(rcx), REG(rdx), REG(rbx), EMIT_REMEMBERED_SET},
+  // StringAddStub::Generate
+  { REG(rcx), REG(rax), REG(rbx), EMIT_REMEMBERED_SET},
   // Null termination.
   { REG(no_reg), REG(no_reg), REG(no_reg), EMIT_REMEMBERED_SET}
 };
 
 #undef REG
 
 bool RecordWriteStub::IsPregenerated() {
   for (AheadOfTimeWriteBarrierStubList* entry = kAheadOfTime;
        !entry->object.is(no_reg);
        entry++) {
@@ skipping 588 matching lines @@
     __ jmp(generic_construct_stub, RelocInfo::CODE_TARGET);
   }
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64