Pretenure ASCII cons string in high promotion mode.

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 5940 matching lines @@
   STATIC_ASSERT(kTwoByteStringTag == 0);
   __ tst(r4, Operand(kStringEncodingMask));
   __ tst(r5, Operand(kStringEncodingMask), ne);
   __ b(eq, &non_ascii);
 
   // Allocate an ASCII cons string.
   __ bind(&ascii_data);
   __ AllocateAsciiConsString(r7, r6, r4, r5, &call_runtime);
   __ bind(&allocated);
   // Fill the fields of the cons string.
+  Label skip_write_barrier, after_writing;
+  ExternalReference high_promotion_mode = ExternalReference::
+      new_space_high_promotion_mode_active_address(masm->isolate());
+  __ mov(r4, Operand(high_promotion_mode));
+  __ ldr(r4, MemOperand(r4, 0));
+  __ cmp(r4, Operand::Zero());
+  __ b(eq, &skip_write_barrier);
+
+  __ str(r0, FieldMemOperand(r7, ConsString::kFirstOffset));
+  __ RecordWriteField(r7,
+                      ConsString::kFirstOffset,
+                      r0,
+                      r4,
+                      kLRHasNotBeenSaved,
+                      kDontSaveFPRegs);
+  __ str(r1, FieldMemOperand(r7, ConsString::kSecondOffset));
+  __ RecordWriteField(r7,
+                      ConsString::kSecondOffset,
+                      r1,
+                      r4,
+                      kLRHasNotBeenSaved,
+                      kDontSaveFPRegs);
+  __ jmp(&after_writing);
+
+  __ bind(&skip_write_barrier);
   __ str(r0, FieldMemOperand(r7, ConsString::kFirstOffset));
   __ str(r1, FieldMemOperand(r7, ConsString::kSecondOffset));
+
+  __ bind(&after_writing);
+
   __ mov(r0, Operand(r7));
   __ IncrementCounter(counters->string_add_native(), 1, r2, r3);
   __ add(sp, sp, Operand(2 * kPointerSize));
   __ Ret();
 
   __ bind(&non_ascii);
   // At least one of the strings is two-byte. Check whether it happens
   // to contain only one byte characters.
   // r4: first instance type.
   // r5: second instance type.
@@ skipping 825 matching lines @@
   // and ElementsTransitionGenerator::GenerateDoubleToObject
   { REG(r2), REG(r3), REG(r9), EMIT_REMEMBERED_SET },
   { REG(r2), REG(r3), REG(r9), OMIT_REMEMBERED_SET },
   // ElementsTransitionGenerator::GenerateDoubleToObject
   { REG(r6), REG(r2), REG(r0), EMIT_REMEMBERED_SET },
   { REG(r2), REG(r6), REG(r9), EMIT_REMEMBERED_SET },
   // StoreArrayLiteralElementStub::Generate
   { REG(r5), REG(r0), REG(r6), EMIT_REMEMBERED_SET },
   // FastNewClosureStub::Generate
   { REG(r2), REG(r4), REG(r1), EMIT_REMEMBERED_SET },
+  // StringAddStub::Generate
+  { REG(r7), REG(r1), REG(r4), EMIT_REMEMBERED_SET },
+  { REG(r7), REG(r0), REG(r4), EMIT_REMEMBERED_SET },
   // Null termination.
   { REG(no_reg), REG(no_reg), REG(no_reg), EMIT_REMEMBERED_SET}
 };
 
 #undef REG
 
 
 bool RecordWriteStub::IsPregenerated() {
   for (const AheadOfTimeWriteBarrierStubList* entry = kAheadOfTime;
        !entry->object.is(no_reg);
@@ skipping 560 matching lines @@
      __ Jump(generic_construct_stub, RelocInfo::CODE_TARGET);
   }
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM