MIPS: Pretenure ASCII cons string in high promotion mode.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index 301e92f23d4653b12c74030067544469fa2a8fbc..81e9ec980e6b8b56e2bf79f275046a4ff1999472 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -3135,8 +3135,34 @@ void MacroAssembler::AllocateAsciiConsString(Register result,
                                              Register scratch1,
                                              Register scratch2,
                                              Label* gc_required) {
-  Allocate(ConsString::kSize, result, scratch1, scratch2, gc_required,
-           TAG_OBJECT);
+  Label allocate_new_space, install_map;
+  AllocationFlags flags = TAG_OBJECT;
+
+  ExternalReference high_promotion_mode = ExternalReference::
+      new_space_high_promotion_mode_active_address(isolate());
+  li(scratch1, Operand(high_promotion_mode));
+  lw(scratch1, MemOperand(scratch1, 0));
+  Branch(&allocate_new_space, eq, scratch1, Operand(zero_reg));
+
+  Allocate(ConsString::kSize,
+           result,
+           scratch1,
+           scratch2,
+           gc_required,
+           static_cast<AllocationFlags>(flags | PRETENURE_OLD_POINTER_SPACE));
+
+  jmp(&install_map);
+
+  bind(&allocate_new_space);
+  Allocate(ConsString::kSize,
+           result,
+           scratch1,
+           scratch2,
+           gc_required,
+           flags);
+
+  bind(&install_map);
+
   InitializeNewString(result,
                       length,
                       Heap::kConsAsciiStringMapRootIndex,