ARM: make MacroAssembler::LoadRoot emit exactly one instruction when in predictable code size scope.

src/arm/full-codegen-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 147 matching lines @@
   }
 
   // Open a frame scope to indicate that there is a frame on the stack.  The
   // MANUAL indicates that the scope shouldn't actually generate code to set up
   // the frame (that is done below).
   FrameScope frame_scope(masm_, StackFrame::MANUAL);
 
   int locals_count = info->scope()->num_stack_slots();
 
   info->set_prologue_offset(masm_->pc_offset());
-  // The following four instructions must remain together and unmodified for
-  // code aging to work properly.
-  __ stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
-  // Load undefined value here, so the value is ready for the loop
-  // below.
-  __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
-  // Adjust fp to point to caller's fp.
-  __ add(fp, sp, Operand(2 * kPointerSize));
+  {
+    PredictableCodeSizeScope predictible_code_size_scope(
+        masm_, kNoCodeAgeSequenceLength * Assembler::kInstrSize);
+    // The following three instructions must remain together and unmodified
+    // for code aging to work properly.
+    __ stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
+    // Load undefined value here, so the value is ready for the loop
+    // below.
+    __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
+    // Adjust FP to point to saved FP.
+    __ add(fp, sp, Operand(2 * kPointerSize));
+  }
 
   { Comment cmnt(masm_, "[ Allocate locals");
     for (int i = 0; i < locals_count; i++) {
       __ push(ip);
     }
   }
 
   bool function_in_register = true;
 
   // Possibly allocate a local context.
@@ skipping 4341 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM