Add a premonomorphic state to the call target cache.

src/a64/code-stubs-a64.cc

 // Copyright 2013 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 3174 matching lines @@
   //  x0 : number of arguments to the construct function
   //  x1 : the function to call
   //  x2 : feedback vector
   //  x3 : slot in feedback vector (smi)
   Label initialize, done, miss, megamorphic, not_array_function;
 
   ASSERT_EQ(*TypeFeedbackInfo::MegamorphicSentinel(masm->isolate()),
             masm->isolate()->heap()->undefined_value());
   ASSERT_EQ(*TypeFeedbackInfo::UninitializedSentinel(masm->isolate()),
             masm->isolate()->heap()->the_hole_value());
+  ASSERT_EQ(*TypeFeedbackInfo::PremonomorphicSentinel(masm->isolate()),
+            masm->isolate()->heap()->null_value());
 
   // Load the cache state.
   __ Add(x4, x2, Operand::UntagSmiAndScale(x3, kPointerSizeLog2));
   __ Ldr(x4, FieldMemOperand(x4, FixedArray::kHeaderSize));
 
   // A monomorphic cache hit or an already megamorphic state: invoke the
   // function without changing the state.
   __ Cmp(x4, x1);
   __ B(eq, &done);
 
   // If we came here, we need to see if we are the array function.
   // If we didn't have a matching function, and we didn't find the megamorph
   // sentinel, then we have in the slot either some other function or an
   // AllocationSite. Do a map check on the object in ecx.
   __ Ldr(x5, FieldMemOperand(x4, AllocationSite::kMapOffset));
   __ JumpIfNotRoot(x5, Heap::kAllocationSiteMapRootIndex, &miss);
 
   // Make sure the function is the Array() function
   __ LoadArrayFunction(x4);
   __ Cmp(x1, x4);
   __ B(ne, &megamorphic);
   __ B(&done);
 
   __ Bind(&miss);
 
   // A monomorphic miss (i.e, here the cache is not uninitialized) goes
   // megamorphic.
-  __ JumpIfRoot(x4, Heap::kTheHoleValueRootIndex, &initialize);
+  Label not_uninitialized;
+  __ JumpIfNotRoot(x4, Heap::kTheHoleValueRootIndex, &not_uninitialized);
+
+  // PremonomorphicSentinel is an immortal immovable object (null) so no
+  // write-barrier is needed.
+  __ Add(x4, x2, Operand::UntagSmiAndScale(x3, kPointerSizeLog2));
+  __ LoadRoot(x10, Heap::kNullValueRootIndex);
+  __ Str(x10, FieldMemOperand(x4, FixedArray::kHeaderSize));
+  __ B(&done);
+
+  // If the cache isn't uninitialized, it is either premonomorphic or
+  // monomorphic. If it is premonomorphic, we initialize it thus making
+  // it monomorphic. Otherwise, we go megamorphic.
+  __ Bind(&not_uninitialized);
+  __ JumpIfRoot(x4, Heap::kNullValueRootIndex, &initialize);
+
   // MegamorphicSentinel is an immortal immovable object (undefined) so no
   // write-barrier is needed.
   __ Bind(&megamorphic);
   __ Add(x4, x2, Operand::UntagSmiAndScale(x3, kPointerSizeLog2));
   __ LoadRoot(x10, Heap::kUndefinedValueRootIndex);
   __ Str(x10, FieldMemOperand(x4, FixedArray::kHeaderSize));
   __ B(&done);
 
   // An uninitialized cache is patched with the function or sentinel to
   // indicate the ElementsKind if function is the Array constructor.
@@ skipping 2479 matching lines @@
                               MemOperand(fp, 6 * kPointerSize),
                               NULL);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64