A64: Optimize a loop by using post-indexing.

src/a64/full-codegen-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 2787 matching lines @@
   __ Mul(descriptors_length, descriptors_length, x15);
   // Calculate location of the first key name.
   __ Add(descriptors, descriptors,
          DescriptorArray::kFirstOffset - kHeapObjectTag);
   // Calculate the end of the descriptor array.
   __ Add(descriptors_end, descriptors,
          Operand(descriptors_length, LSL, kPointerSizeLog2));
 
   // Loop through all the keys in the descriptor array. If one of these is the
   // string "valueOf" the result is false.
-  // TODO(all): optimise this loop to combine the add and ldr into an
-  // addressing mode.
   Register valueof_string = x1;
+  int descriptor_size = DescriptorArray::kDescriptorSize * kPointerSize;
   __ Mov(valueof_string, Operand(isolate()->factory()->value_of_string()));
   __ Bind(&loop);
-  __ Ldr(x15, MemOperand(descriptors));
+  __ Ldr(x15, MemOperand(descriptors, descriptor_size, PostIndex));
   __ Cmp(x15, valueof_string);
   __ B(eq, if_false);
-  __ Add(descriptors, descriptors,
-         DescriptorArray::kDescriptorSize * kPointerSize);
   __ Cmp(descriptors, descriptors_end);
   __ B(ne, &loop);
 
   __ Bind(&done);
 
   // Set the bit in the map to indicate that there is no local valueOf field.
   __ Ldrb(x2, FieldMemOperand(map, Map::kBitField2Offset));
   __ Orr(x2, x2, 1 << Map::kStringWrapperSafeForDefaultValueOf);
   __ Strb(x2, FieldMemOperand(map, Map::kBitField2Offset));
 
@@ skipping 2176 matching lines @@
   return previous_;
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64