A64: Optimize a loop by using post-indexing.

src/a64/full-codegen-a64.cc

Index: src/a64/full-codegen-a64.cc
diff --git a/src/a64/full-codegen-a64.cc b/src/a64/full-codegen-a64.cc
index eca3f064f37a3f9784eda69cac4f819e3e199b2a..ec5d3397818dc0e11254ac8af21ef9ec5516acae 100644
--- a/src/a64/full-codegen-a64.cc
+++ b/src/a64/full-codegen-a64.cc
@@ -2805,16 +2805,13 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
 
   // 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);