Add "has fast elements" bit to maps and use it in inlined keyed loads.

src/arm/codegen-arm.cc

 // Copyright 2010 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 6098 matching lines @@
       Label check_inlined_codesize;
       masm_->bind(&check_inlined_codesize);
 #endif
       __ mov(scratch2, Operand(Factory::null_value()));
       __ cmp(scratch1, scratch2);
       deferred->Branch(ne);
 
       // Get the elements array from the receiver and check that it
       // is not a dictionary.
       __ ldr(scratch1, FieldMemOperand(receiver, JSObject::kElementsOffset));
-      __ ldr(scratch2, FieldMemOperand(scratch1, JSObject::kMapOffset));
-      __ LoadRoot(ip, Heap::kFixedArrayMapRootIndex);
-      __ cmp(scratch2, ip);
-      deferred->Branch(ne);
+      if (FLAG_debug_code) {
+        __ ldr(scratch2, FieldMemOperand(scratch1, JSObject::kMapOffset));
+        __ LoadRoot(ip, Heap::kFixedArrayMapRootIndex);
+        __ cmp(scratch2, ip);
+        __ Assert(eq, "JSObject with fast elements map has slow elements");
+      }
 
       // Check that key is within bounds. Use unsigned comparison to handle
       // negative keys.
       __ ldr(scratch2, FieldMemOperand(scratch1, FixedArray::kLengthOffset));
       __ cmp(scratch2, key);
       deferred->Branch(ls);  // Unsigned less equal.
 
       // Load and check that the result is not the hole (key is a smi).
       __ LoadRoot(scratch2, Heap::kTheHoleValueRootIndex);
       __ add(scratch1,
              scratch1,
              Operand(FixedArray::kHeaderSize - kHeapObjectTag));
       __ ldr(scratch1,
              MemOperand(scratch1, key, LSL,
                         kPointerSizeLog2 - (kSmiTagSize + kSmiShiftSize)));
       __ cmp(scratch1, scratch2);
       deferred->Branch(eq);
 
       __ mov(r0, scratch1);
       // Make sure that the expected number of instructions are generated.
-      ASSERT_EQ(kInlinedKeyedLoadInstructionsAfterPatch,
+      ASSERT_EQ(GetInlinedKeyedLoadInstructionsAfterPatch(),
                 masm_->InstructionsGeneratedSince(&check_inlined_codesize));
     }
 
     deferred->BindExit();
   }
 }
 
 
 void CodeGenerator::EmitKeyedStore(StaticType* key_type) {
   // Generate inlined version of the keyed store if the code is in a loop
@@ skipping 4542 matching lines @@
   __ bind(&string_add_runtime);
   __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM