Eliminate redundant smi checks

src/arm/lithium-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 2735 matching lines @@
   Register scratch = scratch0();
 
   // Load the result.
   __ add(scratch, elements, Operand(key, LSL, kPointerSizeLog2));
   uint32_t offset = FixedArray::kHeaderSize +
                     (instr->additional_index() << kPointerSizeLog2);
   __ ldr(result, FieldMemOperand(scratch, offset));
 
   // Check for the hole value.
   if (instr->hydrogen()->RequiresHoleCheck()) {
-    __ LoadRoot(scratch, Heap::kTheHoleValueRootIndex);
-    __ cmp(result, scratch);
-    DeoptimizeIf(eq, instr->environment());
+    if (IsFastSmiElementsKind(elements_kind())) {
+      __ tst(result, Operand(kSmiTagMask));
+      DeoptimizeIf(ne, instr->environment());
+    } else {
+      __ LoadRoot(scratch, Heap::kTheHoleValueRootIndex);
+      __ cmp(result, scratch);
+      DeoptimizeIf(eq, instr->environment());
+    }
   }
 }
 
 
 void LCodeGen::DoLoadKeyedFastDoubleElement(
     LLoadKeyedFastDoubleElement* instr) {
   Register elements = ToRegister(instr->elements());
   bool key_is_constant = instr->key()->IsConstantOperand();
   Register key = no_reg;
   DwVfpRegister result = ToDoubleRegister(instr->result());
@@ skipping 2590 matching lines @@
   __ sub(scratch, result, Operand(index, LSL, kPointerSizeLog2 - kSmiTagSize));
   __ ldr(result, FieldMemOperand(scratch,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal