Eliminate redundant smi checks

src/ia32/lithium-codegen-ia32.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 2417 matching lines @@
   // Load the result.
   __ mov(result,
          BuildFastArrayOperand(instr->elements(),
                                instr->key(),
                                FAST_ELEMENTS,
                                FixedArray::kHeaderSize - kHeapObjectTag,
                                instr->additional_index()));
 
   // Check for the hole value.
   if (instr->hydrogen()->RequiresHoleCheck()) {
-    __ cmp(result, factory()->the_hole_value());
-    DeoptimizeIf(equal, instr->environment());
+    if (IsFastSmiElementsKind(instr->hydrogen()->elements_kind())) {
+      __ test(result, Immediate(kSmiTagMask));
+      DeoptimizeIf(not_equal, instr->environment());
+    } else {
+      __ cmp(result, factory()->the_hole_value());
+      DeoptimizeIf(equal, instr->environment());
+    }
   }
 }
 
 
 void LCodeGen::DoLoadKeyedFastDoubleElement(
     LLoadKeyedFastDoubleElement* instr) {
   XMMRegister result = ToDoubleRegister(instr->result());
 
   if (instr->hydrogen()->RequiresHoleCheck()) {
     int offset = FixedDoubleArray::kHeaderSize - kHeapObjectTag +
@@ skipping 1417 matching lines @@
   __ SmiTag(ToRegister(input));
 }
 
 
 void LCodeGen::DoSmiUntag(LSmiUntag* instr) {
   LOperand* input = instr->InputAt(0);
   ASSERT(input->IsRegister() && input->Equals(instr->result()));
   if (instr->needs_check()) {
     __ test(ToRegister(input), Immediate(kSmiTagMask));
     DeoptimizeIf(not_zero, instr->environment());
+  } else {
+    if (FLAG_debug_code) {
+      __ AbortIfNotSmi(ToRegister(input));
+    }
   }
   __ SmiUntag(ToRegister(input));
 }
 
 
 void LCodeGen::EmitNumberUntagD(Register input_reg,
                                 Register temp_reg,
                                 XMMRegister result_reg,
                                 bool deoptimize_on_undefined,
                                 bool deoptimize_on_minus_zero,
@@ skipping 1221 matching lines @@
                               FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32