Fix FastPixelArrayStore on X64 platform.

src/x64/code-stubs-x64.cc

 // Copyright 2011 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 4819 matching lines @@
     __ CheckMap(elements, Factory::pixel_array_map(), not_pixel_array, true);
   } else {
     if (FLAG_debug_code) {
       // Map check should have already made sure that elements is a pixel array.
       __  Cmp(FieldOperand(elements, HeapObject::kMapOffset),
               Factory::pixel_array_map());
       __ Assert(equal, "Elements isn't a pixel array");
     }
   }
 
-  // Some callers already have verified that the key is a smi.  key_not_smi is
-  // set to NULL as a sentinel for that case.  Otherwise, add an explicit check
-  // to ensure the key is a smi must be added.
-  if (key_not_smi != NULL) {
-    __ JumpIfNotSmi(key, key_not_smi);
-  } else {
-    if (FLAG_debug_code) {
-      __ AbortIfNotSmi(key);
-    }
-  }
-
   // Key must be a smi and it must be in range.
   if (key_is_untagged) {
     untagged_key = key;
   } else {
+    // Some callers already have verified that the key is a smi.  key_not_smi is
+    // set to NULL as a sentinel for that case.  Otherwise, add an explicit
+    // check to ensure the key is a smi.
+    if (key_not_smi != NULL) {
+      __ JumpIfNotSmi(key, key_not_smi);
+    } else {
+      if (FLAG_debug_code) {
+        __ AbortIfNotSmi(key);
+      }
+    }
     __ SmiToInteger32(untagged_key, key);
   }
   __ cmpl(untagged_key, FieldOperand(elements, PixelArray::kLengthOffset));
   __ j(above_equal, out_of_range);  // unsigned check handles negative keys.
 
   // Value must be a smi.
   __ JumpIfNotSmi(value, value_not_smi);
   __ SmiToInteger32(untagged_value, value);
 
   {  // Clamp the value to [0..255].
     NearLabel done;
     __ testl(untagged_value, Immediate(0xFFFFFF00));
     __ j(zero, &done);
     __ setcc(negative, untagged_value);  // 1 if negative, 0 if positive.
     __ decb(untagged_value);  // 0 if negative, 255 if positive.
     __ bind(&done);
   }
 
   __ movq(external_pointer,
           FieldOperand(elements, PixelArray::kExternalPointerOffset));
   __ movb(Operand(external_pointer, untagged_key, times_1, 0), untagged_value);
   __ ret(0);  // Return value in eax.
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64