X64: Many small tweaks and more usages of "load smi as int32".

src/x64/macro-assembler-x64.h

 // Copyright 2009 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 192 matching lines @@
   // NOTICE: Destroys the dst register even if unsuccessful!
   void Integer32ToSmi(Register dst, Register src, Label* on_overflow);
 
   // Adds constant to src and tags the result as a smi.
   // Result must be a valid smi.
   void Integer64PlusConstantToSmi(Register dst, Register src, int constant);
 
   // Convert smi to 32-bit integer. I.e., not sign extended into
   // high 32 bits of destination.
   void SmiToInteger32(Register dst, Register src);
+  void SmiToInteger32(Register dst, const Operand& src);
 
   // Convert smi to 64-bit integer (sign extended if necessary).
   void SmiToInteger64(Register dst, Register src);
 
   // Multiply a positive smi's integer value by a power of two.
   // Provides result as 64-bit integer value.
   void PositiveSmiTimesPowerOfTwoToInteger64(Register dst,
                                              Register src,
                                              int power);
 
@@ skipping 653 matching lines @@
   }                                                                       \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_