Berkeley CSUA MOTD:Entry 35291
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2025/04/04 [General] UID:1000 Activity:popular
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2004/12/14-15 [Computer/SW/Compilers] UID:35291 Activity:moderate
12/14   If I have a C function like this
        void foo(void) {
          static const char unused1[] = "one";
          const char * const unused2 = "two";
          ...... some code ......
          return;
        }
        Is a compiler allowed to optimize away both unused1 and unused2?  When
        I do this in M$ C/C++ v13, it only optimizes away unused2 but not
        unused1.  I can't find any compiler switch to tell it to throw away
        unused1.  Any idea?  TIA.
        \_ I'm not certain of this, but I think the static declaration is
           preventing the compiler from optimizing away unused1.  If memory
           serves, internal static variables, external static variables, and
           global variables are all stored in the same region of memory
           (though I could see how alternate implementations are possible).
           Thus, at a certain point in the compilation process, static
           variables become indistinguishable from global variables.  Local
           variables are much easier to optimize away than global variables.
           I'm guessing that the optimizer either lacks the context needed
           or simply isn't smart enough to make the distinction so it doesn't
           even bother trying to optimize unused1 away. -dans
           \_ A compiler can optimize away any code if it doesn't affect the
              program.  You describe a common implementation but one that isn't
              required by the standard.  This is really a QoI question (Quality
              of Implementation).
        \_ v13?  What is that?
           \_ I meant Version 13.
              \_ And what is "Version 13" of an MS compiler?  Is that the
                 version of cl.exe for Visual Studio .Net?
                 \_ It's the version of cl.exe that comes with my DDK.
                    "Microsoft (R) 32-bit C/C++ Optimizing Compiler Version
                     13.00.9176 for 80x86"
                     \_ Okay, that's from Visual Studio .Net (7.0), not the
                        latest from http://VS.Net2003 (7.1).  Just checking.
2025/04/04 [General] UID:1000 Activity:popular
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