run incorrecly using -O?

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  • Onix
    #1

    run incorrecly using -O?

    I wrote a program and when compile it with g++ without optimized
    option -O, the final program runs correctly, but if I compile it using
    -O then the final program produced error.

    Is there anything I need to aware when using -O?
    Tags: None
    • Victor Bazarov
      #2
      Re: run incorrecly using -O?

      Onix wrote:
      I wrote a program and when compile it with g++ without optimized
      option -O, the final program runs correctly, but if I compile it using
      -O then the final program produced error.
      >
      Is there anything I need to aware when using -O?
      Your program most likely has undefined behaviour which changes if it
      is compiled (optimized) a bit more than not at all. You need to aware
      how to debug your program, and spend some time doing that.

      V
      --
      Please remove capital 'A's when replying by e-mail
      I do not respond to top-posted replies, please don't ask


        Comment

        • utab
          #3
          Re: run incorrecly using -O?

          On Apr 10, 8:45 pm, Onix <onix.x...@gmai l.comwrote:
          I wrote a program and when compile it with g++ without optimized
          option -O, the final program runs correctly, but if I compile it using
          -O then the final program produced error.
          >
          Is there anything I need to aware when using -O?
          It is best if you paste some code to comment on?

          Rgds,

            Comment

            • red floyd
              #4
              Re: run incorrecly using -O?

              Victor Bazarov wrote:
              Onix wrote:
              >I wrote a program and when compile it with g++ without optimized
              >option -O, the final program runs correctly, but if I compile it using
              >-O then the final program produced error.
              >>
              >Is there anything I need to aware when using -O?
              >
              Your program most likely has undefined behaviour which changes if it
              is compiled (optimized) a bit more than not at all. You need to aware
              how to debug your program, and spend some time doing that.
              >
              That's not necessarily the case. I dealt with some (C -- not C++) code
              where gcc did some overly aggressive optimizations that led to segfaults
              and bus errors (granted, the code was using ugly constructs, but they
              were well-defined).

                Comment

                • Victor Bazarov
                  #5
                  Re: run incorrecly using -O?

                  red floyd wrote:
                  Victor Bazarov wrote:
                  >Onix wrote:
                  >>I wrote a program and when compile it with g++ without optimized
                  >>option -O, the final program runs correctly, but if I compile it
                  >>using -O then the final program produced error.
                  >>>
                  >>Is there anything I need to aware when using -O?
                  >>
                  >Your program most likely has undefined behaviour which changes if it
                  >is compiled (optimized) a bit more than not at all. You need to
                  >aware how to debug your program, and spend some time doing that.
                  >>
                  That's not necessarily the case. I dealt with some (C -- not C++)
                  code where gcc did some overly aggressive optimizations that led to
                  segfaults and bus errors (granted, the code was using ugly
                  constructs, but they were well-defined).
                  Right. Compiler/optimizer defects can affect the outcome as well,
                  although they are *less likely*. First thing to check is the case
                  of uninitialised pointer. But this cannot be concluded with any
                  certainty without looking at the code.

                  V
                  --
                  Please remove capital 'A's when replying by e-mail
                  I do not respond to top-posted replies, please don't ask


                    Comment

                    • Victor Bazarov
                      #6
                      Re: run incorrecly using -O?

                      red floyd wrote:
                      Victor Bazarov wrote:
                      >Onix wrote:
                      >>I wrote a program and when compile it with g++ without optimized
                      >>option -O, the final program runs correctly, but if I compile it
                      >>using -O then the final program produced error.
                      >>>
                      >>Is there anything I need to aware when using -O?
                      >>
                      >Your program most likely has undefined behaviour which changes if it
                      >is compiled (optimized) a bit more than not at all. You need to
                      >aware how to debug your program, and spend some time doing that.
                      >>
                      That's not necessarily the case. I dealt with some (C -- not C++)
                      code where gcc did some overly aggressive optimizations that led to
                      segfaults and bus errors (granted, the code was using ugly
                      constructs, but they were well-defined).
                      Right. Compiler/optimizer defects can affect the outcome as well,
                      although they are *less likely*. First thing to check is the case
                      of uninitialised pointer. But this cannot be concluded with any
                      certainty without looking at the code.

                      V
                      --
                      Please remove capital 'A's when replying by e-mail
                      I do not respond to top-posted replies, please don't ask


                        Comment

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