Why is the AVR GCC compiler using a full `CALL` even though I have set the `-mshort-calls` flag?





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I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...



enter image description here



Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...



    ...
35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
35fa: f8 94 cli
...


What am I doing wrong?










share|improve this question











$endgroup$



















    1












    $begingroup$


    I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...



    enter image description here



    Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...



        ...
    35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
    35fa: f8 94 cli
    ...


    What am I doing wrong?










    share|improve this question











    $endgroup$















      1












      1








      1





      $begingroup$


      I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...



      enter image description here



      Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...



          ...
      35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
      35fa: f8 94 cli
      ...


      What am I doing wrong?










      share|improve this question











      $endgroup$




      I have set the -mshort-calls flag which is documented to replace the 4 byte long CALL instruction with the 2 byte long RCALL instruction when possible to save flash space and and cycles...



      enter image description here



      Unfortunately the compiler is still using full CALL instructions even for a call that is only 2 bytes away...



          ...
      35f6: 0e 94 fd 1a call 0x35fa ; 0x35fa
      35fa: f8 94 cli
      ...


      What am I doing wrong?







      avr gcc rcall






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited 2 hours ago







      bigjosh

















      asked 2 hours ago









      bigjoshbigjosh

      7,2801736




      7,2801736






















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          $begingroup$

          It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.



          The new option is called -mrelax on the compiler command line or --relax on the linker command line...



          https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html



          After adding that flag, the above code compiled to...



          ...
          3584: 00 d0 rcall .+0 ; 0x3586
          3586: f8 94 cli
          ...


          If you happened to be using Atmel Studio, I put the flag here...



          enter image description here



          In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.






          share|improve this answer











          $endgroup$














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            $begingroup$

            It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.



            The new option is called -mrelax on the compiler command line or --relax on the linker command line...



            https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html



            After adding that flag, the above code compiled to...



            ...
            3584: 00 d0 rcall .+0 ; 0x3586
            3586: f8 94 cli
            ...


            If you happened to be using Atmel Studio, I put the flag here...



            enter image description here



            In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.






            share|improve this answer











            $endgroup$


















              4












              $begingroup$

              It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.



              The new option is called -mrelax on the compiler command line or --relax on the linker command line...



              https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html



              After adding that flag, the above code compiled to...



              ...
              3584: 00 d0 rcall .+0 ; 0x3586
              3586: f8 94 cli
              ...


              If you happened to be using Atmel Studio, I put the flag here...



              enter image description here



              In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.






              share|improve this answer











              $endgroup$
















                4












                4








                4





                $begingroup$

                It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.



                The new option is called -mrelax on the compiler command line or --relax on the linker command line...



                https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html



                After adding that flag, the above code compiled to...



                ...
                3584: 00 d0 rcall .+0 ; 0x3586
                3586: f8 94 cli
                ...


                If you happened to be using Atmel Studio, I put the flag here...



                enter image description here



                In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.






                share|improve this answer











                $endgroup$



                It appears that this option changed at some point and not all the documentation was updated. Atmel Studio also still uses the obsolete flag.



                The new option is called -mrelax on the compiler command line or --relax on the linker command line...



                https://gcc.gnu.org/onlinedocs/gcc-4.9.2/gcc/AVR-Options.html



                After adding that flag, the above code compiled to...



                ...
                3584: 00 d0 rcall .+0 ; 0x3586
                3586: f8 94 cli
                ...


                If you happened to be using Atmel Studio, I put the flag here...



                enter image description here



                In my case, this change resulted in significant flash savings. If you are here because you also need to save flash space and/or cycles, I'd also recommend looking into enabling Link Time Optimization which also offers great savings at no cost.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited 2 hours ago

























                answered 2 hours ago









                bigjoshbigjosh

                7,2801736




                7,2801736






























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