Optimization levels vs. debugging levels

If you are specifying the -g, -G0, or -G1 compiler options for debugging purposes (e.g., in preparation for running your program with totalview), be aware that these options may have an effect on the optimization levels you specified:

If you specify -G0 (or equivalently -g), the compiler will automatically use -O0, overriding any -O options you specified.

If you specify -G1, things get a little more complicated. See the reference, or get a compiler listing (as explained in the next paragraph).

To see what compiler options are actually used in these cases (or in any case), you can request a compiler listing by using one of the -r options. For example:

   f90 -r0 ... myprog.f

will create a listing file and put it in file myprog.lst.

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