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(g77-295.info)Overly Convenient Options

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Overly Convenient Command-line Options
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   These options should be used only as a quick-and-dirty way to
determine how well your program will run under different compilation
models without having to change the source.  Some are more problematic
than others, depending on how portable and maintainable you want the
program to be (and, of course, whether you are allowed to change it at
all is crucial).

   You should not continue to use these command-line options to compile
a given program, but rather should make changes to the source code:

`-finit-local-zero'
     (This option specifies that any uninitialized local variables and
     arrays have default initialization to binary zeros.)

     Many other compilers do this automatically, which means lots of
     Fortran code developed with those compilers depends on it.

     It is safer (and probably would produce a faster program) to find
     the variables and arrays that need such initialization and provide
     it explicitly via `DATA', so that `-finit-local-zero' is not
     needed.

     Consider using `-Wuninitialized' (which requires `-O') to find
     likely candidates, but do not specify `-finit-local-zero' or
     `-fno-automatic', or this technique won't work.

`-fno-automatic'
     (This option specifies that all local variables and arrays are to
     be treated as if they were named in `SAVE' statements.)

     Many other compilers do this automatically, which means lots of
     Fortran code developed with those compilers depends on it.

     The effect of this is that all non-automatic variables and arrays
     are made static, that is, not placed on the stack or in heap
     storage.  This might cause a buggy program to appear to work
     better.  If so, rather than relying on this command-line option
     (and hoping all compilers provide the equivalent one), add `SAVE'
     statements to some or all program unit sources, as appropriate.
     Consider using `-Wuninitialized' (which requires `-O') to find
     likely candidates, but do not specify `-finit-local-zero' or
     `-fno-automatic', or this technique won't work.

     The default is `-fautomatic', which tells `g77' to try and put
     variables and arrays on the stack (or in fast registers) where
     possible and reasonable.  This tends to make programs faster.

     *Note:* Automatic variables and arrays are not affected by this
     option.  These are variables and arrays that are *necessarily*
     automatic, either due to explicit statements, or due to the way
     they are declared.  Examples include local variables and arrays
     not given the `SAVE' attribute in procedures declared `RECURSIVE',
     and local arrays declared with non-constant bounds (automatic
     arrays).  Currently, `g77' supports only automatic arrays, not
     `RECURSIVE' procedures or other means of explicitly specifying
     that variables or arrays are automatic.

`-fGROUP-intrinsics-hide'
     Change the source code to use `EXTERNAL' for any external procedure
     that might be the name of an intrinsic.  It is easy to find these
     using `-fGROUP-intrinsics-disable'.