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(g77-300.info)Program Speed

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Program Speed
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   `g77' has the potential to better optimize code than `f2c', even
when `gcc' is used to compile the output of `f2c', because `f2c' must
necessarily translate Fortran into a somewhat lower-level language (C)
that cannot preserve all the information that is potentially useful for
optimization, while `g77' can gather, preserve, and transmit that
information directly to the GBE.

   For example, `g77' implements `ASSIGN' and assigned `GOTO' using
direct assignment of pointers to labels and direct jumps to labels,
whereas `f2c' maps the assigned labels to integer values and then uses
a C `switch' statement to encode the assigned `GOTO' statements.

   However, as is typical, theory and reality don't quite match, at
least not in all cases, so it is still the case that `f2c' plus `gcc'
can generate code that is faster than `g77'.

   Version 0.5.18 of `g77' offered default settings and options, via
patches to the `gcc' back end, that allow for better program speed,
though some of these improvements also affected the performance of
programs translated by `f2c' and then compiled by `g77''s version of
`gcc'.

   Version 0.5.20 of `g77' offers further performance improvements, at
least one of which (alias analysis) is not generally applicable to
`f2c' (though `f2c' could presumably be changed to also take advantage
of this new capability of the `gcc' back end, assuming this is made
available in an upcoming release of `gcc').