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(g77-295.info)Efficiency

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Improve Efficiency
==================

   Don't bother doing any performance analysis until most of the
following items are taken care of, because there's no question they
represent serious space/time problems, although some of them show up
only given certain kinds of (popular) input.

   * Improve `malloc' package and its uses to specify more info about
     memory pools and, where feasible, use obstacks to implement them.

   * Skip over uninitialized portions of aggregate areas (arrays,
     `COMMON' areas, `EQUIVALENCE' areas) so zeros need not be output.
     This would reduce memory usage for large initialized aggregate
     areas, even ones with only one initialized element.

     As of version 0.5.18, a portion of this item has already been
     accomplished.

   * Prescan the statement (in `sta.c') so that the nature of the
     statement is determined as much as possible by looking entirely at
     its form, and not looking at any context (previous statements,
     including types of symbols).  This would allow ripping out of the
     statement-confirmation, symbol retraction/confirmation, and
     diagnostic inhibition mechanisms.  Plus, it would result in
     much-improved diagnostics.  For example, `CALL
     some-intrinsic(...)', where the intrinsic is not a subroutine
     intrinsic, would result actual error instead of the
     unimplemented-statement catch-all.

   * Throughout `g77', don't pass line/column pairs where a simple
     `ffewhere' type, which points to the error as much as is desired
     by the configuration, will do, and don't pass `ffelexToken' types
     where a simple `ffewhere' type will do.  Then, allow new default
     configuration of `ffewhere' such that the source line text is not
     preserved, and leave it to things like Emacs' next-error function
     to point to them (now that `next-error' supports column, or,
     perhaps, character-offset, numbers).  The change in calling
     sequences should improve performance somewhat, as should not
     having to save source lines.  (Whether this whole item will
     improve performance is questionable, but it should improve
     maintainability.)

   * Handle `DATA (A(I),I=1,1000000)/1000000*2/' more efficiently,
     especially as regards the assembly output.  Some of this might
     require improving the back end, but lots of improvement in
     space/time required in `g77' itself can be fairly easily obtained
     without touching the back end.  Maybe type-conversion, where
     necessary, can be speeded up as well in cases like the one shown
     (converting the `2' into `2.').

   * If analysis shows it to be worthwhile, optimize `lex.c'.

   * Consider redesigning `lex.c' to not need any feedback during
     tokenization, by keeping track of enough parse state on its own.