(g77.info) Better Optimization

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 Better Optimization
 ===================
 
    Much of this work should be put off until after `g77' has all the
 features necessary for its widespread acceptance as a useful F77
 compiler.  However, perhaps this work can be done in parallel during
 the feature-adding work.
 
    * Do the equivalent of the trick of putting `extern inline' in front
      of every function definition in `libg2c' and #include'ing the
      resulting file in `f2c'+`gcc'--that is, inline all
      run-time-library functions that are at all worth inlining.  (Some
      of this has already been done, such as for integral
      exponentiation.)
 
    * When doing `CHAR_VAR = CHAR_FUNC(...)', and it's clear that types
      line up and `CHAR_VAR' is addressable or not a `VAR_DECL', make
      `CHAR_VAR', not a temporary, be the receiver for `CHAR_FUNC'.
      (This is now done for `COMPLEX' variables.)
 
    * Design and implement Fortran-specific optimizations that don't
      really belong in the back end, or where the front end needs to
      give the back end more info than it currently does.
 
    * Design and implement a new run-time library interface, with the
      code going into `libgcc' so no special linking is required to link
      Fortran programs using standard language features.  This library
      would speed up lots of things, from I/O (using precompiled formats,
      doing just one, or, at most, very few, calls for arrays or array
      sections, and so on) to general computing (array/section
      implementations of various intrinsics, implementation of commonly
      performed loops that aren't likely to be optimally compiled
      otherwise, etc.).
 
      Among the important things the library would do are:
 
         * Be a one-stop-shop-type library, hence shareable and usable
           by all, in that what are now library-build-time options in
           `libg2c' would be moved at least to the `g77' compile phase,
           if not to finer grains (such as choosing how list-directed
           I/O formatting is done by default at `OPEN' time, for
           preconnected units via options or even statements in the main
           program unit, maybe even on a per-I/O basis with appropriate
           pragma-like devices).
 
    * Probably requiring the new library design, change interface to
      normally have `COMPLEX' functions return their values in the way
      `gcc' would if they were declared `__complex__ float', rather than
      using the mechanism currently used by `CHARACTER' functions
      (whereby the functions are compiled as returning void and their
      first arg is a pointer to where to store the result).  (Don't
      append underscores to external names for `COMPLEX' functions in
      some cases once `g77' uses `gcc' rather than `f2c' calling
      conventions.)
 
    * Do something useful with `doiter' references where possible.  For
      example, `CALL FOO(I)' cannot modify `I' if within a `DO' loop
      that uses `I' as the iteration variable, and the back end might
      find that info useful in determining whether it needs to read `I'
      back into a register after the call.  (It normally has to do that,
      unless it knows `FOO' never modifies its passed-by-reference
      argument, which is rarely the case for Fortran-77 code.)
 

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