Re: gcc compile-time performance

[Neil Booth <neil at daikokuya dot demon dot co dot uk>]

Robert Dewar wrote:-

> > Many of the "proprietary compilers" will shame GCC under the table for
> > compilation times.  If you're knocking down a gig or more of source,
> > that absolutely does matter.
> 
> Well in the case of Ada, GNAT compares reasonably favorably with other
> proprietary Ada compilers in compilation speed, and very favorably in
> terms of generated code, though there are exceptions to the latter. 
> The front end of GNAT is very fast, so usually by far the larger part
> of the time is spent in the backend. How does this compare with the C++ case?

I think a big killer for GCC is the combination of overly-complex bison
parsers (necessary to keep state for various wacky things we want to do;
it's much easier to keep state for these things with a recursive descent
parser) and the genericity of "tree".  I strongly believe this is a
performance issue in the C family of front ends; for example in the
C front end there are many contortions in place for no other reason
than we use bison.

[Not to mention that if "tree" died to become a bunch of separate tree
types something with the improved type safety that would imply, many of
the tree checking macros could die too, reducing bootstrap times.]

Neil.