Technique for finding regressions in the C++ parser

[Craig Rodrigues <rodrigc at attbi dot com>]

Hi,

I'm very interested in C++ support in GCC, so I try
to help where I can by isolating C++ bugs once in a while.
C++ seems like an insane language for a compiler writer. :)

This technique may seem very obvious to those of
you more familiar with GCC, but I just stumbled across
it in the past few days, and it seems to work.

The methodology involves:
(1)  For a piece of code which causes a compiler Internal
     Compiler Error (ICE), get preprocessed source
     with the -save-temps flag, or create a small reproduceable
     testcase.  Volker Reichelt and Wolfgang Bangerth
     seem pretty good at creating small testcases.

(2)  Check out gcc from the read-only CVS repository with the CVSROOT
     :pserver:anoncvs@subversions.gnu.org:/cvsroot/gcc
     (be kind to developers who use the read/write repository)
     according to the instructions at http://gcc.gnu.org/cvs.html

(3)  Follow the instructions to configure GCC at:
     http://gcc.gnu.org/install/configure.html

(4)  Instead of following the full bootstrap procedure, do the following:
     cd objdir
     make all-libiberty
     cd gcc
     make cc1plus

     This will build libiberty and cc1plus.  When you have cc1plus, you
     can feed your source code snippet to it:
     cc1plus -quiet testcase.ii

You can repeat steps (2)-(4), but use the cvs co -D [DATE] to check out
a version of GCC from a different date.  You can then do:
cvs diff -D [DATE1] -D [DATE2] [file] 
to find out what changes occured on a file or directory.

If you have a fast machine, and a fast net connection, then this
process goes by quickly. :)

It's pretty brute force, but the alternative is for me to learn how
to write a C++ compiler. ;)

Thanks, GCC crew, for a great piece of software!

-- 
Craig Rodrigues        
http://www.gis.net/~craigr    
rodrigc@attbi.com