Date: Wed, 5 Nov 1997 19:45:50 -0800 (PST)
Message-Id: <199711060345.TAA03134@adit.ap.net>
Mime-Version: 1.0
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To: d DOT pearson AT EXT DOT canterbury DOT ac DOT nz, djgpp AT delorie DOT com
From: Nate Eldredge <eldredge AT ap DOT net>
Subject: Re: G++ can't optimise my code!
Precedence: bulk

At 02:29  11/6/1997 +1200, Davin Pearson wrote:
>I find it hard to believe that very many people seriously
>use G++.  On many occaisons it has barked something like this:
>
>cd ~/skid/
>make run CCOPT=-O2
>gcc -c -O2  main.cc -o main.o
>axle.h: In method `void Car::evolve()':
>In file included from main.cc:8:
>axle.h:273: Internal compiler error.
>axle.h:273: Please submit a full bug report to
>`bug-g++@prep.ai.mit.edu'.
>make.exe: *** [main.o] Error 1
>
>Having just read the DJGPP FAQ on this problem, I can report having no
>joy with -fno-strength-reduce, and "gcc -v" says version 2.7.2.
Here's my experience:
The code compiled okay on my machine. I am using GCC 2.7.2.1, with
`cc1plus.exe' stubedited to 1MB of stack. (Also, I'm using Allegro 2.2.)
But, it took almost 2 minutes to compile (P133, 16MB ram, 8MB free after
ramdisk, cache, etc). Adding `-dm' to the compiler command line revealed
that it took about 22 MB of memory (!). This seems to be a pathological
case, since it doesn't seem to be a particularly complicated source.

I would try either upgrading to 2.7.2.1, or stubediting `cc1plus' to a
larger stack, or both. Stack overflow can, IIRC, cause `Internal Compiler
Error'.
>
>I have submitted a similar bug report in the past (Having tracked down
>that bug to a particular construct), only to receive no
>acknowledgement of my bug report! 
The GCC/G++ maintainers are very busy, and frequently don't respond to bug
reports. Did you give them all the details and a preprocessed file, like the
manual says to?

>If only the optimisation-part of G++ is buggy, then perhaps I could
>use a free-ware/gnu-ware C++ to C convertor and use the output of that
>to feed into the (hopefully bugfree) GNU C compiler.  Does anyone know
>of a such a program? 
This gets asked frequently. It seems the only such beast that ever existed
was AT&T's `cfront', which is by now quite obsolete and definitely not free.

>Why is G++ so bad?  Is it C++'s fault or something?  I assume that Gcc
>is a lot less buggy since I have compiled some large projects with it.
Well, the C part gets pounded on a lot more, especially in Unix-land.  Also,
C++ is a *much* more complicated language, and a C++ compiler gets
proportionally more complicated, harder to maintain, and buggy. I think it's
also possible you may have hit a special case. Please continue to report
bugs to GNU folk, even if they don't respond. Then we can all enjoy a better
compiler.


Nate Eldredge
eldredge AT ap DOT net