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Date: Thu, 2 Mar 2000 15:39:56 +0100 (MET)
From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
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To: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
cc: djgpp-workers AT delorie DOT com
Subject: Re: Debugging difficulties with GCC 2.95.2
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On Thu, 2 Mar 2000, Eli Zaretskii wrote:

> Funny, a similar problem seems to be bugging the GDB test suite.  You 
> might find the thread whose subject is "Regressions problem (200 
> failures)" interesting.  If you don't read gdb AT sourceware DOT cygnus DOT com, you 
> can browse it via the Web at http://sourceware.cygnus.com/ml/gdb/2000-q1.

I'll see, if I find the time. Spare online time is harder to get at than
spare time at home, where I can brood over the GCC source tree as long as
I don't fall off my chair sleeping :-)

> > Compiling with '-g -O1 -mno-schedule-prologue' seemed to fix the problem.
> 
> What happens if you use -O2 -mno-schedule-prologue?  

No difference at all, in the test case. My test function is so simple
that -O2 makes no difference whatsoever, compared to -O1 (I removed the
sqrt() call and #include <math.h>, to get more easily diff-able output
from all stages, including the '-d<letter>' RTL debugging dumps.

> If that still 
> produces correct debug info, perhaps we want to introduce 
> -mno-schedule-prologue into specs? 

I think the more important question would be: does the bug really only
happen in ultra-short (<= 2 active code lines) functions, where this
workaround would probably fix it? And, of course, _how_ does
'-mno-schedule-prologue' manage to work around the problem? Is it
an optimization <-> debug info problem, or is there a bug in the
RTL introduced to implement the pro/epilogues? 

I've had a glance at this week's snapshot of gcc (egcs-20000228), and
there's been quite some activity in the i386 stack frame handling stuff,
recently, including the prologue/epilogue generator.

Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.