optimization/9279: [3.2 regression] [Sparc] combine bug

[Gabriel Dos_Reis]

The following reply was made to PR optimization/9279; it has been noted by GNATS.

From: Gabriel Dos_Reis <gdosreis@sophia.inria.fr>
To: Eric Botcazou <ebotcazou@libertysurf.fr>
Cc: Matthias Klose <doko@cs.tu-berlin.de>, frank@g-n-u.de,
   gcc-bugs@gcc.gnu.org, gcc-gnats@gcc.gnu.org
Subject: Re: optimization/9279: [3.2 regression] [Sparc] combine bug
Date: Wed, 29 Jan 2003 02:29:15 +0100 (MET)

 | > As I explained to Eric, I would have been pleased to apply that
 | > patch.  However it turned out that it introduces (1) a performance
 | > regression; (2) possibly a wrong code generation -- David gave some
 | > references.
 | 
 | Note that, as I said to David, I'm very skeptical about (2) for the patch 
 | _alone_ because it simply pessimizes (however rightfully, they are just 
 | plain wrong in the general case) the values returned by two predicate 
 | functions:
 
 Sorry, I mistranslated your agreement on David's statement:
 
   >       This patch and the necessary PowerPC patch exposed other bugs in
   > the compiler regarding REG_EQUAL notes in loop unrolling:
   >
   > 2002-10-04  David Edelsohn  <edelsohn@gnu.org>
   >
   >         * unroll.c (copy_loop_body): Remove REG_EQUAL note attached to
   >         copied instruction if the note is not loop invariant.
   >
   > The patches may have other co-dependencies we do not know about.
 
   Ok.
 
 [...]
 
 | > I would suggest that, right after 3.2.2 release, interested parties
 | > investigate the issue and submit a complete patch which we would
 | > have sufficient time to test.
 | 
 | I'm not very optimistic about this happening. I guess most of the developer
 | resources will be focused on the 3.3 branch instead.
 
 Well, that is just a suggestion.  I hope 3.3 will be ready in time so 
 that 3.2-branch becomes obselete.
 
 -- Gaby