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Re: GCC build failed with your patch on 2001-01-09T11:35:00Z.
- To: dje at watson dot ibm dot com
- Subject: Re: GCC build failed with your patch on 2001-01-09T11:35:00Z.
- From: Geoff Keating <geoffk at geoffk dot org>
- Date: Tue, 9 Jan 2001 13:23:39 -0800
- CC: mark at codesourcery dot com, aoliva at redhat dot com, rth at redhat dot com, gcc at gcc dot gnu dot org, gcc-regression at gcc dot gnu dot org, grahams at redhat dot com, jsm28 at cam dot ac dot uk, mhayes at redhat dot com, neil at daikokuya dot demon dot co dot uk, osk at hem dot passagen dot se
- References: <200101092050.PAA38976@mal-ach.watson.ibm.com>
- Reply-to: Geoff Keating <geoffk at redhat dot com>
> Date: Tue, 09 Jan 2001 15:50:57 -0500
> From: David Edelsohn <email@example.com>
> Mark> - Why does this change cause correctness problems?
> Mark> I tried to read some of the mail, and couldn't figure it out.
> Mark> For example, do back-ends make explicit assumptions about how
> Mark> many bits are in a HOST_WIDE_INT? Do they assume that left-shifts
> Mark> will cause high-order bits to "disappear", but now they don't
> Mark> because the types are wider? What are the correctness problems?
> I do not know the root cause of all of the problems, but there are
> problems in the rs6000 port which assumes that an int is sign-extended.
> Basically, the port is not safe in the face of 64-bit CONST_INT.
Actually, it's the other way around. The rs6000 port usually
correctly assumes that ints should be sign-extended, but it's a known
problem that the rest of the compiler doesn't always do this.
See for instance
> I would love to have the rs6000 port fixed. I have been examining
> this recently and Geoff also investigated this in the past. Richard and
> Mark both would be helped by being able to run the rs6000 port hosted on
> 64-bit systems. If we want to make a concerted effort to fix this and
> strenuously test it, I will be happy to help. Fixing the rs6000 port
> means destabilizing it, and possibly common parts of the compiler as well.
As you can see from the first message above, part of the fix is known
to cause a problem on PA.
- Geoffrey Keating <firstname.lastname@example.org>