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Re: GCC build failed with your patch on 2001-01-09T11:35:00Z.

> Date: Tue, 09 Jan 2001 15:50:57 -0500
> From: David Edelsohn <>

> 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 <>

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