This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Checking out PR4483 (constant overflow on PPC, problems compiling Linux kernel)
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: Corey Minyard <minyard at acm dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: 29 Nov 2001 03:08:11 -0200
- Subject: Re: Checking out PR4483 (constant overflow on PPC, problems compiling Linux kernel)
- Organization: GCC Team, Red Hat
- References: <3C053AA4.1020806@acm.org>
On Nov 28, 2001, Corey Minyard <minyard@acm.org> wrote:
> In the situation, an INSN references two other registers that are
> constants (one is 0xffffffff80000000, the other is 42) and subtracts
> the second from the first (MINUS code). In validate_replace_rtx_1
> (recog.c), it replaces the registers with constants, then adds
> them. This results in a constant 0xffffffff7fffffd6, which is
> obviously now too negative to fit into an SI register. The original
> constant was positive (0x80000000UL in the source). Since constants
> don't have modes, the addition code doesn't handle this (and it
> doesn't look like it cares, anyway).
Constants have modes implied from the contexts in which they're used,
and this is the mode that should be used to sign-extend them after any
operation. CONST_INT should be changed to have a mode one of these
days. In any case, it's the addition that should take the
responsibility of making the result a valid constant for the expected
mode.
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist *Please* write to mailing lists, not to me