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Re: [RFC] Combine related fail of gcc.target/powerpc/ti_math1.c
- From: Oleg Endo <oleg dot endo at t-online dot de>
- To: Richard Henderson <rth at redhat dot com>
- Cc: Segher Boessenkool <segher at kernel dot crashing dot org>, gcc at gcc dot gnu dot org, Alan Modra <amodra at gmail dot com>
- Date: Thu, 21 May 2015 23:11:26 +0200
- Subject: Re: [RFC] Combine related fail of gcc.target/powerpc/ti_math1.c
- Authentication-results: sourceware.org; auth=none
- References: <20150521103604 dot GK6140 at bubble dot grove dot modra dot org> <20150521123916 dot GA26096 at gate dot crashing dot org> <555E2526 dot 5070301 at redhat dot com> <20150521184431 dot GC10871 at gate dot crashing dot org> <555E2B09 dot 8020206 at redhat dot com>
On Thu, 2015-05-21 at 11:59 -0700, Richard Henderson wrote:
> On 05/21/2015 11:44 AM, Segher Boessenkool wrote:
> > On Thu, May 21, 2015 at 11:34:14AM -0700, Richard Henderson wrote:
> >> Actually, I believe that the way CA is modeled at the moment is dangerous.
> >> It's not a 64-bit value, but a 1-bit value.
> >
> > It's a fixed register and it is only ever set to 0 or 1. There are
> > more targets that do such things, and it is safe.
>
> Old Cygnus proverb: Lie to the compiler and it will always bite you in the end.
Just for the record, the same is being done on SH with the T bit. It's
a fixed 1 bit hardreg, but declared and treated as SImode, because all
the other integer arithmetic is done primarily in SImode, too. No
significant problems with that.
Cheers,
Oleg