A question about doloop
Hello,
Doloop optimization fails to be applied on the following kernel from
tescase sms-4.c with mainline (-r 162294) due to 'Possible infinite
iteration
case' message; taken from the loop2_doloop dump. (please see below).
With an older version of gcc (-r 146278) doloop succeeded to be applied
and I appreciate an explanation about the change of behavior.
Thanks,
Revital
The kernel:
unsigned int i, n = size;
int changed = 0;
for (i = 0; i < n; i++)
{
const int tmp = *ap++ | (*bp++ & *cp++);
changed |= *dstp ^ tmp;
*dstp++ = tmp;
}
The messages from loop2_doloop dump:
Doloop: Possible infinite iteration case.
Doloop: The loop is not suitable.
Loop 1 is simple:
simple exit 4 -> 5
infinite if: (expr_list:REG_DEP_TRUE (ne:SI (and:DI (minus:DI (plus:DI
(ashift:DI (reg:DI 200)
(const_int 2 [0x2]))
(reg/v/f:DI 194 [ ap ]))
(reg:DI 168 [ ivtmp.19 ]))
(const_int 3 [0x3]))
(const_int 0 [0]))
(nil))
Re: A question about doloop
On Mon, 26 Jul 2010, Revital1 Eres wrote: > > Hello, > > Doloop optimization fails to be applied on the following kernel from > tescase sms-4.c with mainline (-r 162294) due to 'Possible infinite > iteration > case' message; taken from the loop2_doloop dump. (please see below). > With an older version of gcc (-r 146278) doloop succeeded to be applied > and I appreciate an explanation about the change of behavior. This may be due to changes in induction variable selection and the ability of loop2_doloop to discover number of iterations for different variants of IV selection (which is not trivial when 'i' variable is eliminated and loop boundary is expressed with pointer comparison). See PR32283 [1] audit trail for an example of a related problem that was discussed before. It is possible that something is missing in simplify-rtx.c so that 'infinite if' condition cannot be simplified and proven to be always false. Zdenek once had to improve simplify-rtx.c for this reason, as the audit trail shows. [1] http://gcc.gnu.org/PR32283 Hope that helps, Alexander
Re: GFDL/GPL issues
> What if we ask the FSF if we can dual license the constraints.md files > under both the GPL and the GFDL? Thanks for the update Mark. I agree that we are likely to get more traction with a request to dual license as opposed to re-license. Although I confess to lingering doubts as to the big picture. This implied documentation license algebra is quite weak and the imagined documentation production toolchains and procedures quite tortured. GPL indexes, but no GFDL direct linkages? Please. Not for the first time I find myself wishing the FSF spent more mental effort on documentation for free software, at every level. -benjamin
Re: GFDL/GPL issues
Benjamin Kosnik wrote: >> What if we ask the FSF if we can dual license the constraints.md files >> under both the GPL and the GFDL? > I agree that we are likely to get more traction with a request to dual > license as opposed to re-license. Well, I've asked -- but RMS shot down that idea. > Not for the first time I find myself wishing the FSF spent more mental > effort on documentation for free software, at every level. I (and I speak here not for the FSF, the SC, CodeSourcery, or anybody else) wish the FSF spent less time "improving" licenses and more time focused on making FSF software attractive to end users. I'm disappointed that a license "improvement" (changing GPL to GFDL on manuals) has made it impossible to do something that we, as developers, used to be able to do (when documentation was under the GPL we could move things back and forth between code and documentation at will), and which benefited users (by making it easier for us to generate better documentation). -- Mark Mitchell CodeSourcery m...@codesourcery.com (650) 331-3385 x713
Re: GFDL/GPL issues
Mark Mitchell wrote: I'm disappointed that a license "improvement" (changing GPL to GFDL on manuals) has made it impossible to do something that we, as developers, used to be able to do (when documentation was under the GPL we could move things back and forth between code and documentation at will), and which benefited users (by making it easier for us to generate better documentation). I agree that it is essential to be able to do this kind of movement backwards and forwards.
Re: GFDL/GPL issues
Mark Mitchell writes: >> I agree that we are likely to get more traction with a request to dual >> license as opposed to re-license. > > Well, I've asked -- but RMS shot down that idea. Did he give reasons, and/or indicate any other possible methods to use? -Miles -- `Suppose Korea goes to the World Cup final against Japan and wins,' Moon said. `All the past could be forgiven.' [NYT]
