> cc: gcc-patches@gcc.gnu.org
> Date: Thu, 25 Apr 2002 15:46:02 -0400
> From: David Edelsohn <dje@watson.ibm.com>
>
> The ICE is caused by a splitter trying to handle a pattern where
> we could not allocate cr0 for an implicit condition set and instead needed
> to re-split the instruction. For most patterns like this, the original
> pattern without the compare did not need a CLOBBER, but this pattern does.
>
> A problem is that the pattern without the compare needs one
> CLOBBER and the pattern with the compare also needs only one CLOBBER. In
> the splitter, the CLOBBER is the intermediate result to be compared.
>
> The question is how to create the additional CLOBBER. The
> splitter only runs after reload, so we cannot create another pseudo. We
> also know that in the overall sequence, the intermediate result really is
> dead. The only options appear to be either list the match_dup twice: once
> as the intermediate result and again as the CLOBBERed reg (which is
> exactly how the compare version of the pattern avoids two CLOBBERS), or
> only allow cr0 for this pattern and disallow a splitter.
>
> The patch below adds the extra CLOBBER and resolves the ICE, but I
> do not know if mentioning the REG as a result and as a CLOBBER is entirely
> safe in the GCC backend even though the use of the register twice in the
> actual sequence of PowerPC instructions is correct. Anyone know for sure
> what is safe in a define_split?
This doesn't make sense. You can't have
(parallel [
(set (reg foo) something)
(set (reg foo) something_else)
])
even if one of the SETs is a CLOBBER.
I presume, from the description, that actually it is possible to execute
(set (match_dup 4)
(plus:SI (eq:SI (match_dup 1)
(match_dup 2))
(match_dup 3)))
without any CLOBBER being necessary, in which case there should be a
pattern to do that.
> Thanks, David
>
>
> * rs6000.md (sCC splitter): Add CLOBBER.
>
> Index: rs6000.md
> ===================================================================
> RCS file: /cvs/gcc/egcs/gcc/config/rs6000/rs6000.md,v
> retrieving revision 1.180
> diff -c -p -r1.180 rs6000.md
> *** rs6000.md 23 Apr 2002 00:19:14 -0000 1.180
> --- rs6000.md 25 Apr 2002 19:25:12 -0000
> ***************
> *** 10894,10903 ****
> (const_int 0)))
> (clobber (match_scratch:SI 4 ""))]
> "! TARGET_POWERPC64 && reload_completed"
> ! [(set (match_dup 4)
> (plus:SI (eq:SI (match_dup 1)
> (match_dup 2))
> (match_dup 3)))
> (set (match_dup 0)
> (compare:CC (match_dup 4)
> (const_int 0)))]
> --- 11131,11141 ----
> (const_int 0)))
> (clobber (match_scratch:SI 4 ""))]
> "! TARGET_POWERPC64 && reload_completed"
> ! [(parallel [(set (match_dup 4)
> (plus:SI (eq:SI (match_dup 1)
> (match_dup 2))
> (match_dup 3)))
> + (clobber (match_dup 4))])
> (set (match_dup 0)
> (compare:CC (match_dup 4)
> (const_int 0)))]
>
--
- Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>