[Bug middle-end/39326] Segmentation fault with -O1, out of memory with -O2

[steven at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39326

--- Comment #38 from Steven Bosscher <steven at gcc dot gnu.org> 2013-03-07 22:15:39 UTC ---
Created attachment 29612
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29612
Punt on loops with more memory references than LIM can handle

For the LIM problem, I'm thinking of a patch like this one (not tested
yet).  Basically, this means giving up on really large loops with many
loads and/or stores.  That's not an unreasonable thing to do anyway.
Code motion from really big loops usually isn't an improvement.

Richi, could you have a look at this, and see if I've got it all right,
more-or-less?  LIM is quite complicated and I'm not sure if I should
look at, or update, the set of optimizable loops somewhere.

With the patch, and with "-O2 -fgcse", I now have:

gap_TlnLv4.c: In function 'RDFT_49152_1':
gap_TlnLv4.c:37502:18: warning: -ftree-loop-im: number of memory references in
loop exceeds the --param loops-max-datarefs-for-datadeps threshold
[-Wdisabled-optimization]
      t12308[500] = t12304[6144*i0+1000];
                  ^

 dead store elim1        :  57.70 ( 8%)
 dead store elim2        :  76.82 (10%)
 combiner                : 360.07 (48%)
 reload CSE regs         :  55.44 ( 7%)
 TOTAL                   : 743.77