[Bug tree-optimization/31169] Bootstrap comparison error at revision 122821

["dave at hiauly1 dot hia dot nrc dot ca" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #24 from dave at hiauly1 dot hia dot nrc dot ca  2007-03-19 00:08 -------
Subject: Re:  Bootstrap comparison error at revision 122821

> <L11>:;
>   D.1641_16 = D.1589_4 + -1;
>   D.1642_15 = &regexp_3(D)->regexp.oneof.regexps[D.1641_16];
>   ivtmp___31_21 = (long unsigned int) D.1642_15;
> 
>   # ivtmp___31_1 = PHI <ivtmp___31_12(5), ivtmp___31_21(7)>
>   # i_18 = PHI <i_11(5), i_5(7)>
> <L2>:;
>   D.1592_10 = MEM[index: ivtmp___31_1];
>   process_alts_for_forming_states (D.1592_10);
>   i_11 = i_18 + -1;
>   if (i_11 >= 0) goto <L0>; else goto <L4>;
> 
> the stage2 compiler then derives a loop trip count based on the size of
> the regexp->regexp.oneof.regexps[] array it seems (a size of 3 actually)
> and replaces the induction variable by the MEM index.
> 
> This doesn't look like a wrong transformation, but I fail to see how
> this could be different from the stage1 and stage2 compiler.
> 
> Zdenek, are we supposed to get a index-only mem-ref?

I've reviewed Steve's findings and concur.

The index-only mem-ref seemed wierd, so I checked whether it is
generated with the third hunk reverted.  It is still present with
the hunk reverted, so I don't think this is the cause of the problem.

Dave


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31169