[Bug middle-end/113734] [14 regression] libarchive miscompiled (fails libarchive_test_read_format_rar5_extra_field_version test) since r14-8768-g85094e2aa6dba7

["tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113734

--- Comment #19 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Ok, removing all the noise shows that this is the same issue as I saw before.

The code out of the vectorizer is correct, but cunroll does a dodgee unrolling.

-fdisable-tree-cunroll confirms it's the unrolling.

cunroll claims:

Loop 4 iterates at most 16 times.                                              
                                                                               
                                                                               
                             Loop 4 likely iterates at most 16 times.          
                                                                               
                                                                               
                                                          Analyzing # of
iterations of loop 4                                                           
                                                                               
                                                                               
                exit condition [1, + , 1](no_overflow) < bnd.157_285 
...
;; Guessed iterations of loop 4 is 7.347979. New upper bound 16.               
                                                                               
                                                                               
                             Making edge 23->36 impossible by redistributing
probability to other edges. Original probability: 93.8% (guessed)              
                                                                               
                                                             misc.c:147:31:
optimized: loop with 16 iterations completely unrolled (header execution count
2859449)                                                                       
                                                                               
               Last iteration exit edge was proved true.                       
                                                                               
                                                                               
                                            Not peeling: number of iterations
is not estimated 

but the i is bounded by i < 306. and VF=8. so binding loop iteration to 16
means it just cut off half the loop.

so it looks like the upper bounds is wrong. Checking what we write out during
loop vect.