[Bug tree-optimization/114403] [14 regression] LLVM miscompiled with -O3 -march=znver2 -fno-vect-cost-model since r14-6822-g01f4251b8775c8

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114403

--- Comment #20 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
This is a bad interaction with early break and peeling for gaps.

when peeling for gaps we set bias_for_lowest to 0, which then negates the ceil
for the upper bound calculation when the div is exact.

We end up doing on a loop that does:

Analyzing # of iterations of loop 1
  exit condition [8, + , 18446744073709551615] != 0
  bounds on difference of bases: -8 ... -8
  result:
    # of iterations 8, bounded by 8

and a VF=4 calculating:

Loop 1 iterates at most 1 times.
Loop 1 likely iterates at most 1 times.
Analyzing # of iterations of loop 1
  exit condition [1, + , 1](no_overflow) < bnd.5505_39
  bounds on difference of bases: 0 ... 4611686018427387902
Matching expression match.pd:2011, generic-match-8.cc:27
Applying pattern match.pd:2067, generic-match-1.cc:4813
  result:
    # of iterations bnd.5505_39 + 18446744073709551615, bounded by
4611686018427387902
Estimating sizes for loop 1
...
   Induction variable computation will be folded away.
  size:   2 if (ivtmp_312 < bnd.5505_39)
   Exit condition will be eliminated in last copy.
size: 24-3, last_iteration: 24-5
  Loop size: 24
  Estimated size after unrolling: 26
;; Guessed iterations of loop 1 is 0.858446. New upper bound 1.

upper bound should be 2 not 1. I have a working patch, trying to create a
standalone testcase for it.