[Bug tree-optimization/114485] [13/14 Regression] Wrong code with -O3 -march=rv64gcv on riscv or `-O3 -march=armv9-a` for aarch64

[rdapp at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114485

--- Comment #4 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Yes, the vectorization looks ok.  The extracted live values are not used
afterwards and therefore the whole vectorized loop is being thrown away.
Then we do one iteration of the epilogue loop, inverting the original c and end
up with -8 instead of 8.  This is pretty similar to what's happening in the
related PR.

We properly populate the phi in question in slpeel_update_phi_nodes_for_guard1:

c_lsm.7_64 = PHI <_56(23), pretmp_34(17)>

but vect_update_ivs_after_vectorizer changes that into

c_lsm.7_64 = PHI <pretmp_34(17), pretmp_34(17)>.

Just as a test, commenting out

      if (!LOOP_VINFO_EARLY_BREAKS_VECT_PEELED (loop_vinfo))
        vect_update_ivs_after_vectorizer (loop_vinfo, niters_vector_mult_vf,
                                          update_e);

at least makes us keep the VEC_EXTRACT and not fail anymore.