[Bug tree-optimization/128433] [15/16/17 Regression] overread causes segfault in masked vect epilogue

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128433

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Kewen Lin from comment #2)
> It seems that the analysis considers we can make use of half-vector
> construction so it unset overrun_p. But the transformation ends up with the
> full vector when partial vector enabled.

Yes, half-vector construction isn't implemented for the mask case - we have to
reject loop masking as the most conservative fix (posted patch) also suitable
for backporting.