[Bug tree-optimization/102794] [12 Regression] missing vrp in evrp dealing with casts and ands

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102794

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #2)
> I haven't looked at this, but there's a pending patch with more
> restrictions for loop threading in the presence of loops.  Does this help?
> 
> https://gcc.gnu.org/pipermail/gcc-patches/2021-October/581637.html
> 
> We really shouldn't be destroying loop info.

Yes I think it does, though I have not tried it.
There was a jump threading here:
  <bb 4> :
  if (d_10 != 0)
    goto <bb 5>; [INV]
  else
    goto <bb 6>; [INV]

  <bb 5> :
  foo ();

  <bb 6> :
  a_12 = a_3 + 1;

  <bb 7> : ;;; loop header
  # a_3 = PHI <-100(2), a_12(6)>
  if (a_3 != 0)
    goto <bb 3>; [INV]
  else
    goto <bb 8>; [INV]

where d_10 is defined as:
  d_10 = (short unsigned int) a_3;


So yes blocking jumping through the loop header would help.
It is very similar to your f3 in ssa-thread-invalid.c testcase.