[Bug regression/71231] [7 Regression]: 300% runtime increase for rnflow

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71231

--- Comment #4 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> Maybe a missing :s or this could be just increasing register pressure.

:s would have no effect, you would need to do it manually

 (simplify
  (bit_and SSA_NAME@0 INTEGER_CST@1)
  (if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
+      && single_use (@0)
       && (get_nonzero_bits (@0) & wi::bit_not (@1)) == 0)
   @0))

but that seems wrong to me.

This is a transformation that only removes an operation, as far as I can tell
it shouldn't even increase register pressure... Maybe some other optimization
relies on the presence of & cst and could be improved to use get_nonzero_bits?
Someone with access to the source needs to see how the missing bit_and changes
the dumps after later passes.