[Bug tree-optimization/93440] scalar unrolled loop makes vectorized code unreachable

[ikonomisma at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93440

--- Comment #3 from ikonomisma at googlemail dot com ---
(In reply to Richard Biener from comment #2)
> Hmm, I get
> 
> /home/space/rguenther/install/gcc-9.2/include/c++/9.2.0/pstl/execution_defs.
> h:155:7: error: no type named ‘type’ in ‘struct std::enable_if<false, int>’
>   155 | using __enable_if_execution_policy =
>       |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> trying to compile this with the FSF 9.2.0 release.

Well, as far as I understand there should be an overload without an execution
policy, both https://en.cppreference.com/w/cpp/algorithm/transform_reduce and
the n4659 c++ draft standard include it.