RFR: JDK-8308994: C2: Re-implement experimental post loop vectorization

[Emanuel Peter]

On Fri, 23 Jun 2023 11:08:23 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> src/hotspot/share/opto/superword.cpp line 4297:
>> 
>>> 4295: 
>>> 4296: bool SWPointer::Tracer::slp_trace_alignment() {
>>> 4297:   return _slp && _slp->is_trace_alignment();
>> 
>> Aha, here you wrap it. You have some uses above that could be replaced with this now. But again, even better would be if we had a general trace flag that could trace it for any context, not just SuperWord.
>
> After all, should the `VectorizeDebug` flag not apply everywhere? See `phase->C->directive()->VectorizeDebugOption`.

I'd also move this to some static functions in a potential "autovectorization.hpp", and move `_vector_loop_debug` there, together with all its `is_trace...` accessors.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/14581#discussion_r1239688884