On Mon, Jan 29, 2018 at 11:05:28AM +0100, Richard Biener wrote:
>
> This fixes another case of the SCEV cache containing references to
> released SSA names. This time it is the vectorizer releasing defs
> of OMP_SIMD uses. Instead of pluggin this hole like the others,
> sprinkling scev_reset[_htab] calls throughout passes, it plugs
> the holes in flush_ssaname_freelist which is called after each
> pass TODO and is used to flip the two SSA name freelists we have
> now.
>
> I'm not sure maintaining SCEV info across passes is worth the
> trouble we're seeing, also given its implementation makes flushing
> info for a particular SSA name / loop expensive (and thus not
> implemented). But it's not the time to change this...
>
> Now, would you rather prefer sticking a scev_reset[_htab] into
> the vectorizer?
But any other pass can invalidate it similarly, can't it?
I think your patch is ok, if the scev_reset_htab call isn't too expensive
all the time. If scalar_evolution_info is NULL, it will return right away,
if it is non-NULL but the htab is empty, it should be just subtraction of
two scalar fields from the htab and finding out the difference is 0 and not
doing anything.
Jakub
