On 11/12/2015 10:05 AM, Jeff Law wrote:
But IIRC you mentioned it should enable vectorization or so? In this
case
that's obviously too late.
The opposite. Path splitting interferes with if-conversion &
vectorization. Path splitting mucks up the CFG enough that
if-conversion won't fire and as a result vectorization is inhibited. It
also creates multi-latch loops, which isn't a great situation either.
It *may* be the case that dropping it that far down in the pipeline and
making the modifications necessary to handle simple latches may in turn
make the path splitting code play better with if-conversion and
vectorization and avoid creation of multi-latch loops. At least that's
how it looks on paper when I draw out the CFG manipulations.
I'll do some experiments.
It doesn't look too terrible to ravamp the recognition code to work
later in the pipeline with simple latches. Sadly that doesn't seem to
have fixed the bad interactions with if-conversion.
*But* that does open up the possibility of moving the path splitting
pass even deeper in the pipeline -- in particular we can move it past
the vectorizer. Which is may be a win.
So the big question is whether or not we'll still see enough benefits
from having it so late in the pipeline. It's still early enough that we
get DOM, VRP, reassoc, forwprop, phiopt, etc.
Ajit, I'll pass along an updated patch after doing some more testing.
Jeff
