On 5/23/19 9:10 AM, Richard Biener wrote:
On Thu, May 23, 2019 at 3:29 AM Andrew MacLeod <amacl...@redhat.com> wrote:
This aspect of symbolics would be handled by a relational/equivalence
processing engine that would be follow on work. Using the same basic
model as ranges, each tree code is taught to understand the relation
between its operands, and then we can answer equivalency and relational
accurately as well. It would be available for any pass to use
independent of ranges. I will expound upon that a bit in the future
directions section.
While I agree that symbolic ranges are a complication and that most
cases it currently handles are not "value-range" things I do not agree
with the idea that we can simply remove handling them and deal
with the fallout in some later point in the future. Eric may also be
able to show you "real" symbolic value-range magic.
sure, I'd love to see a case we can't get that having symbolics in the
range helps with. (note I see you guys have replied with an example.
I'll reply there, but will note it is actually a relation issue, so my
assertion stands)
And we aren't talking about utting this code in and someday getting
around to it. Equivalencies/relations are the very next thing to
tackle, and I expected at least a proof of concept as a requirement. I
just don't want to proceed with any follow up work until a direction is
set for the core aspects.
Note that symbolic ranges are already restricted to PLUS_EXPR
and MINUS_EXPR (and NEGATE_EXPR I think). There are
also "symbolic" (non-integer constant) ranges like [&a, &a].
I've never seen [&a, &MEM[&a + 4]] but we wouldn't reject those
I think.
You may have noticed that EVRP does not use symbolic ranges.
Other than for equivalences? it appears to still track them via ranges
to eliminate things like :
if (a == b && b == c)
if (a == c)
Intersecting
int [c_7(D), c_7(D)] EQUIVALENCES: { b_6(D) c_7(D) } (2 elements)
and
VARYING
to
int [c_7(D), c_7(D)] EQUIVALENCES: { b_6(D) c_7(D) } (2 elements)
I noticed this is how it continues to handle relational problems, so
they are there.
As already said I'd like to see VRP go but obstackles are
symbolic ranges and jump-threading (with Jeff promising
to handle the jump-threading part in the past).
I also consider symbolics an obstacle, only in a different way :-)
Andrew
