Re: [PATCH] Implement global ranges for all vrange types (SSA_NAME_RANGE_INFO).

[Jeff Law <jeffreyalaw@gmail.com>]

On 7/6/2022 11:10 AM, Aldy Hernandez via Gcc-patches wrote:
> Currently SSA_NAME_RANGE_INFO only handles integer ranges, and loses
> half the precision in the process because its use of legacy
> value_range's.  This patch rewrites all the SSA_NAME_RANGE_INFO
> (nonzero bits included) to use the recently contributed
> vrange_storage.  With it, we'll be able to efficiently save any ranges
> supported by ranger in GC memory.  Presently this will only be
> irange's, but shortly we'll add floating ranges and others to the mix.
>
> As per the discussion with the trailing_wide_ints adjustments and
> vrange_storage, we'll be able to save integer ranges with a maximum of
> 5 sub-ranges.  This could be adjusted later if more sub-ranges are
> needed (unlikely).
>
> Since this is a behavior changing patch, I would like to take a few
> days for discussion, and commit early next week if all goes well.
>
> A few notes.
>
> First, we get rid of the SSA_NAME_ANTI_RANGE_P bit in the SSA_NAME
> since we store full resolution ranges.  Perhaps it could be re-used
> for something else.
>
> The range_info_def struct is gone in favor of an opaque type handled
> by vrange_storage.  It currently supports irange, but will support
> frange, prange, etc, in due time.
>
>  From the looks of it, set_range_info was an update operation despite
> its name, as we improved the nonzero bits with each call, even though
> we clobbered the ranges.  Presumably this was because doing a proper
> intersect of ranges lost information with the anti-range hack.  We no
> longer have this limitation so now we formalize both set_range_info
> and set_nonzero_bits to an update operation.  After all, we should
> never be losing information, but enhancing it whenever possible.  This
> means, that if folks' finger-memory is not offended, as a follow-up,
> I'd like to rename set_nonzero_bits and set_range_info to update_*.
>
> I have kept the same global API we had in tree-ssanames.h, with the
> caveat that all set operations are now update as discussed above.
>
> There is a 2% performance penalty for evrp and a 3% penalty for VRP
> that is coincidentally in line with a previous improvement of the same
> amount in the vrange abstraction patchset.  Interestingly, this
> penalty is mostly due to the wide int to tree dance we keep doing with
> irange and legacy.  In a first draft of this patch where I was
> streaming trees directly, there was actually a small improvement
> instead.  I hope to get some of the gain back when we move irange's to
> wide-ints, though I'm not in a hurry ;-).
>
> Tested and benchmarked on x86-64 Linux.  I will also test on ppc64le
> before the final commit.
>
> Comments welcome.
>
> gcc/ChangeLog:
>
> 	* gimple-range.cc (gimple_ranger::export_global_ranges): Remove
> 	verification against legacy value_range.
> 	* tree-core.h (struct range_info_def): Remove.
> 	(struct irange_storage_slot): New.
> 	(struct tree_base): Remove SSA_NAME_ANTI_RANGE_P documentation.
> 	(struct tree_ssa_name): Add vrange_storage support.
> 	* tree-ssanames.cc (range_info_p): New.
> 	(range_info_fits_p): New.
> 	(range_info_alloc): New.
> 	(range_info_free): New.
> 	(range_info_get_range): New.
> 	(range_info_set_range): New.
> 	(set_range_info_raw): Remove.
> 	(set_range_info): Adjust to use vrange_storage.
> 	(set_nonzero_bits): Same.
> 	(get_nonzero_bits): Same.
> 	(duplicate_ssa_name_range_info): Remove overload taking
> 	value_range_kind.
> 	Rewrite tree overload to use vrange_storage.
> 	(duplicate_ssa_name_fn): Adjust to use vrange_storage.
> 	* tree-ssanames.h (struct range_info_def): Remove.
> 	(set_range_info): Adjust prototype to take vrange.
> 	* tree-vrp.cc (vrp_asserts::remove_range_assertions): Call
> 	duplicate_ssa_name_range_info.
> 	* tree.h (SSA_NAME_ANTI_RANGE_P): Remove.
> 	(SSA_NAME_RANGE_TYPE): Remove.
> 	* value-query.cc (get_ssa_name_range_info): Adjust to use
> 	vrange_storage.
> 	(update_global_range): Use int_range_max.
> 	(get_range_global): Remove as_a<irange>.
I'll be so happy once we don't have to keep doing the conversions 
between the types.

Anti-ranges no more!

I've got no real concerns here.  So unless someone objects, your plan is OK.

jeff