Re: [PATCH] [PR68097] Try to avoid recursing for floats in tree_*_nonnegative_warnv_p.

[Aldy Hernandez <aldyh@redhat.com>]

On Mon, Nov 14, 2022 at 10:12 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Sat, Nov 12, 2022 at 7:30 PM Aldy Hernandez <aldyh@redhat.com> wrote:
> >
> > It irks me that a PR named "we should track ranges for floating-point
> > hasn't been closed in this release.  This is an attempt to do just
> > that.
> >
> > As mentioned in the PR, even though we track ranges for floats, it has
> > been suggested that avoiding recursing through SSA defs in
> > gimple_assign_nonnegative_warnv_p is also a goal.  We can do this with
> > various ranger components without the need for a heavy handed approach
> > (i.e. a full ranger).
> >
> > I have implemented two versions of known_float_sign_p() that answer
> > the question whether we definitely know the sign for an operation or a
> > tree expression.
> >
> > Both versions use get_global_range_query, which is a wrapper to query
> > global ranges.  This means, that no caching or propagation is done.
> > In the case of an SSA, we just return the global range for it (think
> > SSA_NAME_RANGE_INFO).  In the case of a tree code with operands, we
> > also use get_global_range_query to resolve the operands, and then call
> > into range-ops, which is our lowest level component.  There is no
> > ranger or gori involved.  All we're doing is resolving the operation
> > with the ranges passed.
> >
> > This is enough to avoid recursing in the case where we definitely know
> > the sign of a range.  Otherwise, we still recurse.
> >
> > Note that instead of get_global_range_query(), we could use
> > get_range_query() which uses a ranger (if active in a pass), or
> > get_global_range_query if not.  This would allow passes that have an
> > active ranger (with enable_ranger) to use a full ranger.  These passes
> > are currently, VRP, loop unswitching, DOM, loop versioning, etc.  If
> > no ranger is active, get_range_query defaults to global ranges, so
> > there's no additional penalty.
> >
> > Would this be acceptable, at least enough to close (or rename the PR ;-))?
>
> I think the checks would belong to the gimple_stmt_nonnegative_warnv_p function
> only (that's the SSA name entry from the fold-const.cc ones)?
>
> I also notice the use of 'bool' for the "sign".  That's not really
> descriptive.  We
> have SIGNED and UNSIGNED (aka enum signop), not sure if that's the
> perfect match vs. NEGATIVE and NONNEGATIVE.  Maybe the functions
> name is just bad and they should be known_float_negative_p?

Yeah, SIGNED and UNSIGNED doesn't seem to be much clearer than "bool signbit".

For instance, we have the following in frange:

  void set_nan (tree type, bool sign);
  void update_nan (bool sign);
  bool maybe_isnan (bool sign) const;
  bool signbit_p (bool &signbit) const;

I'm OK changing them to enum signop if you prefer.  I'm just not
totally convinced it's more readable.

??

Aldy