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Date: Tue, 16 Aug 2022 09:28:38 +0000 (UTC)
From: Richard Biener <rguenther@suse.de>
To: Aldy Hernandez <aldyh@redhat.com>
cc: gcc-patches <gcc-patches@gcc.gnu.org>, 
 "MacLeod, Andrew" <amacleod@redhat.com>
Subject: Re: [PATCH] Tame path_range_query::compute_imports
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On Tue, 16 Aug 2022, Aldy Hernandez wrote:

> On Tue, Aug 16, 2022 at 11:08 AM Aldy Hernandez <aldyh@redhat.com> wrote:
> >
> > On Tue, Aug 16, 2022 at 10:32 AM Richard Biener <rguenther@suse.de> wrote:
> > >
> > > On Tue, 16 Aug 2022, Aldy Hernandez wrote:
> > >
> > > > On Thu, Aug 11, 2022 at 1:42 PM Richard Biener <rguenther@suse.de> wrote:
> > > >
> > > > > @@ -599,6 +592,30 @@ path_range_query::compute_imports (bitmap imports, const vec<basic_block> &path)
> > > > >                 worklist.safe_push (arg);
> > > > >             }
> > > > >         }
> > > > > +      else if (gassign *ass = dyn_cast <gassign *> (def_stmt))
> > > > > +       {
> > > > > +         tree ssa[3];
> > > > > +         if (range_op_handler (ass))
> > > > > +           {
> > > > > +             ssa[0] = gimple_range_ssa_p (gimple_range_operand1 (ass));
> > > > > +             ssa[1] = gimple_range_ssa_p (gimple_range_operand2 (ass));
> > > > > +             ssa[2] = NULL_TREE;
> > > > > +           }
> > > > > +         else if (gimple_assign_rhs_code (ass) == COND_EXPR)
> > > > > +           {
> > > > > +             ssa[0] = gimple_range_ssa_p (gimple_assign_rhs1 (ass));
> > > > > +             ssa[1] = gimple_range_ssa_p (gimple_assign_rhs2 (ass));
> > > > > +             ssa[2] = gimple_range_ssa_p (gimple_assign_rhs3 (ass));
> > > > > +           }
> > > > > +         else
> > > > > +           continue;
> > > > > +         for (unsigned j = 0; j < 3; ++j)
> > > > > +           {
> > > > > +             tree rhs = ssa[j];
> > > > > +             if (rhs && add_to_imports (rhs, imports))
> > > > > +               worklist.safe_push (rhs);
> > > > > +           }
> > > > > +       }
> > > >
> > > > We seem to have 3 copies of this copy now: this one, the
> > > > threadbackward one, and the original one.
> > > >
> > > > Could we abstract this somehow?
> > >
> > > I've thought about this but didn't find any good solution since the
> > > use of the operands is always a bit different.  But I was wondering
> > > why/if the COND_EXPR special-casing is necessary, that is, why
> > > don't we have a range_op_handler for it and if we don't why
> > > do we care about it?
> >
> > I think it's because we don't have a range-op handler for COND_EXPR,
> > opting to handle the relational operators instead in range-ops.  We
> > have similar code in the folder:
> >
> >   if (range_op_handler (s))
> >     res = range_of_range_op (r, s, src);
> >   else if (is_a<gphi *>(s))
> >     res = range_of_phi (r, as_a<gphi *> (s), src);
> >   else if (is_a<gcall *>(s))
> >     res = range_of_call (r, as_a<gcall *> (s), src);
> >   else if (is_a<gassign *> (s) && gimple_assign_rhs_code (s) == COND_EXPR)
> >     res = range_of_cond_expr (r, as_a<gassign *> (s), src);
> >
> > Andrew, do you have any suggestions here?
> 
> Hmmm, so thinking about this, perhaps special casing it is the way to go ??

It looks like so.  Though a range_op_handler could, for
_1 = _2 ? _3 : _4; derive a range for _3 from _1 if _2 is
known true?