Re: [PATCH] Loop unswitching: support gswitch statements.

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Dec 2, 2021 at 2:10 PM Martin Liška <mliska@suse.cz> wrote:
>
> On 12/2/21 13:01, Richard Biener wrote:
> > On Thu, Dec 2, 2021 at 12:45 PM Martin Liška <mliska@suse.cz> wrote:
> >>
> >> On 12/1/21 19:21, Andrew MacLeod wrote:
> >>> On 12/1/21 09:48, Martin Liška wrote:
> >>>> On 12/1/21 15:34, Richard Biener wrote:
> >>>>> On Wed, Dec 1, 2021 at 3:25 PM Martin Liška <mliska@suse.cz> wrote:
> >>>>>>
> >>>>>> On 12/1/21 15:19, Richard Biener wrote:
> >>>>>>> which is compute the range of 'lhs' on edge_true into predicate->true_range,
> >>>>>>> assign that same range to ->false_range and then invert it to get the
> >>>>>>> range on the false_edge.  What I am saying is that for better precision
> >>>>>>> you should do
> >>>>>>>
> >>>>>>>         ranger->range_on_edge (predicate->false_range, edge_false, lhs);
> >>>>>>>
> >>>>>>> rather than prematurely optimize this to the inversion of the true range
> >>>>>>> since yes, ranger is CFG sensitive and only the_last_ predicate on a
> >>>>>>> long CFG path is actually inverted.
> >>>>>>>
> >>>>>>> What am I missing?
> >>>>>>
> >>>>>> I might be misunderstood, but I think it's the problem defined here:
> >>>>>> https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584605.html
> >>>>>>
> >>>>>> where I used the ranger->range_on_edge on the false_edge.
> >>>>>
> >>>>> Ah, OK.  But then even the true_edge range is possibly wrong, no?
> >>>>
> >>>> You are of course correct, I've just proved that in debugger ://
> >>>>
> >>>>> Consider
> >>>>>
> >>>>>     for (;;)
> >>>>>        {
> >>>>>            if (a < 100)
> >>>>>              if (a > 50)  // unswitch on this
> >>>>>                /* .. */
> >>>>>            if (a < 120)
> >>>>>                /* ... */
> >>>>>        }
> >>>>>
> >>>>> then you record [51, 99] for true_range of the a > 50 predicate and thus
> >>>>> simplification will simplify the if (a < 120) check, no?
> >>>>
> >>>> Yep.
> >>>>
> >>>>>
> >>>>> You can only record the range from the (CFG independent) a > 50 check,
> >>>>> thus [51, +INF] but of course at simplification time you can also use
> >>>>> the CFG context at each simplification location.
> >>>>
> >>>> @Andrew: How can I easily get irange based just on a stmt? Something like fold_range
> >>>> with int_range_max as the 3rd argument?
> >>>>
> >>> Sorry, I miss these things if I'm not directly CC'd a lot :-)
> >>>
> >>> So you just want to know the basic range the stmt generates without context?    Sure, what you say would be fine, but your want to initialize it to the type range:
> >>
> >> Yes, I want to know range of LHS in a gcond statement and the same for cases in a gswitch statement.
> >>
> >>>
> >>> int_range_max range (TREE_TYPE (name));
> >>>
> >>> you can also simply trigger it using the current SSA_NAME_RANGE_INFO global  values query instead of the default current contextual one... which , if there isnt a global range, will automatically use the range of the type of the argument.. so maybe just try
> >>>
> >>> fold_range (r, stmt, get_global_range_query ())
> >>
> >> Doing
> >>
> >>         predicate->true_range = int_range_max (TREE_TYPE (lhs));
> >>         fold_range (predicate->true_range, stmt, get_global_range_query ());
> >>         predicate->true_range.debug();
> >>
> >> gives me _Bool VARYING.
> >
> > Likely because that gives a range for the bool result rather than
> > a range for the LHS of a LHS op RHS on the true or false edge.
>
> Yes :) I guess Andrew can help us.

some grepping and poking found be gimple_range_calc_op1 which should
eventually do the trick (for constant gimple_cond_rhs at least).

> > I would guess no stmt level API gives that.  In previous VRP
> > incarnation assert expr discovery would yield the asserts
> > that hold for the LHS on the respective edge and from the asserts
> > ranges could be determined.
>
> About the gswitch statements, I need similarly irange for a switch statement
> on an edge e.

Well, you simply want a range (and condition to generate the if from)
from a CASE_LABEL_EXPR.  Given that's either a single integer constant
or a RANGE_EXPR it should be easy to use some of the irange CTORs here.

Richard.

> Thanks for help,
> Martin
>
> >
> > Richard.
> >
> >>
> >> Martin
> >>
> >>>
> >>> Andrew
> >>>
> >>>
> >>>
> >>>
> >>
>