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

[Andrew MacLeod <amacleod@redhat.com>]

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:

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 ())

Andrew