[Bug tree-optimization/94021] -Wformat-truncation false positive due to excessive integer range

["amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94021

--- Comment #9 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Jakub Jelinek from comment #6)
> CCing Andrew and Aldy to see what the ranger does or can do, talking about
>  I mean, if we have:
>   h_1 = x_2 / 3600;
>   if (x_2 <= -3599 && x_2 <= 89999)
>     use (h_1);
> figure out that h_1 is set to x_2 / 3600 and even when that
> SSA_NAME_DEF_STMT is not in a guarded block, its use is in one and so from
> the [-3599, 89999] range of x_2 at the point of use derive that h_1 there is
> [0, 24]?
> Surely if it is like:
>   if (x_2 <= -3599 && x_2 <= 89999)
>     {
>       h_1 = x_2 / 3600;
>       use (h_1);
>     }
> I'd expect it to handle it that way.


Certainly we get the latter case.  The earlier case is currently...
inconsistent.  Something I hope to address in the next release.

if we have precisely:
   h_1 = x_2 / 3600;
   if (x_2 <= -3599 && x_2 <= 89999)
     use (h_1);
and if that is calculated in such a way that all of the conditions are
evaluated in a single basic block, then the GORI engine well mark h1 and x_2
both as exports and the evaluator will calculate the desired value for h_1.

Once we start to pull them further apart, the current implementation loses the
ability to recalculate h_1 when we get new ranges for x_2.

I have plans to segregate the def chains from the export lists in blocks, and
allow for greater ability to recalculate things like this.

When I look at #c4 in EVRP, I see:
=========== BB 4 ============
    <bb 4> :
    # x_10 = PHI <x_13(D)(2), x_14(3)>
    h_15 = x_10 / 3600;
    _1 = x_10 % 3600;
    m_16 = _1 / 60;
    h.0_2 = (unsigned int) h_15;
    _3 = h.0_2 > 23;
    _5 = _3;
    if (_5 != 0)
      goto <bb 6>; [INV]
    else
      goto <bb 5>; [INV]

_1 : int [0, 3599]
h.0_2 : unsigned int [0, 596523]
x_10 : int [0, +INF]
h_15 : int [0, 596523]
m_16 : int [0, 59]
4->6  (T) h.0_2 :       unsigned int [0, 596523]
4->6  (T) _5 :  _Bool [1, 1]
4->6  (T) x_10 :        int [0, +INF]
4->6  (T) h_15 :        int [0, 596523]
4->5  (F) h.0_2 :       unsigned int [0, 596523]
4->5  (F) _5 :  _Bool [0, 0]
4->5  (F) x_10 :        int [0, +INF]
4->5  (F) h_15 :        int [0, 596523]

and then later on:
=========== BB 8 ============
x_10    int [0, +INF]
    <bb 8> :
    if (x_10 <= 89999)
      goto <bb 9>; [INV]
    else
      goto <bb 10>; [INV]

8->9  (T) x_10 :        int [0, 89999]
8->10  (F) x_10 :       int [90000, +INF]

=========== BB 9 ============
    <bb 9> :
    __builtin_snprintf (&a, 8, "%s%02i%02i", "+", h_15, m_16);


The defchains already indicate that h_15 is dependant on the value of x_10, and
I am hoping to enable recalculation of h_15 when a dependant range has
changed.. and not just when they are exported from the same block.

 so in this case, when we ask for the range of h_15 in BB_9, we should be able
to see that x_10 has a range of int [0, 89999] and trigger a recalculation of
h_15 using "current" values. and come up with h_15 = [0,24] 

The pieces are all there, but they need to be assembled in a non time consuming
way :-)

It is on the radar for next release.