[Bug middle-end/111799] [14 Regression] Missed Dead Code Elimination since r14-2365-g2e406f0753e

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111799

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
          Component|tree-optimization           |middle-end
     Ever confirmed|0                           |1
           Keywords|                            |TREE
   Last reconfirmed|                            |2023-10-18

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Theodoros Theodoridis from comment #4)
> Oops, there was a bug in my reduction, here's the fixed code:
> 
> https://godbolt.org/z/shxffzs8E
> 
> void foo(void);
> typedef unsigned short uint16_t;
> static int b;
> static int ****c;
> static int *f = &b;
> static int *****ad;
> static char(a)(char g, char h) { return g + h; }
> static char(d)(char g, char h) { return g * h; }
> static void(e)(uint16_t g) {
>     if (!(((g) >= 1) && ((g) <= 65459))) {
>         __builtin_unreachable();
>     }
> }
> int main() {
>     b = 0;
>     for (;; b = 1) {
>         char i = d(126 | 1, 205);
>         e(i);
>         short j;
>         int k = *f;
>         j = -21;
>         for (; j; j = a(j, 7)) e((j ^ k && *f) <= *f);
>         if (b) break;
>         ad = &c;
>     }
>     if (ad)
>         ;
>     else
>         foo();
>     ;
> }


Confirmed with this testcase but what is interesting is that the optimization
of calling foo away does NOT happen at the gimple level but at the RTL level
and just happens on x86_64 but NOT on aarch64.

on aarch64 for GCC 13, we even have:
        mov     w0, 1
        str     wzr, [x1, #:lo12:.LANCHOR0]
        cbz     w0, .L13

Which is obvious should have been removed ...

Anyways this is a missed jump threading that should have happened at the gimple
level. I have not looked into why it is not done.