[Bug tree-optimization/115864] right shift being optimised out incorrectly

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115864

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
uint16_t ah = a >> 16;
        uint16_t bh = b >> 16;
        uint16_t al = a;
        uint16_t bl = b;

        uint32_t q = ah * bl;
        uint32_t r = al * bh;


You have a signed integer overflow here.


Ah*al is really ((int)ah)*((int)al) due to integer promotion in c.