[Bug target/102483] Reduction of 4 chars can be improved

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102483

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|tree-optimization           |target
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-09-25
             Target|                            |x86_64-linux-gnu
            Summary|Regression in codegen of    |Reduction of 4 chars can be
                   |reduction of 4 chars        |improved
     Ever confirmed|0                           |1
           Keywords|                            |missed-optimization

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
There is a cost model issue as the backend does not implement a reduction add
for vector(4) char.

Note just a slightly different function (doing a store rather than a return)
produces way different results too (even on LLMV):
void foo (unsigned char* p, unsigned char *t)
 {
   char sum = 0;
    for (int i = 0; i != 4; i++)
    sum += p[i];
   *t= sum;
  }