[Bug target/59371] [9/10/11/12 Regression] Performance regression in GCC 4.8/9/10/11/12 and later versions.

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59371

--- Comment #28 from Jiu Fu Guo <guojiufu at gcc dot gnu.org> ---
If change code as below, 'i' is not starting from '0', and 'compare code' is
'!='
then wrap/overflow on 'i' may happen, and optimizations (e.g. vectorization)
are not applied.
The below patch is trying to optimize this kind of loop.
https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570424.html

int foo (int *p, unsigned short u_n, unsigned short i)
{
  int x = 0;
  for (; i != u_n; i++) {
    x = x + p[i];
  }
  return x;
}