[Bug tree-optimization/80617] [missed optimization] Storing constant in two possibly-aliased locations

["herring at lanl dot gov" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80617

--- Comment #7 from S. Davis Herring <herring at lanl dot gov> ---
We can extend the C test case (thanks for that) with a shared, non-constant
value (and more savings by having dead code as in the original C++ example):

void foo(int *p,int *q,int x) {
  *q=*p=x;
  if(*p!=x) abort();  /* dead */
}