[Bug tree-optimization/110519] New: Optimize loop that only assigns to a local variable

[roland.illig at gmx dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110519

            Bug ID: 110519
           Summary: Optimize loop that only assigns to a local variable
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roland.illig at gmx dot de
  Target Milestone: ---

~~~c
struct symbol {
    struct symbol *next;
};

void f(const struct symbol *sym)
{
    for (const struct symbol *s = sym; s != (void *)0; s = s->next)
        do { } while (0);
}
~~~

The above code was extracted from
<https://github.com/NetBSD/src/blob/f74666e8d086952b27d76155223a5d497e69f5a8/usr.bin/xlint/lint1/decl.c#L1319>.

Several other compilers know that this loop has no side effects, even at low
optimization levels, see <https://godbolt.org/z/Y85EGcW3d>.