On 1/16/19 3:49 PM, Jakub Jelinek wrote:
> Hi!
>
> While looking at this PR (I've just started) I've noticed that
> add_stack_var_conflict is quite often called with x == y.
> We don't really need to record that a variable conflicts with itself,
> the only reader of the conflicts bitmaps, stack_var_conflict_p,
> starts with
> if (x == y)
> return false;
> conflicts bitmap are set either by this function, or by the
> EXECUTE_IF_SET_IN_BITMAP (work, 0, i, bi)
> {
> struct stack_var *a = &stack_vars[i];
> if (!a->conflicts)
> a->conflicts = BITMAP_ALLOC (&stack_var_bitmap_obstack);
> bitmap_ior_into (a->conflicts, work);
> }
> code (where work isn't derived from any conflicts bitmap though, so
> doesn't care if we've added those self-conflicts or not). The above
> bitmap_ior_into stuff actually always sets self-conflicts (if you think
> bitmap_clear_bit is worth it, I can add it afterwards though).
>
> But I think the following patch is helpful, don't create the conflicts
> bitmaps at all if all we'd record is just self-conflict which we'll ignore.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2019-01-16 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/86214
> * cfgexpand.c (add_stack_var_conflict): Don't add any conflicts
> if x == y.
Yea. Seems reasonable.
jeff
