------- Comment #5 from rguenth at gcc dot gnu dot org 2010-01-30 16:52 -------
(In reply to comment #3)
> Hack that may be worth trying:
> Index: tree-ssa-dce.c
> ===================================================================
> --- tree-ssa-dce.c (revision 156352)
> +++ tree-ssa-dce.c (working copy)
> @@ -683,7 +683,10 @@ propagate_necessity (struct edge_list *e
> {
> for (k = 0; k < gimple_phi_num_args (stmt); k++)
> {
> + tree t = gimple_phi_arg_def (stmt, k);
> basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
> + if (is_gimple_min_invariant (t))
> + continue;
> if (arg_bb != ENTRY_BLOCK_PTR
> && ! TEST_BIT (visited_control_parents, arg_bb->index))
> {
>
But that would break for example
if (i)
j = 1;
else
j = 0;
where the PHI only has constants. I think the problem is that the control
dependence for the constant is the wrong one (if we didn't have a constant
argument in the PHI but an assignment as in the original source the same
thing would happen - we'd mark an unrelated control stmt necessary).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42906
