assure_different_constraints():

we can safely IGNORE the should_be_different constraint, iff
we have only one, one should be same and both inputs are identical, for instance in
sbb(x,x)

[r19702]

diff --git a/ir/be/belower.c b/ir/be/belower.c
index ea01678..bdef206 100644 (file)
--- a/ir/be/belower.c
+++ b/ir/be/belower.c
@@ -633,6 +633,22 @@ static void assure_different_constraints(ir_node *irn, constraint_env_t *env) {
                const unsigned other = req->other_different;
                int i;
 
+               if (arch_register_req_is(req, should_be_same)) {
+                       const unsigned same = req->other_same;
+
+                       if (is_po2(other) && is_po2(same)) {
+                               int idx_other = ntz(other);
+                               int idx_same  = ntz(same);
+
+                               /*
+                                * We can safely ignore a should_be_same x should_be_different y
+                                * IFF both nodes are equal!
+                                */
+                               if (get_irn_n(irn, idx_other) == get_irn_n(irn, idx_same)) {
+                                       return;
+                               }
+                       }
+               }
                for (i = 0; 1U << i <= other; ++i) {
                        if (other & (1U << i)) {
                                ir_node *different_from = get_irn_n(belower_skip_proj(irn), i);