Prevent optimization if compare relation is trivial.

This fixes opt/fehler302.c.

ir/ir/iropt.c

@@ -5398,11 +5398,12 @@ cmp_x_eq_0:
 
 		/* for integer modes, we have more */
 		if (mode_is_int(mode) && !is_Const(left)) {
+			if (!is_relation(ir_relation_false, relation, possible) &&
+			    !is_relation(ir_relation_true,  relation, possible)) {
 				if ((relation == ir_relation_less || relation == ir_relation_greater_equal) &&
 					tarval_cmp(tv, get_mode_null(mode)) == ir_relation_greater) {
 					bitinfo const *const bl = get_bitinfo(left);
-				if (bl && !is_relation(ir_relation_false, relation, possible)
-				       && !is_relation(ir_relation_true,  relation, possible)) {
+					if (bl) {
 						ir_tarval *const uneq = tarval_or(tarval_andnot(tv, bl->z), tarval_andnot(bl->o, tv));
 						int        const hi   = get_tarval_highest_bit(uneq);
 						if (hi >= 0) {
@@ -5427,8 +5428,7 @@ cmp_x_eq_0:
 				} else if ((relation == ir_relation_greater || relation == ir_relation_less_equal) &&
 					tarval_cmp(tv, get_mode_null(mode)) == ir_relation_less) {
 					bitinfo const *const bl = get_bitinfo(left);
-				if (bl && !is_relation(ir_relation_false, relation, possible)
-				       && !is_relation(ir_relation_true,  relation, possible)) {
+					if (bl) {
 						ir_tarval *const uneq = tarval_or(tarval_andnot(tv, bl->z), tarval_andnot(bl->o, tv));
 						int        const hi   = get_tarval_highest_bit(uneq);
 						if (hi >= 0) {
@@ -5457,6 +5457,7 @@ reduced_tv:
 					changedc  = true;
 					DBG_OPT_ALGSIM0(n, n, FS_OPT_CMP_CNST_MAGN);
 				}
+			}
 
 			/* the following reassociations work only for == and != */
 			if (rel_eq != ir_relation_false) {