Fixed local optimization.

The transformation (a << c1) | c2 => (a | (c2 >> c1)) << c1
is only valid if the lower bits of c2 are clean.

This fixes opt/pr37102.c.

diff --git a/ir/ir/iropt.c b/ir/ir/iropt.c
index ba9a141..bd58883 100644 (file)
--- a/ir/ir/iropt.c
+++ b/ir/ir/iropt.c
@@ -3108,6 +3108,14 @@ static ir_node *transform_node_bitop_shift(ir_node *n)
 
        if (is_Shl(left)) {
                tv_bitop = tarval_shr(tv2, tv1);
+
+               /* Check whether we have lost some bits during the right shift. */
+               if (is_Or(n) || is_Eor(n)) {
+                       ir_tarval *tv_back_again = tarval_shl(tv_bitop, tv1);
+
+                       if (tarval_cmp(tv_back_again, tv2) != ir_relation_equal)
+                               return n;
+               }
        } else if (is_Shr(left)) {
                if (is_Or(n) || is_Eor(n)) {
                        /*