[avr,committed] Fix PR90622

[avr,committed] Fix PR90622

[Georg-Johann Lay]

This patch fixes a minor optimization issue for an avr specific builtin.
Applied as obvious.

https://gcc.gnu.org/r14-1025

Johann

--


target/90622: __builtin_avr_insert bits: Use BLD/BST for one bit in place.

If just one bit is inserted in the same position like with:
     __builtin_avr_insert_bits (0xFFFFF2FF, src, dst);
a BLD/BST sequence is better than XOR/AND/XOR.  Thus, don't fold that
case to the latter sequence.

gcc/
         PR target/90622
         * config/avr/avr.cc (avr_fold_builtin) [AVR_BUILTIN_INSERT_BITS]:
         Don't fold to XOR / AND / XOR if just one bit is copied to the
         same position.

diff --git a/gcc/config/avr/avr.cc b/gcc/config/avr/avr.cc
index d5af40f7091..9fa50ca230d 100644
--- a/gcc/config/avr/avr.cc
+++ b/gcc/config/avr/avr.cc
@@ -14425,10 +14425,13 @@ avr_fold_builtin (tree fndecl, int n_args 
ATTRIBUTE_UNUSED, tree *arg,
          if (changed)
            return build_call_expr (fndecl, 3, tmap, tbits, tval);

-        /* If bits don't change their position we can use vanilla logic
-           to merge the two arguments.  */
+        /* If bits don't change their position, we can use vanilla logic
+           to merge the two arguments...  */

-       if (avr_map_metric (map, MAP_NONFIXED_0_7) == 0)
+        if (avr_map_metric (map, MAP_NONFIXED_0_7) == 0
+            // ...except when we are copying just one bit. In that
+            // case, BLD/BST is better than XOR/AND/XOR, see PR90622.
+            && avr_map_metric (map, MAP_FIXED_0_7) != 1)
            {
              int mask_f = avr_map_metric (map, MAP_MASK_PREIMAGE_F);
              tree tres, tmask = build_int_cst (val_type, mask_f ^ 0xff);