[Bug middle-end/118994] GCC fails to optimize (a >> 1) + (b >> 1) + ((a | b) & 1) to PAVGB/PAVGW (or equivalent instruction)

[liuhongt at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118994

--- Comment #7 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
diff --git a/gcc/match.pd b/gcc/match.pd
index 5c679848bdf..d6a465c963c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -11348,3 +11348,28 @@ and,
       }
       (if (full_perm_p)
        (vec_perm (op@3 @0 @1) @3 @2))))))
+
+#if GIMPLE
+/* Simplify (a >> 1) + (b >> 1) + ((a | b) & 1) to .AVG_CEIL (a, b).
+   Similar for (a | b) - ((a ^ b) >> 1).  */
+
+(simplify
+  (plus:c
+    (plus (rshift @0 integer_onep@1) (rshift @2 @1))
+    (bit_and (bit_ior @0 @2) integer_onep@3))
+  (if (cfun && (cfun->curr_properties & PROP_last_full_fold) != 0
+      && VECTOR_TYPE_P (type)
+      && direct_internal_fn_supported_p (IFN_AVG_CEIL,
+      type, OPTIMIZE_FOR_BOTH))
+      (IFN_AVG_CEIL @0 @2)))
+
+(simplify
+  (minus
+    (bit_ior @0 @2)
+    (rshift (bit_xor @0 @2) integer_onep@1))
+  (if (cfun && (cfun->curr_properties & PROP_last_full_fold) != 0
+      && VECTOR_TYPE_P (type)
+      && direct_internal_fn_supported_p (IFN_AVG_CEIL,
+      type, OPTIMIZE_FOR_BOTH))
+      (IFN_AVG_CEIL @0 @2)))
+#endif

I'm testing the above.