microblaze: Fix atomic side effects.

In atomic_compare_and_swapsi, add side effects to prevent incorrect
assumptions during optimization. Previously, the outputs were
considered unused; this generated assembly code with
undefined side effects after invocation of the atomic.

Signed-off-by: Kirk Meyer <kirk.meyer@sencore.com>
Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>

Conflicts:
	gcc/config/microblaze/microblaze.md

Attempts to fix picolibc Issue #460. Patch file taken and applied from:
https://github.com/Xilinx/meta-xilinx/blob/master/meta-microblaze/recipes-devtools/gcc/gcc-12/0008-Patch-microblaze-Fix-atomic-side-effects.patch

Signed-off-by: Alp Sayin <alpsayin@gmail.com>

gcc/config/microblaze/microblaze.md

@@ -43,6 +43,9 @@
   (UNSPEC_TLS           106)    ;; jump table
   (UNSPEC_SET_TEXT      107)    ;; set text start
   (UNSPEC_TEXT          108)    ;; data text relative
+  (UNSPECV_CAS_BOOL     201)    ;; compare and swap (bool)
+  (UNSPECV_CAS_VAL      202)    ;; compare and swap (val)
+  (UNSPECV_CAS_MEM      203)    ;; compare and swap (mem)
 ])
 
 (define_c_enum "unspec" [

gcc/config/microblaze/sync.md

@@ -18,14 +18,19 @@
 ;; <http://www.gnu.org/licenses/>.
 
 (define_insn "atomic_compare_and_swapsi"
-  [(match_operand:SI 0 "register_operand" "=&d")	;; bool output
-   (match_operand:SI 1 "register_operand" "=&d")	;; val output
-   (match_operand:SI 2 "nonimmediate_operand" "+Q")	;; memory
-   (match_operand:SI 3 "register_operand" "d")		;; expected value
-   (match_operand:SI 4 "register_operand" "d")		;; desired value
-   (match_operand:SI 5 "const_int_operand" "")		;; is_weak
-   (match_operand:SI 6 "const_int_operand" "")		;; mod_s
-   (match_operand:SI 7 "const_int_operand" "")		;; mod_f
+  [(set (match_operand:SI 0 "register_operand" "=&d")		;; bool output
+        (unspec_volatile:SI
+          [(match_operand:SI 2 "nonimmediate_operand" "+Q")	;; memory
+           (match_operand:SI 3 "register_operand" "d")		;; expected value
+           (match_operand:SI 4 "register_operand" "d")]		;; desired value
+          UNSPECV_CAS_BOOL))
+   (set (match_operand:SI 1 "register_operand" "=&d")		;; val output
+        (unspec_volatile:SI [(const_int 0)] UNSPECV_CAS_VAL))
+   (set (match_dup 2)
+        (unspec_volatile:SI [(const_int 0)] UNSPECV_CAS_MEM))
+   (match_operand:SI 5 "const_int_operand" "")			;; is_weak
+   (match_operand:SI 6 "const_int_operand" "")			;; mod_s
+   (match_operand:SI 7 "const_int_operand" "")			;; mod_f
    (clobber (match_scratch:SI 8 "=&d"))]
   ""
   {