master: Guard a thing with backend-subfeatures

The branch "master" has been updated in SBCL:
       via  40aa19c16995d8e83be62a924644fc6f012f3ca7 (commit)
      from  4d06d766bb133ab113458de91bf71424a5b2aa84 (commit)

- Log -----------------------------------------------------------------
commit 40aa19c16995d8e83be62a924644fc6f012f3ca7
Author: Douglas Katzman <[email protected]>
Date:   Thu Aug 6 01:42:54 2026 +0000

    Guard a thing with backend-subfeatures
---
 src/code/setf-funs.lisp | 44 +++++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 21 deletions(-)

diff --git a/src/code/setf-funs.lisp b/src/code/setf-funs.lisp
index ab49e56f0..17a5b3071 100644
--- a/src/code/setf-funs.lisp
+++ b/src/code/setf-funs.lisp
@@ -92,27 +92,29 @@
                     instance-pointer-lowtag))
            (type (dsd-type dsd)))
       (declare (ignorable disp type))
-      #+(or arm64 riscv64 x86-64)
-      (multiple-value-bind (sc primtype)
-          (ecase (dsd-raw-type dsd)
-            (t (if (eq type 'fixnum)
-                   (values 'any-reg 'tagged-num)
-                   (values 'descriptor-reg 't)))
-            (signed-word (values 'signed-reg 'signed-num))
-            (word (values 'unsigned-reg 'unsigned-num)))
-        `(truly-the ,type
-          (inline-vop (((instance descriptor-reg t) (the ,(dd-name (car info)) ,instance))
-                       ((val ,sc ,primtype) (the ,type ,value))
-                       ((temp)))
-                      ((res ,sc ,primtype))
-           #+arm64 (progn (inst add temp instance ,disp)
-                          (inst swpal val res temp))
-           #+riscv (progn (inst addi temp instance ,disp)
-                          (inst amoswap res val temp :aq :rl))
-           #+x86-64 (progn (move temp val)
-                           (inst xchg temp (ea ,disp instance)) ; LOCK is implicit
-                           (move res temp)))))
-      #-(or arm64 riscv64 x86-64)
+      (when (or #+(or riscv64 x86-64) t
+                #+arm64 (member :arm-v8.1 *backend-subfeatures*))
+        (return-from %atomic-exchange
+          (multiple-value-bind (sc primtype)
+              (ecase (dsd-raw-type dsd)
+                (t (if (eq type 'fixnum)
+                       (values 'any-reg 'tagged-num)
+                       (values 'descriptor-reg 't)))
+                (signed-word (values 'signed-reg 'signed-num))
+                (word (values 'unsigned-reg 'unsigned-num)))
+            `(truly-the ,type
+              (inline-vop (((instance descriptor-reg t) (the ,(dd-name (car info)) ,instance))
+                           ((val ,sc ,primtype) (the ,type ,value))
+                           ((temp)))
+                          ((res ,sc ,primtype))
+               #+arm64 (progn (inst add temp instance ,disp)
+                              (inst swpal val res temp))
+               #+riscv (progn (inst addi temp instance ,disp)
+                              (inst amoswap res val temp :aq :rl))
+               #+x86-64 (progn (move temp val)
+                               (inst xchg temp (ea ,disp instance)) ; LOCK is implicit
+                               (move res temp)))))))
+      ;; fallback variant
       `(let* ((.instance. ,instance) ; GET-CAS-EXPANSION exists. I don't care
               (.new. ,value)
               (.old. (,accessor .instance.)))

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