master: x86-64: fix mask-signed-field-integer for 64 and any-reg result

The branch "master" has been updated in SBCL:
       via  d81da0bd3fd665cbe99b26878b2fcfd1e4b29915 (commit)
      from  79752fb42ac4af7026c808375371abcd776a7ade (commit)

- Log -----------------------------------------------------------------
commit d81da0bd3fd665cbe99b26878b2fcfd1e4b29915
Author: Stas Boukarev <[email protected]>
Date:   Mon Apr 20 22:57:30 2026 +0300

    x86-64: fix mask-signed-field-integer for 64 and any-reg result
---
 src/compiler/x86-64/arith.lisp | 16 +++++++++++-----
 tests/arith-2.pure.lisp        | 10 ++++++++++
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/src/compiler/x86-64/arith.lisp b/src/compiler/x86-64/arith.lisp
index f9083f8a7..6d2c167e8 100644
--- a/src/compiler/x86-64/arith.lisp
+++ b/src/compiler/x86-64/arith.lisp
@@ -4375,10 +4375,16 @@
     (:vop-var vop)
     (:generator 6
       (move r x)
-      (inst sar r n-fixnum-tag-bits)
-      (inst jmp :nc (if (> width n-fixnum-bits)
-                        DONE
-                        DO))
+      (cond ((and (sc-is r any-reg)
+                  (= width n-word-bits))
+             (inst test :byte r fixnum-tag-mask)
+             (inst jmp :z DONE))
+            (t
+             (inst sar r n-fixnum-tag-bits)
+             (inst jmp :nc (if (> width n-fixnum-bits)
+                               DONE
+                               DO))))
+
       (let* ((integerp (eq (tn-kind temp) :unused))
              (error (unless integerp
                       (generate-error-code vop 'object-not-integer-error x))))
@@ -4398,7 +4404,7 @@
            (cond
              ((zerop shift)
               (when (sc-is r any-reg)
-                (inst sar r n-fixnum-tag-bits)))
+                (inst shl r n-fixnum-tag-bits)))
              (t
               (inst shl r shift)
               (inst sar r (if (sc-is r any-reg)
diff --git a/tests/arith-2.pure.lisp b/tests/arith-2.pure.lisp
index 58eda9c91..76956d874 100644
--- a/tests/arith-2.pure.lisp
+++ b/tests/arith-2.pure.lisp
@@ -2522,3 +2522,13 @@
            (ldb (byte sb-vm:n-fixnum-bits 0) (ash 1 b))))
     (((1- sb-vm:n-fixnum-bits)) (ash 1 (1- sb-vm:n-fixnum-bits)))
     ((0) nil)))
+
+(with-test (:name :mask-signed-field-fixnum-result)
+  (checked-compile-and-assert
+   ()
+   `(lambda (x)
+      (truly-the fixnum (sb-c::mask-signed-field sb-vm:n-word-bits x)))
+   (((* most-positive-fixnum (ash 2 sb-vm:n-fixnum-tag-bits)))
+    (ash -2 sb-vm:n-fixnum-tag-bits))
+   ((10)
+    10)))

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