master: Better type derivation (truncate x integer-union-with-zero)

The branch "master" has been updated in SBCL:
       via  01ab3579451ff4fc3c046542da3cf6390b0c20b6 (commit)
      from  1f72eef99e028a04b85e028054cce075a9c73336 (commit)

- Log -----------------------------------------------------------------
commit 01ab3579451ff4fc3c046542da3cf6390b0c20b6
Author: Stas Boukarev <[email protected]>
Date:   Wed Apr 8 04:53:59 2026 +0300

    Better type derivation (truncate x integer-union-with-zero)
---
 src/compiler/srctran.lisp | 6 ++++--
 tests/arith-2.pure.lisp   | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/compiler/srctran.lisp b/src/compiler/srctran.lisp
index b4cb3145c..de3626fce 100644
--- a/src/compiler/srctran.lisp
+++ b/src/compiler/srctran.lisp
@@ -2383,7 +2383,9 @@
                         (interval-high number-interval)
                         (interval-low divisor-interval)
                         (interval-high divisor-interval))))
-             (specifier-type (if (listp res) res 'integer))))
+             (if (eq res t)
+                 *empty-type*
+                 (specifier-type (if (listp res) res 'integer)))))
           (t
            (multiple-value-bind (quot conservative)
                (if (and (member (interval-high divisor-interval) '(1 1f0 1d0))
@@ -2412,7 +2414,7 @@
                 (numberp (interval-high divisor-interval))
                 (zerop (interval-low divisor-interval))
                 (zerop (interval-high divisor-interval)))
-           nil)
+           *empty-type*)
           ((eq rem-type 'integer)
            ;; Since the remainder type is INTEGER, both args are
            ;; INTEGERs.
diff --git a/tests/arith-2.pure.lisp b/tests/arith-2.pure.lisp
index 117e3e122..05172c2d2 100644
--- a/tests/arith-2.pure.lisp
+++ b/tests/arith-2.pure.lisp
@@ -2466,3 +2466,12 @@
                 `(lambda (x)
                    (ash (the (signed-byte ,(* 2 sb-vm:n-word-bits)) x)
                         ,(- sb-vm:n-word-bits)))))))
+
+
+(with-test (:name :truncate-by-zero-type)
+  (assert-type
+   (lambda (n x)
+     (declare ((integer -9 9) n)
+              ((and integer (not (member 1 -1))) x))
+     (truncate n x))
+   (values (integer -4 4) (integer -9 9) &optional)))

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