Re: master: Don't flush division operations

Could we instead replace flushed combinations with a truly-the cast or something similar so that we can still flush the combinations but keep the type constraint?


On Friday, January 30, 2026, 2:48 AM, stassats via Sbcl-commits <[email protected]> wrote:

The branch "master" has been updated in SBCL:
      via  0ca806dfb37d380eb7aa10757410a209d9b76114 (commit)
      from  3d42fce84d4394a6efcc38c741ef701dff6042ef (commit)

- Log -----------------------------------------------------------------
commit 0ca806dfb37d380eb7aa10757410a209d9b76114
Author: Stas Boukarev <[email protected]>
Date:  Fri Jan 30 04:29:55 2026 +0300

    Don't flush division operations
    
    Division operations produce constraints that the divisor is not zero
    afterwards. Which is probably more helpful than not calling them.
---
 src/compiler/fndb.lisp    | 18 +++++++++---------
 src/compiler/ir1util.lisp | 13 ++++++++-----
 src/compiler/srctran.lisp |  9 +++++++++
 3 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/src/compiler/fndb.lisp b/src/compiler/fndb.lisp
index 5dddc1f66..188fef512 100644
--- a/src/compiler/fndb.lisp
+++ b/src/compiler/fndb.lisp
@@ -237,7 +237,7 @@
 (defknown - (number &rest number) number
  (movable foldable flushable))
 (defknown / (number &rest number) number
-  (movable foldable unsafely-flushable))
+  (movable foldable))
 (defknown (1+ 1-) (number) number
  (movable foldable flushable))
 
@@ -251,7 +251,7 @@
 
 (defknown sb-kernel::integer-/-integer
  (integer integer) rational
-  (no-verify-arg-count unsafely-flushable))
+  (no-verify-arg-count))
 
 (defknown (two-arg-< two-arg-= two-arg-> two-arg-<= two-arg->=)
    (number number) boolean
@@ -360,20 +360,20 @@
 
 (defknown (floor ceiling)
  (real &optional real) (values integer real)
-  (movable foldable flushable))
+  (movable foldable))
 
 (defknown (truncate round)
  (real &optional real) (values integer real)
-  (movable foldable flushable recursive))
+  (movable foldable recursive))
 
 (defknown (sb-kernel::floor1 sb-kernel::ceiling1) (real real) integer
-  (movable foldable flushable no-verify-arg-count))
+  (movable foldable no-verify-arg-count))
 
 (defknown (sb-kernel::truncate1 sb-kernel::round1) (real real) integer
-  (movable foldable flushable recursive no-verify-arg-count))
+  (movable foldable recursive no-verify-arg-count))
 
 (defknown (sb-kernel::ftruncate1 sb-kernel::ffloor1 sb-kernel::fceiling1 sb-kernel::fround1) (real real) float
-  (movable foldable flushable no-verify-arg-count))
+  (movable foldable no-verify-arg-count))
 
 (defknown unary-truncate (real) (values integer real)
  (movable foldable flushable no-verify-arg-count))
@@ -431,11 +431,11 @@
  (movable foldable flushable no-verify-arg-count))
 
 (defknown (mod rem) (real real) real
-    (movable foldable flushable))
+    (movable foldable))
 
 (defknown (ffloor fceiling fround ftruncate)
  (real &optional real) (values float real)
-  (movable foldable flushable))
+  (movable foldable))
 
 (defknown decode-float (float) (values float float-exponent float)
  (movable foldable unsafely-flushable))
diff --git a/src/compiler/ir1util.lisp b/src/compiler/ir1util.lisp
index 80c485e29..e93471b0d 100644
--- a/src/compiler/ir1util.lisp
+++ b/src/compiler/ir1util.lisp
@@ -1466,11 +1466,14 @@
  (let ((kind (combination-kind call))
        (info (combination-fun-info call)))
    (or (when (and (eq kind :known) (fun-info-p info))
-          (let ((attr (fun-info-attributes info)))
-            (and (if (policy call (= safety 3))
-                    (ir1-attributep attr flushable)
-                    (ir1-attributep attr unsafely-flushable))
-                (flushable-combination-args-p call info))))
+          (let ((attr (fun-info-attributes info))
+                (flushable-test (fun-info-flushable info)))
+            (if flushable-test
+                (funcall flushable-test call)
+                (and (if (policy call (= safety 3))
+                        (ir1-attributep attr flushable)
+                        (ir1-attributep attr unsafely-flushable))
+                    (flushable-combination-args-p call info)))))
        ;; Is it declared flushable locally?
        (let ((name (lvar-fun-name (combination-fun call) t)))
          (memq name (lexenv-flushable (node-lexenv call)))))))
diff --git a/src/compiler/srctran.lisp b/src/compiler/srctran.lisp
index 87807bfbf..0d62506b4 100644
--- a/src/compiler/srctran.lisp
+++ b/src/compiler/srctran.lisp
@@ -6240,6 +6240,15 @@
  (def ffloor)
  (def fceiling))
 
+(defoptimizers flushable (truncate ceiling floor round ftruncate fceiling ffloor fround)
+    ((number &optional divisor))
+  (or (not divisor)
+      (not (types-equal-or-intersect (lvar-type divisor) (specifier-type '(real 0 0))))))
+
+(defoptimizer (/ flushable) ((number &optional divisor))
+  (not (types-equal-or-intersect (lvar-type (or divisor number))
+                                (specifier-type '(or (real 0 0) complex)))))
+
 
 ;;;; character operations
 

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