master: Clarify a comment

The branch "master" has been updated in SBCL:
       via  98ec86bb1260ab0fc6a77221372211f1b4817bd9 (commit)
      from  773469344bcb9da70284f722f0d1a414796dfa7e (commit)

- Log -----------------------------------------------------------------
commit 98ec86bb1260ab0fc6a77221372211f1b4817bd9
Author: Douglas Katzman <[email protected]>
Date:   Wed Jul 29 00:05:47 2026 -0400

    Clarify a comment
---
 src/compiler/constraint.lisp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/compiler/constraint.lisp b/src/compiler/constraint.lisp
index 6d9a4f5a4..4c0cd0720 100644
--- a/src/compiler/constraint.lisp
+++ b/src/compiler/constraint.lisp
@@ -155,10 +155,13 @@
   (defun conset-adjoin (constraint conset) (sset-adjoin constraint conset))
   (defun conset-delete (constraint conset) (sset-delete constraint conset))
   (defun conset= (conset1 conset2) (sset= conset1 conset2))
-  ;; Note: CP doesn't ever care whether union, intersection, and
-  ;; difference change the first set.  (This is an important degree of
-  ;; freedom, since some ways of implementing sets lose a great deal
-  ;; when these operations are required to track changes.)
+  ;; Note: CP doesn't need the boolean result from {union, intersection, difference}
+  ;; indicating whether CONSET1 actually changed due to the operation.
+  ;; Hence we return 0 values to explicitly discard the result of the SSET call.
+  ;; The #+bitmapped-conset approach doesn't even try to compute a similar result.
+  ;; (This is an important degree of freedom, since some ways of implementing sets
+  ;; suffer in performance when algebraic operations are required to compute
+  ;; a truth value based on whether the operation had an effect.)
   (defun conset-union (conset1 conset2)
     (sset-union conset1 conset2) (values))
   (defun conset-intersection (conset1 conset2)

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