master 828c49ae29f 2/2: Fix `cond` miscompilation bug

[Mattias Engdegård]

branch: master
commit 828c49ae29fd318547d7bbe4e7fdc65da316e309
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Fix `cond` miscompilation bug
    
    This fixes a bug that miscompiled
    
      (cond ... C S1...Sn)
    
    where S1...Sn are switch clauses (that can be compiled into a switch
    op) and C a non-switch clause, by tucking on an extra copy of C at the
    end.  This was a serious wrong-code bug when the condition of C had
    side-effects; otherwise it was only a waste of time and space.
    
    * lisp/emacs-lisp/bytecomp.el (byte-compile-cond): Fix.
    * test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
    Add test case.
---
 lisp/emacs-lisp/bytecomp.el            | 1 +
 test/lisp/emacs-lisp/bytecomp-tests.el | 9 +++++++++
 2 files changed, 10 insertions(+)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 095468ad978..6f3d7a70903 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4590,6 +4590,7 @@ Return (TAIL VAR TEST CASES), where:
         (if switch-prefix
             (progn
               (byte-compile-cond-jump-table (cdr switch-prefix) donetag)
+              (setq clause nil)
               (setq clauses (car switch-prefix)))
           (setq clause (car clauses))
           (cond ((or (eq (car clause) t)
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el 
b/test/lisp/emacs-lisp/bytecomp-tests.el
index b6dcfeedb0c..10b009a261c 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -757,6 +757,15 @@ inner loops respectively."
         (bytecomp-test-identity 3)
       (error 'bad)
       (:success))                       ; empty handler
+
+    ;; `cond' miscompilation bug
+    (let ((fn (lambda (x)
+                (let ((y nil))
+                  (cond ((progn (setq x (1+ x)) (> x 10)) (setq y 'a))
+                        ((eq x 1) (setq y 'b))
+                        ((eq x 2) (setq y 'c)))
+                  (list x y)))))
+      (mapcar fn (bytecomp-test-identity '(0 1 2 3 10 11))))
     )
   "List of expressions for cross-testing interpreted and compiled code.")