make check error in native compiler resulting from commit 1cd188799f86bcb13ad76e82e3436b1b7e9f9e9f on 2021-12-30.

[Alan Mackenzie]

Hello, Andrea.

In that patch, I made the following change so that a comparison
involving Qnil would not go through the (newly) expensive emit_EQ:

diff --git a/lisp/emacs-lisp/comp.el b/lisp/emacs-lisp/comp.el
index 0a10505257..8581fe8066 100644
--- a/lisp/emacs-lisp/comp.el
+++ b/lisp/emacs-lisp/comp.el
@@ -1829,9 +1829,7 @@ comp-limplify-lap-inst
       (byte-listp auto)
       (byte-eq auto)
       (byte-memq auto)
-      (byte-not
-       (comp-emit-set-call (comp-call 'eq (comp-slot-n (comp-sp))
-                                      (make-comp-mvar :constant nil))))
+      (byte-not null)
       (byte-car auto)
       (byte-cdr auto)
       (byte-cons auto)

..  Since then, there has been a mismatch in
test/lisp/emacs-lisp/comp-tests.log, comp-tests-ret-type-spec-55, where
the returned ret-type has now become t, whereas previously it was (not
integer).

I don't really understand what ret-type is.  The mismatch between what
this ret-type "should" be, and what it now is doesn't seem to be causing
any problems.  Would you please say whether this is, in fact, true.
Would you also please advise on the best way to fix this bug in make
check.

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).