More robust optimisation of `ignore`

Treat `ignore` as any other function during source-level optimisation,
to avoid having its warning-suppression effects cancelled by repeated
passes.  Instead, define a custom code generation function.

* lisp/emacs-lisp/byte-opt.el (byte-optimize-form-code-walker):
Don't treat `ignore' specially here.
(side-effect-free-fns): Don't mark `ignore` as side-effect-free
or error-free (although it is), since that would allow the optimiser
to elide calls.
* lisp/emacs-lisp/bytecomp.el (ignore, byte-compile-ignore):
Define and register a code-gen function.

1 files changed, 6 insertions, 0 deletions

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 145cdbaa6ed..8ea591b5d0e 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4207,6 +4207,7 @@ discarding."
 (byte-defop-compiler-1 funcall)
 (byte-defop-compiler-1 let)
 (byte-defop-compiler-1 let* byte-compile-let)
+(byte-defop-compiler-1 ignore)
 
 (defun byte-compile-progn (form)
   (byte-compile-body-do-effect (cdr form)))
@@ -4222,6 +4223,11 @@ discarding."
       (if ,discard 'byte-goto-if-nil 'byte-goto-if-nil-else-pop))
     ,tag))
 
+(defun byte-compile-ignore (form)
+  (dolist (arg (cdr form))
+    (byte-compile-form arg t))
+  (byte-compile-form nil))
+
 ;; Return the list of items in CONDITION-PARAM that match PRED-LIST.
 ;; Only return items that are not in ONLY-IF-NOT-PRESENT.
 (defun byte-compile-find-bound-condition (condition-param