# HG changeset patch
# User Aidan Kehoe <kehoea@parhasard.net>
# Date 1317715334 -3600
# Node ID 0b6e7ae1e78f6d81a1aab4a45315f53c894d81a6
# Parent  071b810ceb18d441cef3e92b141882ab42bc62e3
Update a comment with a better understanding of the optimizer, bytecomp.el

lisp/ChangeLog addition:

2011-10-04  Aidan Kehoe  <kehoea@parhasard.net>

	* bytecomp.el (byte-compile-funcall):
	Correct a comment here, explaining why the optimizer doesn't
	expand (funcall #'(lambda ...)) in some contexts with inline
	labels, and why it's reasonable to do it here.

diff -r 071b810ceb18 -r 0b6e7ae1e78f lisp/ChangeLog
--- a/lisp/ChangeLog	Mon Oct 03 20:16:14 2011 +0100
+++ b/lisp/ChangeLog	Tue Oct 04 09:02:14 2011 +0100
@@ -1,3 +1,10 @@
+2011-10-04  Aidan Kehoe  <kehoea@parhasard.net>
+
+	* bytecomp.el (byte-compile-funcall):
+	Correct a comment here, explaining why the optimizer doesn't
+	expand (funcall #'(lambda ...)) in some contexts with inline
+	labels, and why it's reasonable to do it here.
+
 2011-10-03  Aidan Kehoe  <kehoea@parhasard.net>
 
 	* simple.el (handle-pre-motion-command-current-command-is-motion):
diff -r 071b810ceb18 -r 0b6e7ae1e78f lisp/bytecomp.el
--- a/lisp/bytecomp.el	Mon Oct 03 20:16:14 2011 +0100
+++ b/lisp/bytecomp.el	Tue Oct 04 09:02:14 2011 +0100
@@ -4164,9 +4164,23 @@
 	     (not (eq (setq form (cons (cadadr form) (cddr form)))
 		      (setq form (byte-compile-unfold-lambda form))))
 	     (prog1 nil (setq form `(funcall #',(car form) ,@(cdr form))))))
-      ;; Sometimes the optimizer fails to unfold well-formed calls of the
-      ;; form (funcall #'(lambda ...)); since we need it to do this for
-      ;; (declare (inline ...)) to work properly with labels, force that here.
+      ;; The byte-compile part of the #'labels implementation, above,
+      ;; happens after macroexpansion and after the source optimizer has
+      ;; done its thing. When labels are to be made inline we can have code
+      ;; that looks like (funcall #'(lambda ...) ...), when the code that
+      ;; the optimizer saw looked like (funcall #<compiled-function ...>
+      ;; ...).
+      ;;
+      ;; So, the optimizer doesn't have the opportunity to transform the
+      ;; former to (let (...) ...), and it's reasonable to do that here (since
+      ;; the labels implementation doesn't change other code that would need
+      ;; running through the optimizer; the lambda itself has already been
+      ;; through the optimizer).
+      ;;
+      ;; Equally reasonable, and conceptually a bit clearer, would be to do
+      ;; the transformation to (funcall #'(lambda ...) ...) in the
+      ;; byte-optimizer, breaking most of the #'sublis calls out of the
+      ;; byte-compile method.
       (byte-compile-form form)
     (mapc 'byte-compile-form (cdr form))
     (byte-compile-out 'byte-call (length (cdr (cdr form))))))