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master 8716f21 2/2: Constant-propagate access to captured variables

From: Mattias Engdegård
Subject: master 8716f21 2/2: Constant-propagate access to captured variables
Date: Sat, 11 Dec 2021 16:20:41 -0500 (EST)

branch: master
commit 8716f21d94bfda0072843e087833fedb38dcf13e
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Constant-propagate access to captured variables
    * lisp/emacs-lisp/byte-opt.el (byte-optimize--substitutable-p):
    Treat (internal-get-closed-var N) as constants for propagation
    purposes, because that is effectively what such forms will be compiled
    to.  This allows for the elimination of some lexical variables.
    * test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases):
    Add test case.
 lisp/emacs-lisp/byte-opt.el            | 8 ++++++--
 test/lisp/emacs-lisp/bytecomp-tests.el | 6 ++++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index f6db803..2bdf1f5 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -342,8 +342,12 @@ for speeding up processing.")
       (numberp expr)
       (stringp expr)
       (and (consp expr)
-           (memq (car expr) '(quote function))
-           (symbolp (cadr expr)))
+           (or (and (memq (car expr) '(quote function))
+                    (symbolp (cadr expr)))
+               ;; (internal-get-closed-var N) can be considered constant for
+               ;; const-prop purposes.
+               (and (eq (car expr) 'internal-get-closed-var)
+                    (integerp (cadr expr)))))
       (keywordp expr)))
 (defmacro byte-optimize--pcase (exp &rest cases)
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el 
index 7e51f82..a442eb4 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -686,6 +686,12 @@ inner loops respectively."
                  (let* ((x 'a))
                    (list x (funcall g) (funcall h)))))))
       (funcall (funcall f 'b)))
+    ;; Test constant-propagation of access to captured variables.
+    (let* ((x 2)
+           (f (lambda ()
+                (let ((y x)) (list y 3 y)))))
+      (funcall f))
   "List of expressions for cross-testing interpreted and compiled code.")

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