From: Mattias Engdegård <mattiase@acm.org>
Date: Mon, 3 Aug 2020 13:29:41 +0000 (+0200)
Subject: Fix byte-compilation of (+ -0.0) (bug#42597)
X-Git-Tag: emacs-28.0.90~6775
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=204273c3b9f0a77459661790aa929f86067a9ab1;p=emacs.git

Fix byte-compilation of (+ -0.0) (bug#42597)

* lisp/emacs-lisp/bytecomp.el (byte-compile-associative):
Translate numerical identity expressions, such as (+ x) and (* x),
into (* x 1) since the previous translation (+ x 0) gets it wrong
for x = -0.0.
* test/lisp/emacs-lisp/bytecomp-tests.el
(byte-opt-testsuite-arith-data): Add test cases.
---

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 22e648e44ba..8f76a3abb99 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -3733,7 +3733,7 @@ discarding."
 ;; Compile a function that accepts one or more args and is right-associative.
 ;; We do it by left-associativity so that the operations
 ;; are done in the same order as in interpreted code.
-;; We treat the one-arg case, as in (+ x), like (+ x 0).
+;; We treat the one-arg case, as in (+ x), like (* x 1).
 ;; in order to convert markers to numbers, and trigger expected errors.
 (defun byte-compile-associative (form)
   (if (cdr form)
@@ -3748,8 +3748,8 @@ discarding."
 	  (setq args (copy-sequence (cdr form)))
 	  (byte-compile-form (car args))
 	  (setq args (cdr args))
-	  (or args (setq args '(0)
-			 opcode (get '+ 'byte-opcode)))
+	  (or args (setq args '(1)
+			 opcode (get '* 'byte-opcode)))
 	  (dolist (arg args)
 	    (byte-compile-form arg)
 	    (byte-compile-out opcode 0))))
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index c235dd43fcc..894914300ae 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -47,6 +47,11 @@
     (let ((a 1.0))				   (/ 3 a 2))
     (let ((a most-positive-fixnum) (b 2.0))	   (* a 2 b))
     (let ((a 3) (b 2))				   (/ a b 1.0))
+    (let ((a -0.0)) (+ a))
+    (let ((a -0.0)) (- a))
+    (let ((a -0.0)) (* a))
+    (let ((a -0.0)) (min a))
+    (let ((a -0.0)) (max a))
     (/ 3 -1)
     (+ 4 3 2 1)
     (+ 4 3 2.0 1)