Subject: 28.0.50; Native-comp optimization bug

From: Yu Han Quek <[email-masked]>
Date: Tue, 16 Feb 2021 03:19:18 +0800

The following function gives an incorrect result when compiled natively
with comp-speed >= 2.

;; -*- lexical-binding: t; -*-

(defun native-comp-bug (body)
  (let ((x (car body))
        (y (cadr body)))
    (unless (and
             (natnump x)
             (natnump y)
             (<= x y))
      (error ""))
    x))

(native-comp-bug '(3 4))

;; Expected result: 3
;; Actual result: 0

The car of the argument is ignored and treated as 0.

This appears to be a minimal repro, manually shrunk from the original
function
discovered in rx.el (rx--translate-bounded-repetition).

If either lexical binding, natnump/inequality checks, or error form is
removed,
the function behaves as expected.

Setting comp-speed to 0 or 1 also causes the function to behave as
expected, but
setting it to 2 or 3 produces the error.

In GNU Emacs 28.0.50 (build 1, x86_64-apple-darwin20.2.0, NS appkit-2022.20
Version 11.1 (Build 20C69))
 of 2021-02-03 built on QYH2.local
Repository revision: e56c26d06f72b58acdc59c7e2958be9b691d3e78
Repository branch: master
System Description:  macOS 11.2.1

Configured using:
 'configure --with-ns --with-modules
 '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-xwidgets --with-nativecomp
 --without-rsvg 'CFLAGS=-I/usr/local/opt/gcc/include -O2 -march=native'
 'LDFLAGS=-L/usr/local/opt/gcc/lib/gcc/10
 -L/usr/local/opt/libgccjit/lib/gcc/10
 -L/usr/local/opt/gcc/lib/gcc/10/gcc/x86_64-apple-darwin20/10.2.0
 -I/usr/local/opt/gcc/include -I/usr/local/opt/libgccjit/include''

Configured features:
ACL GIF GMP GNUTLS JPEG JSON LCMS2 LIBXML2 MODULES NATIVE_COMP NOTIFY
KQUEUE NS PDUMPER PNG THREADS TIFF TOOLKIT_SCROLL_BARS XWIDGETS ZLIB

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LC_CTYPE: UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs auth-source eieio eieio-core eieio-loaddefs
password-cache json map text-property-search time-date mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
term/xterm xterm comp comp-cstr warnings subr-x rx cl-seq cl-macs
cl-extra help-mode easymenu seq byte-opt gv cl-loaddefs cl-lib bytecomp
byte-compile cconv iso-transl tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel term/ns-win ns-win ucs-normalize
mule-util term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice button
loaddefs faces cus-face pcase macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads xwidget-internal kqueue cocoa
ns lcms2 multi-tty make-network-process nativecomp emacs)

Memory information:
((conses 16 79127 4281)
 (symbols 48 8088 1)
 (strings 32 20784 4357)
 (string-bytes 1 680668)
 (vectors 16 13082)
 (vector-slots 8 220094 8657)
 (floats 8 27 13)
 (intervals 56 213 0)
 (buffers 984 11))