Package: gcc-12
Version: 12.2.0-14
Severity: normal
Tags: upstream
Forwarded: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98447
On the following program
void f (unsigned long *p, int r, int i)
{
int b = 64, n = r % 64;
while (i >= 0 && b >= 0)
{
if (b <= n)
p[i--] = 1UL << b;
b -= n;
}
}
gcc-12 emits the following incorrect warning:
$ gcc-12 -fanalyzer -c warn-shiftcount.c
warn-shiftcount.c: In function ‘f’:
warn-shiftcount.c:8:22: warning: shift by count (‘64’) >= precision of type
(‘6’) [-Wanalyzer-shift-count-overflow]
8 | p[i--] = 1UL << b;
| ~~~~^~~~
‘f’: events 1-5
|
| 5 | while (i >= 0 && b >= 0)
| | ~~~~~~~^~~~~~~~~
| | |
| | (1) following ‘true’ branch...
| 6 | {
| 7 | if (b <= n)
| | ~
| | |
| | (2) ...to here
| | (3) following ‘true’ branch (when ‘b <= n’)...
| 8 | p[i--] = 1UL << b;
| | ~~~ ~~~~~~~~
| | | |
| | | (5) shift by count ‘64’ here
| | (4) ...to here
|
Here, due to the "n = r % 64", one has n <= 63, so that "1UL << b"
can be executed only when b <= 63, and the shift is necessarily valid
(no overflow).
Note: gcc-11 is affected too, but not gcc-10.
-- System Information:
Debian Release: bookworm/sid
APT prefers unstable-debug
APT policy: (500, 'unstable-debug'), (500, 'stable-updates'), (500,
'stable-security'), (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1,
'experimental')
merged-usr: no
Architecture: amd64 (x86_64)
Kernel: Linux 6.1.0-5-amd64 (SMP w/8 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE,
TAINT_UNSIGNED_MODULE
Locale: LANG=POSIX, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled
Versions of packages gcc-12 depends on:
ii binutils 2.40-2
ii cpp-12 12.2.0-14
ii gcc-12-base 12.2.0-14
ii libc6 2.36-8
ii libcc1-0 12.2.0-14
ii libgcc-12-dev 12.2.0-14
ii libgcc-s1 12.2.0-14
ii libgmp10 2:6.2.1+dfsg1-1.1
ii libisl23 0.25-1
ii libmpc3 1.3.1-1
ii libmpfr6 4.2.0-1
ii libstdc++6 12.2.0-14
ii libzstd1 1.5.4+dfsg2-3
ii zlib1g 1:1.2.13.dfsg-1
Versions of packages gcc-12 recommends:
ii libc6-dev 2.36-8
Versions of packages gcc-12 suggests:
ii gcc-12-doc 12.2.0-1
ii gcc-12-locales 12.2.0-14
ii gcc-12-multilib 12.2.0-14
-- no debconf information
--
Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
