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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103194] [12 Regression] ice in optimize_atomic_bit_test_and with __sync_fetch_and_and since r12-5102-gfb161782545224f5
Date: Tue, 16 Nov 2021 02:39:46 +0000 [thread overview]
Message-ID: <bug-103194-4-PxP8N7viLg@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-103194-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103194
--- Comment #16 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Hongtao.liu from comment #15)
> (In reply to H.J. Lu from comment #13)
> > (In reply to Hongtao.liu from comment #8)
> > > unsigned long pscc_a_2_3;
> > > int pscc_a_1_4;
> > > unsigned long pc2;
> > > void pscc(int n)
> > > {
> > > long mask = 1ll << n;
> > > pc2 = __sync_fetch_and_or(&pscc_a_2_3, mask) & mask;
> > > }
> > >
> > > void pscc1(int n)
> > > {
> > > long mask = 1ll << 65;
> > > pc2 = __sync_fetch_and_or(&pscc_a_2_3, mask) & mask;
> > > }
> > >
> > > pscc and pscc1 have different behavior when n >= 64, It seems unsafe to
> > > optimize variable mask?
> >
> > Is the behavior well defined for n >= 64? I got
> >
> > foo.c:11:19: warning: left shift count >= width of type
> > [-Wshift-count-overflow]
> > 11 | long mask = 1ll << 65;
> > | ^~
> According to C99
> The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are
> filled with zeros. If E1 has an unsigned type, the value of the result is E1
> × 2E2, reduced modulo one more than the maximum value representable in the
> result type. If E1 has a signed type and nonnegative value, and E1 × 2E2 is
> representable in the result type, then that is the resulting value;
> otherwise, the behavior is undefined.
>
> So yes, it's well defined, and the result is zero.
This is the existing behavior since GCC 7.
next prev parent reply other threads:[~2021-11-16 2:39 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 16:48 [Bug c/103194] New: ice in optimize_atomic_bit_test_and, at tree-ssa-ccp.c:3626 dcb314 at hotmail dot com
2021-11-11 16:50 ` [Bug c/103194] " dcb314 at hotmail dot com
2021-11-11 17:20 ` [Bug tree-optimization/103194] [12 Regression] ice in optimize_atomic_bit_test_and with __sync_fetch_and_and pinskia at gcc dot gnu.org
2021-11-11 18:56 ` hjl.tools at gmail dot com
2021-11-12 7:35 ` rguenth at gcc dot gnu.org
2021-11-12 9:29 ` [Bug tree-optimization/103194] [12 Regression] ice in optimize_atomic_bit_test_and with __sync_fetch_and_and since r12-5102-gfb161782545224f5 marxin at gcc dot gnu.org
2021-11-12 13:43 ` hjl.tools at gmail dot com
2021-11-13 15:04 ` hjl.tools at gmail dot com
2021-11-13 15:11 ` hjl.tools at gmail dot com
2021-11-15 1:23 ` crazylht at gmail dot com
2021-11-15 2:47 ` crazylht at gmail dot com
2021-11-15 8:32 ` crazylht at gmail dot com
2021-11-15 9:06 ` crazylht at gmail dot com
2021-11-15 9:12 ` pinskia at gcc dot gnu.org
2021-11-16 1:30 ` crazylht at gmail dot com
2021-11-16 1:49 ` hjl.tools at gmail dot com
2021-11-16 1:51 ` hjl.tools at gmail dot com
2021-11-16 2:24 ` crazylht at gmail dot com
2021-11-16 2:39 ` hjl.tools at gmail dot com [this message]
2021-11-16 3:26 ` hjl.tools at gmail dot com
2021-11-16 6:19 ` crazylht at gmail dot com
2021-11-16 6:45 ` crazylht at gmail dot com
2021-11-24 1:01 ` cvs-commit at gcc dot gnu.org
2021-11-24 1:02 ` crazylht at gmail dot com
2021-12-15 12:47 ` jakub at gcc dot gnu.org
2021-12-16 1:27 ` crazylht at gmail dot com
2021-12-19 23:47 ` hjl.tools at gmail dot com
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