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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 01:49:38 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103194

--- Comment #13 from H.J. Lu <hjl.tools at gmail dot com> ---
(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 =3D 1ll << n;
>   pc2 =3D __sync_fetch_and_or(&pscc_a_2_3, mask) & mask;
> }
>=20
> void pscc1(int n)
> {
>   long mask =3D 1ll << 65;
>   pc2 =3D __sync_fetch_and_or(&pscc_a_2_3, mask) & mask;
> }
>=20
> pscc and pscc1 have different behavior when n >=3D 64, It seems unsafe to
> optimize variable mask?

Is the behavior well defined for n >=3D 64? I got

foo.c:11:19: warning: left shift count >=3D width of type
[-Wshift-count-overflow]
   11 |   long mask =3D 1ll << 65;
      |                   ^~=