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[Bug middle-end/25186] (short)(((int)short_var) <<1) should be folded so that the shift is done in the short type
- From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 1 Dec 2005 12:46:16 -0000
- Subject: [Bug middle-end/25186] (short)(((int)short_var) <<1) should be folded so that the shift is done in the short type
- References: <bug-25186-6528@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #5 from rguenth at gcc dot gnu dot org 2005-12-01 12:46 -------
I.e. 6.3.1.3/3 says that conversion from type T to signed type is
implementation defined if the value doesn't fit. And we define it to reducing
it modulo 2^N.
So, for !flag_wrapv
(short)((int)0x8000 << 1) == 0
but
0x8000 << 1 is undefined.
So this transformation is only ok for flag_wrapv.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25186