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From: "segher at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/112758] [13/14 Regression] Inconsistent
 Bitwise AND Operation Result between int and long long int
Date: Sun, 10 Dec 2023 12:16:12 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112758

--- Comment #12 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Eric Botcazou from comment #11)
> > It says those upper bits are well-defined, i.e. whatever MD pattern is =
used
> > for it eventually will emit machine code that has the exact same result=
 for
> > those upper bits.
>=20
> No, that's not true, the set of "register operations" is restricted.

Who what where?  That is not how it is documented.  There is
word_register_operation_p as a bandaid to make it *somewhat* work, added
decades
later, but it still won't fly :-(

Different parts of the compiler think it has much more stringent semantics =
btw.=