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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/95663] static_cast checks for null even when
 the pointer is dereferenced
Date: Thu, 07 Jan 2021 20:00:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95663

--- Comment #18 from Jeffrey A. Law <law at redhat dot com> ---
Jon, there's no way for the optimizers to improve the to_derived_bad case as
there's nothing in the IL after we leave the front-end that's useful.  In t=
he
.original dump we have:

;; Function derived& to_derived_bad(base2*) (null)
;; enabled by -tree-original


return <retval> =3D b !=3D 0B ? (struct derived &) b + 18446744073709551612=
 : 0;


There's just nothing the optimizers can do with that.  The front-end would =
have
to provide more information or remove the check itself (as is done for the
to_derived_good case which has this .original dump):

;; Function derived& to_derived_good(base2*) (null)
;; enabled by -tree-original


return <retval> =3D (struct derived &) NON_LVALUE_EXPR <b> +
18446744073709551612;=