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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109443] missed optimization of std::vector access (Related
 to issue 35269)
Date: Wed, 12 Apr 2023 15:10:12 +0000
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X-Bugzilla-Keywords: alias, missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109443

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |jason at gcc dot gnu.org,
                   |                            |mpolacek at gcc dot gnu.org

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the middle-end could figure this out by itself, such PARM_DECLs or
RESULT_DECLs
are DECL_BY_REFERENCE and TREE_ADDRESSABLE (TREE_TYPE (TREE_TYPE
(parm_or_decl))).
I think that means that if one calls a function with two arguments the two
arguments won't alias:
struct S { S (); ~S (); S (const S &); int s; };
void
foo (S a, S b)
{
}
void
bar (S c)
{
  foo (c, c);
}
Inside of the function one can take address of such a parameter as many tim=
es
as one wants and dereference through that of course.  But I think one can
assume that when the
function is called, the argument (i.e. the address of the object in the cal=
ler)
isn't stored anywhere else.=