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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/109609] [12/13/14 Regression] tail call for function
 even when passing a ptr which references a local array still
Date: Tue, 25 Apr 2023 07:06:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109609

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
On the first testcase reverting the offending rev. shows that it causes

   <bb 2> [local count: 137085152]:
-  MEM[(char *)&buf + 12B] =3D 0;
-  _19 =3D *id_8(D);
-  if (_19 !=3D 0)
+  _18 =3D *id_7(D);
+  if (_18 !=3D 0)

thus we DSE the store to the end.

The issue is that the fnspec we have for strncpy says the access size
is specified by argument 3 but what it specified there is the _maximum_
size read, not the actual size.  So instead of "1cO313" it should be
"1cO31 " ('1' is somewhat odd then, it says we copy 'src' to 'dst'
but we only say the 'dst' write covers arg 3 size - I guess that's OK
for points-to analysis, the additional zeros written do not have pointers,
but if we use it differently it might be a wrong spec?)

I'm scanning other builtins for similar issues.=