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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug ipa/97264] [11 Regression] -fpa-modref breaks va_arg on glibc
Date: Thu, 01 Oct 2020 11:31:31 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97264

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andreas Schwab from comment #5)
> Why doesn't gcc warn about that?

It does:

unsigned char **q;
void foo (char *p)
{
  q =3D (unsigned char **)&p;
}

> gcc t.c -fstrict-aliasing -Wstrict-aliasing=3D2 -S
t.i: In function 'foo':
t.i:4:3: warning: dereferencing type-punned pointer will break strict-alias=
ing
rules [-Wstrict-aliasing]
   q =3D (unsigned char **)&p;
   ^

note the default level of -Wstrict-aliasing when enabled is 3 which will
not warn when the pointer is not dereferenced in the same expression.=