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From: "terra at gnome dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/56888] memcpy implementation optimized as a call to
 memcpy
Date: Tue, 19 Dec 2023 02:07:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D56888

--- Comment #48 from M Welinder <terra at gnome dot org> ---
It's your (1).  gcc is changing a program that can rely on errno not being
changed to one where the C library can change it.  (The current C library or
any future library that the resulting binary may be dynamically linked
against.)

Consider code like this

   fd =3D open(filename, ...);
   if (fd < 0) {
     fprintf(stderr, "%*s: %s\n",
             MIN(20, mystrlen (filename)), ;
             filename,
             strerror(errno));
     ...;
   }

If the C library is in a bad mood you will print the wrong error message.

strlen isn't the obvious candidate for a C library function changing errno,=
 but
I can see an instrumented library do it.

Is there any real-world situation that benefits from introducing these call=
s?=20
It has the feel of optimizing for a benchmark.=