From: Toshi Morita <tm314159@yahoo.com>
To: "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Possible missed optimization opportunity with const?
Date: Wed, 17 Aug 2016 00:25:00 -0000 [thread overview]
Message-ID: <1637972460.15325965.1471393300211.JavaMail.yahoo@mail.yahoo.com> (raw)
In-Reply-To: <1637972460.15325965.1471393300211.JavaMail.yahoo.ref@mail.yahoo.com>
I was involved in a discussion over the semantics of "const" in C, and the following code was posted:
#include <stdio.h>
int foo = 0;
const int *pfoo = &foo;
void bar (void)
{
foo +=3D;
}
int main(void)
{
int a, b;
a = *pfoo;
bar();
b = *pfoo;
printf("a: %d, b: %d\n", a, b);
}
This code when compiled with gcc 4.8.2 using the optimization option -O3 produces:
a: 0, b: 1
So it appears even though pfoo is a const int *, the value *pfoo is read twice.
Would it be valid for the code to print a:0, b: 0?
If so, is this a missed optimization opportunity?
Toshi
next parent reply other threads:[~2016-08-17 0:25 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1637972460.15325965.1471393300211.JavaMail.yahoo.ref@mail.yahoo.com>
2016-08-17 0:25 ` Toshi Morita [this message]
2016-08-17 14:15 ` David Brown
[not found] ` <1646493700.16522102.1471473899633.JavaMail.yahoo@mail.yahoo.com>
2016-08-18 13:04 ` David Brown
2016-08-17 14:27 ` lhmouse
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