Interesting example indeed!
Replace the declaration of s to
char s[] = hello;
and see Hello being printed :-)
The point is: in your program is is only a pointer. When you pass s
as a parameter to printf, the compiler assumes that only s is being
used so the (effective) assignment
*s
On Tue, Sep 14, 2010 at 11:50:11PM +0530, Uday P. Khedker wrote:
The point is: in your program is is only a pointer. When you pass s
as a parameter to printf, the compiler assumes that only s is being
used so the (effective) assignment
*s = 'H'
is deleted as dead code when optimization
Godmar Back god...@gmail.com writes:
this may be a FAQ - in my class today when discussing how gcc
generates code for x86, I was stumped when I showed an example of how
gcc handles attempts to modify (read-only) string literals/constants.
(I'm sending this to gcc rather than gcc-help because
Hello Uday,
On Tue, Sep 14, 2010 at 11:50:11PM +0530, Uday P. Khedker wrote:
[..]
The point is: in your program is is only a pointer. When you pass s
as a parameter to printf, the compiler assumes that only s is being
used so the (effective) assignment
*s = 'H'
is deleted as dead code
Attached please find two dumps t.c.032t.mergephi1 and t.c.033t.cddce1.
The assignment is present in the former while it disappears in the
latter. The latter dump is the output of the dead code elimination
pass pass_cd_dce. So this is indeed an instance of dead code elimination.
But may be you
On Tue, Sep 14, 2010 at 11:47 AM, Uday P. Khedker u...@cse.iitb.ac.in wrote:
Attached please find two dumps t.c.032t.mergephi1 and t.c.033t.cddce1.
The assignment is present in the former while it disappears in the
latter. The latter dump is the output of the dead code elimination
pass
You got me there :-)
Yes you are right. The reason I gave for dead code elimination is not
sound! Should have thought a bit before writing :-(
Uday.
Axel Freyn wrote, On Wednesday 15 September 2010 12:05 AM:
Hello Uday,
On Tue, Sep 14, 2010 at 11:50:11PM +0530, Uday P. Khedker wrote:
[..]
On Tue, Sep 14, 2010 at 2:35 PM, Ian Lance Taylor i...@google.com wrote:
I think this is simply a bug. It doesn't happen with current gcc. With
gcc 4.4.3 the assignment is being eliminated because it is considered to
be dead code.
I agree that it is an error for gcc to simply eliminate
On 14/09/2010 19:47, Uday P. Khedker wrote:
But may be you are right, what facilitate dead code elimination
be based on modification of read-only data. However, if that is
the case, I wonder what is the reason why change happens when s is
an array...
Because the array, unlike the string,
Andrew Pinski pins...@gmail.com writes:
On Tue, Sep 14, 2010 at 11:47 AM, Uday P. Khedker u...@cse.iitb.ac.in wrote:
Attached please find two dumps t.c.032t.mergephi1 and t.c.033t.cddce1.
The assignment is present in the former while it disappears in the
latter. The latter dump is the output
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