------- Comment #12 from dberlin at gcc dot gnu dot org 2007-06-20 20:03
-------
Subject: Re: [4.2 Regression] -fstrict-aliasing causes skipped code
On 20 Jun 2007 15:12:53 -0000, rguenth at gcc dot gnu dot org
<[EMAIL PROTECTED]> wrote:
>
>
> ------- Comment #9 from rguenth at gcc dot gnu dot org 2007-06-20 15:12
> -------
> Confirmed.
>
> struct barstruct { char const* some_string; };
>
> void changethepointer(struct barstruct**);
>
> void baz()
> {
> struct barstruct bar1;
> struct barstruct* barptr = &bar1;
> changethepointer(&barptr);
> barptr->some_string = "Everything's OK!";
> }
>
>
> We end up with
>
> baz ()
> {
> struct barstruct * barptr;
> struct barstruct bar1;
> struct barstruct * barptr.0;
>
> <bb 2>:
> # barptr_2 = V_MUST_DEF <barptr_1>;
> barptr = &bar1;
> # barptr_6 = V_MAY_DEF <barptr_2>;
> # SFT.1_7 = V_MAY_DEF <SFT.1_4>;
> # NONLOCAL.7_8 = V_MAY_DEF <NONLOCAL.7_5>;
> changethepointer (&barptr);
> # VUSE <barptr_6>;
> barptr.0_3 = barptr;
> # SFT.1_9 = V_MAY_DEF <SFT.1_7>;
> barptr.0_3->some_string = &"Everything\'s OK!"[0];
> return;
>
> }
>
> because of a wrong points-to set again:
Why do you believe this is wrong?
It looks exactly right
>
> barptr.0_3 = { bar1 }
>
> The constraints are
>
> Constraints:
>
> ANYTHING = &ANYTHING
> READONLY = &ANYTHING
> INTEGER = &ANYTHING
> ESCAPED_VARS = *ESCAPED_VARS
> NONLOCAL.7 = ESCAPED_VARS
> ESCAPED_VARS = &NONLOCAL.7
> ESCAPED_VARS = &NONLOCAL.7
> barptr = &bar1
> ESCAPED_VARS = &bar1
> ESCAPED_VARS = &barptr
> barptr.0_3 = barptr
>
> where ESCAPED_VARS = &barptr looks wrong? I'd say it needs to be
> ESCAPED_VARS = barptr instead.
No, it's right on that part. It says ESCAPED_VARS points to barptr.
ESCAPED_VARS = *ESCAPED_VARS will take care of making it point what
barptr points to.
What is missing here is that we should be doing barptr = ESCAPED_VARS
when we see &barptr passed to the call.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32328
