[Bug tree-optimization/23659] New: Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[Bug tree-optimization/23659] New: Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[pinskia at gcc dot gnu dot org]

An example of this comes from PR 18298:
extern "C" int strcmp (const char*, const char*);

char s[2048] = "a";

inline bool foo(const char *str) {
  return !strcmp(s,str);
}
int main() {
  while(!(foo(""))) {
    s[0] = '\0';
  }
  return 0;
}

In fab, we replace:
  #   VUSE <s_1>;
  D.1754_4 = strcmp (&s[0], &""[0]);

With   
  D.1777_6 = (const unsigned char *) &s[0];
  D.1778_9 = *D.1777_6;
  D.1779_3 = (int) D.1778_9;
  D.1754_4 = D.1779_3;

And the "  D.1778_9 = *D.1777_6;" statement does not have a VUSE which causes wrong code if we 
have a V_MAY_DEF/V_MUST_DEF above (which happens in the testcase).

The main reason why I am asking this question so that in the tree combiner, I don't want to rerun 
may_alias after each time I run the tree combiner which just becomes too expensive.

An example for the tree combiner would be:
int f(char *a)
{
  int b = strlen(a);
  return b == 0;
}

-- 
           Summary: Should able to add dereferencing (statements with VUSE)
                    without rerunning may_alias
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: tree-optimization
        AssignedTo: dnovillo at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2005-08-31 17:00:14
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2005-08-31 21:38 -------
Can the alias gurus please give their view on this one? 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org, dnovillo at gcc dot gnu
                   |                            |dot org
           Keywords|                            |alias


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[dnovillo at gcc dot gnu dot org]

------- Additional Comments From dnovillo at gcc dot gnu dot org  2005-08-31 21:41 -------

Working on it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed a long time ago.

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[dnovillo at gcc dot gnu dot org]

------- Comment #5 from dnovillo at gcc dot gnu dot org  2006-03-01 14:30 -------
(In reply to comment #4)

> are you still working on this PR?
> 
Yes.  In fact, it's one of the kind of manipulations that drove the design
decisions in memory SSA.

> I think something similar to the attached patch should fix the problem -- it
> makes us remember alias class --> TMT mapping globally, and uses it to set up
> TMT's for the new pointers.  Could you please comment on whether you consider
> this the right approach, or propose an alternative one?
> 
Whenever a new pointer symbol is introduced, it should receive a type tag. 
This type tag is then assigned a set of aliases (or not, depending on context).
 In fact, my plan is for these manually added type tags to be marked so that
subsequent alias passes don't affect them.  This should help the vectorizer and
other passes introduce a pointer symbol with a specific set of points-to
aliases that the aliaser may not have a chance of compute so accurately
otherwise.

> On a side note, things like this might become even more difficult with the new
> memory ssa approach.
> 
Huh.  What makes you think that?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[rakdver at gcc dot gnu dot org]

------- Comment #4 from rakdver at gcc dot gnu dot org  2006-03-01 12:10 -------
Created an attachment (id=10944)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10944&action=view)
Possible patch

(In reply to comment #2)
> Working on it.
> 

are you still working on this PR?

I think something similar to the attached patch should fix the problem -- it
makes us remember alias class --> TMT mapping globally, and uses it to set up
TMT's for the new pointers.  Could you please comment on whether you consider
this the right approach, or propose an alternative one?

On a side note, things like this might become even more difficult with the new
memory ssa approach.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659

[Bug tree-optimization/23659] Should able to add dereferencing (statements with VUSE) without rerunning may_alias

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2005-11-12 05:32 -------
This should remove the need to change may_alias to a TODO (PR 23330).


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
OtherBugsDependingO|                            |23330
              nThis|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23659