[Bug tree-optimization/27799] New: adding unused char field inhibits optimization

[Bug tree-optimization/27799] New: adding unused char field inhibits optimization

[dann at godzilla dot ics dot uci dot edu]

For this code:

struct X {double m; int x;};
struct Y {int y; short d;};
struct YY {int y; short d; char c;};

int foo(struct X *x,  struct Y *y)
{
  x->x =  0;
  y->y =  1;
  if (x->x != 0)
    abort ();
}

int foo_no(struct X *x,  struct YY *y)
{
  x->x =  0;
  y->y =  1;
  if (x->x != 0)
    abort ();
}

the "if" does not get optimized away (by the dom1 pass) for the "foo_no"
function, but it is optimized for "foo" 
The only difference between the 2 functions is that foo_no takes as a parameter
a pointer to a struct that has a "char" field that is not accessed in this
function.

It would be nice if both functions were optimized in the same way.


-- 
           Summary: adding unused char field inhibits optimization
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dann at godzilla dot ics dot uci dot edu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-05-29 18:50 -------
Confirmed, the problem is that char is recognized as something which can alias
anything which is why it is not optimized.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2006-05-29 18:50:17
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2006-05-30 12:41 -------
Variable: x, UID 1535, struct X *, symbol memory tag: SMT.4, default def: x_1
Variable: y, UID 1536, struct YY *, symbol memory tag: SMT.5, default def: y_2
Variable: SMT.4, UID 1549, struct X, is addressable, is global, call clobbered
(, is global var, is incoming pointer ), may aliases: { SMT.5 }

but this aliasing cannot really happen.

Flow-insensitive alias information for foo_no

Aliased symbols

SMT.5, UID 1550, struct YY, is aliased, is addressable, is global, call
clobbered (, is global var, is incoming pointer )
SMT.4, UID 1549, struct X, is addressable, is global, call clobbered (, is
global var, is incoming pointer ), may aliases: { SMT.5 }

record_component_aliases is likely too conservative here.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org
 GCC target triplet|i686-pc-linux-gnu           |
           Keywords|                            |alias


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2008-03-04 20:35 -------
Actually alias_sets_conflict_p is the cuplrit, as we have in the alias subset
of struct YY alias set zero (entered for the char member, accesses conflict
with accesses through char *):

  /* See if the first alias set is a subset of the second.  */
  ase = get_alias_set_entry (set1);
  if (ase != 0
      && (ase->has_zero_child
          || splay_tree_lookup (ase->children,
                                (splay_tree_key) set2)))
    return 1;

which IMHO should do

  if (ase != 0
      && ((ase->has_zero_child && set2 == 0)
          || splay_tree_lookup (ase->children, (splay_tree_key) set2))
    return 1;

where then both cases are optimized?


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dnovillo at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #4 from rguenth at gcc dot gnu dot org  2008-03-04 21:00 -------
http://gcc.gnu.org/ml/gcc-patches/2008-03/msg00243.html


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |rguenth at gcc dot gnu dot
                   |dot org                     |org
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2006-05-29 18:50:17         |2008-03-04 21:00:03
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[dann at godzilla dot ics dot uci dot edu]

------- Comment #5 from dann at godzilla dot ics dot uci dot edu  2008-03-04 21:19 -------
(In reply to comment #4)
> http://gcc.gnu.org/ml/gcc-patches/2008-03/msg00243.html

Thanks for working on this!
Have you looked at the impact?
Probably the generated code won't too different because the RTL alias analysis
probably catches this.
But it would be interesting to see what is the difference for the tree dumps
before and after this patch.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #6 from rguenth at gcc dot gnu dot org  2008-03-04 21:22 -------
Actually RTL alias is just using the same routines. The IL difference is

  # SMT.4_6 = VDEF <SMT.4_4(D)>
  # SMT.5_7 = VDEF <SMT.5_5(D)>
  x_1(D)->x = 0;
  # SMT.5_8 = VDEF <SMT.5_7>
  y_2(D)->y = 1;

vs.

  # SMT.18_5 = VDEF <SMT.18_4(D)>
  x_1(D)->x = 0;
  # SMT.19_7 = VDEF <SMT.19_6(D)>
  y_2(D)->y = 1;


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[dann at godzilla dot ics dot uci dot edu]

------- Comment #7 from dann at godzilla dot ics dot uci dot edu  2008-03-04 21:32 -------
(In reply to comment #6)
> Actually RTL alias is just using the same routines.
Might be, but the RTL level code that optimizes away the abort() in both
testcases (if I remember well nonoverlapping_component_refs_p). 

> 
>   # SMT.4_6 = VDEF <SMT.4_4(D)>
>   # SMT.5_7 = VDEF <SMT.5_5(D)>
>   x_1(D)->x = 0;
>   # SMT.5_8 = VDEF <SMT.5_7>
>   y_2(D)->y = 1;
> 
> vs.
> 
>   # SMT.18_5 = VDEF <SMT.18_4(D)>
>   x_1(D)->x = 0;
>   # SMT.19_7 = VDEF <SMT.19_6(D)>
>   y_2(D)->y = 1;

That is for this testcase, but what about the impact on .final_cleanup for
something big like combine.c? 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenther at suse dot de]

------- Comment #8 from rguenther at suse dot de  2008-03-04 21:35 -------
Subject: Re:  adding unused char field inhibits
 optimization

On Tue, 4 Mar 2008, dann at godzilla dot ics dot uci dot edu wrote:

> ------- Comment #7 from dann at godzilla dot ics dot uci dot edu  2008-03-04 21:32 -------
> (In reply to comment #6)
> > Actually RTL alias is just using the same routines.
> Might be, but the RTL level code that optimizes away the abort() in both
> testcases (if I remember well nonoverlapping_component_refs_p). 

I still have the abort () with -O2.

> > 
> >   # SMT.4_6 = VDEF <SMT.4_4(D)>
> >   # SMT.5_7 = VDEF <SMT.5_5(D)>
> >   x_1(D)->x = 0;
> >   # SMT.5_8 = VDEF <SMT.5_7>
> >   y_2(D)->y = 1;
> > 
> > vs.
> > 
> >   # SMT.18_5 = VDEF <SMT.18_4(D)>
> >   x_1(D)->x = 0;
> >   # SMT.19_7 = VDEF <SMT.19_6(D)>
> >   y_2(D)->y = 1;
> 
> That is for this testcase, but what about the impact on .final_cleanup for
> something big like combine.c? 

No idea, but feel free to check.

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[dann at godzilla dot ics dot uci dot edu]

------- Comment #9 from dann at godzilla dot ics dot uci dot edu  2008-03-04 21:43 -------
(In reply to comment #8)
> Subject: Re:  adding unused char field inhibits
>  optimization
> 
> On Tue, 4 Mar 2008, dann at godzilla dot ics dot uci dot edu wrote:
> 
> > ------- Comment #7 from dann at godzilla dot ics dot uci dot edu  2008-03-04 21:32 -------
> > (In reply to comment #6)
> > > Actually RTL alias is just using the same routines.
> > Might be, but the RTL level code that optimizes away the abort() in both
> > testcases (if I remember well nonoverlapping_component_refs_p). 
> 
> I still have the abort () with -O2.

Argghh, sorry, my bad: typo in the "grep abort file.s" command ...


> > That is for this testcase, but what about the impact on .final_cleanup for
> > something big like combine.c? 
> 
> No idea, but feel free to check.

I don't have a recent build... 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2008-04-23 14:09 -------
Subject: Bug 27799

Author: rguenth
Date: Wed Apr 23 14:08:25 2008
New Revision: 134598

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=134598
Log:
2008-04-23  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27799
        PR tree-optimization/32921
        PR tree-optimization/32624
        * tree-ssa-structalias.c (merge_smts_into): Only merge the
        SMTs aliases and the tag itself into the solution.
        * tree-ssa-alias.c (compute_flow_sensitive_aliasing): Do not
        merge the points-to solution back into the SMT aliases.
        (may_alias_p): Use alias_set_subset_of instead of
        aliases_conflict_p.  A pointer which points to
        memory with alias set zero may access any variable.

        * gcc.dg/tree-ssa/pr27799.c: New testcase.
        * gcc.dg/tree-ssa/20030807-7.c: Remove xfail, scan vrp dump.

Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr27799.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/tree-ssa/20030807-7.c
    trunk/gcc/tree-ssa-alias.c
    trunk/gcc/tree-ssa-structalias.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799

[Bug tree-optimization/27799] adding unused char field inhibits optimization

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2008-04-23 14:09 -------
Subject: Bug 27799

Author: rguenth
Date: Wed Apr 23 14:08:25 2008
New Revision: 134598

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=134598
Log:
2008-04-23  Richard Guenther  <rguenther@suse.de>

        PR tree-optimization/27799
        PR tree-optimization/32921
        PR tree-optimization/32624
        * tree-ssa-structalias.c (merge_smts_into): Only merge the
        SMTs aliases and the tag itself into the solution.
        * tree-ssa-alias.c (compute_flow_sensitive_aliasing): Do not
        merge the points-to solution back into the SMT aliases.
        (may_alias_p): Use alias_set_subset_of instead of
        aliases_conflict_p.  A pointer which points to
        memory with alias set zero may access any variable.

        * gcc.dg/tree-ssa/pr27799.c: New testcase.
        * gcc.dg/tree-ssa/20030807-7.c: Remove xfail, scan vrp dump.

Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr27799.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/tree-ssa/20030807-7.c
    trunk/gcc/tree-ssa-alias.c
    trunk/gcc/tree-ssa-structalias.c


------- Comment #11 from rguenth at gcc dot gnu dot org  2008-04-23 14:09 -------
Fixed.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27799