Re: [tree-ssa] vdefs question (to make vectorizer pass verify ssa)

[Dorit Naishlos <DORIT at il dot ibm dot com>]

> As it should.  You have seemingly removed all references to variable
> 'a', but have not marked it for renaming.  In the current scheme, we do
> not manipulate virtual operands directly.  These are added/removed by
> get_stmt_operands when a statement is marked modified.
>
> Question: is your transformation removing *all* references to variable
> 'a'?  If so, then all you need to do is mark 'a' for renaming and call
> rewrite_into_ssa, which will DTRT.
>
> If 'a' is still referenced somewhere in the code, then you ought to add
> 'a' to the may-alias set for the memory tag of _vect_a.117 (I assume it
> has one, right?).

I managed to pass verify_ssa doing the following:

- when creating a pointer T0 in the vectorizer:

    T0 = create_tmp_var (ptr_type, new_name);
    add_referenced_tmp_var (T0);
#if 0
->  if (STMT_VINFO_TYPE (stmt_info) == store_vec_info_type)
->    var_ann (T0)->is_dereferenced_store = 1;
->  else if (STMT_VINFO_TYPE (stmt_info) == load_vec_info_type)
->    var_ann (T0)->is_dereferenced_load = 1;
#endif
*   bitmap_set_bit (vars_to_rename, var_ann (array_base)->uid);

- in tree-optimize.c:

  if (flag_tree_vectorize)
    {
*     bitmap_clear (vars_to_rename);
      vectorize_loops (fndecl, vars_to_rename, loops, ev_info, TDI_vect);
#if 0
->    compute_may_aliases (fndecl);
#endif
*     if (bitmap_first_set_bit (vars_to_rename) >= 0)
*       rewrite_into_ssa (fndecl, vars_to_rename, TDI_vect);
    }

The lines marked with '*' are the new source lines I added that solved the
problem and allowed the vectorized code to pass the verifiers.

The lines marked with '->' are not required in order to successfully pass
verify_ssa, but update the may-aliases and result in vector loads/stores
that have vdefs/vuses. However, I did not find an API exposed out side of
tree-dfa.c that lets you create new mem-tags and compute may-aliases on
demand; so for now I called compute_may_aliases(), which resulted in over
conservative vdefs/vuses - the pointers I created ended-up aliasing all the
arrays in the function, whereas if I could explicitely set their may-alias
set in the vectorizer I would make each pointer alias only the array it
points to. Is there an API that lets you do that?

thanks,
dorit

----- Forwarded by Dorit Naishlos/Haifa/IBM on 01/01/2004 15:45 -----
                                                                                                                                  
                      Dorit Naishlos                                                                                              
                                               To:      Diego Novillo <dnovillo@redhat.com>                                       
                      31/12/2003 21:08         cc:      gcc@gcc.gnu.org                                                           
                                               From:    Dorit Naishlos/Haifa/IBM@IBMIL                                            
                                               Subject: Re: [tree-ssa] vdefs question (to make vectorizer pass verify ssa)        
                                               (Document link: Dorit Naishlos)                                                    
                                                                                                                                  



> > 4 _vect_a.117_35 = _vect_var.116_34 + _vect_a.114_32;
> >
> I'd prefer if you emitted the PLUS_EXPR with the pointer as the first
> operand.  It's an unwritten convention, but I believe a call to fold()
> will switch it around for you.

ok, I'll change that.

> Question: is your transformation removing *all* references to variable
> 'a'?

not necessarily, just those that are vectorized. Within the loop that is
vectorized all the references to 'a' are replaced with references via
pointers.

> If so, then all you need to do is mark 'a' for renaming and call
> rewrite_into_ssa, which will DTRT.
> If 'a' is still referenced somewhere in the code, then you ought to add
> 'a' to the may-alias set for the memory tag of _vect_a.117 (I assume it
> has one, right?).

So how do I add a memory tag to a pointer and a variable to its may-alias
set? basically, what are the things I need to do when I'm creating a new
pointer? is there an example somewhere?

thanks,
dorit



                                                                                                                                  
                      Diego Novillo                                                                                               
                      <dnovillo@redhat.        To:       Dorit Naishlos/Haifa/IBM@IBMIL                                           
                      com>                     cc:       "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>                                      
                                               Subject:  Re: [tree-ssa] vdefs question (to make vectorizer pass verify ssa)       
                      31/12/2003 19:31                                                                                            
                                                                                                                                  




On Wed, 2003-12-31 at 08:12, Dorit Naishlos wrote:

> The problem I have is with vectorizing a store operation, like the one
> below:
>
> a_2 = PHI <a_21(0), a_25(1)>;
>
> # a_25 = VDEF <a_2>
> a[i] = x;
>
> The vector store that replaces it is of the form
> "*(_vect_a + 16 * i) = vx"
> where _vect_a is a pointer that points to the base of array a (stmt 5
> below):
> 1 _vect_a.114_32 = &a;
> 2 _vect_var.115_33 = (<unnamed type>)i_1;
> 3 _vect_var.116_34 = _vect_var.115_33 * 16;
> 4 _vect_a.117_35 = _vect_var.116_34 + _vect_a.114_32;
>
I'd prefer if you emitted the PLUS_EXPR with the pointer as the first
operand.  It's an unwritten convention, but I believe a call to fold()
will switch it around for you.

> 5 *_vect_a.117_35 = _vect_var.109_31;
>
> The scalar store is removed, and the vector store does not have a vdef,
so
> I fail on:
>
As it should.  You have seemingly removed all references to variable
'a', but have not marked it for renaming.  In the current scheme, we do
not manipulate virtual operands directly.  These are added/removed by
get_stmt_operands when a statement is marked modified.

Question: is your transformation removing *all* references to variable
'a'?  If so, then all you need to do is mark 'a' for renaming and call
rewrite_into_ssa, which will DTRT.

If 'a' is still referenced somewhere in the code, then you ought to add
'a' to the may-alias set for the memory tag of _vect_a.117 (I assume it
has one, right?).


Diego.