[PATCH] Fix PR56270

[Richard Biener <rguenther at suse dot de>]

This fixes PR56270 - when two SLP instances share a load
we fail to properly initialize the vectorized SLP stmts.
In fact, there is no support in SLP to "share" vectorized
code between instances - the only support that's explicitely
wired in is to have different permutations of a load inside
a single SLP instance.

Without digging further into cross-instance SLP vectorized
code sharing (or even intra-instance sharing) the following
avoids the special early-out cross-instance by resetting
the instances loads vector-stmts after scheduling it.

Another fix would possibly to do

      /* Check if the chain of loads is already vectorized.  */
      if (STMT_VINFO_VEC_STMT (vinfo_for_stmt (first_stmt)))
        {
          *vec_stmt = STMT_VINFO_VEC_STMT (stmt_info);
          return true;
        }

only for !slp and for SLP figure out an equivalent condition
using SLP_TREE_VEC_STMTS.

Jakub, do you have any insights into this code, especially
what kind of permutations we support?

Bootstrap and regtest running on x86_64-unknown-linux-gnu.

Thanks,
Richard.

2013-03-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/56270
	* tree-vect-slp.c (vect_schedule_slp): Clear vectorized stmts
	of loads after scheduling an SLP instance.

	* gcc.dg/vect/slp-38.c: New testcase.

Index: gcc/tree-vect-slp.c
===================================================================
*** gcc/tree-vect-slp.c	(revision 196423)
--- gcc/tree-vect-slp.c	(working copy)
*************** vect_schedule_slp (loop_vec_info loop_vi
*** 3138,3144 ****
  {
    vec<slp_instance> slp_instances;
    slp_instance instance;
!   unsigned int i, vf;
    bool is_store = false;
  
    if (loop_vinfo)
--- 3148,3155 ----
  {
    vec<slp_instance> slp_instances;
    slp_instance instance;
!   slp_tree loads_node;
!   unsigned int i, j, vf;
    bool is_store = false;
  
    if (loop_vinfo)
*************** vect_schedule_slp (loop_vec_info loop_vi
*** 3157,3162 ****
--- 3168,3181 ----
        /* Schedule the tree of INSTANCE.  */
        is_store = vect_schedule_slp_instance (SLP_INSTANCE_TREE (instance),
                                               instance, vf);
+ 
+       /* Clear STMT_VINFO_VEC_STMT of all loads.  With shared loads
+          between SLP instances we fail to properly initialize the
+ 	 vectorized SLP stmts and confuse different load permutations.  */
+       FOR_EACH_VEC_ELT (SLP_INSTANCE_LOADS (instance), j, loads_node)
+ 	STMT_VINFO_VEC_STMT
+ 	  (vinfo_for_stmt (SLP_TREE_SCALAR_STMTS (loads_node)[0])) = NULL;
+ 
        if (dump_enabled_p ())
  	dump_printf_loc (MSG_NOTE, vect_location,
                           "vectorizing stmts using SLP.");
Index: gcc/testsuite/gcc.dg/vect/slp-38.c
===================================================================
*** gcc/testsuite/gcc.dg/vect/slp-38.c	(revision 0)
--- gcc/testsuite/gcc.dg/vect/slp-38.c	(working copy)
***************
*** 0 ****
--- 1,24 ----
+ /* { dg-do compile } */
+ 
+ typedef struct {
+     float l, h;
+ } tFPinterval;
+ 
+ tFPinterval X[1024];
+ tFPinterval Y[1024];
+ tFPinterval Z[1024];
+ 
+ void Compute(void)
+ {
+   int d;
+   for (d= 0; d < 1024; d++)
+     {
+       Y[d].l= X[d].l + X[d].h;
+       Y[d].h= Y[d].l;
+       Z[d].l= X[d].l;
+       Z[d].h= X[d].h;
+     }
+ }
+ 
+ /* { dg-final { scan-tree-dump-times "vectorized 1 loops in function" 1 "vect" { target { vect_float && vect_perm } } } } */
+ /* { dg-final { cleanup-tree-dump "vect" } } */