Avoid recomputing data references in BB SLP

[Richard Sandiford <richard dot sandiford at arm dot com>]

If the first attempt at applying BB SLP to a region fails, the main loop
in vect_slp_bb recomputes the region's bounds and datarefs for the next
vector size.  AFAICT this isn't needed any more; we should be able
to reuse the datarefs from the first attempt instead.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Richard


2019-10-19  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-slp.c (vect_slp_analyze_bb_1): Call save_datarefs
	when processing the given datarefs for the first time and
	check_datarefs subsequently.
	(vect_slp_bb_region): New function, split out of...
	(vect_slp_bb): ...here.  Don't recompute the region bounds and
	dataref sets when retrying with a different vector size.

Index: gcc/tree-vect-slp.c
===================================================================
*** gcc/tree-vect-slp.c	2019-10-11 15:43:55.439484181 +0100
--- gcc/tree-vect-slp.c	2019-10-19 16:03:30.000000000 +0100
*************** vect_slp_analyze_bb_1 (gimple_stmt_itera
*** 2852,2857 ****
--- 2852,2858 ----
    slp_instance instance;
    int i;
    poly_uint64 min_vf = 2;
+   bool first_time_p = shared->datarefs.is_empty ();
  
    /* The first group of checks is independent of the vector size.  */
    fatal = true;
*************** vect_slp_analyze_bb_1 (gimple_stmt_itera
*** 2871,2877 ****
      return NULL;
  
    BB_VINFO_DATAREFS (bb_vinfo) = datarefs;
!   bb_vinfo->shared->save_datarefs ();
  
    /* Analyze the data references.  */
  
--- 2872,2881 ----
      return NULL;
  
    BB_VINFO_DATAREFS (bb_vinfo) = datarefs;
!   if (first_time_p)
!     bb_vinfo->shared->save_datarefs ();
!   else
!     bb_vinfo->shared->check_datarefs ();
  
    /* Analyze the data references.  */
  
*************** vect_slp_analyze_bb_1 (gimple_stmt_itera
*** 3007,3022 ****
    return bb_vinfo;
  }
  
! 
! /* Main entry for the BB vectorizer.  Analyze and transform BB, returns
!    true if anything in the basic-block was vectorized.  */
! 
! bool
! vect_slp_bb (basic_block bb)
  {
    bb_vec_info bb_vinfo;
-   gimple_stmt_iterator gsi;
-   bool any_vectorized = false;
    auto_vector_sizes vector_sizes;
  
    /* Autodetect first vector size we try.  */
--- 3011,3028 ----
    return bb_vinfo;
  }
  
! /* Subroutine of vect_slp_bb.  Try to vectorize the statements between
!    REGION_BEGIN (inclusive) and REGION_END (exclusive), returning true
!    on success.  The region has N_STMTS statements and has the datarefs
!    given by DATAREFS.  */
! 
! static bool
! vect_slp_bb_region (gimple_stmt_iterator region_begin,
! 		    gimple_stmt_iterator region_end,
! 		    vec<data_reference_p> datarefs,
! 		    unsigned int n_stmts)
  {
    bb_vec_info bb_vinfo;
    auto_vector_sizes vector_sizes;
  
    /* Autodetect first vector size we try.  */
*************** vect_slp_bb (basic_block bb)
*** 3024,3069 ****
    targetm.vectorize.autovectorize_vector_sizes (&vector_sizes, false);
    unsigned int next_size = 0;
  
!   gsi = gsi_start_bb (bb);
  
    poly_uint64 autodetected_vector_size = 0;
    while (1)
      {
-       if (gsi_end_p (gsi))
- 	break;
- 
-       gimple_stmt_iterator region_begin = gsi;
-       vec<data_reference_p> datarefs = vNULL;
-       int insns = 0;
- 
-       for (; !gsi_end_p (gsi); gsi_next (&gsi))
- 	{
- 	  gimple *stmt = gsi_stmt (gsi);
- 	  if (is_gimple_debug (stmt))
- 	    continue;
- 	  insns++;
- 
- 	  if (gimple_location (stmt) != UNKNOWN_LOCATION)
- 	    vect_location = stmt;
- 
- 	  if (!vect_find_stmt_data_reference (NULL, stmt, &datarefs))
- 	    break;
- 	}
- 
-       /* Skip leading unhandled stmts.  */
-       if (gsi_stmt (region_begin) == gsi_stmt (gsi))
- 	{
- 	  gsi_next (&gsi);
- 	  continue;
- 	}
- 
-       gimple_stmt_iterator region_end = gsi;
- 
        bool vectorized = false;
        bool fatal = false;
-       vec_info_shared shared;
        bb_vinfo = vect_slp_analyze_bb_1 (region_begin, region_end,
! 					datarefs, insns, fatal, &shared);
        if (bb_vinfo
  	  && dbg_cnt (vect_slp))
  	{
--- 3030,3044 ----
    targetm.vectorize.autovectorize_vector_sizes (&vector_sizes, false);
    unsigned int next_size = 0;
  
!   vec_info_shared shared;
  
    poly_uint64 autodetected_vector_size = 0;
    while (1)
      {
        bool vectorized = false;
        bool fatal = false;
        bb_vinfo = vect_slp_analyze_bb_1 (region_begin, region_end,
! 					datarefs, n_stmts, fatal, &shared);
        if (bb_vinfo
  	  && dbg_cnt (vect_slp))
  	{
*************** vect_slp_bb (basic_block bb)
*** 3090,3097 ****
  	}
        delete bb_vinfo;
  
-       any_vectorized |= vectorized;
- 
        if (next_size == 0)
  	autodetected_vector_size = current_vector_size;
  
--- 3065,3070 ----
*************** vect_slp_bb (basic_block bb)
*** 3105,3137 ****
  	  /* If vect_slp_analyze_bb_1 signaled that analysis for all
  	     vector sizes will fail do not bother iterating.  */
  	  || fatal)
  	{
! 	  if (gsi_end_p (region_end))
! 	    break;
  
! 	  /* Skip the unhandled stmt.  */
! 	  gsi_next (&gsi);
  
! 	  /* And reset vector sizes.  */
! 	  current_vector_size = 0;
! 	  next_size = 0;
! 	}
!       else
  	{
! 	  /* Try the next biggest vector size.  */
! 	  current_vector_size = vector_sizes[next_size++];
! 	  if (dump_enabled_p ())
! 	    {
! 	      dump_printf_loc (MSG_NOTE, vect_location,
! 			       "***** Re-trying analysis with "
! 			       "vector size ");
! 	      dump_dec (MSG_NOTE, current_vector_size);
! 	      dump_printf (MSG_NOTE, "\n");
! 	    }
  
! 	  /* Start over.  */
! 	  gsi = region_begin;
  	}
      }
  
    return any_vectorized;
--- 3078,3145 ----
  	  /* If vect_slp_analyze_bb_1 signaled that analysis for all
  	     vector sizes will fail do not bother iterating.  */
  	  || fatal)
+ 	return vectorized;
+ 
+       /* Try the next biggest vector size.  */
+       current_vector_size = vector_sizes[next_size++];
+       if (dump_enabled_p ())
  	{
! 	  dump_printf_loc (MSG_NOTE, vect_location,
! 			   "***** Re-trying analysis with "
! 			   "vector size ");
! 	  dump_dec (MSG_NOTE, current_vector_size);
! 	  dump_printf (MSG_NOTE, "\n");
! 	}
!     }
! }
  
! /* Main entry for the BB vectorizer.  Analyze and transform BB, returns
!    true if anything in the basic-block was vectorized.  */
  
! bool
! vect_slp_bb (basic_block bb)
! {
!   gimple_stmt_iterator gsi;
!   bool any_vectorized = false;
! 
!   gsi = gsi_start_bb (bb);
!   while (!gsi_end_p (gsi))
!     {
!       gimple_stmt_iterator region_begin = gsi;
!       vec<data_reference_p> datarefs = vNULL;
!       int insns = 0;
! 
!       for (; !gsi_end_p (gsi); gsi_next (&gsi))
  	{
! 	  gimple *stmt = gsi_stmt (gsi);
! 	  if (is_gimple_debug (stmt))
! 	    continue;
! 	  insns++;
! 
! 	  if (gimple_location (stmt) != UNKNOWN_LOCATION)
! 	    vect_location = stmt;
  
! 	  if (!vect_find_stmt_data_reference (NULL, stmt, &datarefs))
! 	    break;
  	}
+ 
+       /* Skip leading unhandled stmts.  */
+       if (gsi_stmt (region_begin) == gsi_stmt (gsi))
+ 	{
+ 	  gsi_next (&gsi);
+ 	  continue;
+ 	}
+ 
+       gimple_stmt_iterator region_end = gsi;
+ 
+       if (vect_slp_bb_region (region_begin, region_end, datarefs, insns))
+ 	any_vectorized = true;
+ 
+       if (gsi_end_p (region_end))
+ 	break;
+ 
+       /* Skip the unhandled stmt.  */
+       gsi_next (&gsi);
      }
  
    return any_vectorized;