re PR libgomp/49490 (suboptimal load balancing in loops)

PR libgomp/49490
	* omp-low.c (expand_omp_for_static_nochunk): Only
	use n ceil/ nthreads size for the first
	n % nthreads threads in the team instead of
	all threads except for the last few ones which
	get less work or none at all.

	* iter.c (gomp_iter_static_next): For chunk size 0
	only use n ceil/ nthreads size for the first
	n % nthreads threads in the team instead of
	all threads except for the last few ones which
	get less work or none at all.
	* iter_ull.c (gomp_iter_ull_static_next): Likewise.
	* env.c (parse_schedule): If OMP_SCHEDULE doesn't have
	chunk argument, set run_sched_modifier to 0 for static
	resp. 1 for other kinds.  If chunk argument is 0
	and not static, set value to 1.

From-SVN: r175315

gcc/ChangeLog

@@ -1,5 +1,12 @@
 2011-06-22  Jakub Jelinek  <jakub@redhat.com>
 
+	PR libgomp/49490
+	* omp-low.c (expand_omp_for_static_nochunk): Only
+	use n ceil/ nthreads size for the first
+	n % nthreads threads in the team instead of
+	all threads except for the last few ones which
+	get less work or none at all.
+
 	PR debug/49496
 	* tree-vect-patterns.c (vect_recog_widen_mult_pattern): Ignore debug
 	uses.

gcc/omp-low.c

@@ -3,7 +3,7 @@
    marshalling to implement data sharing and copying clauses.
    Contributed by Diego Novillo <dnovillo@redhat.com>
 
-   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
+   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
 
 This file is part of GCC.
@@ -4108,9 +4108,14 @@ expand_omp_for_generic (struct omp_region *region,
 	else
 	  n = (adj + N2 - N1) / STEP;
 	q = n / nthreads;
-	q += (q * nthreads != n);
+	tt = n % nthreads;
-	s0 = q * threadid;
+	if (threadid < tt) goto L3; else goto L4;
-	e0 = min(s0 + q, n);
+    L3:
+	tt = 0;
+	q = q + 1;
+    L4:
+	s0 = q * threadid + tt;
+	e0 = s0 + q;
 	V = s0 * STEP + N1;
 	if (s0 >= e0) goto L2; else goto L0;
     L0:
@@ -4126,12 +4131,14 @@ static void
 expand_omp_for_static_nochunk (struct omp_region *region,
 			       struct omp_for_data *fd)
 {
-  tree n, q, s0, e0, e, t, nthreads, threadid;
+  tree n, q, s0, e0, e, t, tt, nthreads, threadid;
   tree type, itype, vmain, vback;
-  basic_block entry_bb, exit_bb, seq_start_bb, body_bb, cont_bb;
+  basic_block entry_bb, second_bb, third_bb, exit_bb, seq_start_bb;
+  basic_block body_bb, cont_bb;
   basic_block fin_bb;
   gimple_stmt_iterator gsi;
   gimple stmt;
+  edge ep;
 
   itype = type = TREE_TYPE (fd->loop.v);
   if (POINTER_TYPE_P (type))
@@ -4185,19 +4192,39 @@ expand_omp_for_static_nochunk (struct omp_region *region,
   t = fold_convert (itype, t);
   n = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT);
 
+  q = create_tmp_var (itype, "q");
   t = fold_build2 (TRUNC_DIV_EXPR, itype, n, nthreads);
-  q = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT);
+  t = force_gimple_operand_gsi (&gsi, t, false, NULL_TREE, true, GSI_SAME_STMT);
+  gsi_insert_before (&gsi, gimple_build_assign (q, t), GSI_SAME_STMT);
 
-  t = fold_build2 (MULT_EXPR, itype, q, nthreads);
+  tt = create_tmp_var (itype, "tt");
-  t = fold_build2 (NE_EXPR, itype, t, n);
+  t = fold_build2 (TRUNC_MOD_EXPR, itype, n, nthreads);
-  t = fold_build2 (PLUS_EXPR, itype, q, t);
+  t = force_gimple_operand_gsi (&gsi, t, false, NULL_TREE, true, GSI_SAME_STMT);
-  q = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT);
+  gsi_insert_before (&gsi, gimple_build_assign (tt, t), GSI_SAME_STMT);
+
+  t = build2 (LT_EXPR, boolean_type_node, threadid, tt);
+  stmt = gimple_build_cond_empty (t);
+  gsi_insert_before (&gsi, stmt, GSI_SAME_STMT);
+
+  second_bb = split_block (entry_bb, stmt)->dest;
+  gsi = gsi_last_bb (second_bb);
+  gcc_assert (gimple_code (gsi_stmt (gsi)) == GIMPLE_OMP_FOR);
+
+  gsi_insert_before (&gsi, gimple_build_assign (tt, build_int_cst (itype, 0)),
+		     GSI_SAME_STMT);
+  stmt = gimple_build_assign_with_ops (PLUS_EXPR, q, q,
+				       build_int_cst (itype, 1));
+  gsi_insert_before (&gsi, stmt, GSI_SAME_STMT);
+
+  third_bb = split_block (second_bb, stmt)->dest;
+  gsi = gsi_last_bb (third_bb);
+  gcc_assert (gimple_code (gsi_stmt (gsi)) == GIMPLE_OMP_FOR);
 
   t = build2 (MULT_EXPR, itype, q, threadid);
+  t = build2 (PLUS_EXPR, itype, t, tt);
   s0 = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT);
 
   t = fold_build2 (PLUS_EXPR, itype, s0, q);
-  t = fold_build2 (MIN_EXPR, itype, t, n);
   e0 = force_gimple_operand_gsi (&gsi, t, true, NULL_TREE, true, GSI_SAME_STMT);
 
   t = build2 (GE_EXPR, boolean_type_node, s0, e0);
@@ -4263,13 +4290,20 @@ expand_omp_for_static_nochunk (struct omp_region *region,
   gsi_remove (&gsi, true);
 
   /* Connect all the blocks.  */
-  find_edge (entry_bb, seq_start_bb)->flags = EDGE_FALSE_VALUE;
+  ep = make_edge (entry_bb, third_bb, EDGE_FALSE_VALUE);
-  find_edge (entry_bb, fin_bb)->flags = EDGE_TRUE_VALUE;
+  ep->probability = REG_BR_PROB_BASE / 4 * 3;
+  ep = find_edge (entry_bb, second_bb);
+  ep->flags = EDGE_TRUE_VALUE;
+  ep->probability = REG_BR_PROB_BASE / 4;
+  find_edge (third_bb, seq_start_bb)->flags = EDGE_FALSE_VALUE;
+  find_edge (third_bb, fin_bb)->flags = EDGE_TRUE_VALUE;
 
   find_edge (cont_bb, body_bb)->flags = EDGE_TRUE_VALUE;
   find_edge (cont_bb, fin_bb)->flags = EDGE_FALSE_VALUE;
 
-  set_immediate_dominator (CDI_DOMINATORS, seq_start_bb, entry_bb);
+  set_immediate_dominator (CDI_DOMINATORS, second_bb, entry_bb);
+  set_immediate_dominator (CDI_DOMINATORS, third_bb, entry_bb);
+  set_immediate_dominator (CDI_DOMINATORS, seq_start_bb, third_bb);
   set_immediate_dominator (CDI_DOMINATORS, body_bb,
 			   recompute_dominator (CDI_DOMINATORS, body_bb));
   set_immediate_dominator (CDI_DOMINATORS, fin_bb,

libgomp/ChangeLog

@@ -1,3 +1,17 @@
+2011-06-22  Jakub Jelinek  <jakub@redhat.com>
+
+	PR libgomp/49490
+	* iter.c (gomp_iter_static_next): For chunk size 0
+	only use n ceil/ nthreads size for the first
+	n % nthreads threads in the team instead of
+	all threads except for the last few ones which
+	get less work or none at all.
+	* iter_ull.c (gomp_iter_ull_static_next): Likewise.
+	* env.c (parse_schedule): If OMP_SCHEDULE doesn't have
+	chunk argument, set run_sched_modifier to 0 for static
+	resp. 1 for other kinds.  If chunk argument is 0
+	and not static, set value to 1.
+
 2011-05-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/49043

libgomp/env.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
+/* Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
    Contributed by Richard Henderson <rth@redhat.com>.
 
@@ -108,7 +108,11 @@ parse_schedule (void)
   while (isspace ((unsigned char) *env))
     ++env;
   if (*env == '\0')
-    return;
+    {
+      gomp_global_icv.run_sched_modifier
+	= gomp_global_icv.run_sched_var != GFS_STATIC;
+      return;
+    }
   if (*env++ != ',')
     goto unknown;
   while (isspace ((unsigned char) *env))
@@ -129,6 +133,8 @@ parse_schedule (void)
   if ((int)value != value)
     goto invalid;
 
+  if (value == 0 && gomp_global_icv.run_sched_var != GFS_STATIC)
+    value = 1;
   gomp_global_icv.run_sched_modifier = value;
   return;
 

libgomp/iter.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2005, 2008, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 2005, 2008, 2009, 2011 Free Software Foundation, Inc.
    Contributed by Richard Henderson <rth@redhat.com>.
 
    This file is part of the GNU OpenMP Library (libgomp).
@@ -59,7 +59,7 @@ gomp_iter_static_next (long *pstart, long *pend)
      trip through the outer loop.  */
   if (ws->chunk_size == 0)
     {
-      unsigned long n, q, i;
+      unsigned long n, q, i, t;
       unsigned long s0, e0;
       long s, e;
 
@@ -74,11 +74,14 @@ gomp_iter_static_next (long *pstart, long *pend)
       /* Compute the "zero-based" start and end points.  That is, as
          if the loop began at zero and incremented by one.  */
       q = n / nthreads;
-      q += (q * nthreads != n);
+      t = n % nthreads;
-      s0 = q * i;
+      if (i < t)
+	{
+	  t = 0;
+	  q++;
+	}
+      s0 = q * i + t;
       e0 = s0 + q;
-      if (e0 > n)
-        e0 = n;
 
       /* Notice when no iterations allocated for this thread.  */
       if (s0 >= e0)

libgomp/iter_ull.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2005, 2008, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 2005, 2008, 2009, 2011 Free Software Foundation, Inc.
    Contributed by Richard Henderson <rth@redhat.com>.
 
    This file is part of the GNU OpenMP Library (libgomp).
@@ -60,7 +60,7 @@ gomp_iter_ull_static_next (gomp_ull *pstart, gomp_ull *pend)
      trip through the outer loop.  */
   if (ws->chunk_size_ull == 0)
     {
-      gomp_ull n, q, i, s0, e0, s, e;
+      gomp_ull n, q, i, t, s0, e0, s, e;
 
       if (thr->ts.static_trip > 0)
 	return 1;
@@ -75,11 +75,14 @@ gomp_iter_ull_static_next (gomp_ull *pstart, gomp_ull *pend)
       /* Compute the "zero-based" start and end points.  That is, as
 	 if the loop began at zero and incremented by one.  */
       q = n / nthreads;
-      q += (q * nthreads != n);
+      t = n % nthreads;
-      s0 = q * i;
+      if (i < t)
+	{
+	  t = 0;
+	  q++;
+	}
+      s0 = q * i + t;
       e0 = s0 + q;
-      if (e0 > n)
-	e0 = n;
 
       /* Notice when no iterations allocated for this thread.  */
       if (s0 >= e0)