diff gcc/tree-ssa-loop-ch.c @ 0:a06113de4d67 gcc-4.4.0

first commit
author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
parents
children 77e2b8dfacca
line wrap: on
line diff
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/tree-ssa-loop-ch.c	Fri Jul 17 14:47:48 2009 +0900
@@ -0,0 +1,281 @@
+/* Loop header copying on trees.
+   Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, Inc.
+   
+This file is part of GCC.
+   
+GCC is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+   
+GCC is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+   
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "hard-reg-set.h"
+#include "basic-block.h"
+#include "output.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-dump.h"
+#include "tree-pass.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "tree-inline.h"
+#include "flags.h"
+#include "tree-inline.h"
+
+/* Duplicates headers of loops if they are small enough, so that the statements
+   in the loop body are always executed when the loop is entered.  This
+   increases effectiveness of code motion optimizations, and reduces the need
+   for loop preconditioning.  */
+
+/* Check whether we should duplicate HEADER of LOOP.  At most *LIMIT
+   instructions should be duplicated, limit is decreased by the actual
+   amount.  */
+
+static bool
+should_duplicate_loop_header_p (basic_block header, struct loop *loop,
+				int *limit)
+{
+  gimple_stmt_iterator bsi;
+  gimple last;
+
+  /* Do not copy one block more than once (we do not really want to do
+     loop peeling here).  */
+  if (header->aux)
+    return false;
+
+  /* Loop header copying usually increases size of the code.  This used not to
+     be true, since quite often it is possible to verify that the condition is
+     satisfied in the first iteration and therefore to eliminate it.  Jump
+     threading handles these cases now.  */
+  if (optimize_loop_for_size_p (loop))
+    return false;
+
+  gcc_assert (EDGE_COUNT (header->succs) > 0);
+  if (single_succ_p (header))
+    return false;
+  if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)
+      && flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 1)->dest))
+    return false;
+
+  /* If this is not the original loop header, we want it to have just
+     one predecessor in order to match the && pattern.  */
+  if (header != loop->header && !single_pred_p (header))
+    return false;
+
+  last = last_stmt (header);
+  if (gimple_code (last) != GIMPLE_COND)
+    return false;
+
+  /* Approximately copy the conditions that used to be used in jump.c --
+     at most 20 insns and no calls.  */
+  for (bsi = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi))
+    {
+      last = gsi_stmt (bsi);
+
+      if (gimple_code (last) == GIMPLE_LABEL)
+	continue;
+
+      if (is_gimple_call (last))
+	return false;
+
+      *limit -= estimate_num_insns (last, &eni_size_weights);
+      if (*limit < 0)
+	return false;
+    }
+
+  return true;
+}
+
+/* Checks whether LOOP is a do-while style loop.  */
+
+static bool
+do_while_loop_p (struct loop *loop)
+{
+  gimple stmt = last_stmt (loop->latch);
+
+  /* If the latch of the loop is not empty, it is not a do-while loop.  */
+  if (stmt
+      && gimple_code (stmt) != GIMPLE_LABEL)
+    return false;
+
+  /* If the header contains just a condition, it is not a do-while loop.  */
+  stmt = last_and_only_stmt (loop->header);
+  if (stmt
+      && gimple_code (stmt) == GIMPLE_COND)
+    return false;
+
+  return true;
+}
+
+/* For all loops, copy the condition at the end of the loop body in front
+   of the loop.  This is beneficial since it increases efficiency of
+   code motion optimizations.  It also saves one jump on entry to the loop.  */
+
+static unsigned int
+copy_loop_headers (void)
+{
+  loop_iterator li;
+  struct loop *loop;
+  basic_block header;
+  edge exit, entry;
+  basic_block *bbs, *copied_bbs;
+  unsigned n_bbs;
+  unsigned bbs_size;
+
+  loop_optimizer_init (LOOPS_HAVE_PREHEADERS
+		       | LOOPS_HAVE_SIMPLE_LATCHES);
+  if (number_of_loops () <= 1)
+    {
+      loop_optimizer_finalize ();
+      return 0;
+    }
+
+#ifdef ENABLE_CHECKING
+  verify_loop_structure ();
+#endif
+
+  bbs = XNEWVEC (basic_block, n_basic_blocks);
+  copied_bbs = XNEWVEC (basic_block, n_basic_blocks);
+  bbs_size = n_basic_blocks;
+
+  FOR_EACH_LOOP (li, loop, 0)
+    {
+      /* Copy at most 20 insns.  */
+      int limit = 20;
+
+      header = loop->header;
+
+      /* If the loop is already a do-while style one (either because it was
+	 written as such, or because jump threading transformed it into one),
+	 we might be in fact peeling the first iteration of the loop.  This
+	 in general is not a good idea.  */
+      if (do_while_loop_p (loop))
+	continue;
+
+      /* Iterate the header copying up to limit; this takes care of the cases
+	 like while (a && b) {...}, where we want to have both of the conditions
+	 copied.  TODO -- handle while (a || b) - like cases, by not requiring
+	 the header to have just a single successor and copying up to
+	 postdominator.  */
+
+      exit = NULL;
+      n_bbs = 0;
+      while (should_duplicate_loop_header_p (header, loop, &limit))
+	{
+	  /* Find a successor of header that is inside a loop; i.e. the new
+	     header after the condition is copied.  */
+	  if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest))
+	    exit = EDGE_SUCC (header, 0);
+	  else
+	    exit = EDGE_SUCC (header, 1);
+	  bbs[n_bbs++] = header;
+	  gcc_assert (bbs_size > n_bbs);
+	  header = exit->dest;
+	}
+
+      if (!exit)
+	continue;
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file,
+		 "Duplicating header of the loop %d up to edge %d->%d.\n",
+		 loop->num, exit->src->index, exit->dest->index);
+
+      /* Ensure that the header will have just the latch as a predecessor
+	 inside the loop.  */
+      if (!single_pred_p (exit->dest))
+	exit = single_pred_edge (split_edge (exit));
+
+      entry = loop_preheader_edge (loop);
+
+      if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs))
+	{
+	  fprintf (dump_file, "Duplication failed.\n");
+	  continue;
+	}
+
+      /* If the loop has the form "for (i = j; i < j + 10; i++)" then
+	 this copying can introduce a case where we rely on undefined
+	 signed overflow to eliminate the preheader condition, because
+	 we assume that "j < j + 10" is true.  We don't want to warn
+	 about that case for -Wstrict-overflow, because in general we
+	 don't warn about overflow involving loops.  Prevent the
+	 warning by setting the no_warning flag in the condition.  */
+      if (warn_strict_overflow > 0)
+	{
+	  unsigned int i;
+
+	  for (i = 0; i < n_bbs; ++i)
+	    {
+	      gimple_stmt_iterator bsi;
+
+	      for (bsi = gsi_start_bb (copied_bbs[i]);
+		   !gsi_end_p (bsi);
+		   gsi_next (&bsi))
+		{
+		  gimple stmt = gsi_stmt (bsi);
+		  if (gimple_code (stmt) == GIMPLE_COND)
+		    gimple_set_no_warning (stmt, true);
+		  else if (is_gimple_assign (stmt))
+		    {
+		      enum tree_code rhs_code = gimple_assign_rhs_code (stmt);
+		      if (TREE_CODE_CLASS (rhs_code) == tcc_comparison)
+			gimple_set_no_warning (stmt, true);
+		    }
+		}
+	    }
+	}
+
+      /* Ensure that the latch and the preheader is simple (we know that they
+	 are not now, since there was the loop exit condition.  */
+      split_edge (loop_preheader_edge (loop));
+      split_edge (loop_latch_edge (loop));
+    }
+
+  free (bbs);
+  free (copied_bbs);
+
+  loop_optimizer_finalize ();
+  return 0;
+}
+
+static bool
+gate_ch (void)
+{
+  return flag_tree_ch != 0;
+}
+
+struct gimple_opt_pass pass_ch = 
+{
+ {
+  GIMPLE_PASS,
+  "ch",					/* name */
+  gate_ch,				/* gate */
+  copy_loop_headers,			/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  TV_TREE_CH,				/* tv_id */
+  PROP_cfg | PROP_ssa,			/* properties_required */
+  0,					/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_cleanup_cfg | TODO_dump_func 
+  | TODO_verify_ssa			/* todo_flags_finish */
+ }
+};