re PR rtl-optimization/39077 (GCSE-optimization causes enormous binary size increase (~20 times !))

* PR rtl-optimization/39077
	* doc/invoke.texi (max-gcse-insertion-ratio): Document.
	* params.h (MAX_GCSE_INSERTION_RATIO): Define.
	* params.def (PARAM_MAX_GCSE_INSERTION_RATIO): Define.
	* lcm.c (pre_edge_lcm): Properly initialize output sbitmaps.
	* gcse.c (prune_insertions_deletions): New function.
	(compute_pre_data): Use it.

From-SVN: r168747

gcc/ChangeLog

@@ -1,3 +1,13 @@
+2011-01-13  Jeff Law  <law@redhat.com>
+
+	* PR rtl-optimization/39077
+	* doc/invoke.texi (max-gcse-insertion-ratio): Document.
+	* params.h (MAX_GCSE_INSERTION_RATIO): Define.
+	* params.def (PARAM_MAX_GCSE_INSERTION_RATIO): Define.
+	* lcm.c (pre_edge_lcm): Properly initialize output sbitmaps.
+	* gcse.c (prune_insertions_deletions): New function.
+	(compute_pre_data): Use it.
+
 2011-01-13  Dodji Seketeli  <dodji@redhat.com>
 
 	PR debug/PR46973

gcc/doc/invoke.texi

@@ -1,5 +1,5 @@
 @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
-@c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
+@c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
 @c Free Software Foundation, Inc.
 @c This is part of the GCC manual.
 @c For copying conditions, see the file gcc.texi.
@@ -8227,6 +8227,11 @@ order to perform the global common subexpression elimination
 optimization.  If more memory than specified is required, the
 optimization will not be done.
 
+@item max-gcse-insertion-ratio
+If the ratio of expression insertions to deletions is larger than this value
+for any expression, then RTL PRE will insert or remove the expression and thus
+leave partially redundant computations in the instruction stream.  The default value is 20.
+
 @item max-pending-list-length
 The maximum number of pending dependencies scheduling will allow
 before flushing the current state and starting over.  Large functions

gcc/gcse.c

@@ -1,7 +1,7 @@
 /* Global common subexpression elimination/Partial redundancy elimination
    and global constant/copy propagation for GNU compiler.
    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
-   2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
+   2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -3396,6 +3396,75 @@ prune_expressions (bool pre_p)
   sbitmap_free (prune_exprs);
 }
 
+/* It may be necessary to insert a large number of insns on edges to
+   make the existing occurrences of expressions fully redundant.  This
+   routine examines the set of insertions and deletions and if the ratio
+   of insertions to deletions is too high for a particular expression, then
+   the expression is removed from the insertion/deletion sets. 
+
+   N_ELEMS is the number of elements in the hash table.  */
+
+static void
+prune_insertions_deletions (int n_elems)
+{
+  sbitmap_iterator sbi;
+  sbitmap prune_exprs;
+
+  /* We always use I to iterate over blocks/edges and J to iterate over
+     expressions.  */
+  unsigned int i, j;
+
+  /* Counts for the number of times an expression needs to be inserted and
+     number of times an expression can be removed as a result.  */
+  int *insertions = GCNEWVEC (int, n_elems);
+  int *deletions = GCNEWVEC (int, n_elems);
+
+  /* Set of expressions which require too many insertions relative to
+     the number of deletions achieved.  We will prune these out of the
+     insertion/deletion sets.  */
+  prune_exprs = sbitmap_alloc (n_elems);
+  sbitmap_zero (prune_exprs);
+
+  /* Iterate over the edges counting the number of times each expression
+     needs to be inserted.  */
+  for (i = 0; i < (unsigned) n_edges; i++)
+    {
+      EXECUTE_IF_SET_IN_SBITMAP (pre_insert_map[i], 0, j, sbi)
+	insertions[j]++;
+    }
+
+  /* Similarly for deletions, but those occur in blocks rather than on
+     edges.  */
+  for (i = 0; i < (unsigned) last_basic_block; i++)
+    {
+      EXECUTE_IF_SET_IN_SBITMAP (pre_delete_map[i], 0, j, sbi)
+	deletions[j]++;
+    }
+
+  /* Now that we have accurate counts, iterate over the elements in the
+     hash table and see if any need too many insertions relative to the
+     number of evaluations that can be removed.  If so, mark them in
+     PRUNE_EXPRS.  */
+  for (j = 0; j < (unsigned) n_elems; j++)
+    if (deletions[j]
+	&& ((unsigned) insertions[j] / deletions[j]) > MAX_GCSE_INSERTION_RATIO)
+      SET_BIT (prune_exprs, j);
+
+  /* Now prune PRE_INSERT_MAP and PRE_DELETE_MAP based on PRUNE_EXPRS.  */
+  EXECUTE_IF_SET_IN_SBITMAP (prune_exprs, 0, j, sbi)
+    {
+      for (i = 0; i < (unsigned) n_edges; i++)
+	RESET_BIT (pre_insert_map[i], j);
+
+      for (i = 0; i < (unsigned) last_basic_block; i++)
+	RESET_BIT (pre_delete_map[i], j);
+    }
+
+  sbitmap_free (prune_exprs);
+  free (insertions);
+  free (deletions);
+}
+
 /* Top level routine to do the dataflow analysis needed by PRE.  */
 
 static void
@@ -3424,6 +3493,8 @@ compute_pre_data (void)
   antloc = NULL;
   sbitmap_vector_free (ae_kill);
   ae_kill = NULL;
+
+  prune_insertions_deletions (expr_hash_table.n_elems);
 }
 
 /* PRE utilities */
@@ -5368,3 +5439,4 @@ struct rtl_opt_pass pass_rtl_hoist =
 };
 
 #include "gt-gcse.h"
+

gcc/lcm.c

@@ -1,6 +1,6 @@
 /* Generic partial redundancy elimination with lazy code motion support.
    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2007, 2008,
-   2010 Free Software Foundation, Inc.
+   2010, 2011 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -451,6 +451,8 @@ pre_edge_lcm (int n_exprs, sbitmap *transp,
 
   *insert = sbitmap_vector_alloc (num_edges, n_exprs);
   *del = sbitmap_vector_alloc (last_basic_block, n_exprs);
+  sbitmap_vector_zero (*insert, num_edges);
+  sbitmap_vector_zero (*del, last_basic_block);
   compute_insert_delete (edge_list, antloc, later, laterin, *insert, *del);
 
   sbitmap_vector_free (laterin);

gcc/params.def

@@ -1,5 +1,6 @@
 /* params.def - Run-time parameters.
-   Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
+   Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
+   2011
    Free Software Foundation, Inc.
    Written by Mark Mitchell <mark@codesourcery.com>.
 
@@ -214,6 +215,13 @@ DEFPARAM(PARAM_MAX_GCSE_MEMORY,
 	 "The maximum amount of memory to be allocated by GCSE",
 	 50 * 1024 * 1024, 0, 0)
 
+/* The GCSE optimization of an expression will avoided if the ratio of
+   insertions to deletions is greater than this value.  */
+DEFPARAM(PARAM_MAX_GCSE_INSERTION_RATIO,
+	 "max-gcse-insertion-ratio",
+	 "The maximum ratio of insertions to deletions of expressions in GCSE",
+	 20, 0, 0)
+
 /* This is the threshold ratio when to perform partial redundancy
    elimination after reload. We perform partial redundancy elimination
    when the following holds:

gcc/params.h

@@ -1,5 +1,5 @@
 /* params.h - Run-time parameters.
-   Copyright (C) 2001, 2003, 2004, 2005, 2007, 2008, 2009, 2010
+   Copyright (C) 2001, 2003, 2004, 2005, 2007, 2008, 2009, 2010, 2011
    Free Software Foundation, Inc.
    Written by Mark Mitchell <mark@codesourcery.com>.
 
@@ -142,6 +142,8 @@ extern void init_param_values (int *params);
   PARAM_VALUE (PARAM_MAX_PENDING_LIST_LENGTH)
 #define MAX_GCSE_MEMORY \
   ((size_t) PARAM_VALUE (PARAM_MAX_GCSE_MEMORY))
+#define MAX_GCSE_INSERTION_RATIO \
+  ((size_t) PARAM_VALUE (PARAM_MAX_GCSE_INSERTION_RATIO))
 #define GCSE_AFTER_RELOAD_PARTIAL_FRACTION \
   PARAM_VALUE (PARAM_GCSE_AFTER_RELOAD_PARTIAL_FRACTION)
 #define GCSE_AFTER_RELOAD_CRITICAL_FRACTION \