GCC 4.2.0 release.

1 files changed, 483 insertions, 0 deletions

diff --git a/contrib/gcc/tree-ssa-dse.c b/contrib/gcc/tree-ssa-dse.c
new file mode 100644
index 000000000000..fe6701594b69
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+++ b/contrib/gcc/tree-ssa-dse.c
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+/* Dead store elimination
+   Copyright (C) 2004, 2005 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 2, 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 COPYING.  If not, write to
+the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+Boston, MA 02110-1301, USA.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "ggc.h"
+#include "tree.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "basic-block.h"
+#include "timevar.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-pass.h"
+#include "tree-dump.h"
+#include "domwalk.h"
+#include "flags.h"
+
+/* This file implements dead store elimination.
+
+   A dead store is a store into a memory location which will later be
+   overwritten by another store without any intervening loads.  In this
+   case the earlier store can be deleted.
+
+   In our SSA + virtual operand world we use immediate uses of virtual
+   operands to detect dead stores.  If a store's virtual definition
+   is used precisely once by a later store to the same location which
+   post dominates the first store, then the first store is dead. 
+
+   The single use of the store's virtual definition ensures that
+   there are no intervening aliased loads and the requirement that
+   the second load post dominate the first ensures that if the earlier
+   store executes, then the later stores will execute before the function
+   exits.
+
+   It may help to think of this as first moving the earlier store to
+   the point immediately before the later store.  Again, the single
+   use of the virtual definition and the post-dominance relationship
+   ensure that such movement would be safe.  Clearly if there are 
+   back to back stores, then the second is redundant.
+
+   Reviewing section 10.7.2 in Morgan's "Building an Optimizing Compiler"
+   may also help in understanding this code since it discusses the
+   relationship between dead store and redundant load elimination.  In
+   fact, they are the same transformation applied to different views of
+   the CFG.  */
+   
+
+struct dse_global_data
+{
+  /* This is the global bitmap for store statements.
+
+     Each statement has a unique ID.  When we encounter a store statement
+     that we want to record, set the bit corresponding to the statement's
+     unique ID in this bitmap.  */
+  bitmap stores;
+};
+
+/* We allocate a bitmap-per-block for stores which are encountered
+   during the scan of that block.  This allows us to restore the 
+   global bitmap of stores when we finish processing a block.  */
+struct dse_block_local_data
+{
+  bitmap stores;
+};
+
+/* Basic blocks of the potentially dead store and the following
+   store, for memory_address_same.  */
+struct address_walk_data
+{
+  basic_block store1_bb, store2_bb;
+};
+
+static bool gate_dse (void);
+static unsigned int tree_ssa_dse (void);
+static void dse_initialize_block_local_data (struct dom_walk_data *,
+					     basic_block,
+					     bool);
+static void dse_optimize_stmt (struct dom_walk_data *,
+			       basic_block,
+			       block_stmt_iterator);
+static void dse_record_phis (struct dom_walk_data *, basic_block);
+static void dse_finalize_block (struct dom_walk_data *, basic_block);
+static void record_voperand_set (bitmap, bitmap *, unsigned int);
+
+static unsigned max_stmt_uid;	/* Maximal uid of a statement.  Uids to phi
+				   nodes are assigned using the versions of
+				   ssa names they define.  */
+
+/* Returns uid of statement STMT.  */
+
+static unsigned
+get_stmt_uid (tree stmt)
+{
+  if (TREE_CODE (stmt) == PHI_NODE)
+    return SSA_NAME_VERSION (PHI_RESULT (stmt)) + max_stmt_uid;
+
+  return stmt_ann (stmt)->uid;
+}
+
+/* Set bit UID in bitmaps GLOBAL and *LOCAL, creating *LOCAL as needed.  */
+
+static void
+record_voperand_set (bitmap global, bitmap *local, unsigned int uid)
+{
+  /* Lazily allocate the bitmap.  Note that we do not get a notification
+     when the block local data structures die, so we allocate the local
+     bitmap backed by the GC system.  */
+  if (*local == NULL)
+    *local = BITMAP_GGC_ALLOC ();
+
+  /* Set the bit in the local and global bitmaps.  */
+  bitmap_set_bit (*local, uid);
+  bitmap_set_bit (global, uid);
+}
+
+/* Initialize block local data structures.  */
+
+static void
+dse_initialize_block_local_data (struct dom_walk_data *walk_data,
+				 basic_block bb ATTRIBUTE_UNUSED,
+				 bool recycled)
+{
+  struct dse_block_local_data *bd
+    = VEC_last (void_p, walk_data->block_data_stack);
+
+  /* If we are given a recycled block local data structure, ensure any
+     bitmap associated with the block is cleared.  */
+  if (recycled)
+    {
+      if (bd->stores)
+	bitmap_clear (bd->stores);
+    }
+}
+
+/* Helper function for memory_address_same via walk_tree.  Returns
+   non-NULL if it finds an SSA_NAME which is part of the address,
+   such that the definition of the SSA_NAME post-dominates the store
+   we want to delete but not the store that we believe makes it
+   redundant.  This indicates that the address may change between
+   the two stores.  */
+
+static tree
+memory_ssa_name_same (tree *expr_p, int *walk_subtrees ATTRIBUTE_UNUSED,
+		      void *data)
+{
+  struct address_walk_data *walk_data = data;
+  tree expr = *expr_p;
+  tree def_stmt;
+  basic_block def_bb;
+
+  if (TREE_CODE (expr) != SSA_NAME)
+    return NULL_TREE;
+
+  /* If we've found a default definition, then there's no problem.  Both
+     stores will post-dominate it.  And def_bb will be NULL.  */
+  if (expr == default_def (SSA_NAME_VAR (expr)))
+    return NULL_TREE;
+
+  def_stmt = SSA_NAME_DEF_STMT (expr);
+  def_bb = bb_for_stmt (def_stmt);
+
+  /* DEF_STMT must dominate both stores.  So if it is in the same
+     basic block as one, it does not post-dominate that store.  */
+  if (walk_data->store1_bb != def_bb
+      && dominated_by_p (CDI_POST_DOMINATORS, walk_data->store1_bb, def_bb))
+    {
+      if (walk_data->store2_bb == def_bb
+	  || !dominated_by_p (CDI_POST_DOMINATORS, walk_data->store2_bb,
+			      def_bb))
+	/* Return non-NULL to stop the walk.  */
+	return def_stmt;
+    }
+
+  return NULL_TREE;
+}
+
+/* Return TRUE if the destination memory address in STORE1 and STORE2
+   might be modified after STORE1, before control reaches STORE2.  */
+
+static bool
+memory_address_same (tree store1, tree store2)
+{
+  struct address_walk_data walk_data;
+
+  walk_data.store1_bb = bb_for_stmt (store1);
+  walk_data.store2_bb = bb_for_stmt (store2);
+
+  return (walk_tree (&TREE_OPERAND (store1, 0), memory_ssa_name_same,
+		     &walk_data, NULL)
+	  == NULL);
+}
+
+/* Attempt to eliminate dead stores in the statement referenced by BSI.
+
+   A dead store is a store into a memory location which will later be
+   overwritten by another store without any intervening loads.  In this
+   case the earlier store can be deleted.
+
+   In our SSA + virtual operand world we use immediate uses of virtual
+   operands to detect dead stores.  If a store's virtual definition
+   is used precisely once by a later store to the same location which
+   post dominates the first store, then the first store is dead.  */
+
+static void
+dse_optimize_stmt (struct dom_walk_data *walk_data,
+		   basic_block bb ATTRIBUTE_UNUSED,
+		   block_stmt_iterator bsi)
+{
+  struct dse_block_local_data *bd
+    = VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd = walk_data->global_data;
+  tree stmt = bsi_stmt (bsi);
+  stmt_ann_t ann = stmt_ann (stmt);
+
+  /* If this statement has no virtual defs, then there is nothing
+     to do.  */
+  if (ZERO_SSA_OPERANDS (stmt, (SSA_OP_VMAYDEF|SSA_OP_VMUSTDEF)))
+    return;
+
+  /* We know we have virtual definitions.  If this is a MODIFY_EXPR that's
+     not also a function call, then record it into our table.  */
+  if (get_call_expr_in (stmt))
+    return;
+
+  if (ann->has_volatile_ops)
+    return;
+
+  if (TREE_CODE (stmt) == MODIFY_EXPR)
+    {
+      use_operand_p first_use_p = NULL_USE_OPERAND_P;
+      use_operand_p use_p = NULL;
+      tree use_stmt, temp;
+      tree defvar = NULL_TREE, usevar = NULL_TREE;
+      bool fail = false;
+      use_operand_p var2;
+      def_operand_p var1;
+      ssa_op_iter op_iter;
+
+      /* We want to verify that each virtual definition in STMT has
+	 precisely one use and that all the virtual definitions are
+	 used by the same single statement.  When complete, we
+	 want USE_STMT to refer to the one statement which uses
+	 all of the virtual definitions from STMT.  */
+      use_stmt = NULL;
+      FOR_EACH_SSA_MUST_AND_MAY_DEF_OPERAND (var1, var2, stmt, op_iter)
+	{
+	  defvar = DEF_FROM_PTR (var1);
+	  usevar = USE_FROM_PTR (var2);
+
+	  /* If this virtual def does not have precisely one use, then
+	     we will not be able to eliminate STMT.  */
+	  if (! has_single_use (defvar))
+	    {
+	      fail = true;
+	      break;
+	    }
+
+	  /* Get the one and only immediate use of DEFVAR.  */
+	  single_imm_use (defvar, &use_p, &temp);
+	  gcc_assert (use_p != NULL_USE_OPERAND_P);
+	  first_use_p = use_p;
+
+	  /* If the immediate use of DEF_VAR is not the same as the
+	     previously find immediate uses, then we will not be able
+	     to eliminate STMT.  */
+	  if (use_stmt == NULL)
+	    use_stmt = temp;
+	  else if (temp != use_stmt)
+	    {
+	      fail = true;
+	      break;
+	    }
+	}
+
+      if (fail)
+	{
+	  record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
+	  return;
+	}
+
+      /* Skip through any PHI nodes we have already seen if the PHI
+	 represents the only use of this store.
+
+	 Note this does not handle the case where the store has
+	 multiple V_{MAY,MUST}_DEFs which all reach a set of PHI nodes in the
+	 same block.  */
+      while (use_p != NULL_USE_OPERAND_P
+	     && TREE_CODE (use_stmt) == PHI_NODE
+	     && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt)))
+	{
+	  /* A PHI node can both define and use the same SSA_NAME if
+	     the PHI is at the top of a loop and the PHI_RESULT is
+	     a loop invariant and copies have not been fully propagated.
+
+	     The safe thing to do is exit assuming no optimization is
+	     possible.  */
+	  if (SSA_NAME_DEF_STMT (PHI_RESULT (use_stmt)) == use_stmt)
+	    return;
+
+	  /* Skip past this PHI and loop again in case we had a PHI
+	     chain.  */
+	  single_imm_use (PHI_RESULT (use_stmt), &use_p, &use_stmt);
+	}
+
+      /* If we have precisely one immediate use at this point, then we may
+	 have found redundant store.  Make sure that the stores are to
+	 the same memory location.  This includes checking that any
+	 SSA-form variables in the address will have the same values.  */
+      if (use_p != NULL_USE_OPERAND_P
+	  && bitmap_bit_p (dse_gd->stores, get_stmt_uid (use_stmt))
+	  && operand_equal_p (TREE_OPERAND (stmt, 0),
+			      TREE_OPERAND (use_stmt, 0), 0)
+	  && memory_address_same (stmt, use_stmt))
+	{
+	  /* Make sure we propagate the ABNORMAL bit setting.  */
+	  if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (first_use_p)))
+	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (usevar) = 1;
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+            {
+              fprintf (dump_file, "  Deleted dead store '");
+              print_generic_expr (dump_file, bsi_stmt (bsi), dump_flags);
+              fprintf (dump_file, "'\n");
+            }
+	  /* Then we need to fix the operand of the consuming stmt.  */
+	  FOR_EACH_SSA_MUST_AND_MAY_DEF_OPERAND (var1, var2, stmt, op_iter)
+	    {
+	      single_imm_use (DEF_FROM_PTR (var1), &use_p, &temp);
+	      SET_USE (use_p, USE_FROM_PTR (var2));
+	    }
+	  /* Remove the dead store.  */
+	  bsi_remove (&bsi, true);
+
+	  /* And release any SSA_NAMEs set in this statement back to the
+	     SSA_NAME manager.  */
+	  release_defs (stmt);
+	}
+
+      record_voperand_set (dse_gd->stores, &bd->stores, ann->uid);
+    }
+}
+
+/* Record that we have seen the PHIs at the start of BB which correspond
+   to virtual operands.  */
+static void
+dse_record_phis (struct dom_walk_data *walk_data, basic_block bb)
+{
+  struct dse_block_local_data *bd
+    = VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd = walk_data->global_data;
+  tree phi;
+
+  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+    if (!is_gimple_reg (PHI_RESULT (phi)))
+      record_voperand_set (dse_gd->stores,
+			   &bd->stores,
+			   get_stmt_uid (phi));
+}
+
+static void
+dse_finalize_block (struct dom_walk_data *walk_data,
+		    basic_block bb ATTRIBUTE_UNUSED)
+{
+  struct dse_block_local_data *bd
+    = VEC_last (void_p, walk_data->block_data_stack);
+  struct dse_global_data *dse_gd = walk_data->global_data;
+  bitmap stores = dse_gd->stores;
+  unsigned int i;
+  bitmap_iterator bi;
+
+  /* Unwind the stores noted in this basic block.  */
+  if (bd->stores)
+    EXECUTE_IF_SET_IN_BITMAP (bd->stores, 0, i, bi)
+      {
+	bitmap_clear_bit (stores, i);
+      }
+}
+
+static unsigned int
+tree_ssa_dse (void)
+{
+  struct dom_walk_data walk_data;
+  struct dse_global_data dse_gd;
+  basic_block bb;
+
+  /* Create a UID for each statement in the function.  Ordering of the
+     UIDs is not important for this pass.  */
+  max_stmt_uid = 0;
+  FOR_EACH_BB (bb)
+    {
+      block_stmt_iterator bsi;
+
+      for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
+	stmt_ann (bsi_stmt (bsi))->uid = max_stmt_uid++;
+    }
+
+  /* We might consider making this a property of each pass so that it
+     can be [re]computed on an as-needed basis.  Particularly since
+     this pass could be seen as an extension of DCE which needs post
+     dominators.  */
+  calculate_dominance_info (CDI_POST_DOMINATORS);
+
+  /* Dead store elimination is fundamentally a walk of the post-dominator
+     tree and a backwards walk of statements within each block.  */
+  walk_data.walk_stmts_backward = true;
+  walk_data.dom_direction = CDI_POST_DOMINATORS;
+  walk_data.initialize_block_local_data = dse_initialize_block_local_data;
+  walk_data.before_dom_children_before_stmts = NULL;
+  walk_data.before_dom_children_walk_stmts = dse_optimize_stmt;
+  walk_data.before_dom_children_after_stmts = dse_record_phis;
+  walk_data.after_dom_children_before_stmts = NULL;
+  walk_data.after_dom_children_walk_stmts = NULL;
+  walk_data.after_dom_children_after_stmts = dse_finalize_block;
+  walk_data.interesting_blocks = NULL;
+
+  walk_data.block_local_data_size = sizeof (struct dse_block_local_data);
+
+  /* This is the main hash table for the dead store elimination pass.  */
+  dse_gd.stores = BITMAP_ALLOC (NULL);
+  walk_data.global_data = &dse_gd;
+
+  /* Initialize the dominator walker.  */
+  init_walk_dominator_tree (&walk_data);
+
+  /* Recursively walk the dominator tree.  */
+  walk_dominator_tree (&walk_data, EXIT_BLOCK_PTR);
+
+  /* Finalize the dominator walker.  */
+  fini_walk_dominator_tree (&walk_data);
+
+  /* Release the main bitmap.  */
+  BITMAP_FREE (dse_gd.stores);
+
+  /* For now, just wipe the post-dominator information.  */
+  free_dominance_info (CDI_POST_DOMINATORS);
+  return 0;
+}
+
+static bool
+gate_dse (void)
+{
+  return flag_tree_dse != 0;
+}
+
+struct tree_opt_pass pass_dse = {
+  "dse",			/* name */
+  gate_dse,			/* gate */
+  tree_ssa_dse,			/* execute */
+  NULL,				/* sub */
+  NULL,				/* next */
+  0,				/* static_pass_number */
+  TV_TREE_DSE,			/* tv_id */
+  PROP_cfg
+    | PROP_ssa
+    | PROP_alias,		/* properties_required */
+  0,				/* properties_provided */
+  0,				/* properties_destroyed */
+  0,				/* todo_flags_start */
+  TODO_dump_func
+    | TODO_ggc_collect
+    | TODO_verify_ssa,		/* todo_flags_finish */
+  0				/* letter */
+};