CbC/CbC_gcc: gcc/tree-ssa-dce.c comparison

comparison gcc/tree-ssa-dce.c @ 55:77e2b8dfacca gcc-4.4.5

update it from 4.4.3 to 4.5.0

author	ryoma <e075725@ie.u-ryukyu.ac.jp>
date	Fri, 12 Feb 2010 23:39:51 +0900
parents	a06113de4d67
children	b7f97abdc517

comparison

equal deleted inserted replaced

-:c156f1bd5cd9
+:77e2b8dfacca
 /* Dead code elimination pass for the GNU compiler.
-Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
+Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
 Free Software Foundation, Inc.
 Contributed by Ben Elliston <bje@redhat.com>
 and Andrew MacLeod <amacleod@redhat.com>
 Adapted to use control dependence by Steven Bosscher, SUSE Labs.
 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/>.  */
 /* Dead code elimination.
 /* Vector indicating that last_stmt if a basic block has already been
 marked as necessary.  */
 static sbitmap last_stmt_necessary;
+/* Vector indicating that BB contains statements that are live.  */
+static sbitmap bb_contains_live_stmts;
 /* Before we can determine whether a control branch is dead, we need to
 compute which blocks are control dependent on which edges.
 We expect each block to be control dependent on very few edges so we
 use a bitmap for each block recording its edges.  An array holds the
 }
 gimple_set_plf (stmt, STMT_NECESSARY, true);
 if (add_to_worklist)
 VEC_safe_push (gimple, heap, worklist, stmt);
+if (bb_contains_live_stmts && !is_gimple_debug (stmt))
+SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
 }
 /* Mark the statement defining operand OP as necessary.  */
 gcc_assert (op);
 ver = SSA_NAME_VERSION (op);
 if (TEST_BIT (processed, ver))
-return;
+{
+stmt = SSA_NAME_DEF_STMT (op);
+gcc_assert (gimple_nop_p (stmt)
+		  || gimple_plf (stmt, STMT_NECESSARY));
+return;
+}
 SET_BIT (processed, ver);
 stmt = SSA_NAME_DEF_STMT (op);
 gcc_assert (stmt);
 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt))
 return;
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "marking necessary through ");
+print_generic_expr (dump_file, op, 0);
+fprintf (dump_file, " stmt ");
+print_gimple_stmt (dump_file, stmt, 0, 0);
+}
 gimple_set_plf (stmt, STMT_NECESSARY, true);
+if (bb_contains_live_stmts)
+SET_BIT (bb_contains_live_stmts, gimple_bb (stmt)->index);
 VEC_safe_push (gimple, heap, worklist, stmt);
 }
 /* Mark STMT as necessary if it obviously is.  Add it to the worklist if
 return;
 case GIMPLE_ASM:
 case GIMPLE_RESX:
 case GIMPLE_RETURN:
-case GIMPLE_CHANGE_DYNAMIC_TYPE:
 mark_stmt_necessary (stmt, true);
 return;
 case GIMPLE_CALL:
 /* Most, but not all function calls are required.  Function calls that
 /* Fall through */
 case GIMPLE_ASSIGN:
 if (!lhs)
 lhs = gimple_assign_lhs (stmt);
-/* These values are mildly magic bits of the EH runtime.  We can't
-	 see the entire lifetime of these values until landing pads are
-	 generated.  */
-if (TREE_CODE (lhs) == EXC_PTR_EXPR
-	  || TREE_CODE (lhs) == FILTER_EXPR)
-	{
-	  mark_stmt_necessary (stmt, true);
-	  return;
-	}
 break;
+case GIMPLE_DEBUG:
+/* Debug temps without a value are not useful.  ??? If we could
+	 easily locate the debug temp bind stmt for a use thereof,
+	 would could refrain from marking all debug temps here, and
+	 mark them only if they're used.  */
+if (gimple_debug_bind_has_value_p (stmt)
+	  || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL)
+	mark_stmt_necessary (stmt, false);
+return;
 case GIMPLE_GOTO:
 gcc_assert (!simple_goto_p (stmt));
 mark_stmt_necessary (stmt, true);
 return;
 basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number);
 if (TEST_BIT (last_stmt_necessary, cd_bb->index))
 	continue;
 SET_BIT (last_stmt_necessary, cd_bb->index);
+SET_BIT (bb_contains_live_stmts, cd_bb->index);
 stmt = last_stmt (cd_bb);
 if (stmt && is_ctrl_stmt (stmt))
 	mark_stmt_necessary (stmt, true);
 }
 	  gimple_set_plf (stmt, STMT_NECESSARY, false);
 	  mark_stmt_if_obviously_necessary (stmt, el != NULL);
 	}
 }
+/* Pure and const functions are finite and thus have no infinite loops in
+them.  */
+if ((TREE_READONLY (current_function_decl)
+|| DECL_PURE_P (current_function_decl))
+&& !DECL_LOOPING_CONST_OR_PURE_P (current_function_decl))
+return;
+/* Prevent the empty possibly infinite loops from being removed.  */
 if (el)
 {
-/* Prevent the loops from being removed.  We must keep the infinite loops,
+loop_iterator li;
-	 and we currently do not have a means to recognize the finite ones.  */
+struct loop *loop;
-FOR_EACH_BB (bb)
+scev_initialize ();
+if (mark_irreducible_loops ())
+	FOR_EACH_BB (bb)
+	  {
+	    edge_iterator ei;
+	    FOR_EACH_EDGE (e, ei, bb->succs)
+	      if ((e->flags & EDGE_DFS_BACK)
+		  && (e->flags & EDGE_IRREDUCIBLE_LOOP))
+		{
+	          if (dump_file)
+	            fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n",
+		    	     e->src->index, e->dest->index);
+		  mark_control_dependent_edges_necessary (e->dest, el);
+		}
+	  }
+FOR_EACH_LOOP (li, loop, 0)
+	if (!finite_loop_p (loop))
+	  {
+	    if (dump_file)
+	      fprintf (dump_file, "can not prove finiteness of loop %i\n", loop->num);
+	    mark_control_dependent_edges_necessary (loop->latch, el);
+	  }
+scev_finalize ();
+}
+}
+/* Return true if REF is based on an aliased base, otherwise false.  */
+static bool
+ref_may_be_aliased (tree ref)
+{
+while (handled_component_p (ref))
+ref = TREE_OPERAND (ref, 0);
+return !(DECL_P (ref)
+	   && !may_be_aliased (ref));
+}
+static bitmap visited = NULL;
+static unsigned int longest_chain = 0;
+static unsigned int total_chain = 0;
+static unsigned int nr_walks = 0;
+static bool chain_ovfl = false;
+/* Worker for the walker that marks reaching definitions of REF,
+which is based on a non-aliased decl, necessary.  It returns
+true whenever the defining statement of the current VDEF is
+a kill for REF, as no dominating may-defs are necessary for REF
+anymore.  DATA points to the basic-block that contains the
+stmt that refers to REF.  */
+static bool
+mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
+{
+gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
+/* All stmts we visit are necessary.  */
+mark_operand_necessary (vdef);
+/* If the stmt lhs kills ref, then we can stop walking.  */
+if (gimple_has_lhs (def_stmt)
+&& TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME)
+{
+tree base, lhs = gimple_get_lhs (def_stmt);
+HOST_WIDE_INT size, offset, max_size;
+ao_ref_base (ref);
+base = get_ref_base_and_extent (lhs, &offset, &size, &max_size);
+/* We can get MEM[symbol: sZ, index: D.8862_1] here,
+	 so base == refd->base does not always hold.  */
+if (base == ref->base)
 	{
-	  edge_iterator ei;
+	  /* For a must-alias check we need to be able to constrain
-	  FOR_EACH_EDGE (e, ei, bb->succs)
+	     the accesses properly.  */
-	    if (e->flags & EDGE_DFS_BACK)
+	  if (size != -1 && size == max_size
-	      mark_control_dependent_edges_necessary (e->dest, el);
+	      && ref->max_size != -1)
+	    {
+	      if (offset <= ref->offset
+		  && offset + size >= ref->offset + ref->max_size)
+		return true;
+	    }
+	  /* Or they need to be exactly the same.  */
+	  else if (ref->ref
+		   /* Make sure there is no induction variable involved
+		      in the references (gcc.c-torture/execute/pr42142.c).
+		      The simplest way is to check if the kill dominates
+		      the use.  */
+		   && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
+				      gimple_bb (def_stmt))
+		   && operand_equal_p (ref->ref, lhs, 0))
+	    return true;
 	}
 }
-}
+/* Otherwise keep walking.  */
+return false;
+}
+static void
+mark_aliased_reaching_defs_necessary (gimple stmt, tree ref)
+{
+unsigned int chain;
+ao_ref refd;
+gcc_assert (!chain_ovfl);
+ao_ref_init (&refd, ref);
+chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt),
+			      mark_aliased_reaching_defs_necessary_1,
+			      gimple_bb (stmt), NULL);
+if (chain > longest_chain)
+longest_chain = chain;
+total_chain += chain;
+nr_walks++;
+}
+/* Worker for the walker that marks reaching definitions of REF, which
+is not based on a non-aliased decl.  For simplicity we need to end
+up marking all may-defs necessary that are not based on a non-aliased
+decl.  The only job of this walker is to skip may-defs based on
+a non-aliased decl.  */
+static bool
+mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED,
+				    tree vdef, void *data ATTRIBUTE_UNUSED)
+{
+gimple def_stmt = SSA_NAME_DEF_STMT (vdef);
+/* We have to skip already visited (and thus necessary) statements
+to make the chaining work after we dropped back to simple mode.  */
+if (chain_ovfl
+&& TEST_BIT (processed, SSA_NAME_VERSION (vdef)))
+{
+gcc_assert (gimple_nop_p (def_stmt)
+		  || gimple_plf (def_stmt, STMT_NECESSARY));
+return false;
+}
+/* We want to skip stores to non-aliased variables.  */
+if (!chain_ovfl
+&& gimple_assign_single_p (def_stmt))
+{
+tree lhs = gimple_assign_lhs (def_stmt);
+if (!ref_may_be_aliased (lhs))
+	return false;
+}
+mark_operand_necessary (vdef);
+return false;
+}
+static void
+mark_all_reaching_defs_necessary (gimple stmt)
+{
+walk_aliased_vdefs (NULL, gimple_vuse (stmt),
+		      mark_all_reaching_defs_necessary_1, NULL, &visited);
+}
+/* Return true for PHI nodes with one or identical arguments
+can be removed.  */
+static bool
+degenerate_phi_p (gimple phi)
+{
+unsigned int i;
+tree op = gimple_phi_arg_def (phi, 0);
+for (i = 1; i < gimple_phi_num_args (phi); i++)
+if (gimple_phi_arg_def (phi, i) != op)
+return false;
+return true;
+}
 /* Propagate necessity using the operands of necessary statements.
 Process the uses on each statement in the worklist, and add all
 feeding statements which contribute to the calculation of this
 value to the worklist.
 In conservative mode, EL is NULL.  */
 static void
 propagate_necessity (struct edge_list *el)
 {
 gimple stmt;
 bool aggressive = (el ? true : false);
 if (dump_file && (dump_flags & TDF_DETAILS))
 fprintf (dump_file, "\nProcessing worklist:\n");
 while (VEC_length (gimple, worklist) > 0)
 	      SET_BIT (visited_control_parents, bb->index);
 	      mark_control_dependent_edges_necessary (bb, el);
 	    }
 	}
-if (gimple_code (stmt) == GIMPLE_PHI)
+if (gimple_code (stmt) == GIMPLE_PHI
+	  /* We do not process virtual PHI nodes nor do we track their
+	     necessity.  */
+	  && is_gimple_reg (gimple_phi_result (stmt)))
 	{
 	  /* PHI nodes are somewhat special in that each PHI alternative has
 	     data and control dependencies.  All the statements feeding the
 	     PHI node's arguments are always necessary.  In aggressive mode,
 	     we also consider the control dependent edges leading to the
 	      tree arg = PHI_ARG_DEF (stmt, k);
 	      if (TREE_CODE (arg) == SSA_NAME)
 		mark_operand_necessary (arg);
 	    }
-	  if (aggressive)
+	  if (aggressive && !degenerate_phi_p (stmt))
 	    {
 	      for (k = 0; k < gimple_phi_num_args (stmt); k++)
 		{
 		  basic_block arg_bb = gimple_phi_arg_edge (stmt, k)->src;
 		  if (arg_bb != ENTRY_BLOCK_PTR
 	    }
 	}
 else
 	{
 	  /* Propagate through the operands.  Examine all the USE, VUSE and
 	     VDEF operands in this statement.  Mark all the statements
-	     which feed this statement's uses as necessary.  The
+	     which feed this statement's uses as necessary.  */
-	     operands of VDEF expressions are also needed as they
-	     represent potential definitions that may reach this
-	     statement (VDEF operands allow us to follow def-def
-	     links).  */
 	  ssa_op_iter iter;
 	  tree use;
-	  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES)
+	  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
 	    mark_operand_necessary (use);
+	  use = gimple_vuse (stmt);
+	  if (!use)
+	    continue;
+	  /* If we dropped to simple mode make all immediately
+	     reachable definitions necessary.  */
+	  if (chain_ovfl)
+	    {
+	      mark_all_reaching_defs_necessary (stmt);
+	      continue;
+	    }
+	  /* For statements that may load from memory (have a VUSE) we
+	     have to mark all reaching (may-)definitions as necessary.
+	     We partition this task into two cases:
+	      1) explicit loads based on decls that are not aliased
+	      2) implicit loads (like calls) and explicit loads not
+	         based on decls that are not aliased (like indirect
+		 references or loads from globals)
+	     For 1) we mark all reaching may-defs as necessary, stopping
+	     at dominating kills.  For 2) we want to mark all dominating
+	     references necessary, but non-aliased ones which we handle
+	     in 1).  By keeping a global visited bitmap for references
+	     we walk for 2) we avoid quadratic behavior for those.  */
+	  if (is_gimple_call (stmt))
+	    {
+	      tree callee = gimple_call_fndecl (stmt);
+	      unsigned i;
+	      /* Calls to functions that are merely acting as barriers
+		 or that only store to memory do not make any previous
+		 stores necessary.  */
+	      if (callee != NULL_TREE
+		  && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL
+		  && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET
+		      || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC
+		      || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE))
+		continue;
+	      /* Calls implicitly load from memory, their arguments
+	         in addition may explicitly perform memory loads.  */
+	      mark_all_reaching_defs_necessary (stmt);
+	      for (i = 0; i < gimple_call_num_args (stmt); ++i)
+		{
+		  tree arg = gimple_call_arg (stmt, i);
+		  if (TREE_CODE (arg) == SSA_NAME
+		      || is_gimple_min_invariant (arg))
+		    continue;
+		  if (!ref_may_be_aliased (arg))
+		    mark_aliased_reaching_defs_necessary (stmt, arg);
+		}
+	    }
+	  else if (gimple_assign_single_p (stmt))
+	    {
+	      tree rhs;
+	      bool rhs_aliased = false;
+	      /* If this is a load mark things necessary.  */
+	      rhs = gimple_assign_rhs1 (stmt);
+	      if (TREE_CODE (rhs) != SSA_NAME
+		  && !is_gimple_min_invariant (rhs))
+		{
+		  if (!ref_may_be_aliased (rhs))
+		    mark_aliased_reaching_defs_necessary (stmt, rhs);
+		  else
+		    rhs_aliased = true;
+		}
+	      if (rhs_aliased)
+		mark_all_reaching_defs_necessary (stmt);
+	    }
+	  else if (gimple_code (stmt) == GIMPLE_RETURN)
+	    {
+	      tree rhs = gimple_return_retval (stmt);
+	      /* A return statement may perform a load.  */
+	      if (TREE_CODE (rhs) != SSA_NAME
+		  && !is_gimple_min_invariant (rhs))
+		{
+		  if (!ref_may_be_aliased (rhs))
+		    mark_aliased_reaching_defs_necessary (stmt, rhs);
+		  else
+		    mark_all_reaching_defs_necessary (stmt);
+		}
+	    }
+	  else if (gimple_code (stmt) == GIMPLE_ASM)
+	    {
+	      unsigned i;
+	      mark_all_reaching_defs_necessary (stmt);
+	      /* Inputs may perform loads.  */
+	      for (i = 0; i < gimple_asm_ninputs (stmt); ++i)
+		{
+		  tree op = TREE_VALUE (gimple_asm_input_op (stmt, i));
+		  if (TREE_CODE (op) != SSA_NAME
+		      && !is_gimple_min_invariant (op)
+		      && !ref_may_be_aliased (op))
+		    mark_aliased_reaching_defs_necessary (stmt, op);
+		}
+	    }
+	  else
+	    gcc_unreachable ();
+	  /* If we over-used our alias oracle budget drop to simple
+	     mode.  The cost metric allows quadratic behavior
+	     (number of uses times number of may-defs queries) up to
+	     a constant maximal number of queries and after that falls back to
+	     super-linear complexity.  */
+	  if (/* Constant but quadratic for small functions.  */
+	      total_chain > 128 * 128
+	      /* Linear in the number of may-defs.  */
+	      && total_chain > 32 * longest_chain
+	      /* Linear in the number of uses.  */
+	      && total_chain > nr_walks * 32)
+	    {
+	      chain_ovfl = true;
+	      if (visited)
+		bitmap_clear (visited);
+	    }
 	}
 }
 }
+/* Replace all uses of result of PHI by underlying variable and mark it
+for renaming.  */
+void
+mark_virtual_phi_result_for_renaming (gimple phi)
+{
+bool used = false;
+imm_use_iterator iter;
+use_operand_p use_p;
+gimple stmt;
+tree result_ssa, result_var;
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "Marking result for renaming : ");
+print_gimple_stmt (dump_file, phi, 0, TDF_SLIM);
+fprintf (dump_file, "\n");
+}
+result_ssa = gimple_phi_result (phi);
+result_var = SSA_NAME_VAR (result_ssa);
+FOR_EACH_IMM_USE_STMT (stmt, iter, result_ssa)
+{
+FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+SET_USE (use_p, result_var);
+update_stmt (stmt);
+used = true;
+}
+if (used)
+mark_sym_for_renaming (result_var);
+}
 /* Remove dead PHI nodes from block BB.  */
 static bool
 remove_dead_phis (basic_block bb)
 for (gsi = gsi_start (phis); !gsi_end_p (gsi);)
 {
 stats.total_phis++;
 phi = gsi_stmt (gsi);
+/* We do not track necessity of virtual PHI nodes.  Instead do
+very simple dead PHI removal here.  */
+if (!is_gimple_reg (gimple_phi_result (phi)))
+	{
+	  /* Virtual PHI nodes with one or identical arguments
+	     can be removed.  */
+	  if (degenerate_phi_p (phi))
+	    {
+	      tree vdef = gimple_phi_result (phi);
+	      tree vuse = gimple_phi_arg_def (phi, 0);
+	      use_operand_p use_p;
+	      imm_use_iterator iter;
+	      gimple use_stmt;
+	      FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef)
+		FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+		  SET_USE (use_p, vuse);
+	      if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef)
+	          && TREE_CODE (vuse) == SSA_NAME)
+		SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1;
+	    }
+	  else
+	    gimple_set_plf (phi, STMT_NECESSARY, true);
+	}
 if (!gimple_plf (phi, STMT_NECESSARY))
 	{
 	  something_changed = true;
 	  if (dump_file && (dump_flags & TDF_DETAILS))
 	    {
 	      fprintf (dump_file, "\n");
 	    }
 	  remove_phi_node (&gsi, true);
 	  stats.removed_phis++;
+	  continue;
 	}
-else
+gsi_next (&gsi);
+}
+return something_changed;
+}
+/* Find first live post dominator of BB.  */
+static basic_block
+get_live_post_dom (basic_block bb)
+{
+basic_block post_dom_bb;
+/* The post dominance info has to be up-to-date.  */
+gcc_assert (dom_info_state (CDI_POST_DOMINATORS) == DOM_OK);
+/* Get the immediate post dominator of bb.  */
+post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
+/* And look for first live one.  */
+while (post_dom_bb != EXIT_BLOCK_PTR
+	 && !TEST_BIT (bb_contains_live_stmts, post_dom_bb->index))
+post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, post_dom_bb);
+return post_dom_bb;
+}
+/* Forward edge E to respective POST_DOM_BB and update PHIs.  */
+static edge
+forward_edge_to_pdom (edge e, basic_block post_dom_bb)
+{
+gimple_stmt_iterator gsi;
+edge e2 = NULL;
+edge_iterator ei;
+if (dump_file && (dump_flags & TDF_DETAILS))
+fprintf (dump_file, "Redirecting edge %i->%i to %i\n", e->src->index,
+	     e->dest->index, post_dom_bb->index);
+e2 = redirect_edge_and_branch (e, post_dom_bb);
+cfg_altered = true;
+/* If edge was already around, no updating is neccesary.  */
+if (e2 != e)
+return e2;
+if (phi_nodes (post_dom_bb))
+{
+/* We are sure that for every live PHI we are seeing control dependent BB.
+This means that we can look up the end of control dependent path leading
+to the PHI itself.  */
+FOR_EACH_EDGE (e2, ei, post_dom_bb->preds)
+	if (e2 != e && dominated_by_p (CDI_POST_DOMINATORS, e->src, e2->src))
+	  break;
+for (gsi = gsi_start_phis (post_dom_bb); !gsi_end_p (gsi);)
 	{
-gsi_next (&gsi);
+	  gimple phi = gsi_stmt (gsi);
+	  tree op;
+	  source_location locus;
+	  /* Dead PHI do not imply control dependency.  */
+if (!gimple_plf (phi, STMT_NECESSARY)
+	      && is_gimple_reg (gimple_phi_result (phi)))
+	    {
+	      gsi_next (&gsi);
+	      continue;
+	    }
+	  if (gimple_phi_arg_def (phi, e->dest_idx))
+	    {
+	      gsi_next (&gsi);
+	      continue;
+	    }
+	  /* We didn't find edge to update.  This can happen for PHIs on virtuals
+	     since there is no control dependency relation on them.  We are lost
+	     here and must force renaming of the symbol.  */
+	  if (!is_gimple_reg (gimple_phi_result (phi)))
+	    {
+	      mark_virtual_phi_result_for_renaming (phi);
+	      remove_phi_node (&gsi, true);
+	      continue;
+	    }
+	  if (!e2)
+	    {
+	      op = gimple_phi_arg_def (phi, e->dest_idx == 0 ? 1 : 0);
+	      locus = gimple_phi_arg_location (phi, e->dest_idx == 0 ? 1 : 0);
+	    }
+	  else
+	    {
+	      op = gimple_phi_arg_def (phi, e2->dest_idx);
+	      locus = gimple_phi_arg_location (phi, e2->dest_idx);
+	    }
+	  add_phi_arg (phi, op, e, locus);
+	  gcc_assert (e2 || degenerate_phi_p (phi));
+	  gsi_next (&gsi);
 	}
 }
-return something_changed;
+return e;
 }
 /* Remove dead statement pointed to by iterator I.  Receives the basic block BB
 containing I so that we don't have to look it up.  */
 static void
 removed by cleanup_tree_cfg if this change in the flow graph makes them
 unreachable.  */
 if (is_ctrl_stmt (stmt))
 {
 basic_block post_dom_bb;
+edge e, e2;
-/* The post dominance info has to be up-to-date.  */
+edge_iterator ei;
-gcc_assert (dom_info_state (CDI_POST_DOMINATORS) == DOM_OK);
-/* Get the immediate post dominator of bb.  */
+post_dom_bb = get_live_post_dom (bb);
-post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb);
+e = find_edge (bb, post_dom_bb);
-/* There are three particularly problematical cases.
+/* If edge is already there, try to use it.  This avoids need to update
-	 1. Blocks that do not have an immediate post dominator.  This
+PHI nodes.  Also watch for cases where post dominator does not exists
-	    can happen with infinite loops.
+	 or is exit block.  These can happen for infinite loops as we create
+	 fake edges in the dominator tree.  */
-	 2. Blocks that are only post dominated by the exit block.  These
+if (e)
-	    can also happen for infinite loops as we create fake edges
+;
-	    in the dominator tree.
+else if (! post_dom_bb || post_dom_bb == EXIT_BLOCK_PTR)
+	e = EDGE_SUCC (bb, 0);
-	 3. If the post dominator has PHI nodes we may be able to compute
-	    the right PHI args for them.
-	 In each of these cases we must remove the control statement
-	 as it may reference SSA_NAMEs which are going to be removed and
-	 we remove all but one outgoing edge from the block.  */
-if (! post_dom_bb
-	  || post_dom_bb == EXIT_BLOCK_PTR
-	  || phi_nodes (post_dom_bb))
-	;
 else
-	{
+e = forward_edge_to_pdom (EDGE_SUCC (bb, 0), post_dom_bb);
-	  /* Redirect the first edge out of BB to reach POST_DOM_BB.  */
+gcc_assert (e);
-	  redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
+e->probability = REG_BR_PROB_BASE;
-	  PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
+e->count = bb->count;
-	  /* It is not sufficient to set cfg_altered below during edge
-	     removal, in case BB has two successors and one of them
-	     is POST_DOM_BB.  */
-	  cfg_altered = true;
-	}
-EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
-EDGE_SUCC (bb, 0)->count = bb->count;
 /* The edge is no longer associated with a conditional, so it does
 	 not have TRUE/FALSE flags.  */
-EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
+e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE);
 /* The lone outgoing edge from BB will be a fallthru edge.  */
-EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU;
+e->flags |= EDGE_FALLTHRU;
-/* Remove the remaining the outgoing edges.  */
+/* Remove the remaining outgoing edges.  */
-while (!single_succ_p (bb))
+for (ei = ei_start (bb->succs); (e2 = ei_safe_edge (ei)); )
-	{
+	if (e != e2)
-	  /* FIXME.  When we remove the edge, we modify the CFG, which
+	  {
-	     in turn modifies the dominator and post-dominator tree.
+	    cfg_altered = true;
-	     Is it safe to postpone recomputing the dominator and
+remove_edge (e2);
-	     post-dominator tree until the end of this pass given that
+	  }
-	     the post-dominators are used above?  */
+	else
-	  cfg_altered = true;
+	  ei_next (&ei);
-remove_edge (EDGE_SUCC (bb, 1));
+}
-	}
-}
+unlink_stmt_vdef (stmt);
+gsi_remove (i, true);
-gsi_remove (i, true);
+release_defs (stmt);
-release_defs (stmt);
+}
-}
 /* Eliminate unnecessary statements. Any instruction not marked as necessary
 contributes nothing to the program, and can be deleted.  */
 static bool
 eliminate_unnecessary_stmts (void)
 {
 bool something_changed = false;
 basic_block bb;
-gimple_stmt_iterator gsi;
+gimple_stmt_iterator gsi, psi;
 gimple stmt;
 tree call;
+VEC (basic_block, heap) *h;
 if (dump_file && (dump_flags & TDF_DETAILS))
 fprintf (dump_file, "\nEliminating unnecessary statements:\n");
 clear_special_calls ();
-FOR_EACH_BB (bb)
-{
+/* Walking basic blocks and statements in reverse order avoids
-/* Remove dead PHI nodes.  */
+releasing SSA names before any other DEFs that refer to them are
-something_changed |= remove_dead_phis (bb);
+released.  This helps avoid loss of debug information, as we get
-}
+a chance to propagate all RHSs of removed SSAs into debug uses,
+rather than only the latest ones.  E.g., consider:
-FOR_EACH_BB (bb)
-{
+x_3 = y_1 + z_2;
+a_5 = x_3 - b_4;
+# DEBUG a => a_5
+If we were to release x_3 before a_5, when we reached a_5 and
+tried to substitute it into the debug stmt, we'd see x_3 there,
+but x_3's DEF, type, etc would have already been disconnected.
+By going backwards, the debug stmt first changes to:
+# DEBUG a => x_3 - b_4
+and then to:
+# DEBUG a => y_1 + z_2 - b_4
+as desired.  */
+gcc_assert (dom_info_available_p (CDI_DOMINATORS));
+h = get_all_dominated_blocks (CDI_DOMINATORS, single_succ (ENTRY_BLOCK_PTR));
+while (VEC_length (basic_block, h))
+{
+bb = VEC_pop (basic_block, h);
 /* Remove dead statements.  */
-for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi)
 	{
 	  stmt = gsi_stmt (gsi);
+	  psi = gsi;
+	  gsi_prev (&psi);
 	  stats.total++;
 	  /* If GSI is not necessary then remove it.  */
 	  if (!gimple_plf (stmt, STMT_NECESSARY))
 	    {
+	      if (!is_gimple_debug (stmt))
+		something_changed = true;
 	      remove_dead_stmt (&gsi, bb);
-	      something_changed = true;
 	    }
 	  else if (is_gimple_call (stmt))
 	    {
 	      call = gimple_call_fndecl (stmt);
 	      if (call)
 		{
 		  tree name;
-		  gimple g;
 		  /* When LHS of var = call (); is dead, simplify it into
 		     call (); saving one operand.  */
 		  name = gimple_call_lhs (stmt);
 		  if (name && TREE_CODE (name) == SSA_NAME
 			{
 			  fprintf (dump_file, "Deleting LHS of call: ");
 			  print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
 			  fprintf (dump_file, "\n");
 			}
-		      push_stmt_changes (gsi_stmt_ptr (&gsi));
+		      gimple_call_set_lhs (stmt, NULL_TREE);
-		      g = gimple_copy (stmt);
+		      maybe_clean_or_replace_eh_stmt (stmt, stmt);
-		      gimple_call_set_lhs (g, NULL_TREE);
+		      update_stmt (stmt);
-		      gsi_replace (&gsi, g, false);
-		      maybe_clean_or_replace_eh_stmt (stmt, g);
-		      mark_symbols_for_renaming (g);
-		      pop_stmt_changes (gsi_stmt_ptr (&gsi));
 		      release_ssa_name (name);
 		    }
 		  notice_special_calls (stmt);
 		}
-	      gsi_next (&gsi);
-	    }
-	  else
-	    {
-	      gsi_next (&gsi);
 	    }
 	}
+}
+VEC_free (basic_block, heap, h);
+/* Since we don't track liveness of virtual PHI nodes, it is possible that we
+rendered some PHI nodes unreachable while they are still in use.
+Mark them for renaming.  */
+if (cfg_altered)
+{
+basic_block prev_bb;
+find_unreachable_blocks ();
+/* Delete all unreachable basic blocks in reverse dominator order.  */
+for (bb = EXIT_BLOCK_PTR->prev_bb; bb != ENTRY_BLOCK_PTR; bb = prev_bb)
+	{
+	  prev_bb = bb->prev_bb;
+	  if (!TEST_BIT (bb_contains_live_stmts, bb->index)
+	      || !(bb->flags & BB_REACHABLE))
+	    {
+	      for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+		if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
+		  {
+		    bool found = false;
+		    imm_use_iterator iter;
+		    FOR_EACH_IMM_USE_STMT (stmt, iter, gimple_phi_result (gsi_stmt (gsi)))
+		      {
+			if (!(gimple_bb (stmt)->flags & BB_REACHABLE))
+			  continue;
+			if (gimple_code (stmt) == GIMPLE_PHI
+			    || gimple_plf (stmt, STMT_NECESSARY))
+			  {
+			    found = true;
+			    BREAK_FROM_IMM_USE_STMT (iter);
+			  }
+		      }
+		    if (found)
+		      mark_virtual_phi_result_for_renaming (gsi_stmt (gsi));
+		  }
+	      if (!(bb->flags & BB_REACHABLE))
+		{
+		  /* Speed up the removal of blocks that don't
+		     dominate others.  Walking backwards, this should
+		     be the common case.  ??? Do we need to recompute
+		     dominators because of cfg_altered?  */
+		  if (!MAY_HAVE_DEBUG_STMTS
+		      || !first_dom_son (CDI_DOMINATORS, bb))
+		    delete_basic_block (bb);
+		  else
+		    {
+		      h = get_all_dominated_blocks (CDI_DOMINATORS, bb);
+		      while (VEC_length (basic_block, h))
+			{
+			  bb = VEC_pop (basic_block, h);
+			  prev_bb = bb->prev_bb;
+			  /* Rearrangements to the CFG may have failed
+			     to update the dominators tree, so that
+			     formerly-dominated blocks are now
+			     otherwise reachable.  */
+			  if (!!(bb->flags & BB_REACHABLE))
+			    continue;
+			  delete_basic_block (bb);
+			}
+		      VEC_free (basic_block, heap, h);
+		    }
+		}
+	    }
+	}
+}
+FOR_EACH_BB (bb)
+{
+/* Remove dead PHI nodes.  */
+something_changed |= remove_dead_phis (bb);
 }
 return something_changed;
 }
 for (i = 0; i < last_basic_block; ++i)
 	control_dependence_map[i] = BITMAP_ALLOC (NULL);
 last_stmt_necessary = sbitmap_alloc (last_basic_block);
 sbitmap_zero (last_stmt_necessary);
+bb_contains_live_stmts = sbitmap_alloc (last_basic_block);
+sbitmap_zero (bb_contains_live_stmts);
 }
 processed = sbitmap_alloc (num_ssa_names + 1);
 sbitmap_zero (processed);
 	BITMAP_FREE (control_dependence_map[i]);
 free (control_dependence_map);
 sbitmap_free (visited_control_parents);
 sbitmap_free (last_stmt_necessary);
+sbitmap_free (bb_contains_live_stmts);
+bb_contains_live_stmts = NULL;
 }
 sbitmap_free (processed);
 VEC_free (gimple, heap, worklist);
 static unsigned int
 perform_tree_ssa_dce (bool aggressive)
 {
 struct edge_list *el = NULL;
 bool something_changed = 0;
+/* Preheaders are needed for SCEV to work.
+Simple lateches and recorded exits improve chances that loop will
+proved to be finite in testcases such as in loop-15.c and loop-24.c  */
+if (aggressive)
+loop_optimizer_init (LOOPS_NORMAL
+			 | LOOPS_HAVE_RECORDED_EXITS);
 tree_dce_init (aggressive);
 if (aggressive)
 {
 mark_dfs_back_edges ();
 }
 find_obviously_necessary_stmts (el);
+if (aggressive)
+loop_optimizer_finalize ();
+longest_chain = 0;
+total_chain = 0;
+nr_walks = 0;
+chain_ovfl = false;
+visited = BITMAP_ALLOC (NULL);
 propagate_necessity (el);
+BITMAP_FREE (visited);
 something_changed |= eliminate_unnecessary_stmts ();
 something_changed |= cfg_altered;
 /* We do not update postdominators, so free them unconditionally.  */
 tree_dce_done (aggressive);
 free_edge_list (el);
 if (something_changed)
 return (TODO_update_ssa | TODO_cleanup_cfg | TODO_ggc_collect
 	    | TODO_remove_unused_locals);
 else
 return 0;
 }

Mercurial > hg > CbC > CbC_gcc

comparison gcc/tree-ssa-dce.c @ 55:77e2b8dfacca gcc-4.4.5