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

comparison gcc/tree-ssa-uncprop.c @ 0:a06113de4d67

first commit

author	kent <kent@cr.ie.u-ryukyu.ac.jp>
date	Fri, 17 Jul 2009 14:47:48 +0900
parents
children	77e2b8dfacca

comparison

equal deleted inserted replaced

--1:000000000000
+:a06113de4d67
+/* Routines for discovering and unpropagating edge equivalences.
+Copyright (C) 2005, 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 "flags.h"
+#include "rtl.h"
+#include "tm_p.h"
+#include "ggc.h"
+#include "basic-block.h"
+#include "output.h"
+#include "expr.h"
+#include "function.h"
+#include "diagnostic.h"
+#include "timevar.h"
+#include "tree-dump.h"
+#include "tree-flow.h"
+#include "domwalk.h"
+#include "real.h"
+#include "tree-pass.h"
+#include "tree-ssa-propagate.h"
+#include "langhooks.h"
+/* The basic structure describing an equivalency created by traversing
+an edge.  Traversing the edge effectively means that we can assume
+that we've seen an assignment LHS = RHS.  */
+struct edge_equivalency
+{
+tree rhs;
+tree lhs;
+};
+/* This routine finds and records edge equivalences for every edge
+in the CFG.
+When complete, each edge that creates an equivalency will have an
+EDGE_EQUIVALENCY structure hanging off the edge's AUX field.
+The caller is responsible for freeing the AUX fields.  */
+static void
+associate_equivalences_with_edges (void)
+{
+basic_block bb;
+/* Walk over each block.  If the block ends with a control statement,
+then it might create a useful equivalence.  */
+FOR_EACH_BB (bb)
+{
+gimple_stmt_iterator gsi = gsi_last_bb (bb);
+gimple stmt;
+/* If the block does not end with a COND_EXPR or SWITCH_EXPR
+	 then there is nothing to do.  */
+if (gsi_end_p (gsi))
+	continue;
+stmt = gsi_stmt (gsi);
+if (!stmt)
+	continue;
+/* A COND_EXPR may create an equivalency in a variety of different
+	 ways.  */
+if (gimple_code (stmt) == GIMPLE_COND)
+	{
+	  edge true_edge;
+	  edge false_edge;
+	  struct edge_equivalency *equivalency;
+	  enum tree_code code = gimple_cond_code (stmt);
+	  extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
+	  /* Equality tests may create one or two equivalences.  */
+	  if (code == EQ_EXPR || code == NE_EXPR)
+	    {
+	      tree op0 = gimple_cond_lhs (stmt);
+	      tree op1 = gimple_cond_rhs (stmt);
+	      /* Special case comparing booleans against a constant as we
+		 know the value of OP0 on both arms of the branch.  i.e., we
+		 can record an equivalence for OP0 rather than COND.  */
+	      if (TREE_CODE (op0) == SSA_NAME
+		  && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0)
+		  && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE
+		  && is_gimple_min_invariant (op1))
+		{
+		  if (code == EQ_EXPR)
+		    {
+		      equivalency = XNEW (struct edge_equivalency);
+		      equivalency->lhs = op0;
+		      equivalency->rhs = (integer_zerop (op1)
+					  ? boolean_false_node
+					  : boolean_true_node);
+		      true_edge->aux = equivalency;
+		      equivalency = XNEW (struct edge_equivalency);
+		      equivalency->lhs = op0;
+		      equivalency->rhs = (integer_zerop (op1)
+					  ? boolean_true_node
+					  : boolean_false_node);
+		      false_edge->aux = equivalency;
+		    }
+		  else
+		    {
+		      equivalency = XNEW (struct edge_equivalency);
+		      equivalency->lhs = op0;
+		      equivalency->rhs = (integer_zerop (op1)
+					  ? boolean_true_node
+					  : boolean_false_node);
+		      true_edge->aux = equivalency;
+		      equivalency = XNEW (struct edge_equivalency);
+		      equivalency->lhs = op0;
+		      equivalency->rhs = (integer_zerop (op1)
+					  ? boolean_false_node
+					  : boolean_true_node);
+		      false_edge->aux = equivalency;
+		    }
+		}
+	      else if (TREE_CODE (op0) == SSA_NAME
+		       && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0)
+		       && (is_gimple_min_invariant (op1)
+			   || (TREE_CODE (op1) == SSA_NAME
+			       && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1))))
+		{
+		  /* For IEEE, -0.0 == 0.0, so we don't necessarily know
+		     the sign of a variable compared against zero.  If
+		     we're honoring signed zeros, then we cannot record
+		     this value unless we know that the value is nonzero.  */
+		  if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (op0)))
+		      && (TREE_CODE (op1) != REAL_CST
+			  || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (op1))))
+		    continue;
+		  equivalency = XNEW (struct edge_equivalency);
+		  equivalency->lhs = op0;
+		  equivalency->rhs = op1;
+		  if (code == EQ_EXPR)
+		    true_edge->aux = equivalency;
+		  else
+		    false_edge->aux = equivalency;
+		}
+	    }
+	  /* ??? TRUTH_NOT_EXPR can create an equivalence too.  */
+	}
+/* For a SWITCH_EXPR, a case label which represents a single
+	 value and which is the only case label which reaches the
+	 target block creates an equivalence.  */
+else if (gimple_code (stmt) == GIMPLE_SWITCH)
+	{
+	  tree cond = gimple_switch_index (stmt);
+	  if (TREE_CODE (cond) == SSA_NAME
+	      && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (cond))
+	    {
+	      int i, n_labels = gimple_switch_num_labels (stmt);
+	      tree *info = XCNEWVEC (tree, n_basic_blocks);
+	      /* Walk over the case label vector.  Record blocks
+		 which are reached by a single case label which represents
+		 a single value.  */
+	      for (i = 0; i < n_labels; i++)
+		{
+		  tree label = gimple_switch_label (stmt, i);
+		  basic_block bb = label_to_block (CASE_LABEL (label));
+		  if (CASE_HIGH (label)
+		      || !CASE_LOW (label)
+		      || info[bb->index])
+		    info[bb->index] = error_mark_node;
+		  else
+		    info[bb->index] = label;
+		}
+	      /* Now walk over the blocks to determine which ones were
+		 marked as being reached by a useful case label.  */
+	      for (i = 0; i < n_basic_blocks; i++)
+		{
+		  tree node = info[i];
+		  if (node != NULL
+		      && node != error_mark_node)
+		    {
+		      tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node));
+		      struct edge_equivalency *equivalency;
+		      /* Record an equivalency on the edge from BB to basic
+			 block I.  */
+		      equivalency = XNEW (struct edge_equivalency);
+		      equivalency->rhs = x;
+		      equivalency->lhs = cond;
+		      find_edge (bb, BASIC_BLOCK (i))->aux = equivalency;
+		    }
+		}
+	      free (info);
+	    }
+	}
+}
+}
+/* Translating out of SSA sometimes requires inserting copies and
+constant initializations on edges to eliminate PHI nodes.
+In some cases those copies and constant initializations are
+redundant because the target already has the value on the
+RHS of the assignment.
+We previously tried to catch these cases after translating
+out of SSA form.  However, that code often missed cases.  Worse
+yet, the cases it missed were also often missed by the RTL
+optimizers.  Thus the resulting code had redundant instructions.
+This pass attempts to detect these situations before translating
+out of SSA form.
+The key concept that this pass is built upon is that these
+redundant copies and constant initializations often occur
+due to constant/copy propagating equivalences resulting from
+COND_EXPRs and SWITCH_EXPRs.
+We want to do those propagations as they can sometimes allow
+the SSA optimizers to do a better job.  However, in the cases
+where such propagations do not result in further optimization,
+we would like to "undo" the propagation to avoid the redundant
+copies and constant initializations.
+This pass works by first associating equivalences with edges in
+the CFG.  For example, the edge leading from a SWITCH_EXPR to
+its associated CASE_LABEL will have an equivalency between
+SWITCH_COND and the value in the case label.
+Once we have found the edge equivalences, we proceed to walk
+the CFG in dominator order.  As we traverse edges we record
+equivalences associated with those edges we traverse.
+When we encounter a PHI node, we walk its arguments to see if we
+have an equivalence for the PHI argument.  If so, then we replace
+the argument.
+Equivalences are looked up based on their value (think of it as
+the RHS of an assignment).   A value may be an SSA_NAME or an
+invariant.  We may have several SSA_NAMEs with the same value,
+so with each value we have a list of SSA_NAMEs that have the
+same value.  */
+/* As we enter each block we record the value for any edge equivalency
+leading to this block.  If no such edge equivalency exists, then we
+record NULL.  These equivalences are live until we leave the dominator
+subtree rooted at the block where we record the equivalency.  */
+static VEC(tree,heap) *equiv_stack;
+/* Global hash table implementing a mapping from invariant values
+to a list of SSA_NAMEs which have the same value.  We might be
+able to reuse tree-vn for this code.  */
+static htab_t equiv;
+/* Main structure for recording equivalences into our hash table.  */
+struct equiv_hash_elt
+{
+/* The value/key of this entry.  */
+tree value;
+/* List of SSA_NAMEs which have the same value/key.  */
+VEC(tree,heap) *equivalences;
+};
+static void uncprop_initialize_block (struct dom_walk_data *, basic_block);
+static void uncprop_finalize_block (struct dom_walk_data *, basic_block);
+static void uncprop_into_successor_phis (struct dom_walk_data *, basic_block);
+/* Hashing and equality routines for the hash table.  */
+static hashval_t
+equiv_hash (const void *p)
+{
+tree const value = ((const struct equiv_hash_elt *)p)->value;
+return iterative_hash_expr (value, 0);
+}
+static int
+equiv_eq (const void *p1, const void *p2)
+{
+tree value1 = ((const struct equiv_hash_elt *)p1)->value;
+tree value2 = ((const struct equiv_hash_elt *)p2)->value;
+return operand_equal_p (value1, value2, 0);
+}
+/* Free an instance of equiv_hash_elt.  */
+static void
+equiv_free (void *p)
+{
+struct equiv_hash_elt *elt = (struct equiv_hash_elt *) p;
+VEC_free (tree, heap, elt->equivalences);
+free (elt);
+}
+/* Remove the most recently recorded equivalency for VALUE.  */
+static void
+remove_equivalence (tree value)
+{
+struct equiv_hash_elt equiv_hash_elt, *equiv_hash_elt_p;
+void **slot;
+equiv_hash_elt.value = value;
+equiv_hash_elt.equivalences = NULL;
+slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT);
+equiv_hash_elt_p = (struct equiv_hash_elt *) *slot;
+VEC_pop (tree, equiv_hash_elt_p->equivalences);
+}
+/* Record EQUIVALENCE = VALUE into our hash table.  */
+static void
+record_equiv (tree value, tree equivalence)
+{
+struct equiv_hash_elt *equiv_hash_elt;
+void **slot;
+equiv_hash_elt = XNEW (struct equiv_hash_elt);
+equiv_hash_elt->value = value;
+equiv_hash_elt->equivalences = NULL;
+slot = htab_find_slot (equiv, equiv_hash_elt, INSERT);
+if (*slot == NULL)
+*slot = (void *) equiv_hash_elt;
+else
+free (equiv_hash_elt);
+equiv_hash_elt = (struct equiv_hash_elt *) *slot;
+VEC_safe_push (tree, heap, equiv_hash_elt->equivalences, equivalence);
+}
+/* Main driver for un-cprop.  */
+static unsigned int
+tree_ssa_uncprop (void)
+{
+struct dom_walk_data walk_data;
+basic_block bb;
+associate_equivalences_with_edges ();
+/* Create our global data structures.  */
+equiv = htab_create (1024, equiv_hash, equiv_eq, equiv_free);
+equiv_stack = VEC_alloc (tree, heap, 2);
+/* We're going to do a dominator walk, so ensure that we have
+dominance information.  */
+calculate_dominance_info (CDI_DOMINATORS);
+/* Setup callbacks for the generic dominator tree walker.  */
+walk_data.walk_stmts_backward = false;
+walk_data.dom_direction = CDI_DOMINATORS;
+walk_data.initialize_block_local_data = NULL;
+walk_data.before_dom_children_before_stmts = uncprop_initialize_block;
+walk_data.before_dom_children_walk_stmts = NULL;
+walk_data.before_dom_children_after_stmts = uncprop_into_successor_phis;
+walk_data.after_dom_children_before_stmts = NULL;
+walk_data.after_dom_children_walk_stmts = NULL;
+walk_data.after_dom_children_after_stmts = uncprop_finalize_block;
+walk_data.global_data = NULL;
+walk_data.block_local_data_size = 0;
+walk_data.interesting_blocks = NULL;
+/* Now initialize the dominator walker.  */
+init_walk_dominator_tree (&walk_data);
+/* Recursively walk the dominator tree undoing unprofitable
+constant/copy propagations.  */
+walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR);
+/* Finalize and clean up.  */
+fini_walk_dominator_tree (&walk_data);
+/* EQUIV_STACK should already be empty at this point, so we just
+need to empty elements out of the hash table, free EQUIV_STACK,
+and cleanup the AUX field on the edges.  */
+htab_delete (equiv);
+VEC_free (tree, heap, equiv_stack);
+FOR_EACH_BB (bb)
+{
+edge e;
+edge_iterator ei;
+FOR_EACH_EDGE (e, ei, bb->succs)
+	{
+	  if (e->aux)
+	    {
+	      free (e->aux);
+	      e->aux = NULL;
+	    }
+	}
+}
+return 0;
+}
+/* We have finished processing the dominator children of BB, perform
+any finalization actions in preparation for leaving this node in
+the dominator tree.  */
+static void
+uncprop_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			basic_block bb ATTRIBUTE_UNUSED)
+{
+/* Pop the topmost value off the equiv stack.  */
+tree value = VEC_pop (tree, equiv_stack);
+/* If that value was non-null, then pop the topmost equivalency off
+its equivalency stack.  */
+if (value != NULL)
+remove_equivalence (value);
+}
+/* Unpropagate values from PHI nodes in successor blocks of BB.  */
+static void
+uncprop_into_successor_phis (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			     basic_block bb)
+{
+edge e;
+edge_iterator ei;
+/* For each successor edge, first temporarily record any equivalence
+on that edge.  Then unpropagate values in any PHI nodes at the
+destination of the edge.  Then remove the temporary equivalence.  */
+FOR_EACH_EDGE (e, ei, bb->succs)
+{
+gimple_seq phis = phi_nodes (e->dest);
+gimple_stmt_iterator gsi;
+/* If there are no PHI nodes in this destination, then there is
+	 no sense in recording any equivalences.  */
+if (!phis)
+	continue;
+/* Record any equivalency associated with E.  */
+if (e->aux)
+	{
+	  struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux;
+	  record_equiv (equiv->rhs, equiv->lhs);
+	}
+/* Walk over the PHI nodes, unpropagating values.  */
+for (gsi = gsi_start (phis) ; !gsi_end_p (gsi); gsi_next (&gsi))
+	{
+	  /* Sigh.  We'll have more efficient access to this one day.  */
+	  gimple phi = gsi_stmt (gsi);
+	  tree arg = PHI_ARG_DEF (phi, e->dest_idx);
+	  struct equiv_hash_elt equiv_hash_elt;
+	  void **slot;
+	  /* If the argument is not an invariant, or refers to the same
+	     underlying variable as the PHI result, then there's no
+	     point in un-propagating the argument.  */
+	  if (!is_gimple_min_invariant (arg)
+	      && SSA_NAME_VAR (arg) != SSA_NAME_VAR (PHI_RESULT (phi)))
+	    continue;
+	  /* Lookup this argument's value in the hash table.  */
+	  equiv_hash_elt.value = arg;
+	  equiv_hash_elt.equivalences = NULL;
+	  slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT);
+	  if (slot)
+	    {
+	      struct equiv_hash_elt *elt = (struct equiv_hash_elt *) *slot;
+	      int j;
+	      /* Walk every equivalence with the same value.  If we find
+		 one with the same underlying variable as the PHI result,
+		 then replace the value in the argument with its equivalent
+		 SSA_NAME.  Use the most recent equivalence as hopefully
+		 that results in shortest lifetimes.  */
+	      for (j = VEC_length (tree, elt->equivalences) - 1; j >= 0; j--)
+		{
+		  tree equiv = VEC_index (tree, elt->equivalences, j);
+		  if (SSA_NAME_VAR (equiv) == SSA_NAME_VAR (PHI_RESULT (phi)))
+		    {
+		      SET_PHI_ARG_DEF (phi, e->dest_idx, equiv);
+		      break;
+		    }
+		}
+	    }
+	}
+/* If we had an equivalence associated with this edge, remove it.  */
+if (e->aux)
+	{
+	  struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux;
+	  remove_equivalence (equiv->rhs);
+	}
+}
+}
+/* Ignoring loop backedges, if BB has precisely one incoming edge then
+return that edge.  Otherwise return NULL.  */
+static edge
+single_incoming_edge_ignoring_loop_edges (basic_block bb)
+{
+edge retval = NULL;
+edge e;
+edge_iterator ei;
+FOR_EACH_EDGE (e, ei, bb->preds)
+{
+/* A loop back edge can be identified by the destination of
+	 the edge dominating the source of the edge.  */
+if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest))
+	continue;
+/* If we have already seen a non-loop edge, then we must have
+	 multiple incoming non-loop edges and thus we return NULL.  */
+if (retval)
+	return NULL;
+/* This is the first non-loop incoming edge we have found.  Record
+	 it.  */
+retval = e;
+}
+return retval;
+}
+static void
+uncprop_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			  basic_block bb)
+{
+basic_block parent;
+edge e;
+bool recorded = false;
+/* If this block is dominated by a single incoming edge and that edge
+has an equivalency, then record the equivalency and push the
+VALUE onto EQUIV_STACK.  Else push a NULL entry on EQUIV_STACK.  */
+parent = get_immediate_dominator (CDI_DOMINATORS, bb);
+if (parent)
+{
+e = single_incoming_edge_ignoring_loop_edges (bb);
+if (e && e->src == parent && e->aux)
+	{
+	  struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux;
+	  record_equiv (equiv->rhs, equiv->lhs);
+	  VEC_safe_push (tree, heap, equiv_stack, equiv->rhs);
+	  recorded = true;
+	}
+}
+if (!recorded)
+VEC_safe_push (tree, heap, equiv_stack, NULL_TREE);
+}
+static bool
+gate_uncprop (void)
+{
+return flag_tree_dom != 0;
+}
+struct gimple_opt_pass pass_uncprop =
+{
+{
+GIMPLE_PASS,
+"uncprop",				/* name */
+gate_uncprop,				/* gate */
+tree_ssa_uncprop,			/* execute */
+NULL,					/* sub */
+NULL,					/* next */
+0,					/* static_pass_number */
+TV_TREE_SSA_UNCPROP,			/* tv_id */
+PROP_cfg | PROP_ssa,			/* properties_required */
+0,					/* properties_provided */
+0,					/* properties_destroyed */
+0,					/* todo_flags_start */
+TODO_dump_func | TODO_verify_ssa	/* todo_flags_finish */
+}
+};

Mercurial > hg > CbC > CbC_gcc

comparison gcc/tree-ssa-uncprop.c @ 0:a06113de4d67