CbC/CbC_gcc: gcc/gimple-ssa-backprop.c comparison

comparison gcc/gimple-ssa-backprop.c @ 111:04ced10e8804

gcc 7

author	kono
date	Fri, 27 Oct 2017 22:46:09 +0900
parents
children	84e7813d76e9

comparison

equal deleted inserted replaced

-:561a7518be6b
+:04ced10e8804
+/* Back-propagation of usage information to definitions.
+Copyright (C) 2015-2017 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/>.  */
+/* This pass propagates information that is common to all uses of an SSA
+name back up through the sequence of statements that generate it,
+simplifying the statements where possible.  Sometimes this can expose
+fully or partially dead code, but the main focus is simplifying
+computations.
+At the moment the pass only handles one piece of information: whether the
+sign of a value matters, and therefore whether sign-changing operations
+can be skipped.  The pass could be extended to more interesting
+information in future, such as which bits of an integer are significant.
+For example, take the function:
+double
+f (double *a, int n, double start)
+{
+double x = fabs (start);
+for (int i = 0; i < n; ++i)
+	 x *= a[i];
+return __builtin_cos (x);
+}
+cos(x) == cos(-x), so the sign of the final x doesn't matter.
+That x is the result of a series of multiplications, and if
+the sign of the result of a multiplication doesn't matter,
+the signs of the inputs don't matter either.
+The pass would replace the incoming value of x (i.e. fabs(start))
+with start.  Since there are no other uses of the fabs result,
+the call would get deleted as dead.
+The algorithm is:
+(1) Do a post-order traversal of the blocks in the function, walking
+each block backwards.  For each potentially-simplifiable statement
+that defines an SSA name X, examine all uses of X to see what
+information is actually significant.  Record this as INFO_MAP[X].
+Optimistically ignore for now any back-edge references to
+unprocessed phis.
+(An alternative would be to record each use when we visit its
+statement and take the intersection as we go along.  However,
+this would lead to more SSA names being entered into INFO_MAP
+unnecessarily, only to be taken out again later.  At the moment
+very few SSA names end up with useful information.)
+(2) Iteratively reduce the optimistic result of (1) until we reach
+a maximal fixed point (which at the moment would mean revisiting
+statements at most once).  First push all SSA names that used an
+optimistic assumption about a backedge phi onto a worklist.
+While the worklist is nonempty, pick off an SSA name X and recompute
+INFO_MAP[X].  If the value changes, push all SSA names used in the
+definition of X onto the worklist.
+(3) Iterate over each SSA name X with info in INFO_MAP, in the
+opposite order to (1), i.e. a forward reverse-post-order walk.
+Try to optimize the definition of X using INFO_MAP[X] and fold
+the result.  (This ensures that we fold definitions before uses.)
+(4) Iterate over each SSA name X with info in INFO_MAP, in the same
+order as (1), and delete any statements that are now dead.
+(This ensures that if a sequence of statements is dead,
+we delete the last statement first.)
+Note that this pass does not deal with direct redundancies,
+such as cos(-x)->cos(x).  match.pd handles those cases instead.  */
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "backend.h"
+#include "tree.h"
+#include "gimple.h"
+#include "gimple-iterator.h"
+#include "ssa.h"
+#include "fold-const.h"
+#include "tree-pass.h"
+#include "cfganal.h"
+#include "gimple-pretty-print.h"
+#include "tree-cfg.h"
+#include "tree-ssa.h"
+#include "tree-ssa-propagate.h"
+#include "gimple-fold.h"
+#include "alloc-pool.h"
+#include "tree-hash-traits.h"
+#include "case-cfn-macros.h"
+namespace {
+/* Information about a group of uses of an SSA name.  */
+struct usage_info
+{
+usage_info () : flag_word (0) {}
+usage_info &operator &= (const usage_info &);
+usage_info operator & (const usage_info &) const;
+bool operator == (const usage_info &) const;
+bool operator != (const usage_info &) const;
+bool is_useful () const;
+static usage_info intersection_identity ();
+union
+{
+struct
+{
+/* True if the uses treat x and -x in the same way.  */
+unsigned int ignore_sign : 1;
+} flags;
+/* All the flag bits as a single int.  */
+unsigned int flag_word;
+};
+};
+/* Return an X such that X & Y == Y for all Y.  This is the most
+optimistic assumption possible.  */
+usage_info
+usage_info::intersection_identity ()
+{
+usage_info ret;
+ret.flag_word = -1;
+return ret;
+}
+/* Intersect *THIS with OTHER, so that *THIS describes all uses covered
+by the original *THIS and OTHER.  */
+usage_info &
+usage_info::operator &= (const usage_info &other)
+{
+flag_word &= other.flag_word;
+return *this;
+}
+/* Return the intersection of *THIS and OTHER, i.e. a structure that
+describes all uses covered by *THIS and OTHER.  */
+usage_info
+usage_info::operator & (const usage_info &other) const
+{
+usage_info info (*this);
+info &= other;
+return info;
+}
+bool
+usage_info::operator == (const usage_info &other) const
+{
+return flag_word == other.flag_word;
+}
+bool
+usage_info::operator != (const usage_info &other) const
+{
+return !operator == (other);
+}
+/* Return true if *THIS is not simply the default, safe assumption.  */
+bool
+usage_info::is_useful () const
+{
+return flag_word != 0;
+}
+/* Start a dump line about SSA name VAR.  */
+static void
+dump_usage_prefix (FILE *file, tree var)
+{
+fprintf (file, "  ");
+print_generic_expr (file, var);
+fprintf (file, ": ");
+}
+/* Print INFO to FILE.  */
+static void
+dump_usage_info (FILE *file, tree var, usage_info *info)
+{
+if (info->flags.ignore_sign)
+{
+dump_usage_prefix (file, var);
+fprintf (file, "sign bit not important\n");
+}
+}
+/* Represents one execution of the pass.  */
+class backprop
+{
+public:
+backprop (function *);
+~backprop ();
+void execute ();
+private:
+const usage_info *lookup_operand (tree);
+void push_to_worklist (tree);
+tree pop_from_worklist ();
+void process_builtin_call_use (gcall *, tree, usage_info *);
+void process_assign_use (gassign *, tree, usage_info *);
+void process_phi_use (gphi *, usage_info *);
+void process_use (gimple *, tree, usage_info *);
+bool intersect_uses (tree, usage_info *);
+void reprocess_inputs (gimple *);
+void process_var (tree);
+void process_block (basic_block);
+void prepare_change (tree);
+void complete_change (gimple *);
+void optimize_builtin_call (gcall *, tree, const usage_info *);
+void replace_assign_rhs (gassign *, tree, tree, tree, tree);
+void optimize_assign (gassign *, tree, const usage_info *);
+void optimize_phi (gphi *, tree, const usage_info *);
+typedef hash_map <tree_ssa_name_hash, usage_info *> info_map_type;
+typedef std::pair <tree, usage_info *> var_info_pair;
+/* The function we're optimizing.  */
+function *m_fn;
+/* Pool for allocating usage_info structures.  */
+object_allocator <usage_info> m_info_pool;
+/* Maps an SSA name to a description of all uses of that SSA name.
+All the usage_infos satisfy is_useful.
+We use a hash_map because the map is expected to be sparse
+(i.e. most SSA names won't have useful information attached to them).
+We could move to a directly-indexed array if that situation changes.  */
+info_map_type m_info_map;
+/* Post-ordered list of all potentially-interesting SSA names,
+along with information that describes all uses.  */
+auto_vec <var_info_pair, 128> m_vars;
+/* A bitmap of blocks that we have finished processing in the initial
+post-order walk.  */
+auto_sbitmap m_visited_blocks;
+/* A worklist of SSA names whose definitions need to be reconsidered.  */
+auto_vec <tree, 64> m_worklist;
+/* The SSA names in M_WORKLIST, identified by their SSA_NAME_VERSION.
+We use a bitmap rather than an sbitmap because most SSA names are
+never added to the worklist.  */
+bitmap m_worklist_names;
+};
+backprop::backprop (function *fn)
+: m_fn (fn),
+m_info_pool ("usage_info"),
+m_visited_blocks (last_basic_block_for_fn (m_fn)),
+m_worklist_names (BITMAP_ALLOC (NULL))
+{
+bitmap_clear (m_visited_blocks);
+}
+backprop::~backprop ()
+{
+BITMAP_FREE (m_worklist_names);
+m_info_pool.release ();
+}
+/* Return usage information for general operand OP, or null if none.  */
+const usage_info *
+backprop::lookup_operand (tree op)
+{
+if (op && TREE_CODE (op) == SSA_NAME)
+{
+usage_info **slot = m_info_map.get (op);
+if (slot)
+	return *slot;
+}
+return NULL;
+}
+/* Add SSA name VAR to the worklist, if it isn't on the worklist already.  */
+void
+backprop::push_to_worklist (tree var)
+{
+if (!bitmap_set_bit (m_worklist_names, SSA_NAME_VERSION (var)))
+return;
+m_worklist.safe_push (var);
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "[WORKLIST] Pushing ");
+print_generic_expr (dump_file, var);
+fprintf (dump_file, "\n");
+}
+}
+/* Remove and return the next SSA name from the worklist.  The worklist
+is known to be nonempty.  */
+tree
+backprop::pop_from_worklist ()
+{
+tree var = m_worklist.pop ();
+bitmap_clear_bit (m_worklist_names, SSA_NAME_VERSION (var));
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "[WORKLIST] Popping ");
+print_generic_expr (dump_file, var);
+fprintf (dump_file, "\n");
+}
+return var;
+}
+/* Make INFO describe all uses of RHS in CALL, which is a call to a
+built-in function.  */
+void
+backprop::process_builtin_call_use (gcall *call, tree rhs, usage_info *info)
+{
+combined_fn fn = gimple_call_combined_fn (call);
+tree lhs = gimple_call_lhs (call);
+switch (fn)
+{
+case CFN_LAST:
+break;
+CASE_CFN_COS:
+CASE_CFN_COSH:
+CASE_CFN_CCOS:
+CASE_CFN_CCOSH:
+CASE_CFN_HYPOT:
+/* The signs of all inputs are ignored.  */
+info->flags.ignore_sign = true;
+break;
+CASE_CFN_COPYSIGN:
+/* The sign of the first input is ignored.  */
+if (rhs != gimple_call_arg (call, 1))
+	info->flags.ignore_sign = true;
+break;
+CASE_CFN_POW:
+{
+	/* The sign of the first input is ignored as long as the second
+	   input is an even real.  */
+	tree power = gimple_call_arg (call, 1);
+	HOST_WIDE_INT n;
+	if (TREE_CODE (power) == REAL_CST
+	    && real_isinteger (&TREE_REAL_CST (power), &n)
+	    && (n & 1) == 0)
+	  info->flags.ignore_sign = true;
+	break;
+}
+CASE_CFN_FMA:
+/* In X * X + Y, where Y is distinct from X, the sign of X doesn't
+	 matter.  */
+if (gimple_call_arg (call, 0) == rhs
+	  && gimple_call_arg (call, 1) == rhs
+	  && gimple_call_arg (call, 2) != rhs)
+	info->flags.ignore_sign = true;
+break;
+default:
+if (negate_mathfn_p (fn))
+	{
+	  /* The sign of the (single) input doesn't matter provided
+	     that the sign of the output doesn't matter.  */
+	  const usage_info *lhs_info = lookup_operand (lhs);
+	  if (lhs_info)
+	    info->flags.ignore_sign = lhs_info->flags.ignore_sign;
+	}
+break;
+}
+}
+/* Make INFO describe all uses of RHS in ASSIGN.  */
+void
+backprop::process_assign_use (gassign *assign, tree rhs, usage_info *info)
+{
+tree lhs = gimple_assign_lhs (assign);
+switch (gimple_assign_rhs_code (assign))
+{
+case ABS_EXPR:
+/* The sign of the input doesn't matter.  */
+info->flags.ignore_sign = true;
+break;
+case COND_EXPR:
+/* For A = B ? C : D, propagate information about all uses of A
+	 to C and D.  */
+if (rhs != gimple_assign_rhs1 (assign))
+	{
+	  const usage_info *lhs_info = lookup_operand (lhs);
+	  if (lhs_info)
+	    *info = *lhs_info;
+	}
+break;
+case FMA_EXPR:
+/* In X * X + Y, where Y is distinct from X, the sign of X doesn't
+	 matter.  */
+if (gimple_assign_rhs1 (assign) == rhs
+	  && gimple_assign_rhs2 (assign) == rhs
+	  && gimple_assign_rhs3 (assign) != rhs)
+	info->flags.ignore_sign = true;
+break;
+case MULT_EXPR:
+/* In X * X, the sign of X doesn't matter.  */
+if (gimple_assign_rhs1 (assign) == rhs
+	  && gimple_assign_rhs2 (assign) == rhs)
+	info->flags.ignore_sign = true;
+/* Fall through.  */
+case NEGATE_EXPR:
+case RDIV_EXPR:
+/* If the sign of the result doesn't matter, the sign of the inputs
+	 doesn't matter either.  */
+if (FLOAT_TYPE_P (TREE_TYPE (rhs)))
+	{
+	  const usage_info *lhs_info = lookup_operand (lhs);
+	  if (lhs_info)
+	    info->flags.ignore_sign = lhs_info->flags.ignore_sign;
+	}
+break;
+default:
+break;
+}
+}
+/* Make INFO describe the uses of PHI's result.  */
+void
+backprop::process_phi_use (gphi *phi, usage_info *info)
+{
+tree result = gimple_phi_result (phi);
+if (const usage_info *result_info = lookup_operand (result))
+*info = *result_info;
+}
+/* Make INFO describe all uses of RHS in STMT.  */
+void
+backprop::process_use (gimple *stmt, tree rhs, usage_info *info)
+{
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "[USE] ");
+print_generic_expr (dump_file, rhs);
+fprintf (dump_file, " in ");
+print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+}
+if (gcall *call = dyn_cast <gcall *> (stmt))
+process_builtin_call_use (call, rhs, info);
+else if (gassign *assign = dyn_cast <gassign *> (stmt))
+process_assign_use (assign, rhs, info);
+else if (gphi *phi = dyn_cast <gphi *> (stmt))
+process_phi_use (phi, info);
+if (dump_file && (dump_flags & TDF_DETAILS))
+dump_usage_info (dump_file, rhs, info);
+}
+/* Make INFO describe all uses of VAR, returning true if the result
+is useful.  If the uses include phis that haven't been processed yet,
+make the most optimistic assumption possible, so that we aim for
+a maximum rather than a minimum fixed point.  */
+bool
+backprop::intersect_uses (tree var, usage_info *info)
+{
+imm_use_iterator iter;
+gimple *stmt;
+*info = usage_info::intersection_identity ();
+FOR_EACH_IMM_USE_STMT (stmt, iter, var)
+{
+if (is_gimple_debug (stmt))
+	continue;
+if (is_a <gphi *> (stmt)
+	  && !bitmap_bit_p (m_visited_blocks, gimple_bb (stmt)->index))
+	{
+	  /* Skip unprocessed phis.  */
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "[BACKEDGE] ");
+	      print_generic_expr (dump_file, var);
+	      fprintf (dump_file, " in ");
+	      print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+	    }
+	}
+else
+	{
+	  usage_info subinfo;
+	  process_use (stmt, var, &subinfo);
+	  *info &= subinfo;
+	  if (!info->is_useful ())
+	    {
+	      BREAK_FROM_IMM_USE_STMT (iter);
+	      return false;
+	    }
+	}
+}
+return true;
+}
+/* Queue for reconsideration any input of STMT that has information
+associated with it.  This is used if that information might be
+too optimistic.  */
+void
+backprop::reprocess_inputs (gimple *stmt)
+{
+use_operand_p use_p;
+ssa_op_iter oi;
+FOR_EACH_PHI_OR_STMT_USE (use_p, stmt, oi, SSA_OP_USE)
+{
+tree var = get_use_from_ptr (use_p);
+if (lookup_operand (var))
+	push_to_worklist (var);
+}
+}
+/* Say that we're recording INFO for SSA name VAR, or that we're deleting
+existing information if INFO is null.  INTRO describes the change.  */
+static void
+dump_var_info (tree var, usage_info *info, const char *intro)
+{
+fprintf (dump_file, "[DEF] %s for ", intro);
+print_gimple_stmt (dump_file, SSA_NAME_DEF_STMT (var), 0, TDF_SLIM);
+if (info)
+dump_usage_info (dump_file, var, info);
+}
+/* Process all uses of VAR and record or update the result in
+M_INFO_MAP and M_VARS.  */
+void
+backprop::process_var (tree var)
+{
+if (has_zero_uses (var))
+return;
+usage_info info;
+intersect_uses (var, &info);
+gimple *stmt = SSA_NAME_DEF_STMT (var);
+if (info.is_useful ())
+{
+bool existed;
+usage_info *&map_info = m_info_map.get_or_insert (var, &existed);
+if (!existed)
+	{
+	  /* Recording information about VAR for the first time.  */
+	  map_info = m_info_pool.allocate ();
+	  *map_info = info;
+	  m_vars.safe_push (var_info_pair (var, map_info));
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    dump_var_info (var, map_info, "Recording new information");
+	  /* If STMT is a phi, reprocess any backedge uses.  This is a
+	     no-op for other uses, which won't have any information
+	     associated with them.  */
+	  if (is_a <gphi *> (stmt))
+	    reprocess_inputs (stmt);
+	}
+else if (info != *map_info)
+	{
+	  /* Recording information that is less optimistic than before.  */
+	  gcc_checking_assert ((info & *map_info) == info);
+	  *map_info = info;
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    dump_var_info (var, map_info, "Updating information");
+	  reprocess_inputs (stmt);
+	}
+}
+else
+{
+if (usage_info **slot = m_info_map.get (var))
+	{
+	  /* Removing previously-recorded information.  */
+	  **slot = info;
+	  m_info_map.remove (var);
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    dump_var_info (var, NULL, "Deleting information");
+	  reprocess_inputs (stmt);
+	}
+else
+	{
+	  /* If STMT is a phi, remove any information recorded for
+	     its arguments.  */
+	  if (is_a <gphi *> (stmt))
+	    reprocess_inputs (stmt);
+	}
+}
+}
+/* Process all statements and phis in BB, during the first post-order walk.  */
+void
+backprop::process_block (basic_block bb)
+{
+for (gimple_stmt_iterator gsi = gsi_last_bb (bb); !gsi_end_p (gsi);
+gsi_prev (&gsi))
+{
+tree lhs = gimple_get_lhs (gsi_stmt (gsi));
+if (lhs && TREE_CODE (lhs) == SSA_NAME)
+	process_var (lhs);
+}
+for (gphi_iterator gpi = gsi_start_phis (bb); !gsi_end_p (gpi);
+gsi_next (&gpi))
+process_var (gimple_phi_result (gpi.phi ()));
+}
+/* Delete the definition of VAR, which has no uses.  */
+static void
+remove_unused_var (tree var)
+{
+gimple *stmt = SSA_NAME_DEF_STMT (var);
+if (dump_file && (dump_flags & TDF_DETAILS))
+{
+fprintf (dump_file, "Deleting ");
+print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+}
+gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+gsi_remove (&gsi, true);
+release_defs (stmt);
+}
+/* Note that we're replacing OLD_RHS with NEW_RHS in STMT.  */
+static void
+note_replacement (gimple *stmt, tree old_rhs, tree new_rhs)
+{
+fprintf (dump_file, "Replacing use of ");
+print_generic_expr (dump_file, old_rhs);
+fprintf (dump_file, " with ");
+print_generic_expr (dump_file, new_rhs);
+fprintf (dump_file, " in ");
+print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM);
+}
+/* If RHS is an SSA name whose definition just changes the sign of a value,
+return that other value, otherwise return null.  */
+static tree
+strip_sign_op_1 (tree rhs)
+{
+if (TREE_CODE (rhs) != SSA_NAME)
+return NULL_TREE;
+gimple *def_stmt = SSA_NAME_DEF_STMT (rhs);
+if (gassign *assign = dyn_cast <gassign *> (def_stmt))
+switch (gimple_assign_rhs_code (assign))
+{
+case ABS_EXPR:
+case NEGATE_EXPR:
+	return gimple_assign_rhs1 (assign);
+default:
+	break;
+}
+else if (gcall *call = dyn_cast <gcall *> (def_stmt))
+switch (gimple_call_combined_fn (call))
+{
+CASE_CFN_COPYSIGN:
+	return gimple_call_arg (call, 0);
+default:
+	break;
+}
+return NULL_TREE;
+}
+/* If RHS is an SSA name whose definition just changes the sign of a value,
+strip all such operations and return the ultimate input to them.
+Return null otherwise.
+Although this could in principle lead to quadratic searching,
+in practice a long sequence of sign manipulations should already
+have been folded down.  E.g. --x -> x, abs(-x) -> abs(x).  We search
+for more than one operation in order to catch cases like -abs(x).  */
+static tree
+strip_sign_op (tree rhs)
+{
+tree new_rhs = strip_sign_op_1 (rhs);
+if (!new_rhs)
+return NULL_TREE;
+while (tree next = strip_sign_op_1 (new_rhs))
+new_rhs = next;
+return new_rhs;
+}
+/* Start a change in the value of VAR that is suitable for all non-debug
+uses of VAR.  We need to make sure that debug statements continue to
+use the original definition of VAR where possible, or are nullified
+otherwise.  */
+void
+backprop::prepare_change (tree var)
+{
+if (MAY_HAVE_DEBUG_STMTS)
+insert_debug_temp_for_var_def (NULL, var);
+reset_flow_sensitive_info (var);
+}
+/* STMT has been changed.  Give the fold machinery a chance to simplify
+and canonicalize it (e.g. by ensuring that commutative operands have
+the right order), then record the updates.  */
+void
+backprop::complete_change (gimple *stmt)
+{
+gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+if (fold_stmt (&gsi))
+{
+if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "  which folds to: ");
+	  print_gimple_stmt (dump_file, gsi_stmt (gsi), 0, TDF_SLIM);
+	}
+}
+update_stmt (gsi_stmt (gsi));
+}
+/* Optimize CALL, a call to a built-in function with lhs LHS, on the
+basis that INFO describes all uses of LHS.  */
+void
+backprop::optimize_builtin_call (gcall *call, tree lhs, const usage_info *info)
+{
+/* If we have an f such that -f(x) = f(-x), and if the sign of the result
+doesn't matter, strip any sign operations from the input.  */
+if (info->flags.ignore_sign
+&& negate_mathfn_p (gimple_call_combined_fn (call)))
+{
+tree new_arg = strip_sign_op (gimple_call_arg (call, 0));
+if (new_arg)
+	{
+	  prepare_change (lhs);
+	  gimple_call_set_arg (call, 0, new_arg);
+	  complete_change (call);
+	}
+}
+}
+/* Optimize ASSIGN, an assignment to LHS, by replacing rhs operand N
+with RHS<N>, if RHS<N> is nonnull.  This may change the value of LHS.  */
+void
+backprop::replace_assign_rhs (gassign *assign, tree lhs, tree rhs1,
+			      tree rhs2, tree rhs3)
+{
+if (!rhs1 && !rhs2 && !rhs3)
+return;
+prepare_change (lhs);
+if (rhs1)
+gimple_assign_set_rhs1 (assign, rhs1);
+if (rhs2)
+gimple_assign_set_rhs2 (assign, rhs2);
+if (rhs3)
+gimple_assign_set_rhs3 (assign, rhs3);
+complete_change (assign);
+}
+/* Optimize ASSIGN, an assignment to LHS, on the basis that INFO
+describes all uses of LHS.  */
+void
+backprop::optimize_assign (gassign *assign, tree lhs, const usage_info *info)
+{
+switch (gimple_assign_rhs_code (assign))
+{
+case MULT_EXPR:
+case RDIV_EXPR:
+/* If the sign of the result doesn't matter, strip sign operations
+	 from both inputs.  */
+if (info->flags.ignore_sign)
+	replace_assign_rhs (assign, lhs,
+			    strip_sign_op (gimple_assign_rhs1 (assign)),
+			    strip_sign_op (gimple_assign_rhs2 (assign)),
+			    NULL_TREE);
+break;
+case COND_EXPR:
+/* If the sign of A ? B : C doesn't matter, strip sign operations
+	 from both B and C.  */
+if (info->flags.ignore_sign)
+	replace_assign_rhs (assign, lhs,
+			    NULL_TREE,
+			    strip_sign_op (gimple_assign_rhs2 (assign)),
+			    strip_sign_op (gimple_assign_rhs3 (assign)));
+break;
+default:
+break;
+}
+}
+/* Optimize PHI, which defines VAR, on the basis that INFO describes all
+uses of the result.  */
+void
+backprop::optimize_phi (gphi *phi, tree var, const usage_info *info)
+{
+/* If the sign of the result doesn't matter, try to strip sign operations
+from arguments.  */
+if (info->flags.ignore_sign)
+{
+basic_block bb = gimple_bb (phi);
+use_operand_p use;
+ssa_op_iter oi;
+bool replaced = false;
+FOR_EACH_PHI_ARG (use, phi, oi, SSA_OP_USE)
+	{
+	  /* Propagating along abnormal edges is delicate, punt for now.  */
+	  const int index = PHI_ARG_INDEX_FROM_USE (use);
+	  if (EDGE_PRED (bb, index)->flags & EDGE_ABNORMAL)
+	    continue;
+	  tree new_arg = strip_sign_op (USE_FROM_PTR (use));
+	  if (new_arg)
+	    {
+	      if (!replaced)
+		prepare_change (var);
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		note_replacement (phi, USE_FROM_PTR (use), new_arg);
+	      replace_exp (use, new_arg);
+	      replaced = true;
+	    }
+	}
+}
+}
+void
+backprop::execute ()
+{
+/* Phase 1: Traverse the function, making optimistic assumptions
+about any phi whose definition we haven't seen.  */
+int *postorder = XNEWVEC (int, n_basic_blocks_for_fn (m_fn));
+unsigned int postorder_num = post_order_compute (postorder, false, false);
+for (unsigned int i = 0; i < postorder_num; ++i)
+{
+process_block (BASIC_BLOCK_FOR_FN (m_fn, postorder[i]));
+bitmap_set_bit (m_visited_blocks, postorder[i]);
+}
+XDELETEVEC (postorder);
+/* Phase 2: Use the initial (perhaps overly optimistic) information
+to create a maximal fixed point solution.  */
+while (!m_worklist.is_empty ())
+process_var (pop_from_worklist ());
+if (dump_file && (dump_flags & TDF_DETAILS))
+fprintf (dump_file, "\n");
+/* Phase 3: Do a reverse post-order walk, using information about
+the uses of SSA names to optimize their definitions.  */
+for (unsigned int i = m_vars.length (); i-- > 0;)
+{
+usage_info *info = m_vars[i].second;
+if (info->is_useful ())
+	{
+	  tree var = m_vars[i].first;
+	  gimple *stmt = SSA_NAME_DEF_STMT (var);
+	  if (gcall *call = dyn_cast <gcall *> (stmt))
+	    optimize_builtin_call (call, var, info);
+	  else if (gassign *assign = dyn_cast <gassign *> (stmt))
+	    optimize_assign (assign, var, info);
+	  else if (gphi *phi = dyn_cast <gphi *> (stmt))
+	    optimize_phi (phi, var, info);
+	}
+}
+/* Phase 4: Do a post-order walk, deleting statements that are no
+longer needed.  */
+for (unsigned int i = 0; i < m_vars.length (); ++i)
+{
+tree var = m_vars[i].first;
+if (has_zero_uses (var))
+	remove_unused_var (var);
+}
+if (dump_file && (dump_flags & TDF_DETAILS))
+fprintf (dump_file, "\n");
+}
+const pass_data pass_data_backprop =
+{
+GIMPLE_PASS, /* type */
+"backprop", /* name */
+OPTGROUP_NONE, /* optinfo_flags */
+TV_TREE_BACKPROP, /* tv_id */
+( PROP_cfg | PROP_ssa ), /* properties_required */
+0, /* properties_provided */
+0, /* properties_destroyed */
+0, /* todo_flags_start */
+0, /* todo_flags_finish */
+};
+class pass_backprop : public gimple_opt_pass
+{
+public:
+pass_backprop (gcc::context *ctxt)
+: gimple_opt_pass (pass_data_backprop, ctxt)
+{}
+/* opt_pass methods: */
+opt_pass * clone () { return new pass_backprop (m_ctxt); }
+virtual bool gate (function *) { return flag_ssa_backprop; }
+virtual unsigned int execute (function *);
+}; // class pass_backprop
+unsigned int
+pass_backprop::execute (function *fn)
+{
+backprop (fn).execute ();
+return 0;
+}
+} // anon namespace
+gimple_opt_pass *
+make_pass_backprop (gcc::context *ctxt)
+{
+return new pass_backprop (ctxt);
+}

Mercurial > hg > CbC > CbC_gcc

comparison gcc/gimple-ssa-backprop.c @ 111:04ced10e8804