CbC/CbC_gcc: gcc/tree-ssa-loop-split.c comparison

comparison gcc/tree-ssa-loop-split.c @ 145:1830386684a0

gcc-9.2.0

author	anatofuz
date	Thu, 13 Feb 2020 11:34:05 +0900
parents	84e7813d76e9
children

comparison

equal deleted inserted replaced

-:84e7813d76e9
+:1830386684a0
 /* Loop splitting.
-Copyright (C) 2015-2018 Free Software Foundation, Inc.
+Copyright (C) 2015-2020 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
 #include "tree-ssa.h"
 #include "tree-ssa-loop-niter.h"
 #include "tree-ssa-loop.h"
 #include "tree-ssa-loop-manip.h"
 #include "tree-into-ssa.h"
+#include "tree-inline.h"
+#include "tree-cfgcleanup.h"
 #include "cfgloop.h"
 #include "tree-scalar-evolution.h"
 #include "gimple-iterator.h"
 #include "gimple-pretty-print.h"
 #include "cfghooks.h"
 #include "gimple-fold.h"
 #include "gimplify-me.h"
-/* This file implements loop splitting, i.e. transformation of loops like
+/* This file implements two kinds of loop splitting.
+One transformation of loops like:
 for (i = 0; i < 100; i++)
 {
 if (i < 50)
 A;
 is true on one side of the iteration space and false on the other,
 and the split point can be computed.  If so, also return the border
 point in *BORDER and the comparison induction variable in IV.  */
 static tree
-split_at_bb_p (struct loop *loop, basic_block bb, tree *border, affine_iv *iv)
+split_at_bb_p (class loop *loop, basic_block bb, tree *border, affine_iv *iv)
 {
 gimple *last;
 gcond *stmt;
 affine_iv iv2;
 if (loop_exits_from_bb_p (loop, bb))
 return NULL_TREE;
 tree op0 = gimple_cond_lhs (stmt);
 tree op1 = gimple_cond_rhs (stmt);
-struct loop *useloop = loop_containing_stmt (stmt);
+class loop *useloop = loop_containing_stmt (stmt);
 if (!simple_iv (loop, useloop, op0, iv, false))
 return NULL_TREE;
 if (!simple_iv (loop, useloop, op1, &iv2, false))
 return NULL_TREE;
 (a post-increment IV) and NEWBOUND (the comparator) adjust the loop
 exit test statement to loop back only if the GUARD statement will
 also be true/false in the next iteration.  */
 static void
-patch_loop_exit (struct loop *loop, gcond *guard, tree nextval, tree newbound,
+patch_loop_exit (class loop *loop, gcond *guard, tree nextval, tree newbound,
 		 bool initial_true)
 {
 edge exit = single_exit (loop);
 gcond *stmt = as_a <gcond *> (last_stmt (exit->src));
 gimple_cond_set_condition (stmt, gimple_cond_code (guard),
 /* Give an induction variable GUARD_IV, and its affine descriptor IV,
 find the loop phi node in LOOP defining it directly, or create
 such phi node.  Return that phi node.  */
 static gphi *
-find_or_create_guard_phi (struct loop *loop, tree guard_iv, affine_iv * /*iv*/)
+find_or_create_guard_phi (class loop *loop, tree guard_iv, affine_iv * /*iv*/)
 {
 gimple *def = SSA_NAME_DEF_STMT (guard_iv);
 gphi *phi;
 if ((phi = dyn_cast <gphi *> (def))
 && gimple_bb (phi) == loop->header)
 /* Returns true if the exit values of all loop phi nodes can be
 determined easily (i.e. that connect_loop_phis can determine them).  */
 static bool
-easy_exit_values (struct loop *loop)
+easy_exit_values (class loop *loop)
 {
 edge exit = single_exit (loop);
 edge latch = loop_latch_edge (loop);
 gphi_iterator psi;
 phi nodes are either the original ones or those at the exit
 of LOOP1.  Insert new phi nodes in LOOP2 pre-header reflecting
 this.  The loops need to fulfill easy_exit_values().  */
 static void
-connect_loop_phis (struct loop *loop1, struct loop *loop2, edge new_e)
+connect_loop_phis (class loop *loop1, class loop *loop2, edge new_e)
 {
 basic_block rest = loop_preheader_edge (loop2)->src;
 gcc_assert (new_e->dest == rest);
 edge skip_first = EDGE_PRED (rest, EDGE_PRED (rest, 0) == new_e);
 The function returns the new edge cond->pre2.
 This doesn't update the SSA form, see connect_loop_phis for that.  */
 static edge
-connect_loops (struct loop *loop1, struct loop *loop2)
+connect_loops (class loop *loop1, class loop *loop2)
 {
 edge exit = single_exit (loop1);
 basic_block skip_bb = split_edge (exit);
 gcond *skip_stmt;
 gimple_stmt_iterator gsi;
 Depending on the direction of the IVs and if the exit tests
 are strict or non-strict we need to use MIN or MAX,
 and add or subtract 1.  This routine computes newend above.  */
 static tree
-compute_new_first_bound (gimple_seq *stmts, struct tree_niter_desc *niter,
+compute_new_first_bound (gimple_seq *stmts, class tree_niter_desc *niter,
 			 tree border,
 			 enum tree_code guard_code, tree guard_init)
 {
 /* The niter structure contains the after-increment IV, we need
 the loop-enter base, so subtract STEP once.  */
 splits the iteration space into two loops.  Returns true if the
 loop was split.  NITER must contain the iteration descriptor for the
 single exit of LOOP.  */
 static bool
-split_loop (struct loop *loop1, struct tree_niter_desc *niter)
+split_loop (class loop *loop1)
 {
+class tree_niter_desc niter;
 basic_block *bbs;
 unsigned i;
 bool changed = false;
 tree guard_iv;
 tree border = NULL_TREE;
 affine_iv iv;
+if (!single_exit (loop1)
+/* ??? We could handle non-empty latches when we split the latch edge
+	 (not the exit edge), and put the new exit condition in the new block.
+	 OTOH this executes some code unconditionally that might have been
+	 skipped by the original exit before.  */
+|| !empty_block_p (loop1->latch)
+|| !easy_exit_values (loop1)
+|| !number_of_iterations_exit (loop1, single_exit (loop1), &niter,
+				     false, true)
+|| niter.cmp == ERROR_MARK
+/* We can't yet handle loops controlled by a != predicate.  */
+|| niter.cmp == NE_EXPR)
+return false;
 bbs = get_loop_body (loop1);
+if (!can_copy_bbs_p (bbs, loop1->num_nodes))
+{
+free (bbs);
+return false;
+}
 /* Find a splitting opportunity.  */
 for (i = 0; i < loop1->num_nodes; i++)
 if ((guard_iv = split_at_bb_p (loop1, bbs[i], &border, &iv)))
 {
 	/* Handling opposite steps is not implemented yet.  Neither
 	   is handling different step sizes.  */
 	if ((tree_int_cst_sign_bit (iv.step)
-	     != tree_int_cst_sign_bit (niter->control.step))
+	     != tree_int_cst_sign_bit (niter.control.step))
-	    || !tree_int_cst_equal (iv.step, niter->control.step))
+	    || !tree_int_cst_equal (iv.step, niter.control.step))
 	  continue;
 	/* Find a loop PHI node that defines guard_iv directly,
 	   or create one doing that.  */
 	gphi *phi = find_or_create_guard_phi (loop1, guard_iv, &iv);
 	/* Now version the loop, placing loop2 after loop1 connecting
 	   them, and fix up SSA form for that.  */
 	initialize_original_copy_tables ();
 	basic_block cond_bb;
-	struct loop *loop2 = loop_version (loop1, cond, &cond_bb,
+	class loop *loop2 = loop_version (loop1, cond, &cond_bb,
 					   profile_probability::always (),
 					   profile_probability::always (),
 					   profile_probability::always (),
 					   profile_probability::always (),
 					   true);
 	   exactly those that the first loop didn't do, but the
 	   iteration space of the first loop is still the original one.
 	   Compute the new bound for the guarding IV and patch the
 	   loop exit to use it instead of original IV and bound.  */
 	gimple_seq stmts = NULL;
-	tree newend = compute_new_first_bound (&stmts, niter, border,
+	tree newend = compute_new_first_bound (&stmts, &niter, border,
 					       guard_code, guard_init);
 	if (stmts)
 	  gsi_insert_seq_on_edge_immediate (loop_preheader_edge (loop1),
 					    stmts);
 	tree guard_next = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop1));
 free (bbs);
 return changed;
 }
+/* Another transformation of loops like:
+for (i = INIT (); CHECK (i); i = NEXT ())
+{
+if (expr (a_1, a_2, ..., a_n))  // expr is pure
+a_j = ...;  // change at least one a_j
+else
+S;          // not change any a_j
+}
+into:
+for (i = INIT (); CHECK (i); i = NEXT ())
+{
+if (expr (a_1, a_2, ..., a_n))
+a_j = ...;
+else
+{
+S;
+i = NEXT ();
+break;
+}
+}
+for (; CHECK (i); i = NEXT ())
+{
+S;
+}
+*/
+/* Data structure to hold temporary information during loop split upon
+semi-invariant conditional statement.  */
+class split_info {
+public:
+/* Array of all basic blocks in a loop, returned by get_loop_body().  */
+basic_block *bbs;
+/* All memory store/clobber statements in a loop.  */
+auto_vec<gimple *> memory_stores;
+/* Whether above memory stores vector has been filled.  */
+int need_init;
+/* Control dependencies of basic blocks in a loop.  */
+auto_vec<hash_set<basic_block> *> control_deps;
+split_info () : bbs (NULL),  need_init (true) { }
+~split_info ()
+{
+if (bbs)
+	free (bbs);
+for (unsigned i = 0; i < control_deps.length (); i++)
+	delete control_deps[i];
+}
+};
+/* Find all statements with memory-write effect in LOOP, including memory
+store and non-pure function call, and keep those in a vector.  This work
+is only done one time, for the vector should be constant during analysis
+stage of semi-invariant condition.  */
+static void
+find_vdef_in_loop (struct loop *loop)
+{
+split_info *info = (split_info *) loop->aux;
+gphi *vphi = get_virtual_phi (loop->header);
+/* Indicate memory store vector has been filled.  */
+info->need_init = false;
+/* If loop contains memory operation, there must be a virtual PHI node in
+loop header basic block.  */
+if (vphi == NULL)
+return;
+/* All virtual SSA names inside the loop are connected to be a cyclic
+graph via virtual PHI nodes.  The virtual PHI node in loop header just
+links the first and the last virtual SSA names, by using the last as
+PHI operand to define the first.  */
+const edge latch = loop_latch_edge (loop);
+const tree first = gimple_phi_result (vphi);
+const tree last = PHI_ARG_DEF_FROM_EDGE (vphi, latch);
+/* The virtual SSA cyclic graph might consist of only one SSA name, who
+is defined by itself.
+.MEM_1 = PHI <.MEM_2(loop entry edge), .MEM_1(latch edge)>
+This means the loop contains only memory loads, so we can skip it.  */
+if (first == last)
+return;
+auto_vec<gimple *> other_stores;
+auto_vec<tree> worklist;
+auto_bitmap visited;
+bitmap_set_bit (visited, SSA_NAME_VERSION (first));
+bitmap_set_bit (visited, SSA_NAME_VERSION (last));
+worklist.safe_push (last);
+do
+{
+tree vuse = worklist.pop ();
+gimple *stmt = SSA_NAME_DEF_STMT (vuse);
+/* We mark the first and last SSA names as visited at the beginning,
+	 and reversely start the process from the last SSA name towards the
+	 first, which ensures that this do-while will not touch SSA names
+	 defined outside the loop.  */
+gcc_assert (gimple_bb (stmt)
+		  && flow_bb_inside_loop_p (loop, gimple_bb (stmt)));
+if (gimple_code (stmt) == GIMPLE_PHI)
+	{
+	  gphi *phi = as_a <gphi *> (stmt);
+	  for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+	    {
+	      tree arg = gimple_phi_arg_def (stmt, i);
+	      if (bitmap_set_bit (visited, SSA_NAME_VERSION (arg)))
+		worklist.safe_push (arg);
+	    }
+	}
+else
+	{
+	  tree prev = gimple_vuse (stmt);
+	  /* Non-pure call statement is conservatively assumed to impact all
+	     memory locations.  So place call statements ahead of other memory
+	     stores in the vector with an idea of of using them as shortcut
+	     terminators to memory alias analysis.  */
+	  if (gimple_code (stmt) == GIMPLE_CALL)
+	    info->memory_stores.safe_push (stmt);
+	  else
+	    other_stores.safe_push (stmt);
+	  if (bitmap_set_bit (visited, SSA_NAME_VERSION (prev)))
+	    worklist.safe_push (prev);
+	}
+} while (!worklist.is_empty ());
+info->memory_stores.safe_splice (other_stores);
+}
+/* Two basic blocks have equivalent control dependency if one dominates to
+the other, and it is post-dominated by the latter.  Given a basic block
+BB in LOOP, find farest equivalent dominating basic block.  For BB, there
+is a constraint that BB does not post-dominate loop header of LOOP, this
+means BB is control-dependent on at least one basic block in LOOP.  */
+static basic_block
+get_control_equiv_head_block (struct loop *loop, basic_block bb)
+{
+while (!bb->aux)
+{
+basic_block dom_bb = get_immediate_dominator (CDI_DOMINATORS, bb);
+gcc_checking_assert (dom_bb && flow_bb_inside_loop_p (loop, dom_bb));
+if (!dominated_by_p (CDI_POST_DOMINATORS, dom_bb, bb))
+	break;
+bb = dom_bb;
+}
+return bb;
+}
+/* Given a BB in LOOP, find out all basic blocks in LOOP that BB is control-
+dependent on.  */
+static hash_set<basic_block> *
+find_control_dep_blocks (struct loop *loop, basic_block bb)
+{
+/* BB has same control dependency as loop header, then it is not control-
+dependent on any basic block in LOOP.  */
+if (dominated_by_p (CDI_POST_DOMINATORS, loop->header, bb))
+return NULL;
+basic_block equiv_head = get_control_equiv_head_block (loop, bb);
+if (equiv_head->aux)
+{
+/* There is a basic block containing control dependency equivalent
+	 to BB.  No need to recompute that, and also set this information
+	 to other equivalent basic blocks.  */
+for (; bb != equiv_head;
+	   bb = get_immediate_dominator (CDI_DOMINATORS, bb))
+	bb->aux = equiv_head->aux;
+return (hash_set<basic_block> *) equiv_head->aux;
+}
+/* A basic block X is control-dependent on another Y iff there exists
+a path from X to Y, in which every basic block other than X and Y
+is post-dominated by Y, but X is not post-dominated by Y.
+According to this rule, traverse basic blocks in the loop backwards
+starting from BB, if a basic block is post-dominated by BB, extend
+current post-dominating path to this block, otherwise it is another
+one that BB is control-dependent on.  */
+auto_vec<basic_block> pdom_worklist;
+hash_set<basic_block> pdom_visited;
+hash_set<basic_block> *dep_bbs = new hash_set<basic_block>;
+pdom_worklist.safe_push (equiv_head);
+do
+{
+basic_block pdom_bb = pdom_worklist.pop ();
+edge_iterator ei;
+edge e;
+if (pdom_visited.add (pdom_bb))
+	continue;
+FOR_EACH_EDGE (e, ei, pdom_bb->preds)
+	{
+	  basic_block pred_bb = e->src;
+	  if (!dominated_by_p (CDI_POST_DOMINATORS, pred_bb, bb))
+	    {
+	      dep_bbs->add (pred_bb);
+	      continue;
+	    }
+	  pred_bb = get_control_equiv_head_block (loop, pred_bb);
+	  if (pdom_visited.contains (pred_bb))
+	    continue;
+	  if (!pred_bb->aux)
+	    {
+	      pdom_worklist.safe_push (pred_bb);
+	      continue;
+	    }
+	  /* If control dependency of basic block is available, fast extend
+	     post-dominating path using the information instead of advancing
+	     forward step-by-step.  */
+	  hash_set<basic_block> *pred_dep_bbs
+			= (hash_set<basic_block> *) pred_bb->aux;
+	  for (hash_set<basic_block>::iterator iter = pred_dep_bbs->begin ();
+	       iter != pred_dep_bbs->end (); ++iter)
+	    {
+	      basic_block pred_dep_bb = *iter;
+	      /* Basic blocks can either be in control dependency of BB, or
+		 must be post-dominated by BB, if so, extend the path from
+		 these basic blocks.  */
+	      if (!dominated_by_p (CDI_POST_DOMINATORS, pred_dep_bb, bb))
+		dep_bbs->add (pred_dep_bb);
+	      else if (!pdom_visited.contains (pred_dep_bb))
+		pdom_worklist.safe_push (pred_dep_bb);
+	    }
+	}
+} while (!pdom_worklist.is_empty ());
+/* Record computed control dependencies in loop so that we can reach them
+when reclaiming resources.  */
+((split_info *) loop->aux)->control_deps.safe_push (dep_bbs);
+/* Associate control dependence with related equivalent basic blocks.  */
+for (equiv_head->aux = dep_bbs; bb != equiv_head;
+bb = get_immediate_dominator (CDI_DOMINATORS, bb))
+bb->aux = dep_bbs;
+return dep_bbs;
+}
+/* Forward declaration */
+static bool
+stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt,
+			 const_basic_block skip_head,
+			 hash_map<gimple *, bool> &stmt_stat);
+/* Given STMT, memory load or pure call statement, check whether it is impacted
+by some memory store in LOOP, excluding trace starting from SKIP_HEAD (the
+trace is composed of SKIP_HEAD and those basic block dominated by it, always
+corresponds to one branch of a conditional statement).  If SKIP_HEAD is
+NULL, all basic blocks of LOOP are checked.  */
+static bool
+vuse_semi_invariant_p (struct loop *loop, gimple *stmt,
+		       const_basic_block skip_head)
+{
+split_info *info = (split_info *) loop->aux;
+tree rhs = NULL_TREE;
+ao_ref ref;
+gimple *store;
+unsigned i;
+/* Collect memory store/clobber statements if haven't done that.  */
+if (info->need_init)
+find_vdef_in_loop (loop);
+if (is_gimple_assign (stmt))
+rhs = gimple_assign_rhs1 (stmt);
+ao_ref_init (&ref, rhs);
+FOR_EACH_VEC_ELT (info->memory_stores, i, store)
+{
+/* Skip basic blocks dominated by SKIP_HEAD, if non-NULL.  */
+if (skip_head
+	  && dominated_by_p (CDI_DOMINATORS, gimple_bb (store), skip_head))
+	continue;
+if (!ref.ref || stmt_may_clobber_ref_p_1 (store, &ref))
+	return false;
+}
+return true;
+}
+/* Suppose one condition branch, led by SKIP_HEAD, is not executed since
+certain iteration of LOOP, check whether an SSA name (NAME) remains
+unchanged in next iteration.  We call this characteristic semi-
+invariantness.  SKIP_HEAD might be NULL, if so, nothing excluded, all basic
+blocks and control flows in the loop will be considered.  Semi-invariant
+state of checked statement is cached in hash map STMT_STAT to avoid
+redundant computation in possible following re-check.  */
+static inline bool
+ssa_semi_invariant_p (struct loop *loop, tree name,
+		      const_basic_block skip_head,
+		      hash_map<gimple *, bool> &stmt_stat)
+{
+gimple *def = SSA_NAME_DEF_STMT (name);
+const_basic_block def_bb = gimple_bb (def);
+/* An SSA name defined outside loop is definitely semi-invariant.  */
+if (!def_bb || !flow_bb_inside_loop_p (loop, def_bb))
+return true;
+return stmt_semi_invariant_p_1 (loop, def, skip_head, stmt_stat);
+}
+/* Check whether a loop iteration PHI node (LOOP_PHI) defines a value that is
+semi-invariant in LOOP.  Basic blocks dominated by SKIP_HEAD (if non-NULL),
+are excluded from LOOP.  */
+static bool
+loop_iter_phi_semi_invariant_p (struct loop *loop, gphi *loop_phi,
+				const_basic_block skip_head)
+{
+const_edge latch = loop_latch_edge (loop);
+tree name = gimple_phi_result (loop_phi);
+tree from = PHI_ARG_DEF_FROM_EDGE (loop_phi, latch);
+gcc_checking_assert (from);
+/* Loop iteration PHI node locates in loop header, and it has two source
+operands, one is an initial value coming from outside the loop, the other
+is a value through latch of the loop, which is derived in last iteration,
+we call the latter latch value.  From the PHI node to definition of latch
+value, if excluding branch trace starting from SKIP_HEAD, except copy-
+assignment or likewise, there is no other kind of value redefinition, SSA
+name defined by the PHI node is semi-invariant.
+loop entry
+|     .--- latch ---.
+|     |             |
+v     v             |
+x_1 = PHI <x_0,  x_3>           |
+|                      |
+v                      |
+.------- if (cond) -------.         |
+|                         |         |
+|                     [ SKIP ]      |
+|                         |         |
+|                     x_2 = ...     |
+|                         |         |
+'---- T ---->.<---- F ----'         |
+|                      |
+v                      |
+x_3 = PHI <x_1, x_2>            |
+|                      |
+'----------------------'
+Suppose in certain iteration, execution flow in above graph goes through
+true branch, which means that one source value to define x_3 in false
+branch (x_2) is skipped, x_3 only comes from x_1, and x_1 in next
+iterations is defined by x_3, we know that x_1 will never changed if COND
+always chooses true branch from then on.  */
+while (from != name)
+{
+/* A new value comes from a CONSTANT.  */
+if (TREE_CODE (from) != SSA_NAME)
+	return false;
+gimple *stmt = SSA_NAME_DEF_STMT (from);
+const_basic_block bb = gimple_bb (stmt);
+/* A new value comes from outside the loop.  */
+if (!bb || !flow_bb_inside_loop_p (loop, bb))
+	return false;
+from = NULL_TREE;
+if (gimple_code (stmt) == GIMPLE_PHI)
+	{
+	  gphi *phi = as_a <gphi *> (stmt);
+	  for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+	    {
+	      if (skip_head)
+		{
+		  const_edge e = gimple_phi_arg_edge (phi, i);
+		  /* Don't consider redefinitions in excluded basic blocks.  */
+		  if (dominated_by_p (CDI_DOMINATORS, e->src, skip_head))
+		    continue;
+		}
+	      tree arg = gimple_phi_arg_def (phi, i);
+	      if (!from)
+		from = arg;
+	      else if (!operand_equal_p (from, arg, 0))
+		/* There are more than one source operands that provide
+		   different values to the SSA name, it is variant.  */
+		return false;
+	    }
+	}
+else if (gimple_code (stmt) == GIMPLE_ASSIGN)
+	{
+	  /* For simple value copy, check its rhs instead.  */
+	  if (gimple_assign_ssa_name_copy_p (stmt))
+	    from = gimple_assign_rhs1 (stmt);
+	}
+/* Any other kind of definition is deemed to introduce a new value
+	 to the SSA name.  */
+if (!from)
+	return false;
+}
+return true;
+}
+/* Check whether conditional predicates that BB is control-dependent on, are
+semi-invariant in LOOP.  Basic blocks dominated by SKIP_HEAD (if non-NULL),
+are excluded from LOOP.  Semi-invariant state of checked statement is cached
+in hash map STMT_STAT.  */
+static bool
+control_dep_semi_invariant_p (struct loop *loop, basic_block bb,
+			      const_basic_block skip_head,
+			      hash_map<gimple *, bool> &stmt_stat)
+{
+hash_set<basic_block> *dep_bbs = find_control_dep_blocks (loop, bb);
+if (!dep_bbs)
+return true;
+for (hash_set<basic_block>::iterator iter = dep_bbs->begin ();
+iter != dep_bbs->end (); ++iter)
+{
+gimple *last = last_stmt (*iter);
+if (!last)
+	return false;
+/* Only check condition predicates.  */
+if (gimple_code (last) != GIMPLE_COND
+	  && gimple_code (last) != GIMPLE_SWITCH)
+	return false;
+if (!stmt_semi_invariant_p_1 (loop, last, skip_head, stmt_stat))
+	return false;
+}
+return true;
+}
+/* Check whether STMT is semi-invariant in LOOP, iff all its operands are
+semi-invariant, consequently, all its defined values are semi-invariant.
+Basic blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP.
+Semi-invariant state of checked statement is cached in hash map
+STMT_STAT.  */
+static bool
+stmt_semi_invariant_p_1 (struct loop *loop, gimple *stmt,
+			 const_basic_block skip_head,
+			 hash_map<gimple *, bool> &stmt_stat)
+{
+bool existed;
+bool &invar = stmt_stat.get_or_insert (stmt, &existed);
+if (existed)
+return invar;
+/* A statement might depend on itself, which is treated as variant.  So set
+state of statement under check to be variant to ensure that.  */
+invar = false;
+if (gimple_code (stmt) == GIMPLE_PHI)
+{
+gphi *phi = as_a <gphi *> (stmt);
+if (gimple_bb (stmt) == loop->header)
+	{
+	  invar = loop_iter_phi_semi_invariant_p (loop, phi, skip_head);
+	  return invar;
+	}
+/* For a loop PHI node that does not locate in loop header, it is semi-
+	 invariant only if two conditions are met.  The first is its source
+	 values are derived from CONSTANT (including loop-invariant value), or
+	 from SSA name defined by semi-invariant loop iteration PHI node.  The
+	 second is its source incoming edges are control-dependent on semi-
+	 invariant conditional predicates.  */
+for (unsigned i = 0; i < gimple_phi_num_args (phi); ++i)
+	{
+	  const_edge e = gimple_phi_arg_edge (phi, i);
+	  tree arg = gimple_phi_arg_def (phi, i);
+	  if (TREE_CODE (arg) == SSA_NAME)
+	    {
+	      if (!ssa_semi_invariant_p (loop, arg, skip_head, stmt_stat))
+		return false;
+	      /* If source value is defined in location from where the source
+		 edge comes in, no need to check control dependency again
+		 since this has been done in above SSA name check stage.  */
+	      if (e->src == gimple_bb (SSA_NAME_DEF_STMT (arg)))
+		continue;
+	    }
+	  if (!control_dep_semi_invariant_p (loop, e->src, skip_head,
+					     stmt_stat))
+	    return false;
+	}
+}
+else
+{
+ssa_op_iter iter;
+tree use;
+/* Volatile memory load or return of normal (non-const/non-pure) call
+	 should not be treated as constant in each iteration of loop.  */
+if (gimple_has_side_effects (stmt))
+	return false;
+/* Check if any memory store may kill memory load at this place.  */
+if (gimple_vuse (stmt) && !vuse_semi_invariant_p (loop, stmt, skip_head))
+	return false;
+/* Although operand of a statement might be SSA name, CONSTANT or
+	 VARDECL, here we only need to check SSA name operands.  This is
+	 because check on VARDECL operands, which involve memory loads,
+	 must have been done prior to invocation of this function in
+	 vuse_semi_invariant_p.  */
+FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+	if (!ssa_semi_invariant_p (loop, use, skip_head, stmt_stat))
+	  return false;
+}
+if (!control_dep_semi_invariant_p (loop, gimple_bb (stmt), skip_head,
+				     stmt_stat))
+return false;
+/* Here we SHOULD NOT use invar = true, since hash map might be changed due
+to new insertion, and thus invar may point to invalid memory.  */
+stmt_stat.put (stmt, true);
+return true;
+}
+/* A helper function to check whether STMT is semi-invariant in LOOP.  Basic
+blocks dominated by SKIP_HEAD (if non-NULL), are excluded from LOOP.  */
+static bool
+stmt_semi_invariant_p (struct loop *loop, gimple *stmt,
+		       const_basic_block skip_head)
+{
+hash_map<gimple *, bool> stmt_stat;
+return stmt_semi_invariant_p_1 (loop, stmt, skip_head, stmt_stat);
+}
+/* Determine when conditional statement never transfers execution to one of its
+branch, whether we can remove the branch's leading basic block (BRANCH_BB)
+and those basic blocks dominated by BRANCH_BB.  */
+static bool
+branch_removable_p (basic_block branch_bb)
+{
+edge_iterator ei;
+edge e;
+if (single_pred_p (branch_bb))
+return true;
+FOR_EACH_EDGE (e, ei, branch_bb->preds)
+{
+if (dominated_by_p (CDI_DOMINATORS, e->src, branch_bb))
+	continue;
+if (dominated_by_p (CDI_DOMINATORS, branch_bb, e->src))
+	continue;
+/* The branch can be reached from opposite branch, or from some
+	  statement not dominated by the conditional statement.  */
+return false;
+}
+return true;
+}
+/* Find out which branch of a conditional statement (COND) is invariant in the
+execution context of LOOP.  That is: once the branch is selected in certain
+iteration of the loop, any operand that contributes to computation of the
+conditional statement remains unchanged in all following iterations.  */
+static edge
+get_cond_invariant_branch (struct loop *loop, gcond *cond)
+{
+basic_block cond_bb = gimple_bb (cond);
+basic_block targ_bb[2];
+bool invar[2];
+unsigned invar_checks = 0;
+for (unsigned i = 0; i < 2; i++)
+{
+targ_bb[i] = EDGE_SUCC (cond_bb, i)->dest;
+/* One branch directs to loop exit, no need to perform loop split upon
+	 this conditional statement.  Firstly, it is trivial if the exit branch
+	 is semi-invariant, for the statement is just to break loop.  Secondly,
+	 if the opposite branch is semi-invariant, it means that the statement
+	 is real loop-invariant, which is covered by loop unswitch.  */
+if (!flow_bb_inside_loop_p (loop, targ_bb[i]))
+	return NULL;
+}
+for (unsigned i = 0; i < 2; i++)
+{
+invar[!i] = false;
+if (!branch_removable_p (targ_bb[i]))
+	continue;
+/* Given a semi-invariant branch, if its opposite branch dominates
+	 loop latch, it and its following trace will only be executed in
+	 final iteration of loop, namely it is not part of repeated body
+	 of the loop.  Similar to the above case that the branch is loop
+	 exit, no need to split loop.  */
+if (dominated_by_p (CDI_DOMINATORS, loop->latch, targ_bb[i]))
+	continue;
+invar[!i] = stmt_semi_invariant_p (loop, cond, targ_bb[i]);
+invar_checks++;
+}
+/* With both branches being invariant (handled by loop unswitch) or
+variant is not what we want.  */
+if (invar[0] ^ !invar[1])
+return NULL;
+/* Found a real loop-invariant condition, do nothing.  */
+if (invar_checks < 2 && stmt_semi_invariant_p (loop, cond, NULL))
+return NULL;
+return EDGE_SUCC (cond_bb, invar[0] ? 0 : 1);
+}
+/* Calculate increased code size measured by estimated insn number if applying
+loop split upon certain branch (BRANCH_EDGE) of a conditional statement.  */
+static int
+compute_added_num_insns (struct loop *loop, const_edge branch_edge)
+{
+basic_block cond_bb = branch_edge->src;
+unsigned branch = EDGE_SUCC (cond_bb, 1) == branch_edge;
+basic_block opposite_bb = EDGE_SUCC (cond_bb, !branch)->dest;
+basic_block *bbs = ((split_info *) loop->aux)->bbs;
+int num = 0;
+for (unsigned i = 0; i < loop->num_nodes; i++)
+{
+/* Do no count basic blocks only in opposite branch.  */
+if (dominated_by_p (CDI_DOMINATORS, bbs[i], opposite_bb))
+	continue;
+num += estimate_num_insns_seq (bb_seq (bbs[i]), &eni_size_weights);
+}
+/* It is unnecessary to evaluate expression of the conditional statement
+in new loop that contains only invariant branch.  This expression should
+be constant value (either true or false).  Exclude code size of insns
+that contribute to computation of the expression.  */
+auto_vec<gimple *> worklist;
+hash_set<gimple *> removed;
+gimple *stmt = last_stmt (cond_bb);
+worklist.safe_push (stmt);
+removed.add (stmt);
+num -= estimate_num_insns (stmt, &eni_size_weights);
+do
+{
+ssa_op_iter opnd_iter;
+use_operand_p opnd_p;
+stmt = worklist.pop ();
+FOR_EACH_PHI_OR_STMT_USE (opnd_p, stmt, opnd_iter, SSA_OP_USE)
+	{
+	  tree opnd = USE_FROM_PTR (opnd_p);
+	  if (TREE_CODE (opnd) != SSA_NAME || SSA_NAME_IS_DEFAULT_DEF (opnd))
+	    continue;
+	  gimple *opnd_stmt = SSA_NAME_DEF_STMT (opnd);
+	  use_operand_p use_p;
+	  imm_use_iterator use_iter;
+	  if (removed.contains (opnd_stmt)
+	      || !flow_bb_inside_loop_p (loop, gimple_bb (opnd_stmt)))
+	    continue;
+	  FOR_EACH_IMM_USE_FAST (use_p, use_iter, opnd)
+	    {
+	      gimple *use_stmt = USE_STMT (use_p);
+	      if (!is_gimple_debug (use_stmt) && !removed.contains (use_stmt))
+		{
+		  opnd_stmt = NULL;
+		  break;
+		}
+	    }
+	  if (opnd_stmt)
+	    {
+	      worklist.safe_push (opnd_stmt);
+	      removed.add (opnd_stmt);
+	      num -= estimate_num_insns (opnd_stmt, &eni_size_weights);
+	    }
+	}
+} while (!worklist.is_empty ());
+gcc_assert (num >= 0);
+return num;
+}
+/* Find out loop-invariant branch of a conditional statement (COND) if it has,
+and check whether it is eligible and profitable to perform loop split upon
+this branch in LOOP.  */
+static edge
+get_cond_branch_to_split_loop (struct loop *loop, gcond *cond)
+{
+edge invar_branch = get_cond_invariant_branch (loop, cond);
+if (!invar_branch)
+return NULL;
+/* When accurate profile information is available, and execution
+frequency of the branch is too low, just let it go.  */
+profile_probability prob = invar_branch->probability;
+if (prob.reliable_p ())
+{
+int thres = param_min_loop_cond_split_prob;
+if (prob < profile_probability::always ().apply_scale (thres, 100))
+	return NULL;
+}
+/* Add a threshold for increased code size to disable loop split.  */
+if (compute_added_num_insns (loop, invar_branch) > param_max_peeled_insns)
+return NULL;
+return invar_branch;
+}
+/* Given a loop (LOOP1) with a loop-invariant branch (INVAR_BRANCH) of some
+conditional statement, perform loop split transformation illustrated
+as the following graph.
+.-------T------ if (true) ------F------.
+|                    .---------------. |
+|                    |               | |
+v                    |               v v
+pre-header                |            pre-header
+| .------------.     |                 | .------------.
+| |            |     |                 | |            |
+| v            |     |                 | v            |
+header           |     |               header           |
+|              |     |                 |              |
+.--- if (cond) ---.     |     |        .--- if (true) ---.     |
+|                 |     |     |        |                 |     |
+invariant             |     |     |    invariant             |     |
+|                 |     |     |        |                 |     |
+'---T--->.<---F---'     |     |        '---T--->.<---F---'     |
+|              |    /                  |              |
+stmts            |   /                 stmts            |
+|              F  T                    |              |
+/ \             | /                    / \             |
+.-------*   *      [ if (cond) ]       .-------*   *            |
+|           |            |             |           |            |
+|         latch          |             |         latch          |
+|           |            |             |           |            |
+|           '------------'             |           '------------'
+'------------------------. .-----------'
+loop1            | |                   loop2
+v v
+exits
+In the graph, loop1 represents the part derived from original one, and
+loop2 is duplicated using loop_version (), which corresponds to the part
+of original one being splitted out.  In original latch edge of loop1, we
+insert a new conditional statement duplicated from the semi-invariant cond,
+and one of its branch goes back to loop1 header as a latch edge, and the
+other branch goes to loop2 pre-header as an entry edge.  And also in loop2,
+we abandon the variant branch of the conditional statement by setting a
+constant bool condition, based on which branch is semi-invariant.  */
+static bool
+do_split_loop_on_cond (struct loop *loop1, edge invar_branch)
+{
+basic_block cond_bb = invar_branch->src;
+bool true_invar = !!(invar_branch->flags & EDGE_TRUE_VALUE);
+gcond *cond = as_a <gcond *> (last_stmt (cond_bb));
+gcc_assert (cond_bb->loop_father == loop1);
+if (dump_enabled_p ())
+dump_printf_loc (MSG_OPTIMIZED_LOCATIONS, cond,
+		     "loop split on semi-invariant condition at %s branch\n",
+		     true_invar ? "true" : "false");
+initialize_original_copy_tables ();
+struct loop *loop2 = loop_version (loop1, boolean_true_node, NULL,
+				     profile_probability::always (),
+				     profile_probability::never (),
+				     profile_probability::always (),
+				     profile_probability::always (),
+				     true);
+if (!loop2)
+{
+free_original_copy_tables ();
+return false;
+}
+basic_block cond_bb_copy = get_bb_copy (cond_bb);
+gcond *cond_copy = as_a<gcond *> (last_stmt (cond_bb_copy));
+/* Replace the condition in loop2 with a bool constant to let PassManager
+remove the variant branch after current pass completes.  */
+if (true_invar)
+gimple_cond_make_true (cond_copy);
+else
+gimple_cond_make_false (cond_copy);
+update_stmt (cond_copy);
+/* Insert a new conditional statement on latch edge of loop1, its condition
+is duplicated from the semi-invariant.  This statement acts as a switch
+to transfer execution from loop1 to loop2, when loop1 enters into
+invariant state.  */
+basic_block latch_bb = split_edge (loop_latch_edge (loop1));
+basic_block break_bb = split_edge (single_pred_edge (latch_bb));
+gimple *break_cond = gimple_build_cond (gimple_cond_code(cond),
+					  gimple_cond_lhs (cond),
+					  gimple_cond_rhs (cond),
+					  NULL_TREE, NULL_TREE);
+gimple_stmt_iterator gsi = gsi_last_bb (break_bb);
+gsi_insert_after (&gsi, break_cond, GSI_NEW_STMT);
+edge to_loop1 = single_succ_edge (break_bb);
+edge to_loop2 = make_edge (break_bb, loop_preheader_edge (loop2)->src, 0);
+to_loop1->flags &= ~EDGE_FALLTHRU;
+to_loop1->flags |= true_invar ? EDGE_FALSE_VALUE : EDGE_TRUE_VALUE;
+to_loop2->flags |= true_invar ? EDGE_TRUE_VALUE : EDGE_FALSE_VALUE;
+update_ssa (TODO_update_ssa);
+/* Due to introduction of a control flow edge from loop1 latch to loop2
+pre-header, we should update PHIs in loop2 to reflect this connection
+between loop1 and loop2.  */
+connect_loop_phis (loop1, loop2, to_loop2);
+free_original_copy_tables ();
+rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop1);
+return true;
+}
+/* Traverse all conditional statements in LOOP, to find out a good candidate
+upon which we can do loop split.  */
+static bool
+split_loop_on_cond (struct loop *loop)
+{
+split_info *info = new split_info ();
+basic_block *bbs = info->bbs = get_loop_body (loop);
+bool do_split = false;
+/* Allocate an area to keep temporary info, and associate its address
+with loop aux field.  */
+loop->aux = info;
+for (unsigned i = 0; i < loop->num_nodes; i++)
+bbs[i]->aux = NULL;
+for (unsigned i = 0; i < loop->num_nodes; i++)
+{
+basic_block bb = bbs[i];
+/* We only consider conditional statement, which be executed at most once
+	 in each iteration of the loop.  So skip statements in inner loops.  */
+if ((bb->loop_father != loop) || (bb->flags & BB_IRREDUCIBLE_LOOP))
+	continue;
+/* Actually this check is not a must constraint.  With it, we can ensure
+	 conditional statement will always be executed in each iteration.  */
+if (!dominated_by_p (CDI_DOMINATORS, loop->latch, bb))
+	continue;
+gimple *last = last_stmt (bb);
+if (!last || gimple_code (last) != GIMPLE_COND)
+	continue;
+gcond *cond = as_a <gcond *> (last);
+edge branch_edge = get_cond_branch_to_split_loop (loop, cond);
+if (branch_edge)
+	{
+	  do_split_loop_on_cond (loop, branch_edge);
+	  do_split = true;
+	  break;
+	}
+}
+delete info;
+loop->aux = NULL;
+return do_split;
+}
 /* Main entry point.  Perform loop splitting on all suitable loops.  */
 static unsigned int
 tree_ssa_split_loops (void)
 {
-struct loop *loop;
+class loop *loop;
 bool changed = false;
 gcc_assert (scev_initialized_p ());
+calculate_dominance_info (CDI_POST_DOMINATORS);
 FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
 loop->aux = NULL;
 /* Go through all loops starting from innermost.  */
 FOR_EACH_LOOP (loop, LI_FROM_INNERMOST)
 {
-struct tree_niter_desc niter;
 if (loop->aux)
 	{
 	  /* If any of our inner loops was split, don't split us,
 	     and mark our containing loop as having had splits as well.  */
 	  loop_outer (loop)->aux = loop;
 	  continue;
 	}
-if (single_exit (loop)
+if (optimize_loop_for_size_p (loop))
-	  /* ??? We could handle non-empty latches when we split
+	continue;
-	     the latch edge (not the exit edge), and put the new
-	     exit condition in the new block.  OTOH this executes some
+if (split_loop (loop) || split_loop_on_cond (loop))
-	     code unconditionally that might have been skipped by the
-	     original exit before.  */
-	  && empty_block_p (loop->latch)
-	  && !optimize_loop_for_size_p (loop)
-	  && easy_exit_values (loop)
-	  && number_of_iterations_exit (loop, single_exit (loop), &niter,
-					false, true)
-	  && niter.cmp != ERROR_MARK
-	  /* We can't yet handle loops controlled by a != predicate.  */
-	  && niter.cmp != NE_EXPR)
 	{
-	  if (split_loop (loop, &niter))
+	  /* Mark our containing loop as having had some split inner loops.  */
-	    {
+	  loop_outer (loop)->aux = loop;
-	      /* Mark our containing loop as having had some split inner
+	  changed = true;
-	         loops.  */
-	      loop_outer (loop)->aux = loop;
-	      changed = true;
-	    }
 	}
 }
 FOR_EACH_LOOP (loop, LI_INCLUDE_ROOT)
 loop->aux = NULL;
+clear_aux_for_blocks ();
+free_dominance_info (CDI_POST_DOMINATORS);
 if (changed)
 return TODO_cleanup_cfg;
 return 0;
 }

Mercurial > hg > CbC > CbC_gcc

comparison gcc/tree-ssa-loop-split.c @ 145:1830386684a0