--- /dev/null
+/* Loop unswitching.
+ Copyright (C) 2004, 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 "rtl.h"
+#include "tm_p.h"
+#include "hard-reg-set.h"
+#include "basic-block.h"
+#include "output.h"
+#include "diagnostic.h"
+#include "tree-flow.h"
+#include "tree-dump.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "domwalk.h"
+#include "params.h"
+#include "tree-pass.h"
+#include "tree-inline.h"
+
+/* This file implements the loop unswitching, i.e. transformation of loops like
+
+ while (A)
+ {
+ if (inv)
+ B;
+
+ X;
+
+ if (!inv)
+ C;
+ }
+
+ where inv is the loop invariant, into
+
+ if (inv)
+ {
+ while (A)
+ {
+ B;
+ X;
+ }
+ }
+ else
+ {
+ while (A)
+ {
+ X;
+ C;
+ }
+ }
+
+ Inv is considered invariant iff the values it compares are both invariant;
+ tree-ssa-loop-im.c ensures that all the suitable conditions are in this
+ shape. */
+
+static struct loop *tree_unswitch_loop (struct loop *, basic_block, tree);
+static bool tree_unswitch_single_loop (struct loop *, int);
+static tree tree_may_unswitch_on (basic_block, struct loop *);
+
+/* Main entry point. Perform loop unswitching on all suitable loops. */
+
+unsigned int
+tree_ssa_unswitch_loops (void)
+{
+ loop_iterator li;
+ struct loop *loop;
+ bool changed = false;
+
+ /* Go through inner loops (only original ones). */
+ FOR_EACH_LOOP (li, loop, LI_ONLY_INNERMOST)
+ {
+ changed |= tree_unswitch_single_loop (loop, 0);
+ }
+
+ if (changed)
+ return TODO_cleanup_cfg;
+ return 0;
+}
+
+/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
+ basic blocks (for what it means see comments below). */
+
+static tree
+tree_may_unswitch_on (basic_block bb, struct loop *loop)
+{
+ gimple stmt, def;
+ tree cond, use;
+ basic_block def_bb;
+ ssa_op_iter iter;
+
+ /* BB must end in a simple conditional jump. */
+ stmt = last_stmt (bb);
+ if (!stmt || gimple_code (stmt) != GIMPLE_COND)
+ return NULL_TREE;
+
+ /* Condition must be invariant. */
+ FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
+ {
+ def = SSA_NAME_DEF_STMT (use);
+ def_bb = gimple_bb (def);
+ if (def_bb
+ && flow_bb_inside_loop_p (loop, def_bb))
+ return NULL_TREE;
+ }
+
+ cond = build2 (gimple_cond_code (stmt), boolean_type_node,
+ gimple_cond_lhs (stmt), gimple_cond_rhs (stmt));
+
+ /* To keep the things simple, we do not directly remove the conditions,
+ but just replace tests with 0/1. Prevent the infinite loop where we
+ would unswitch again on such a condition. */
+ if (integer_zerop (cond) || integer_nonzerop (cond))
+ return NULL_TREE;
+
+ return cond;
+}
+
+/* Simplifies COND using checks in front of the entry of the LOOP. Just very
+ simplish (sufficient to prevent us from duplicating loop in unswitching
+ unnecessarily). */
+
+static tree
+simplify_using_entry_checks (struct loop *loop, tree cond)
+{
+ edge e = loop_preheader_edge (loop);
+ gimple stmt;
+
+ while (1)
+ {
+ stmt = last_stmt (e->src);
+ if (stmt
+ && gimple_code (stmt) == GIMPLE_COND
+ && gimple_cond_code (stmt) == TREE_CODE (cond)
+ && operand_equal_p (gimple_cond_lhs (stmt),
+ TREE_OPERAND (cond, 0), 0)
+ && operand_equal_p (gimple_cond_rhs (stmt),
+ TREE_OPERAND (cond, 1), 0))
+ return (e->flags & EDGE_TRUE_VALUE
+ ? boolean_true_node
+ : boolean_false_node);
+
+ if (!single_pred_p (e->src))
+ return cond;
+
+ e = single_pred_edge (e->src);
+ if (e->src == ENTRY_BLOCK_PTR)
+ return cond;
+ }
+}
+
+/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow
+ it to grow too much, it is too easy to create example on that the code would
+ grow exponentially. */
+
+static bool
+tree_unswitch_single_loop (struct loop *loop, int num)
+{
+ basic_block *bbs;
+ struct loop *nloop;
+ unsigned i;
+ tree cond = NULL_TREE;
+ gimple stmt;
+ bool changed = false;
+
+ /* Do not unswitch too much. */
+ if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
+ return false;
+ }
+
+ /* Only unswitch innermost loops. */
+ if (loop->inner)
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
+ return false;
+ }
+
+ /* Do not unswitch in cold regions. */
+ if (optimize_loop_for_size_p (loop))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Not unswitching cold loops\n");
+ return false;
+ }
+
+ /* The loop should not be too large, to limit code growth. */
+ if (tree_num_loop_insns (loop, &eni_size_weights)
+ > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Not unswitching, loop too big\n");
+ return false;
+ }
+
+ i = 0;
+ bbs = get_loop_body (loop);
+
+ while (1)
+ {
+ /* Find a bb to unswitch on. */
+ for (; i < loop->num_nodes; i++)
+ if ((cond = tree_may_unswitch_on (bbs[i], loop)))
+ break;
+
+ if (i == loop->num_nodes)
+ {
+ free (bbs);
+ return changed;
+ }
+
+ cond = simplify_using_entry_checks (loop, cond);
+ stmt = last_stmt (bbs[i]);
+ if (integer_nonzerop (cond))
+ {
+ /* Remove false path. */
+ gimple_cond_set_condition_from_tree (stmt, boolean_true_node);
+ changed = true;
+ }
+ else if (integer_zerop (cond))
+ {
+ /* Remove true path. */
+ gimple_cond_set_condition_from_tree (stmt, boolean_false_node);
+ changed = true;
+ }
+ else
+ break;
+
+ update_stmt (stmt);
+ i++;
+ }
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Unswitching loop\n");
+
+ initialize_original_copy_tables ();
+ /* Unswitch the loop on this condition. */
+ nloop = tree_unswitch_loop (loop, bbs[i], cond);
+ if (!nloop)
+ {
+ free_original_copy_tables ();
+ free (bbs);
+ return changed;
+ }
+
+ /* Update the SSA form after unswitching. */
+ update_ssa (TODO_update_ssa);
+ free_original_copy_tables ();
+
+ /* Invoke itself on modified loops. */
+ tree_unswitch_single_loop (nloop, num + 1);
+ tree_unswitch_single_loop (loop, num + 1);
+ free (bbs);
+ return true;
+}
+
+/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support
+ unswitching of innermost loops. COND is the condition determining which
+ loop is entered -- the new loop is entered if COND is true. Returns NULL
+ if impossible, new loop otherwise. */
+
+static struct loop *
+tree_unswitch_loop (struct loop *loop,
+ basic_block unswitch_on, tree cond)
+{
+ unsigned prob_true;
+ edge edge_true, edge_false;
+
+ /* Some sanity checking. */
+ gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
+ gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
+ gcc_assert (loop->inner == NULL);
+
+ extract_true_false_edges_from_block (unswitch_on, &edge_true, &edge_false);
+ prob_true = edge_true->probability;
+ return loop_version (loop, unshare_expr (cond),
+ NULL, prob_true, prob_true,
+ REG_BR_PROB_BASE - prob_true, false);
+}
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