293 lines
7.2 KiB
C
293 lines
7.2 KiB
C
/* Loop unswitching.
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Copyright (C) 2004, 2005 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 2, or (at your option) any
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later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to the Free
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Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301, USA. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "tree.h"
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#include "rtl.h"
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#include "tm_p.h"
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#include "hard-reg-set.h"
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#include "basic-block.h"
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#include "output.h"
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#include "diagnostic.h"
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#include "tree-flow.h"
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#include "tree-dump.h"
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#include "timevar.h"
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#include "cfgloop.h"
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#include "domwalk.h"
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#include "params.h"
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#include "tree-pass.h"
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/* This file implements the loop unswitching, i.e. transformation of loops like
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while (A)
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{
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if (inv)
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B;
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X;
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if (!inv)
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C;
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}
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where inv is the loop invariant, into
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if (inv)
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{
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while (A)
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{
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B;
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X;
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}
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}
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else
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{
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while (A)
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{
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X;
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C;
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}
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}
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Inv is considered invariant iff the values it compares are both invariant;
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tree-ssa-loop-im.c ensures that all the suitable conditions are in this
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shape. */
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static struct loop *tree_unswitch_loop (struct loops *, struct loop *, basic_block,
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tree);
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static bool tree_unswitch_single_loop (struct loops *, struct loop *, int);
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static tree tree_may_unswitch_on (basic_block, struct loop *);
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/* Main entry point. Perform loop unswitching on all suitable LOOPS. */
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unsigned int
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tree_ssa_unswitch_loops (struct loops *loops)
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{
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int i, num;
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struct loop *loop;
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bool changed = false;
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/* Go through inner loops (only original ones). */
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num = loops->num;
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for (i = 1; i < num; i++)
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{
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/* Removed loop? */
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loop = loops->parray[i];
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if (!loop)
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continue;
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if (loop->inner)
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continue;
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changed |= tree_unswitch_single_loop (loops, loop, 0);
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}
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if (changed)
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return TODO_cleanup_cfg;
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return 0;
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}
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/* Checks whether we can unswitch LOOP on condition at end of BB -- one of its
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basic blocks (for what it means see comments below). */
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static tree
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tree_may_unswitch_on (basic_block bb, struct loop *loop)
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{
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tree stmt, def, cond, use;
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basic_block def_bb;
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ssa_op_iter iter;
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/* BB must end in a simple conditional jump. */
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stmt = last_stmt (bb);
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if (!stmt || TREE_CODE (stmt) != COND_EXPR)
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return NULL_TREE;
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/* Condition must be invariant. */
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FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)
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{
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def = SSA_NAME_DEF_STMT (use);
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def_bb = bb_for_stmt (def);
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if (def_bb
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&& flow_bb_inside_loop_p (loop, def_bb))
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return NULL_TREE;
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}
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cond = COND_EXPR_COND (stmt);
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/* To keep the things simple, we do not directly remove the conditions,
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but just replace tests with 0/1. Prevent the infinite loop where we
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would unswitch again on such a condition. */
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if (integer_zerop (cond) || integer_nonzerop (cond))
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return NULL_TREE;
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return cond;
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}
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/* Simplifies COND using checks in front of the entry of the LOOP. Just very
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simplish (sufficient to prevent us from duplicating loop in unswitching
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unnecessarily). */
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static tree
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simplify_using_entry_checks (struct loop *loop, tree cond)
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{
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edge e = loop_preheader_edge (loop);
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tree stmt;
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while (1)
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{
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stmt = last_stmt (e->src);
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if (stmt
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&& TREE_CODE (stmt) == COND_EXPR
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&& operand_equal_p (COND_EXPR_COND (stmt), cond, 0))
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return (e->flags & EDGE_TRUE_VALUE
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? boolean_true_node
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: boolean_false_node);
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if (!single_pred_p (e->src))
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return cond;
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e = single_pred_edge (e->src);
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if (e->src == ENTRY_BLOCK_PTR)
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return cond;
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}
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}
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/* Unswitch single LOOP. NUM is number of unswitchings done; we do not allow
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it to grow too much, it is too easy to create example on that the code would
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grow exponentially. */
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static bool
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tree_unswitch_single_loop (struct loops *loops, struct loop *loop, int num)
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{
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basic_block *bbs;
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struct loop *nloop;
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unsigned i;
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tree cond = NULL_TREE, stmt;
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bool changed = false;
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/* Do not unswitch too much. */
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if (num > PARAM_VALUE (PARAM_MAX_UNSWITCH_LEVEL))
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{
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file, ";; Not unswitching anymore, hit max level\n");
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return false;
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}
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/* Only unswitch innermost loops. */
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if (loop->inner)
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{
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
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return false;
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}
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/* The loop should not be too large, to limit code growth. */
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if (tree_num_loop_insns (loop)
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> (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
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{
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file, ";; Not unswitching, loop too big\n");
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return false;
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}
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i = 0;
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bbs = get_loop_body (loop);
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while (1)
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{
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/* Find a bb to unswitch on. */
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for (; i < loop->num_nodes; i++)
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if ((cond = tree_may_unswitch_on (bbs[i], loop)))
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break;
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if (i == loop->num_nodes)
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{
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free (bbs);
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return changed;
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}
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cond = simplify_using_entry_checks (loop, cond);
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stmt = last_stmt (bbs[i]);
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if (integer_nonzerop (cond))
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{
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/* Remove false path. */
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COND_EXPR_COND (stmt) = boolean_true_node;
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changed = true;
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}
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else if (integer_zerop (cond))
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{
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/* Remove true path. */
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COND_EXPR_COND (stmt) = boolean_false_node;
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changed = true;
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}
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else
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break;
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update_stmt (stmt);
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i++;
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}
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file, ";; Unswitching loop\n");
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initialize_original_copy_tables ();
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/* Unswitch the loop on this condition. */
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nloop = tree_unswitch_loop (loops, loop, bbs[i], cond);
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if (!nloop)
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{
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free_original_copy_tables ();
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free (bbs);
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return changed;
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}
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/* Update the SSA form after unswitching. */
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update_ssa (TODO_update_ssa);
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free_original_copy_tables ();
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/* Invoke itself on modified loops. */
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tree_unswitch_single_loop (loops, nloop, num + 1);
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tree_unswitch_single_loop (loops, loop, num + 1);
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free (bbs);
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return true;
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}
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/* Unswitch a LOOP w.r. to given basic block UNSWITCH_ON. We only support
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unswitching of innermost loops. COND is the condition determining which
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loop is entered -- the new loop is entered if COND is true. Returns NULL
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if impossible, new loop otherwise. */
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static struct loop *
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tree_unswitch_loop (struct loops *loops, struct loop *loop,
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basic_block unswitch_on, tree cond)
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{
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basic_block condition_bb;
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/* Some sanity checking. */
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gcc_assert (flow_bb_inside_loop_p (loop, unswitch_on));
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gcc_assert (EDGE_COUNT (unswitch_on->succs) == 2);
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gcc_assert (loop->inner == NULL);
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return loop_version (loops, loop, unshare_expr (cond),
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&condition_bb, false);
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}
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