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264 lines
7.4 KiB
C
264 lines
7.4 KiB
C
/* Loop header copying on trees.
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Copyright (C) 2004, 2005, 2006, 2007 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 "tree-pass.h"
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#include "timevar.h"
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#include "cfgloop.h"
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#include "tree-inline.h"
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#include "flags.h"
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#include "tree-inline.h"
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/* Duplicates headers of loops if they are small enough, so that the statements
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in the loop body are always executed when the loop is entered. This
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increases effectiveness of code motion optimizations, and reduces the need
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for loop preconditioning. */
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/* Check whether we should duplicate HEADER of LOOP. At most *LIMIT
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instructions should be duplicated, limit is decreased by the actual
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amount. */
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static bool
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should_duplicate_loop_header_p (basic_block header, struct loop *loop,
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int *limit)
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{
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block_stmt_iterator bsi;
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tree last;
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/* Do not copy one block more than once (we do not really want to do
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loop peeling here). */
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if (header->aux)
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return false;
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gcc_assert (EDGE_COUNT (header->succs) > 0);
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if (single_succ_p (header))
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return false;
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if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest)
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&& flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 1)->dest))
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return false;
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/* If this is not the original loop header, we want it to have just
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one predecessor in order to match the && pattern. */
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if (header != loop->header && !single_pred_p (header))
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return false;
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last = last_stmt (header);
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if (TREE_CODE (last) != COND_EXPR)
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return false;
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/* Approximately copy the conditions that used to be used in jump.c --
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at most 20 insns and no calls. */
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for (bsi = bsi_start (header); !bsi_end_p (bsi); bsi_next (&bsi))
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{
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last = bsi_stmt (bsi);
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if (TREE_CODE (last) == LABEL_EXPR)
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continue;
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if (get_call_expr_in (last))
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return false;
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*limit -= estimate_num_insns (last);
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if (*limit < 0)
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return false;
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}
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return true;
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}
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/* Checks whether LOOP is a do-while style loop. */
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static bool
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do_while_loop_p (struct loop *loop)
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{
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tree stmt = last_stmt (loop->latch);
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/* If the latch of the loop is not empty, it is not a do-while loop. */
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if (stmt
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&& TREE_CODE (stmt) != LABEL_EXPR)
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return false;
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/* If the header contains just a condition, it is not a do-while loop. */
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stmt = last_and_only_stmt (loop->header);
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if (stmt
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&& TREE_CODE (stmt) == COND_EXPR)
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return false;
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return true;
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}
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/* For all loops, copy the condition at the end of the loop body in front
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of the loop. This is beneficial since it increases efficiency of
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code motion optimizations. It also saves one jump on entry to the loop. */
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static unsigned int
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copy_loop_headers (void)
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{
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struct loops *loops;
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unsigned i;
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struct loop *loop;
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basic_block header;
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edge exit, entry;
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basic_block *bbs, *copied_bbs;
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unsigned n_bbs;
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unsigned bbs_size;
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loops = loop_optimizer_init (LOOPS_HAVE_PREHEADERS
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| LOOPS_HAVE_SIMPLE_LATCHES);
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if (!loops)
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return 0;
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#ifdef ENABLE_CHECKING
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verify_loop_structure (loops);
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#endif
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bbs = XNEWVEC (basic_block, n_basic_blocks);
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copied_bbs = XNEWVEC (basic_block, n_basic_blocks);
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bbs_size = n_basic_blocks;
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for (i = 1; i < loops->num; i++)
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{
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/* Copy at most 20 insns. */
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int limit = 20;
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loop = loops->parray[i];
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if (!loop)
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continue;
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header = loop->header;
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/* If the loop is already a do-while style one (either because it was
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written as such, or because jump threading transformed it into one),
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we might be in fact peeling the first iteration of the loop. This
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in general is not a good idea. */
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if (do_while_loop_p (loop))
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continue;
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/* Iterate the header copying up to limit; this takes care of the cases
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like while (a && b) {...}, where we want to have both of the conditions
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copied. TODO -- handle while (a || b) - like cases, by not requiring
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the header to have just a single successor and copying up to
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postdominator. */
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exit = NULL;
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n_bbs = 0;
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while (should_duplicate_loop_header_p (header, loop, &limit))
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{
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/* Find a successor of header that is inside a loop; i.e. the new
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header after the condition is copied. */
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if (flow_bb_inside_loop_p (loop, EDGE_SUCC (header, 0)->dest))
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exit = EDGE_SUCC (header, 0);
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else
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exit = EDGE_SUCC (header, 1);
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bbs[n_bbs++] = header;
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gcc_assert (bbs_size > n_bbs);
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header = exit->dest;
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}
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if (!exit)
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continue;
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if (dump_file && (dump_flags & TDF_DETAILS))
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fprintf (dump_file,
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"Duplicating header of the loop %d up to edge %d->%d.\n",
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loop->num, exit->src->index, exit->dest->index);
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/* Ensure that the header will have just the latch as a predecessor
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inside the loop. */
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if (!single_pred_p (exit->dest))
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exit = single_pred_edge (loop_split_edge_with (exit, NULL));
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entry = loop_preheader_edge (loop);
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if (!tree_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs))
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{
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fprintf (dump_file, "Duplication failed.\n");
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continue;
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}
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/* If the loop has the form "for (i = j; i < j + 10; i++)" then
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this copying can introduce a case where we rely on undefined
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signed overflow to eliminate the preheader condition, because
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we assume that "j < j + 10" is true. We don't want to warn
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about that case for -Wstrict-overflow, because in general we
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don't warn about overflow involving loops. Prevent the
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warning by setting TREE_NO_WARNING. */
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if (warn_strict_overflow > 0)
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{
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unsigned int i;
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for (i = 0; i < n_bbs; ++i)
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{
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tree last;
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last = last_stmt (copied_bbs[i]);
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if (TREE_CODE (last) == COND_EXPR)
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TREE_NO_WARNING (last) = 1;
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}
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}
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/* Ensure that the latch and the preheader is simple (we know that they
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are not now, since there was the loop exit condition. */
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loop_split_edge_with (loop_preheader_edge (loop), NULL);
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loop_split_edge_with (loop_latch_edge (loop), NULL);
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}
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free (bbs);
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free (copied_bbs);
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loop_optimizer_finalize (loops);
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return 0;
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}
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static bool
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gate_ch (void)
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{
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return flag_tree_ch != 0;
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}
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struct tree_opt_pass pass_ch =
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{
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"ch", /* name */
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gate_ch, /* gate */
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copy_loop_headers, /* execute */
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NULL, /* sub */
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NULL, /* next */
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0, /* static_pass_number */
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TV_TREE_CH, /* tv_id */
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PROP_cfg | PROP_ssa, /* properties_required */
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0, /* properties_provided */
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0, /* properties_destroyed */
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0, /* todo_flags_start */
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TODO_cleanup_cfg | TODO_dump_func
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| TODO_verify_ssa, /* todo_flags_finish */
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0 /* letter */
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};
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