b8698a0f37
2009-11-25 H.J. 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From-SVN: r154645
285 lines
8.0 KiB
C
285 lines
8.0 KiB
C
/* Loop header copying on trees.
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Copyright (C) 2004, 2005, 2006, 2007, 2008 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 3, 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 COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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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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gimple_stmt_iterator bsi;
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gimple 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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/* Loop header copying usually increases size of the code. This used not to
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be true, since quite often it is possible to verify that the condition is
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satisfied in the first iteration and therefore to eliminate it. Jump
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threading handles these cases now. */
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if (optimize_loop_for_size_p (loop))
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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 (gimple_code (last) != GIMPLE_COND)
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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 = gsi_start_bb (header); !gsi_end_p (bsi); gsi_next (&bsi))
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{
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last = gsi_stmt (bsi);
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if (gimple_code (last) == GIMPLE_LABEL)
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continue;
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if (is_gimple_debug (last))
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continue;
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if (is_gimple_call (last))
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return false;
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*limit -= estimate_num_insns (last, &eni_size_weights);
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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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gimple 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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&& gimple_code (stmt) != GIMPLE_LABEL)
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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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&& gimple_code (stmt) == GIMPLE_COND)
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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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loop_iterator li;
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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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loop_optimizer_init (LOOPS_HAVE_PREHEADERS
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| LOOPS_HAVE_SIMPLE_LATCHES);
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if (number_of_loops () <= 1)
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{
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loop_optimizer_finalize ();
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return 0;
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}
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#ifdef ENABLE_CHECKING
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verify_loop_structure ();
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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_EACH_LOOP (li, loop, 0)
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{
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/* Copy at most 20 insns. */
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int limit = 20;
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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 (split_edge (exit));
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entry = loop_preheader_edge (loop);
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if (!gimple_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 the no_warning flag in the condition. */
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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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gimple_stmt_iterator bsi;
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for (bsi = gsi_start_bb (copied_bbs[i]);
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!gsi_end_p (bsi);
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gsi_next (&bsi))
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{
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gimple stmt = gsi_stmt (bsi);
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if (gimple_code (stmt) == GIMPLE_COND)
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gimple_set_no_warning (stmt, true);
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else if (is_gimple_assign (stmt))
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{
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enum tree_code rhs_code = gimple_assign_rhs_code (stmt);
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if (TREE_CODE_CLASS (rhs_code) == tcc_comparison)
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gimple_set_no_warning (stmt, true);
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}
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}
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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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split_edge (loop_preheader_edge (loop));
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split_edge (loop_latch_edge (loop));
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}
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free (bbs);
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free (copied_bbs);
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loop_optimizer_finalize ();
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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 gimple_opt_pass pass_ch =
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{
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{
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GIMPLE_PASS,
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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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}
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};
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