418 lines
11 KiB
C
418 lines
11 KiB
C
/* The tracer pass for the GNU compiler.
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Contributed by Jan Hubicka, SuSE Labs.
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Copyright (C) 2001, 2002, 2003, 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
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the Free Software Foundation; either version 2, or (at your option)
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any 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
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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License 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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/* This pass performs the tail duplication needed for superblock formation.
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For more information see:
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Design and Analysis of Profile-Based Optimization in Compaq's
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Compilation Tools for Alpha; Journal of Instruction-Level
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Parallelism 3 (2000) 1-25
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Unlike Compaq's implementation we don't do the loop peeling as most
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probably a better job can be done by a special pass and we don't
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need to worry too much about the code size implications as the tail
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duplicates are crossjumped again if optimizations are not
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performed. */
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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 "hard-reg-set.h"
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#include "basic-block.h"
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#include "output.h"
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#include "cfglayout.h"
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#include "fibheap.h"
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#include "flags.h"
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#include "timevar.h"
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#include "params.h"
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#include "coverage.h"
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#include "tree-pass.h"
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static int count_insns (basic_block);
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static bool ignore_bb_p (basic_block);
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static bool better_p (edge, edge);
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static edge find_best_successor (basic_block);
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static edge find_best_predecessor (basic_block);
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static int find_trace (basic_block, basic_block *);
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static void tail_duplicate (void);
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static void layout_superblocks (void);
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/* Minimal outgoing edge probability considered for superblock formation. */
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static int probability_cutoff;
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static int branch_ratio_cutoff;
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/* Return true if BB has been seen - it is connected to some trace
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already. */
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#define seen(bb) (bb->il.rtl->visited || bb->aux)
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/* Return true if we should ignore the basic block for purposes of tracing. */
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static bool
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ignore_bb_p (basic_block bb)
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{
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if (bb->index < NUM_FIXED_BLOCKS)
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return true;
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if (!maybe_hot_bb_p (bb))
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return true;
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return false;
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}
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/* Return number of instructions in the block. */
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static int
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count_insns (basic_block bb)
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{
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rtx insn;
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int n = 0;
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for (insn = BB_HEAD (bb);
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insn != NEXT_INSN (BB_END (bb));
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insn = NEXT_INSN (insn))
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if (active_insn_p (insn))
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n++;
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return n;
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}
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/* Return true if E1 is more frequent than E2. */
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static bool
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better_p (edge e1, edge e2)
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{
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if (e1->count != e2->count)
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return e1->count > e2->count;
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if (e1->src->frequency * e1->probability !=
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e2->src->frequency * e2->probability)
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return (e1->src->frequency * e1->probability
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> e2->src->frequency * e2->probability);
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/* This is needed to avoid changes in the decision after
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CFG is modified. */
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if (e1->src != e2->src)
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return e1->src->index > e2->src->index;
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return e1->dest->index > e2->dest->index;
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}
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/* Return most frequent successor of basic block BB. */
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static edge
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find_best_successor (basic_block bb)
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{
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edge e;
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edge best = NULL;
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edge_iterator ei;
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FOR_EACH_EDGE (e, ei, bb->succs)
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if (!best || better_p (e, best))
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best = e;
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if (!best || ignore_bb_p (best->dest))
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return NULL;
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if (best->probability <= probability_cutoff)
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return NULL;
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return best;
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}
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/* Return most frequent predecessor of basic block BB. */
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static edge
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find_best_predecessor (basic_block bb)
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{
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edge e;
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edge best = NULL;
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edge_iterator ei;
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FOR_EACH_EDGE (e, ei, bb->preds)
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if (!best || better_p (e, best))
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best = e;
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if (!best || ignore_bb_p (best->src))
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return NULL;
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if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
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< bb->frequency * branch_ratio_cutoff)
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return NULL;
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return best;
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}
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/* Find the trace using bb and record it in the TRACE array.
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Return number of basic blocks recorded. */
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static int
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find_trace (basic_block bb, basic_block *trace)
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{
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int i = 0;
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edge e;
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if (dump_file)
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fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
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while ((e = find_best_predecessor (bb)) != NULL)
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{
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basic_block bb2 = e->src;
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if (seen (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
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|| find_best_successor (bb2) != e)
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break;
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if (dump_file)
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fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
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bb = bb2;
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}
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if (dump_file)
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fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
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trace[i++] = bb;
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/* Follow the trace in forward direction. */
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while ((e = find_best_successor (bb)) != NULL)
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{
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bb = e->dest;
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if (seen (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
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|| find_best_predecessor (bb) != e)
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break;
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if (dump_file)
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fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
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trace[i++] = bb;
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}
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if (dump_file)
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fprintf (dump_file, "\n");
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return i;
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}
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/* Look for basic blocks in frequency order, construct traces and tail duplicate
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if profitable. */
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static void
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tail_duplicate (void)
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{
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fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
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basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
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int *counts = XNEWVEC (int, last_basic_block);
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int ninsns = 0, nduplicated = 0;
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gcov_type weighted_insns = 0, traced_insns = 0;
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fibheap_t heap = fibheap_new ();
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gcov_type cover_insns;
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int max_dup_insns;
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basic_block bb;
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if (profile_info && flag_branch_probabilities)
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probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
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else
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probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
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probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
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branch_ratio_cutoff =
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(REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
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FOR_EACH_BB (bb)
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{
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int n = count_insns (bb);
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if (!ignore_bb_p (bb))
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blocks[bb->index] = fibheap_insert (heap, -bb->frequency,
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bb);
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counts [bb->index] = n;
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ninsns += n;
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weighted_insns += n * bb->frequency;
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}
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if (profile_info && flag_branch_probabilities)
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cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
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else
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cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
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cover_insns = (weighted_insns * cover_insns + 50) / 100;
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max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
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while (traced_insns < cover_insns && nduplicated < max_dup_insns
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&& !fibheap_empty (heap))
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{
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basic_block bb = fibheap_extract_min (heap);
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int n, pos;
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if (!bb)
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break;
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blocks[bb->index] = NULL;
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if (ignore_bb_p (bb))
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continue;
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gcc_assert (!seen (bb));
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n = find_trace (bb, trace);
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bb = trace[0];
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traced_insns += bb->frequency * counts [bb->index];
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if (blocks[bb->index])
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{
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fibheap_delete_node (heap, blocks[bb->index]);
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blocks[bb->index] = NULL;
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}
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for (pos = 1; pos < n; pos++)
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{
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basic_block bb2 = trace[pos];
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if (blocks[bb2->index])
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{
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fibheap_delete_node (heap, blocks[bb2->index]);
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blocks[bb2->index] = NULL;
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}
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traced_insns += bb2->frequency * counts [bb2->index];
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if (EDGE_COUNT (bb2->preds) > 1
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&& can_duplicate_block_p (bb2))
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{
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edge e;
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basic_block old = bb2;
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e = find_edge (bb, bb2);
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nduplicated += counts [bb2->index];
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bb2 = duplicate_block (bb2, e, bb);
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/* Reconsider the original copy of block we've duplicated.
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Removing the most common predecessor may make it to be
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head. */
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blocks[old->index] =
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fibheap_insert (heap, -old->frequency, old);
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if (dump_file)
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fprintf (dump_file, "Duplicated %i as %i [%i]\n",
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old->index, bb2->index, bb2->frequency);
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}
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bb->aux = bb2;
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bb2->il.rtl->visited = 1;
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bb = bb2;
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/* In case the trace became infrequent, stop duplicating. */
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if (ignore_bb_p (bb))
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break;
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}
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if (dump_file)
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fprintf (dump_file, " covered now %.1f\n\n",
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traced_insns * 100.0 / weighted_insns);
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}
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if (dump_file)
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fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
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nduplicated * 100 / ninsns);
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free (blocks);
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free (trace);
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free (counts);
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fibheap_delete (heap);
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}
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/* Connect the superblocks into linear sequence. At the moment we attempt to keep
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the original order as much as possible, but the algorithm may be made smarter
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later if needed. BB reordering pass should void most of the benefits of such
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change though. */
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static void
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layout_superblocks (void)
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{
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basic_block end = single_succ (ENTRY_BLOCK_PTR);
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basic_block bb = end->next_bb;
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while (bb != EXIT_BLOCK_PTR)
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{
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edge_iterator ei;
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edge e, best = NULL;
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while (end->aux)
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end = end->aux;
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FOR_EACH_EDGE (e, ei, end->succs)
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if (e->dest != EXIT_BLOCK_PTR
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&& e->dest != single_succ (ENTRY_BLOCK_PTR)
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&& !e->dest->il.rtl->visited
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&& (!best || EDGE_FREQUENCY (e) > EDGE_FREQUENCY (best)))
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best = e;
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if (best)
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{
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end->aux = best->dest;
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best->dest->il.rtl->visited = 1;
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}
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else
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for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
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{
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if (!bb->il.rtl->visited)
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{
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end->aux = bb;
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bb->il.rtl->visited = 1;
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break;
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}
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}
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}
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}
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/* Main entry point to this file. FLAGS is the set of flags to pass
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to cfg_layout_initialize(). */
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void
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tracer (unsigned int flags)
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{
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if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
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return;
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cfg_layout_initialize (flags);
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mark_dfs_back_edges ();
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if (dump_file)
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dump_flow_info (dump_file, dump_flags);
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tail_duplicate ();
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layout_superblocks ();
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if (dump_file)
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dump_flow_info (dump_file, dump_flags);
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cfg_layout_finalize ();
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/* Merge basic blocks in duplicated traces. */
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cleanup_cfg (CLEANUP_EXPENSIVE);
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}
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static bool
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gate_handle_tracer (void)
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{
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return (optimize > 0 && flag_tracer);
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}
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/* Run tracer. */
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static unsigned int
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rest_of_handle_tracer (void)
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{
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if (dump_file)
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dump_flow_info (dump_file, dump_flags);
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tracer (0);
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cleanup_cfg (CLEANUP_EXPENSIVE);
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reg_scan (get_insns (), max_reg_num ());
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return 0;
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}
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struct tree_opt_pass pass_tracer =
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{
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"tracer", /* name */
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gate_handle_tracer, /* gate */
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rest_of_handle_tracer, /* 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_TRACER, /* tv_id */
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0, /* 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_dump_func, /* todo_flags_finish */
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'T' /* letter */
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};
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