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/* The tracer pass for the GNU compiler.
Contributed by Jan Hubicka, SuSE Labs.
Adapted to work on GIMPLE instead of RTL by Robert Kidd, UIUC.
Copyright (C) 2001-2017 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/>. */
/* This pass performs the tail duplication needed for superblock formation.
For more information see:
Design and Analysis of Profile-Based Optimization in Compaq's
Compilation Tools for Alpha; Journal of Instruction-Level
Parallelism 3 (2000) 1-25
Unlike Compaq's implementation we don't do the loop peeling as most
probably a better job can be done by a special pass and we don't
need to worry too much about the code size implications as the tail
duplicates are crossjumped again if optimizations are not
performed. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "backend.h"
#include "rtl.h"
#include "tree.h"
#include "gimple.h"
#include "cfghooks.h"
#include "tree-pass.h"
#include "profile.h"
#include "cfganal.h"
#include "params.h"
#include "gimple-iterator.h"
#include "tree-cfg.h"
#include "tree-ssa.h"
#include "tree-inline.h"
#include "cfgloop.h"
#include "fibonacci_heap.h"
#include "tracer.h"
static int count_insns (basic_block);
static bool better_p (const_edge, const_edge);
static edge find_best_successor (basic_block);
static edge find_best_predecessor (basic_block);
static int find_trace (basic_block, basic_block *);
/* Minimal outgoing edge probability considered for superblock formation. */
static int probability_cutoff;
static int branch_ratio_cutoff;
/* A bit BB->index is set if BB has already been seen, i.e. it is
connected to some trace already. */
static sbitmap bb_seen;
static inline void
mark_bb_seen (basic_block bb)
{
unsigned int size = SBITMAP_SIZE (bb_seen);
if ((unsigned int)bb->index >= size)
bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
bitmap_set_bit (bb_seen, bb->index);
}
static inline bool
bb_seen_p (basic_block bb)
{
return bitmap_bit_p (bb_seen, bb->index);
}
/* Return true if we should ignore the basic block for purposes of tracing. */
bool
ignore_bb_p (const_basic_block bb)
{
if (bb->index < NUM_FIXED_BLOCKS)
return true;
if (optimize_bb_for_size_p (bb))
return true;
if (gimple *g = last_stmt (CONST_CAST_BB (bb)))
{
/* A transaction is a single entry multiple exit region. It
must be duplicated in its entirety or not at all. */
if (gimple_code (g) == GIMPLE_TRANSACTION)
return true;
/* An IFN_UNIQUE call must be duplicated as part of its group,
or not at all. */
if (is_gimple_call (g)
&& gimple_call_internal_p (g)
&& gimple_call_internal_unique_p (g))
return true;
}
return false;
}
/* Return number of instructions in the block. */
static int
count_insns (basic_block bb)
{
gimple_stmt_iterator gsi;
gimple *stmt;
int n = 0;
for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
stmt = gsi_stmt (gsi);
n += estimate_num_insns (stmt, &eni_size_weights);
}
return n;
}
/* Return true if E1 is more frequent than E2. */
static bool
better_p (const_edge e1, const_edge e2)
{
if (e1->count != e2->count)
return e1->count > e2->count;
if (e1->src->frequency * e1->probability !=
e2->src->frequency * e2->probability)
return (e1->src->frequency * e1->probability
> e2->src->frequency * e2->probability);
/* This is needed to avoid changes in the decision after
CFG is modified. */
if (e1->src != e2->src)
return e1->src->index > e2->src->index;
return e1->dest->index > e2->dest->index;
}
/* Return most frequent successor of basic block BB. */
static edge
find_best_successor (basic_block bb)
{
edge e;
edge best = NULL;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->succs)
if (!best || better_p (e, best))
best = e;
if (!best || ignore_bb_p (best->dest))
return NULL;
if (best->probability <= probability_cutoff)
return NULL;
return best;
}
/* Return most frequent predecessor of basic block BB. */
static edge
find_best_predecessor (basic_block bb)
{
edge e;
edge best = NULL;
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->preds)
if (!best || better_p (e, best))
best = e;
if (!best || ignore_bb_p (best->src))
return NULL;
if (EDGE_FREQUENCY (best) * REG_BR_PROB_BASE
< bb->frequency * branch_ratio_cutoff)
return NULL;
return best;
}
/* Find the trace using bb and record it in the TRACE array.
Return number of basic blocks recorded. */
static int
find_trace (basic_block bb, basic_block *trace)
{
int i = 0;
edge e;
if (dump_file)
fprintf (dump_file, "Trace seed %i [%i]", bb->index, bb->frequency);
while ((e = find_best_predecessor (bb)) != NULL)
{
basic_block bb2 = e->src;
if (bb_seen_p (bb2) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
|| find_best_successor (bb2) != e)
break;
if (dump_file)
fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
bb = bb2;
}
if (dump_file)
fprintf (dump_file, " forward %i [%i]", bb->index, bb->frequency);
trace[i++] = bb;
/* Follow the trace in forward direction. */
while ((e = find_best_successor (bb)) != NULL)
{
bb = e->dest;
if (bb_seen_p (bb) || (e->flags & (EDGE_DFS_BACK | EDGE_COMPLEX))
|| find_best_predecessor (bb) != e)
break;
if (dump_file)
fprintf (dump_file, ",%i [%i]", bb->index, bb->frequency);
trace[i++] = bb;
}
if (dump_file)
fprintf (dump_file, "\n");
return i;
}
/* Duplicate block BB2, placing it after BB in the CFG. Return the
newly created block. */
basic_block
transform_duplicate (basic_block bb, basic_block bb2)
{
edge e;
basic_block copy;
e = find_edge (bb, bb2);
copy = duplicate_block (bb2, e, bb);
flush_pending_stmts (e);
add_phi_args_after_copy (&copy, 1, NULL);
return (copy);
}
/* Look for basic blocks in frequency order, construct traces and tail duplicate
if profitable. */
static bool
tail_duplicate (void)
{
auto_vec<fibonacci_node<long, basic_block_def>*> blocks;
blocks.safe_grow_cleared (last_basic_block_for_fn (cfun));
basic_block *trace = XNEWVEC (basic_block, n_basic_blocks_for_fn (cfun));
int *counts = XNEWVEC (int, last_basic_block_for_fn (cfun));
int ninsns = 0, nduplicated = 0;
gcov_type weighted_insns = 0, traced_insns = 0;
fibonacci_heap<long, basic_block_def> heap (LONG_MIN);
gcov_type cover_insns;
int max_dup_insns;
basic_block bb;
bool changed = false;
/* Create an oversized sbitmap to reduce the chance that we need to
resize it. */
bb_seen = sbitmap_alloc (last_basic_block_for_fn (cfun) * 2);
bitmap_clear (bb_seen);
initialize_original_copy_tables ();
if (profile_info && flag_branch_probabilities)
probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
else
probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
branch_ratio_cutoff =
(REG_BR_PROB_BASE / 100 * PARAM_VALUE (TRACER_MIN_BRANCH_RATIO));
FOR_EACH_BB_FN (bb, cfun)
{
int n = count_insns (bb);
if (!ignore_bb_p (bb))
blocks[bb->index] = heap.insert (-bb->frequency, bb);
counts [bb->index] = n;
ninsns += n;
weighted_insns += n * bb->frequency;
}
if (profile_info && flag_branch_probabilities)
cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE_FEEDBACK);
else
cover_insns = PARAM_VALUE (TRACER_DYNAMIC_COVERAGE);
cover_insns = (weighted_insns * cover_insns + 50) / 100;
max_dup_insns = (ninsns * PARAM_VALUE (TRACER_MAX_CODE_GROWTH) + 50) / 100;
while (traced_insns < cover_insns && nduplicated < max_dup_insns
&& !heap.empty ())
{
basic_block bb = heap.extract_min ();
int n, pos;
if (!bb)
break;
blocks[bb->index] = NULL;
if (ignore_bb_p (bb))
continue;
gcc_assert (!bb_seen_p (bb));
n = find_trace (bb, trace);
bb = trace[0];
traced_insns += bb->frequency * counts [bb->index];
if (blocks[bb->index])
{
heap.delete_node (blocks[bb->index]);
blocks[bb->index] = NULL;
}
for (pos = 1; pos < n; pos++)
{
basic_block bb2 = trace[pos];
if (blocks[bb2->index])
{
heap.delete_node (blocks[bb2->index]);
blocks[bb2->index] = NULL;
}
traced_insns += bb2->frequency * counts [bb2->index];
if (EDGE_COUNT (bb2->preds) > 1
&& can_duplicate_block_p (bb2)
/* We have the tendency to duplicate the loop header
of all do { } while loops. Do not do that - it is
not profitable and it might create a loop with multiple
entries or at least rotate the loop. */
&& bb2->loop_father->header != bb2)
{
nduplicated += counts [bb2->index];
basic_block copy = transform_duplicate (bb, bb2);
/* Reconsider the original copy of block we've duplicated.
Removing the most common predecessor may make it to be
head. */
blocks[bb2->index] = heap.insert (-bb2->frequency, bb2);
if (dump_file)
fprintf (dump_file, "Duplicated %i as %i [%i]\n",
bb2->index, copy->index, copy->frequency);
bb2 = copy;
changed = true;
}
mark_bb_seen (bb2);
bb = bb2;
/* In case the trace became infrequent, stop duplicating. */
if (ignore_bb_p (bb))
break;
}
if (dump_file)
fprintf (dump_file, " covered now %.1f\n\n",
traced_insns * 100.0 / weighted_insns);
}
if (dump_file)
fprintf (dump_file, "Duplicated %i insns (%i%%)\n", nduplicated,
nduplicated * 100 / ninsns);
free_original_copy_tables ();
sbitmap_free (bb_seen);
free (trace);
free (counts);
return changed;
}
namespace {
const pass_data pass_data_tracer =
{
GIMPLE_PASS, /* type */
"tracer", /* name */
OPTGROUP_NONE, /* optinfo_flags */
TV_TRACER, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_update_ssa, /* todo_flags_finish */
};
class pass_tracer : public gimple_opt_pass
{
public:
pass_tracer (gcc::context *ctxt)
: gimple_opt_pass (pass_data_tracer, ctxt)
{}
/* opt_pass methods: */
virtual bool gate (function *)
{
return (optimize > 0 && flag_tracer && flag_reorder_blocks);
}
virtual unsigned int execute (function *);
}; // class pass_tracer
unsigned int
pass_tracer::execute (function *fun)
{
bool changed;
if (n_basic_blocks_for_fn (fun) <= NUM_FIXED_BLOCKS + 1)
return 0;
mark_dfs_back_edges ();
if (dump_file)
brief_dump_cfg (dump_file, dump_flags);
/* Trace formation is done on the fly inside tail_duplicate */
changed = tail_duplicate ();
if (changed)
{
free_dominance_info (CDI_DOMINATORS);
/* If we changed the CFG schedule loops for fixup by cleanup_cfg. */
loops_state_set (LOOPS_NEED_FIXUP);
}
if (dump_file)
brief_dump_cfg (dump_file, dump_flags);
return changed ? TODO_cleanup_cfg : 0;
}
} // anon namespace
gimple_opt_pass *
make_pass_tracer (gcc::context *ctxt)
{
return new pass_tracer (ctxt);
}