Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

401 lines (335 sloc) 11.013 kB
/* 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, 2002, 2003, 2004, 2005, 2006, 2007, 2008
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 "tm.h"
#include "tree.h"
#include "rtl.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "output.h"
#include "cfglayout.h"
#include "fibheap.h"
#include "flags.h"
#include "timevar.h"
#include "params.h"
#include "coverage.h"
#include "tree-pass.h"
#include "tree-flow.h"
#include "tree-inline.h"
static int count_insns (basic_block);
static bool ignore_bb_p (const_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 *);
static void tail_duplicate (void);
/* 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. */
sbitmap bb_seen;
static inline void
mark_bb_seen (basic_block bb)
{
unsigned int size = SBITMAP_SIZE_BYTES (bb_seen) * 8;
if ((unsigned int)bb->index >= size)
bb_seen = sbitmap_resize (bb_seen, size * 2, 0);
SET_BIT (bb_seen, bb->index);
}
static inline bool
bb_seen_p (basic_block bb)
{
return TEST_BIT (bb_seen, bb->index);
}
/* Return true if we should ignore the basic block for purposes of tracing. */
static 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;
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;
}
/* Look for basic blocks in frequency order, construct traces and tail duplicate
if profitable. */
static void
tail_duplicate (void)
{
fibnode_t *blocks = XCNEWVEC (fibnode_t, last_basic_block);
basic_block *trace = XNEWVEC (basic_block, n_basic_blocks);
int *counts = XNEWVEC (int, last_basic_block);
int ninsns = 0, nduplicated = 0;
gcov_type weighted_insns = 0, traced_insns = 0;
fibheap_t heap = fibheap_new ();
gcov_type cover_insns;
int max_dup_insns;
basic_block bb;
/* Create an oversized sbitmap to reduce the chance that we need to
resize it. */
bb_seen = sbitmap_alloc (last_basic_block * 2);
sbitmap_zero (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 (bb)
{
int n = count_insns (bb);
if (!ignore_bb_p (bb))
blocks[bb->index] = fibheap_insert (heap, -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
&& !fibheap_empty (heap))
{
basic_block bb = (basic_block) fibheap_extract_min (heap);
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])
{
fibheap_delete_node (heap, blocks[bb->index]);
blocks[bb->index] = NULL;
}
for (pos = 1; pos < n; pos++)
{
basic_block bb2 = trace[pos];
if (blocks[bb2->index])
{
fibheap_delete_node (heap, 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))
{
edge e;
basic_block copy;
nduplicated += counts [bb2->index];
e = find_edge (bb, bb2);
copy = duplicate_block (bb2, e, bb);
flush_pending_stmts (e);
add_phi_args_after_copy (&copy, 1, NULL);
/* Reconsider the original copy of block we've duplicated.
Removing the most common predecessor may make it to be
head. */
blocks[bb2->index] =
fibheap_insert (heap, -bb2->frequency, bb2);
if (dump_file)
fprintf (dump_file, "Duplicated %i as %i [%i]\n",
bb2->index, copy->index, copy->frequency);
bb2 = copy;
}
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 (blocks);
free (trace);
free (counts);
fibheap_delete (heap);
}
/* Main entry point to this file. */
static unsigned int
tracer (void)
{
gcc_assert (current_ir_type () == IR_GIMPLE);
if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1)
return 0;
mark_dfs_back_edges ();
if (dump_file)
dump_flow_info (dump_file, dump_flags);
/* Trace formation is done on the fly inside tail_duplicate */
tail_duplicate ();
/* FIXME: We really only need to do this when we know tail duplication
has altered the CFG. */
free_dominance_info (CDI_DOMINATORS);
if (dump_file)
dump_flow_info (dump_file, dump_flags);
return 0;
}
static bool
gate_tracer (void)
{
return (optimize > 0 && flag_tracer && flag_reorder_blocks);
}
struct gimple_opt_pass pass_tracer =
{
{
GIMPLE_PASS,
"tracer", /* name */
gate_tracer, /* gate */
tracer, /* execute */
NULL, /* sub */
NULL, /* next */
0, /* static_pass_number */
TV_TRACER, /* tv_id */
0, /* properties_required */
0, /* properties_provided */
0, /* properties_destroyed */
0, /* todo_flags_start */
TODO_dump_func
| TODO_update_ssa
| TODO_verify_ssa /* todo_flags_finish */
}
};
Jump to Line
Something went wrong with that request. Please try again.