mirror of
https://git.FreeBSD.org/src.git
synced 2024-12-23 11:18:54 +00:00
583 lines
16 KiB
C
583 lines
16 KiB
C
/* Induction variable canonicalization.
|
|
Copyright (C) 2004, 2005 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 2, 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 COPYING. If not, write to the Free
|
|
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
|
|
02110-1301, USA. */
|
|
|
|
/* This pass detects the loops that iterate a constant number of times,
|
|
adds a canonical induction variable (step -1, tested against 0)
|
|
and replaces the exit test. This enables the less powerful rtl
|
|
level analysis to use this information.
|
|
|
|
This might spoil the code in some cases (by increasing register pressure).
|
|
Note that in the case the new variable is not needed, ivopts will get rid
|
|
of it, so it might only be a problem when there are no other linear induction
|
|
variables. In that case the created optimization possibilities are likely
|
|
to pay up.
|
|
|
|
Additionally in case we detect that it is beneficial to unroll the
|
|
loop completely, we do it right here to expose the optimization
|
|
possibilities to the following passes. */
|
|
|
|
#include "config.h"
|
|
#include "system.h"
|
|
#include "coretypes.h"
|
|
#include "tm.h"
|
|
#include "tree.h"
|
|
#include "rtl.h"
|
|
#include "tm_p.h"
|
|
#include "hard-reg-set.h"
|
|
#include "basic-block.h"
|
|
#include "output.h"
|
|
#include "diagnostic.h"
|
|
#include "tree-flow.h"
|
|
#include "tree-dump.h"
|
|
#include "cfgloop.h"
|
|
#include "tree-pass.h"
|
|
#include "ggc.h"
|
|
#include "tree-chrec.h"
|
|
#include "tree-scalar-evolution.h"
|
|
#include "params.h"
|
|
#include "flags.h"
|
|
#include "tree-inline.h"
|
|
|
|
/* Specifies types of loops that may be unrolled. */
|
|
|
|
enum unroll_level
|
|
{
|
|
UL_SINGLE_ITER, /* Only loops that exit immediately in the first
|
|
iteration. */
|
|
UL_NO_GROWTH, /* Only loops whose unrolling will not cause increase
|
|
of code size. */
|
|
UL_ALL /* All suitable loops. */
|
|
};
|
|
|
|
/* Adds a canonical induction variable to LOOP iterating NITER times. EXIT
|
|
is the exit edge whose condition is replaced. */
|
|
|
|
static void
|
|
create_canonical_iv (struct loop *loop, edge exit, tree niter)
|
|
{
|
|
edge in;
|
|
tree cond, type, var;
|
|
block_stmt_iterator incr_at;
|
|
enum tree_code cmp;
|
|
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
{
|
|
fprintf (dump_file, "Added canonical iv to loop %d, ", loop->num);
|
|
print_generic_expr (dump_file, niter, TDF_SLIM);
|
|
fprintf (dump_file, " iterations.\n");
|
|
}
|
|
|
|
cond = last_stmt (exit->src);
|
|
in = EDGE_SUCC (exit->src, 0);
|
|
if (in == exit)
|
|
in = EDGE_SUCC (exit->src, 1);
|
|
|
|
/* Note that we do not need to worry about overflows, since
|
|
type of niter is always unsigned and all comparisons are
|
|
just for equality/nonequality -- i.e. everything works
|
|
with a modulo arithmetics. */
|
|
|
|
type = TREE_TYPE (niter);
|
|
niter = fold_build2 (PLUS_EXPR, type,
|
|
niter,
|
|
build_int_cst (type, 1));
|
|
incr_at = bsi_last (in->src);
|
|
create_iv (niter,
|
|
build_int_cst (type, -1),
|
|
NULL_TREE, loop,
|
|
&incr_at, false, NULL, &var);
|
|
|
|
cmp = (exit->flags & EDGE_TRUE_VALUE) ? EQ_EXPR : NE_EXPR;
|
|
COND_EXPR_COND (cond) = build2 (cmp, boolean_type_node,
|
|
var,
|
|
build_int_cst (type, 0));
|
|
update_stmt (cond);
|
|
}
|
|
|
|
/* Computes an estimated number of insns in LOOP. */
|
|
|
|
unsigned
|
|
tree_num_loop_insns (struct loop *loop)
|
|
{
|
|
basic_block *body = get_loop_body (loop);
|
|
block_stmt_iterator bsi;
|
|
unsigned size = 1, i;
|
|
|
|
for (i = 0; i < loop->num_nodes; i++)
|
|
for (bsi = bsi_start (body[i]); !bsi_end_p (bsi); bsi_next (&bsi))
|
|
size += estimate_num_insns (bsi_stmt (bsi));
|
|
free (body);
|
|
|
|
return size;
|
|
}
|
|
|
|
/* Estimate number of insns of completely unrolled loop. We assume
|
|
that the size of the unrolled loop is decreased in the
|
|
following way (the numbers of insns are based on what
|
|
estimate_num_insns returns for appropriate statements):
|
|
|
|
1) exit condition gets removed (2 insns)
|
|
2) increment of the control variable gets removed (2 insns)
|
|
3) All remaining statements are likely to get simplified
|
|
due to constant propagation. Hard to estimate; just
|
|
as a heuristics we decrease the rest by 1/3.
|
|
|
|
NINSNS is the number of insns in the loop before unrolling.
|
|
NUNROLL is the number of times the loop is unrolled. */
|
|
|
|
static unsigned HOST_WIDE_INT
|
|
estimated_unrolled_size (unsigned HOST_WIDE_INT ninsns,
|
|
unsigned HOST_WIDE_INT nunroll)
|
|
{
|
|
HOST_WIDE_INT unr_insns = 2 * ((HOST_WIDE_INT) ninsns - 4) / 3;
|
|
if (unr_insns <= 0)
|
|
unr_insns = 1;
|
|
unr_insns *= (nunroll + 1);
|
|
|
|
return unr_insns;
|
|
}
|
|
|
|
/* Tries to unroll LOOP completely, i.e. NITER times. LOOPS is the
|
|
loop tree. UL determines which loops we are allowed to unroll.
|
|
EXIT is the exit of the loop that should be eliminated. */
|
|
|
|
static bool
|
|
try_unroll_loop_completely (struct loops *loops ATTRIBUTE_UNUSED,
|
|
struct loop *loop,
|
|
edge exit, tree niter,
|
|
enum unroll_level ul)
|
|
{
|
|
unsigned HOST_WIDE_INT n_unroll, ninsns, max_unroll, unr_insns;
|
|
tree old_cond, cond, dont_exit, do_exit;
|
|
|
|
if (loop->inner)
|
|
return false;
|
|
|
|
if (!host_integerp (niter, 1))
|
|
return false;
|
|
n_unroll = tree_low_cst (niter, 1);
|
|
|
|
max_unroll = PARAM_VALUE (PARAM_MAX_COMPLETELY_PEEL_TIMES);
|
|
if (n_unroll > max_unroll)
|
|
return false;
|
|
|
|
if (n_unroll)
|
|
{
|
|
if (ul == UL_SINGLE_ITER)
|
|
return false;
|
|
|
|
ninsns = tree_num_loop_insns (loop);
|
|
|
|
if (n_unroll * ninsns
|
|
> (unsigned) PARAM_VALUE (PARAM_MAX_COMPLETELY_PEELED_INSNS))
|
|
return false;
|
|
|
|
if (ul == UL_NO_GROWTH)
|
|
{
|
|
unr_insns = estimated_unrolled_size (ninsns, n_unroll);
|
|
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
{
|
|
fprintf (dump_file, " Loop size: %d\n", (int) ninsns);
|
|
fprintf (dump_file, " Estimated size after unrolling: %d\n",
|
|
(int) unr_insns);
|
|
}
|
|
|
|
if (unr_insns > ninsns)
|
|
{
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
fprintf (dump_file, "Not unrolling loop %d:\n", loop->num);
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (exit->flags & EDGE_TRUE_VALUE)
|
|
{
|
|
dont_exit = boolean_false_node;
|
|
do_exit = boolean_true_node;
|
|
}
|
|
else
|
|
{
|
|
dont_exit = boolean_true_node;
|
|
do_exit = boolean_false_node;
|
|
}
|
|
cond = last_stmt (exit->src);
|
|
|
|
if (n_unroll)
|
|
{
|
|
sbitmap wont_exit;
|
|
edge *edges_to_remove = XNEWVEC (edge, n_unroll);
|
|
unsigned int n_to_remove = 0;
|
|
|
|
old_cond = COND_EXPR_COND (cond);
|
|
COND_EXPR_COND (cond) = dont_exit;
|
|
update_stmt (cond);
|
|
initialize_original_copy_tables ();
|
|
|
|
wont_exit = sbitmap_alloc (n_unroll + 1);
|
|
sbitmap_ones (wont_exit);
|
|
RESET_BIT (wont_exit, 0);
|
|
|
|
if (!tree_duplicate_loop_to_header_edge (loop, loop_preheader_edge (loop),
|
|
loops, n_unroll, wont_exit,
|
|
exit, edges_to_remove,
|
|
&n_to_remove,
|
|
DLTHE_FLAG_UPDATE_FREQ
|
|
| DLTHE_FLAG_COMPLETTE_PEEL))
|
|
{
|
|
COND_EXPR_COND (cond) = old_cond;
|
|
update_stmt (cond);
|
|
free_original_copy_tables ();
|
|
free (wont_exit);
|
|
free (edges_to_remove);
|
|
return false;
|
|
}
|
|
free (wont_exit);
|
|
free (edges_to_remove);
|
|
free_original_copy_tables ();
|
|
}
|
|
|
|
COND_EXPR_COND (cond) = do_exit;
|
|
update_stmt (cond);
|
|
|
|
update_ssa (TODO_update_ssa);
|
|
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
fprintf (dump_file, "Unrolled loop %d completely.\n", loop->num);
|
|
|
|
return true;
|
|
}
|
|
|
|
/* Adds a canonical induction variable to LOOP if suitable. LOOPS is the loops
|
|
tree. CREATE_IV is true if we may create a new iv. UL determines
|
|
which loops we are allowed to completely unroll. If TRY_EVAL is true, we try
|
|
to determine the number of iterations of a loop by direct evaluation.
|
|
Returns true if cfg is changed. */
|
|
|
|
static bool
|
|
canonicalize_loop_induction_variables (struct loops *loops, struct loop *loop,
|
|
bool create_iv, enum unroll_level ul,
|
|
bool try_eval)
|
|
{
|
|
edge exit = NULL;
|
|
tree niter;
|
|
|
|
niter = number_of_iterations_in_loop (loop);
|
|
if (TREE_CODE (niter) == INTEGER_CST)
|
|
{
|
|
exit = loop->single_exit;
|
|
if (!just_once_each_iteration_p (loop, exit->src))
|
|
return false;
|
|
|
|
/* The result of number_of_iterations_in_loop is by one higher than
|
|
we expect (i.e. it returns number of executions of the exit
|
|
condition, not of the loop latch edge). */
|
|
niter = fold_build2 (MINUS_EXPR, TREE_TYPE (niter), niter,
|
|
build_int_cst (TREE_TYPE (niter), 1));
|
|
}
|
|
else
|
|
{
|
|
/* If the loop has more than one exit, try checking all of them
|
|
for # of iterations determinable through scev. */
|
|
if (!loop->single_exit)
|
|
niter = find_loop_niter (loop, &exit);
|
|
|
|
/* Finally if everything else fails, try brute force evaluation. */
|
|
if (try_eval
|
|
&& (chrec_contains_undetermined (niter)
|
|
|| TREE_CODE (niter) != INTEGER_CST))
|
|
niter = find_loop_niter_by_eval (loop, &exit);
|
|
|
|
if (chrec_contains_undetermined (niter)
|
|
|| TREE_CODE (niter) != INTEGER_CST)
|
|
return false;
|
|
}
|
|
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
{
|
|
fprintf (dump_file, "Loop %d iterates ", loop->num);
|
|
print_generic_expr (dump_file, niter, TDF_SLIM);
|
|
fprintf (dump_file, " times.\n");
|
|
}
|
|
|
|
if (try_unroll_loop_completely (loops, loop, exit, niter, ul))
|
|
return true;
|
|
|
|
if (create_iv)
|
|
create_canonical_iv (loop, exit, niter);
|
|
|
|
return false;
|
|
}
|
|
|
|
/* The main entry point of the pass. Adds canonical induction variables
|
|
to the suitable LOOPS. */
|
|
|
|
unsigned int
|
|
canonicalize_induction_variables (struct loops *loops)
|
|
{
|
|
unsigned i;
|
|
struct loop *loop;
|
|
bool changed = false;
|
|
|
|
for (i = 1; i < loops->num; i++)
|
|
{
|
|
loop = loops->parray[i];
|
|
|
|
if (loop)
|
|
changed |= canonicalize_loop_induction_variables (loops, loop,
|
|
true, UL_SINGLE_ITER,
|
|
true);
|
|
}
|
|
|
|
/* Clean up the information about numbers of iterations, since brute force
|
|
evaluation could reveal new information. */
|
|
scev_reset ();
|
|
|
|
if (changed)
|
|
return TODO_cleanup_cfg;
|
|
return 0;
|
|
}
|
|
|
|
/* Unroll LOOPS completely if they iterate just few times. Unless
|
|
MAY_INCREASE_SIZE is true, perform the unrolling only if the
|
|
size of the code does not increase. */
|
|
|
|
unsigned int
|
|
tree_unroll_loops_completely (struct loops *loops, bool may_increase_size)
|
|
{
|
|
unsigned i;
|
|
struct loop *loop;
|
|
bool changed = false;
|
|
enum unroll_level ul;
|
|
|
|
for (i = 1; i < loops->num; i++)
|
|
{
|
|
loop = loops->parray[i];
|
|
|
|
if (!loop)
|
|
continue;
|
|
|
|
if (may_increase_size && maybe_hot_bb_p (loop->header))
|
|
ul = UL_ALL;
|
|
else
|
|
ul = UL_NO_GROWTH;
|
|
changed |= canonicalize_loop_induction_variables (loops, loop,
|
|
false, ul,
|
|
!flag_tree_loop_ivcanon);
|
|
}
|
|
|
|
/* Clean up the information about numbers of iterations, since complete
|
|
unrolling might have invalidated it. */
|
|
scev_reset ();
|
|
|
|
if (changed)
|
|
return TODO_cleanup_cfg;
|
|
return 0;
|
|
}
|
|
|
|
/* Checks whether LOOP is empty. */
|
|
|
|
static bool
|
|
empty_loop_p (struct loop *loop)
|
|
{
|
|
edge exit;
|
|
struct tree_niter_desc niter;
|
|
tree phi, def;
|
|
basic_block *body;
|
|
block_stmt_iterator bsi;
|
|
unsigned i;
|
|
tree stmt;
|
|
|
|
/* If the loop has multiple exits, it is too hard for us to handle.
|
|
Similarly, if the exit is not dominating, we cannot determine
|
|
whether the loop is not infinite. */
|
|
exit = single_dom_exit (loop);
|
|
if (!exit)
|
|
return false;
|
|
|
|
/* The loop must be finite. */
|
|
if (!number_of_iterations_exit (loop, exit, &niter, false))
|
|
return false;
|
|
|
|
/* Values of all loop exit phi nodes must be invariants. */
|
|
for (phi = phi_nodes (exit->dest); phi; phi = PHI_CHAIN (phi))
|
|
{
|
|
if (!is_gimple_reg (PHI_RESULT (phi)))
|
|
continue;
|
|
|
|
def = PHI_ARG_DEF_FROM_EDGE (phi, exit);
|
|
|
|
if (!expr_invariant_in_loop_p (loop, def))
|
|
return false;
|
|
}
|
|
|
|
/* And there should be no memory modifying or from other reasons
|
|
unremovable statements. */
|
|
body = get_loop_body (loop);
|
|
for (i = 0; i < loop->num_nodes; i++)
|
|
{
|
|
/* Irreducible region might be infinite. */
|
|
if (body[i]->flags & BB_IRREDUCIBLE_LOOP)
|
|
{
|
|
free (body);
|
|
return false;
|
|
}
|
|
|
|
for (bsi = bsi_start (body[i]); !bsi_end_p (bsi); bsi_next (&bsi))
|
|
{
|
|
stmt = bsi_stmt (bsi);
|
|
if (!ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_DEFS)
|
|
|| stmt_ann (stmt)->has_volatile_ops)
|
|
{
|
|
free (body);
|
|
return false;
|
|
}
|
|
|
|
/* Also, asm statements and calls may have side effects and we
|
|
cannot change the number of times they are executed. */
|
|
switch (TREE_CODE (stmt))
|
|
{
|
|
case RETURN_EXPR:
|
|
case MODIFY_EXPR:
|
|
stmt = get_call_expr_in (stmt);
|
|
if (!stmt)
|
|
break;
|
|
|
|
case CALL_EXPR:
|
|
if (TREE_SIDE_EFFECTS (stmt))
|
|
{
|
|
free (body);
|
|
return false;
|
|
}
|
|
break;
|
|
|
|
case ASM_EXPR:
|
|
/* We cannot remove volatile assembler. */
|
|
if (ASM_VOLATILE_P (stmt))
|
|
{
|
|
free (body);
|
|
return false;
|
|
}
|
|
break;
|
|
|
|
default:
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
free (body);
|
|
|
|
return true;
|
|
}
|
|
|
|
/* Remove LOOP by making it exit in the first iteration. */
|
|
|
|
static void
|
|
remove_empty_loop (struct loop *loop)
|
|
{
|
|
edge exit = single_dom_exit (loop), non_exit;
|
|
tree cond_stmt = last_stmt (exit->src);
|
|
tree do_exit;
|
|
basic_block *body;
|
|
unsigned n_before, freq_in, freq_h;
|
|
gcov_type exit_count = exit->count;
|
|
|
|
non_exit = EDGE_SUCC (exit->src, 0);
|
|
if (non_exit == exit)
|
|
non_exit = EDGE_SUCC (exit->src, 1);
|
|
|
|
if (exit->flags & EDGE_TRUE_VALUE)
|
|
do_exit = boolean_true_node;
|
|
else
|
|
do_exit = boolean_false_node;
|
|
|
|
COND_EXPR_COND (cond_stmt) = do_exit;
|
|
update_stmt (cond_stmt);
|
|
|
|
/* Let us set the probabilities of the edges coming from the exit block. */
|
|
exit->probability = REG_BR_PROB_BASE;
|
|
non_exit->probability = 0;
|
|
non_exit->count = 0;
|
|
|
|
/* Update frequencies and counts. Everything before
|
|
the exit needs to be scaled FREQ_IN/FREQ_H times,
|
|
where FREQ_IN is the frequency of the entry edge
|
|
and FREQ_H is the frequency of the loop header.
|
|
Everything after the exit has zero frequency. */
|
|
freq_h = loop->header->frequency;
|
|
freq_in = EDGE_FREQUENCY (loop_preheader_edge (loop));
|
|
if (freq_h != 0)
|
|
{
|
|
body = get_loop_body_in_dom_order (loop);
|
|
for (n_before = 1; n_before <= loop->num_nodes; n_before++)
|
|
if (body[n_before - 1] == exit->src)
|
|
break;
|
|
scale_bbs_frequencies_int (body, n_before, freq_in, freq_h);
|
|
scale_bbs_frequencies_int (body + n_before, loop->num_nodes - n_before,
|
|
0, 1);
|
|
free (body);
|
|
}
|
|
|
|
/* Number of executions of exit is not changed, thus we need to restore
|
|
the original value. */
|
|
exit->count = exit_count;
|
|
}
|
|
|
|
/* Removes LOOP if it is empty. Returns true if LOOP is removed. CHANGED
|
|
is set to true if LOOP or any of its subloops is removed. */
|
|
|
|
static bool
|
|
try_remove_empty_loop (struct loop *loop, bool *changed)
|
|
{
|
|
bool nonempty_subloop = false;
|
|
struct loop *sub;
|
|
|
|
/* First, all subloops must be removed. */
|
|
for (sub = loop->inner; sub; sub = sub->next)
|
|
nonempty_subloop |= !try_remove_empty_loop (sub, changed);
|
|
|
|
if (nonempty_subloop || !empty_loop_p (loop))
|
|
return false;
|
|
|
|
remove_empty_loop (loop);
|
|
*changed = true;
|
|
return true;
|
|
}
|
|
|
|
/* Remove the empty LOOPS. */
|
|
|
|
unsigned int
|
|
remove_empty_loops (struct loops *loops)
|
|
{
|
|
bool changed = false;
|
|
struct loop *loop;
|
|
|
|
for (loop = loops->tree_root->inner; loop; loop = loop->next)
|
|
try_remove_empty_loop (loop, &changed);
|
|
|
|
if (changed)
|
|
{
|
|
scev_reset ();
|
|
return TODO_cleanup_cfg;
|
|
}
|
|
return 0;
|
|
}
|