/* Branch prediction routines for the GNU compiler.
- Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
+ Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2007
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
+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
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. */
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
/* References:
#include "timevar.h"
#include "tree-scalar-evolution.h"
#include "cfgloop.h"
+#include "pointer-set.h"
/* real constants: 0, 1, 1-1/REG_BR_PROB_BASE, REG_BR_PROB_BASE,
1/REG_BR_PROB_BASE, 0.5, BB_FREQ_MAX. */
static void combine_predictions_for_insn (rtx, basic_block);
static void dump_prediction (FILE *, enum br_predictor, int, basic_block, int);
static void predict_paths_leading_to (basic_block, int *, enum br_predictor, enum prediction);
-static bool last_basic_block_p (basic_block);
static void compute_function_frequency (void);
static void choose_function_section (void);
-static bool can_predict_insn_p (rtx);
+static bool can_predict_insn_p (const_rtx);
/* Information we hold about each branch predictor.
Filled using information from predict.def. */
for maximal performance. */
bool
-maybe_hot_bb_p (basic_block bb)
+maybe_hot_bb_p (const_basic_block bb)
{
if (profile_info && flag_branch_probabilities
&& (bb->count
< profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
return false;
+ if (!profile_info || !flag_branch_probabilities)
+ {
+ if (cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
+ return false;
+ if (cfun->function_frequency == FUNCTION_FREQUENCY_HOT)
+ return true;
+ }
if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
return false;
return true;
/* Return true in case BB is cold and should be optimized for size. */
bool
-probably_cold_bb_p (basic_block bb)
+probably_cold_bb_p (const_basic_block bb)
{
if (profile_info && flag_branch_probabilities
&& (bb->count
< profile_info->sum_max / PARAM_VALUE (HOT_BB_COUNT_FRACTION)))
return true;
+ if ((!profile_info || !flag_branch_probabilities)
+ && cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
+ return true;
if (bb->frequency < BB_FREQ_MAX / PARAM_VALUE (HOT_BB_FREQUENCY_FRACTION))
return true;
return false;
/* Return true in case BB is probably never executed. */
bool
-probably_never_executed_bb_p (basic_block bb)
+probably_never_executed_bb_p (const_basic_block bb)
{
if (profile_info && flag_branch_probabilities)
return ((bb->count + profile_info->runs / 2) / profile_info->runs) == 0;
+ if ((!profile_info || !flag_branch_probabilities)
+ && cfun->function_frequency == FUNCTION_FREQUENCY_UNLIKELY_EXECUTED)
+ return true;
return false;
}
PREDICTOR. */
bool
-rtl_predicted_by_p (basic_block bb, enum br_predictor predictor)
+rtl_predicted_by_p (const_basic_block bb, enum br_predictor predictor)
{
rtx note;
if (!INSN_P (BB_END (bb)))
return false;
}
+/* This map contains for a basic block the list of predictions for the
+ outgoing edges. */
+
+static struct pointer_map_t *bb_predictions;
+
/* Return true if the one of outgoing edges is already predicted by
PREDICTOR. */
bool
-tree_predicted_by_p (basic_block bb, enum br_predictor predictor)
+tree_predicted_by_p (const_basic_block bb, enum br_predictor predictor)
{
struct edge_prediction *i;
- for (i = bb->predictions; i; i = i->ep_next)
+ void **preds = pointer_map_contains (bb_predictions, bb);
+
+ if (!preds)
+ return false;
+
+ for (i = *preds; i; i = i->ep_next)
if (i->ep_predictor == predictor)
return true;
return false;
/* Same predicate as above, working on edges. */
bool
-edge_probability_reliable_p (edge e)
+edge_probability_reliable_p (const_edge e)
{
return probability_reliable_p (e->probability);
}
/* Same predicate as edge_probability_reliable_p, working on notes. */
bool
-br_prob_note_reliable_p (rtx note)
+br_prob_note_reliable_p (const_rtx note)
{
gcc_assert (REG_NOTE_KIND (note) == REG_BR_PROB);
return probability_reliable_p (INTVAL (XEXP (note, 0)));
if ((e->src != ENTRY_BLOCK_PTR && EDGE_COUNT (e->src->succs) > 1)
&& flag_guess_branch_prob && optimize)
{
- struct edge_prediction *i = ggc_alloc (sizeof (struct edge_prediction));
+ struct edge_prediction *i = XNEW (struct edge_prediction);
+ void **preds = pointer_map_insert (bb_predictions, e->src);
- i->ep_next = e->src->predictions;
- e->src->predictions = i;
+ i->ep_next = *preds;
+ *preds = i;
i->ep_probability = probability;
i->ep_predictor = predictor;
i->ep_edge = e;
void
remove_predictions_associated_with_edge (edge e)
{
- if (e->src->predictions)
+ void **preds;
+
+ if (!bb_predictions)
+ return;
+
+ preds = pointer_map_contains (bb_predictions, e->src);
+
+ if (preds)
{
- struct edge_prediction **prediction = &e->src->predictions;
+ struct edge_prediction **prediction = (struct edge_prediction **) preds;
+ struct edge_prediction *next;
+
while (*prediction)
{
if ((*prediction)->ep_edge == e)
- *prediction = (*prediction)->ep_next;
+ {
+ next = (*prediction)->ep_next;
+ free (*prediction);
+ *prediction = next;
+ }
else
prediction = &((*prediction)->ep_next);
}
}
}
+/* Clears the list of predictions stored for BB. */
+
+static void
+clear_bb_predictions (basic_block bb)
+{
+ void **preds = pointer_map_contains (bb_predictions, bb);
+ struct edge_prediction *pred, *next;
+
+ if (!preds)
+ return;
+
+ for (pred = *preds; pred; pred = next)
+ {
+ next = pred->ep_next;
+ free (pred);
+ }
+ *preds = NULL;
+}
+
/* Return true when we can store prediction on insn INSN.
At the moment we represent predictions only on conditional
jumps, not at computed jump or other complicated cases. */
static bool
-can_predict_insn_p (rtx insn)
+can_predict_insn_p (const_rtx insn)
{
return (JUMP_P (insn)
&& any_condjump_p (insn)
int nedges = 0;
edge e, first = NULL, second = NULL;
edge_iterator ei;
+ void **preds;
FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
{
if (!bb->count)
set_even_probabilities (bb);
- bb->predictions = NULL;
+ clear_bb_predictions (bb);
if (dump_file)
fprintf (dump_file, "%i edges in bb %i predicted to even probabilities\n",
nedges, bb->index);
if (dump_file)
fprintf (dump_file, "Predictions for bb %i\n", bb->index);
- /* We implement "first match" heuristics and use probability guessed
- by predictor with smallest index. */
- for (pred = bb->predictions; pred; pred = pred->ep_next)
+ preds = pointer_map_contains (bb_predictions, bb);
+ if (preds)
{
- int predictor = pred->ep_predictor;
- int probability = pred->ep_probability;
+ /* We implement "first match" heuristics and use probability guessed
+ by predictor with smallest index. */
+ for (pred = *preds; pred; pred = pred->ep_next)
+ {
+ int predictor = pred->ep_predictor;
+ int probability = pred->ep_probability;
- if (pred->ep_edge != first)
- probability = REG_BR_PROB_BASE - probability;
+ if (pred->ep_edge != first)
+ probability = REG_BR_PROB_BASE - probability;
- found = true;
- if (best_predictor > predictor)
- best_probability = probability, best_predictor = predictor;
+ found = true;
+ if (best_predictor > predictor)
+ best_probability = probability, best_predictor = predictor;
- d = (combined_probability * probability
- + (REG_BR_PROB_BASE - combined_probability)
- * (REG_BR_PROB_BASE - probability));
+ d = (combined_probability * probability
+ + (REG_BR_PROB_BASE - combined_probability)
+ * (REG_BR_PROB_BASE - probability));
- /* Use FP math to avoid overflows of 32bit integers. */
- if (d == 0)
- /* If one probability is 0% and one 100%, avoid division by zero. */
- combined_probability = REG_BR_PROB_BASE / 2;
- else
- combined_probability = (((double) combined_probability) * probability
- * REG_BR_PROB_BASE / d + 0.5);
+ /* Use FP math to avoid overflows of 32bit integers. */
+ if (d == 0)
+ /* If one probability is 0% and one 100%, avoid division by zero. */
+ combined_probability = REG_BR_PROB_BASE / 2;
+ else
+ combined_probability = (((double) combined_probability)
+ * probability
+ * REG_BR_PROB_BASE / d + 0.5);
+ }
}
/* Decide which heuristic to use. In case we didn't match anything,
combined_probability = best_probability;
dump_prediction (dump_file, PRED_COMBINED, combined_probability, bb, true);
- for (pred = bb->predictions; pred; pred = pred->ep_next)
+ if (preds)
{
- int predictor = pred->ep_predictor;
- int probability = pred->ep_probability;
+ for (pred = *preds; pred; pred = pred->ep_next)
+ {
+ int predictor = pred->ep_predictor;
+ int probability = pred->ep_probability;
- if (pred->ep_edge != EDGE_SUCC (bb, 0))
- probability = REG_BR_PROB_BASE - probability;
- dump_prediction (dump_file, predictor, probability, bb,
- !first_match || best_predictor == predictor);
+ if (pred->ep_edge != EDGE_SUCC (bb, 0))
+ probability = REG_BR_PROB_BASE - probability;
+ dump_prediction (dump_file, predictor, probability, bb,
+ !first_match || best_predictor == predictor);
+ }
}
- bb->predictions = NULL;
+ clear_bb_predictions (bb);
if (!bb->count)
{
for (j = 0; VEC_iterate (edge, exits, j, ex); j++)
{
tree niter = NULL;
+ HOST_WIDE_INT nitercst;
+ int max = PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS);
+ int probability;
+ enum br_predictor predictor;
if (number_of_iterations_exit (loop, ex, &niter_desc, false))
niter = niter_desc.niter;
if (TREE_CODE (niter) == INTEGER_CST)
{
- int probability;
- int max = PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS);
if (host_integerp (niter, 1)
&& compare_tree_int (niter, max-1) == -1)
- {
- HOST_WIDE_INT nitercst = tree_low_cst (niter, 1) + 1;
- probability = ((REG_BR_PROB_BASE + nitercst / 2)
- / nitercst);
- }
+ nitercst = tree_low_cst (niter, 1) + 1;
else
- probability = ((REG_BR_PROB_BASE + max / 2) / max);
+ nitercst = max;
+ predictor = PRED_LOOP_ITERATIONS;
+ }
+ /* If we have just one exit and we can derive some information about
+ the number of iterations of the loop from the statements inside
+ the loop, use it to predict this exit. */
+ else if (n_exits == 1)
+ {
+ nitercst = estimated_loop_iterations_int (loop, false);
+ if (nitercst < 0)
+ continue;
+ if (nitercst > max)
+ nitercst = max;
- predict_edge (ex, PRED_LOOP_ITERATIONS, probability);
+ predictor = PRED_LOOP_ITERATIONS_GUESSED;
}
+ else
+ continue;
+
+ probability = ((REG_BR_PROB_BASE + nitercst / 2) / nitercst);
+ predict_edge (ex, predictor, probability);
}
VEC_free (edge, heap, exits);
/* Loop exit heuristics - predict an edge exiting the loop if the
conditional has no loop header successors as not taken. */
- if (!header_found)
+ if (!header_found
+ /* If we already used more reliable loop exit predictors, do not
+ bother with PRED_LOOP_EXIT. */
+ && !predicted_by_p (bb, PRED_LOOP_ITERATIONS_GUESSED)
+ && !predicted_by_p (bb, PRED_LOOP_ITERATIONS))
{
/* For loop with many exits we don't want to predict all exits
with the pretty large probability, because if all exits are
if (DECL_BUILT_IN_CLASS (decl) == BUILT_IN_NORMAL
&& DECL_FUNCTION_CODE (decl) == BUILT_IN_EXPECT)
{
- tree arglist = TREE_OPERAND (expr, 1);
tree val;
- if (arglist == NULL_TREE
- || TREE_CHAIN (arglist) == NULL_TREE)
- return NULL;
- val = TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr, 1)));
+ if (call_expr_nargs (expr) != 2)
+ return NULL;
+ val = CALL_EXPR_ARG (expr, 0);
if (TREE_CONSTANT (val))
return val;
- return TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr, 1)));
+ return CALL_EXPR_ARG (expr, 1);
}
}
if (BINARY_CLASS_P (expr) || COMPARISON_CLASS_P (expr))
{
tree stmt = bsi_stmt (bi);
tree fndecl;
- tree arglist;
+ tree call;
if (TREE_CODE (stmt) == GIMPLE_MODIFY_STMT
- && TREE_CODE (GIMPLE_STMT_OPERAND (stmt, 1)) == CALL_EXPR
- && (fndecl = get_callee_fndecl (GIMPLE_STMT_OPERAND (stmt, 1)))
+ && (call = GIMPLE_STMT_OPERAND (stmt, 1))
+ && TREE_CODE (call) == CALL_EXPR
+ && (fndecl = get_callee_fndecl (call))
&& DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL
&& DECL_FUNCTION_CODE (fndecl) == BUILT_IN_EXPECT
- && (arglist = TREE_OPERAND (GIMPLE_STMT_OPERAND (stmt, 1), 1))
- && TREE_CHAIN (arglist))
+ && call_expr_nargs (call) == 2)
{
- GIMPLE_STMT_OPERAND (stmt, 1) = TREE_VALUE (arglist);
+ GIMPLE_STMT_OPERAND (stmt, 1) = CALL_EXPR_ARG (call, 0);
update_stmt (stmt);
}
}
&& (!integer_zerop (val) && !integer_onep (val)))
{
*prediction = TAKEN;
- return PRED_NEGATIVE_RETURN;
+ return PRED_CONST_RETURN;
}
}
return PRED_NO_PREDICTION;
FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
{
return_stmt = last_stmt (e->src);
- if (TREE_CODE (return_stmt) == RETURN_EXPR)
+ if (return_stmt
+ && TREE_CODE (return_stmt) == RETURN_EXPR)
break;
}
if (!e)
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
{
tree stmt = bsi_stmt (bsi);
+ tree decl;
switch (TREE_CODE (stmt))
{
case GIMPLE_MODIFY_STMT:
if (call_expr_flags (stmt) & ECF_NORETURN)
predict_paths_leading_to (bb, heads, PRED_NORETURN,
NOT_TAKEN);
+ decl = get_callee_fndecl (stmt);
+ if (decl
+ && lookup_attribute ("cold",
+ DECL_ATTRIBUTES (decl)))
+ predict_paths_leading_to (bb, heads, PRED_COLD_FUNCTION,
+ NOT_TAKEN);
break;
default:
break;
free (heads);
}
+#ifdef ENABLE_CHECKING
+
+/* Callback for pointer_map_traverse, asserts that the pointer map is
+ empty. */
+
+static bool
+assert_is_empty (const void *key ATTRIBUTE_UNUSED, void **value,
+ void *data ATTRIBUTE_UNUSED)
+{
+ gcc_assert (!*value);
+ return false;
+}
+#endif
+
/* Predict branch probabilities and estimate profile of the tree CFG. */
static unsigned int
tree_estimate_probability (void)
basic_block bb;
loop_optimizer_init (0);
- if (current_loops && dump_file && (dump_flags & TDF_DETAILS))
+ if (dump_file && (dump_flags & TDF_DETAILS))
flow_loops_dump (dump_file, NULL, 0);
add_noreturn_fake_exit_edges ();
connect_infinite_loops_to_exit ();
- calculate_dominance_info (CDI_DOMINATORS);
+ /* We use loop_niter_by_eval, which requires that the loops have
+ preheaders. */
+ create_preheaders (CP_SIMPLE_PREHEADERS);
calculate_dominance_info (CDI_POST_DOMINATORS);
+ bb_predictions = pointer_map_create ();
tree_bb_level_predictions ();
mark_irreducible_loops ();
- if (current_loops)
+ record_loop_exits ();
+ if (number_of_loops () > 1)
predict_loops ();
FOR_EACH_BB (bb)
{
/* Predict early returns to be probable, as we've already taken
care for error returns and other cases are often used for
- fast paths through function. */
- if (e->dest == EXIT_BLOCK_PTR
- && TREE_CODE (last_stmt (bb)) == RETURN_EXPR
- && !single_pred_p (bb))
+ fast paths through function.
+
+ Since we've already removed the return statements, we are
+ looking for CFG like:
+
+ if (conditional)
+ {
+ ..
+ goto return_block
+ }
+ some other blocks
+ return_block:
+ return_stmt. */
+ if (e->dest != bb->next_bb
+ && e->dest != EXIT_BLOCK_PTR
+ && single_succ_p (e->dest)
+ && single_succ_edge (e->dest)->dest == EXIT_BLOCK_PTR
+ && TREE_CODE (last_stmt (e->dest)) == RETURN_EXPR)
{
edge e1;
edge_iterator ei1;
- FOR_EACH_EDGE (e1, ei1, bb->preds)
- if (!predicted_by_p (e1->src, PRED_NULL_RETURN)
- && !predicted_by_p (e1->src, PRED_CONST_RETURN)
- && !predicted_by_p (e1->src, PRED_NEGATIVE_RETURN)
- && !last_basic_block_p (e1->src))
- predict_edge_def (e1, PRED_TREE_EARLY_RETURN, NOT_TAKEN);
+ if (single_succ_p (bb))
+ {
+ FOR_EACH_EDGE (e1, ei1, bb->preds)
+ if (!predicted_by_p (e1->src, PRED_NULL_RETURN)
+ && !predicted_by_p (e1->src, PRED_CONST_RETURN)
+ && !predicted_by_p (e1->src, PRED_NEGATIVE_RETURN))
+ predict_edge_def (e1, PRED_TREE_EARLY_RETURN, NOT_TAKEN);
+ }
+ else
+ if (!predicted_by_p (e->src, PRED_NULL_RETURN)
+ && !predicted_by_p (e->src, PRED_CONST_RETURN)
+ && !predicted_by_p (e->src, PRED_NEGATIVE_RETURN))
+ predict_edge_def (e, PRED_TREE_EARLY_RETURN, NOT_TAKEN);
}
/* Look for block we are guarding (ie we dominate it,
FOR_EACH_BB (bb)
combine_predictions_for_bb (bb);
+#ifdef ENABLE_CHECKING
+ pointer_map_traverse (bb_predictions, assert_is_empty, NULL);
+#endif
+ pointer_map_destroy (bb_predictions);
+ bb_predictions = NULL;
+
strip_builtin_expect ();
estimate_bb_frequencies ();
free_dominance_info (CDI_POST_DOMINATORS);
return 0;
}
\f
-/* Check whether this is the last basic block of function. Commonly
- there is one extra common cleanup block. */
-static bool
-last_basic_block_p (basic_block bb)
-{
- if (bb == EXIT_BLOCK_PTR)
- return false;
-
- return (bb->next_bb == EXIT_BLOCK_PTR
- || (bb->next_bb->next_bb == EXIT_BLOCK_PTR
- && single_succ_p (bb)
- && single_succ (bb)->next_bb == EXIT_BLOCK_PTR));
-}
-
/* Sets branch probabilities according to PREDiction and
FLAGS. HEADS[bb->index] should be index of basic block in that we
need to alter branch predictions (i.e. the first of our dominators
basic_block bb;
/* Start by estimating the frequencies in the loops. */
- if (current_loops)
+ if (number_of_loops () > 1)
estimate_loops_at_level (current_loops->tree_root->inner);
/* Now propagate the frequencies through all the blocks. */
basic_block bb;
if (!profile_info || !flag_branch_probabilities)
- return;
+ {
+ if (lookup_attribute ("cold", DECL_ATTRIBUTES (current_function_decl))
+ != NULL)
+ cfun->function_frequency = FUNCTION_FREQUENCY_UNLIKELY_EXECUTED;
+ else if (lookup_attribute ("hot", DECL_ATTRIBUTES (current_function_decl))
+ != NULL)
+ cfun->function_frequency = FUNCTION_FREQUENCY_HOT;
+ return;
+ }
cfun->function_frequency = FUNCTION_FREQUENCY_UNLIKELY_EXECUTED;
FOR_EACH_BB (bb)
{
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