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predict.c (return_prediction): New function.

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* predict.c (return_prediction): New function.
	(apply_return_prediction): Likewise.
	(tree_bb_level_predictions): Likewise.
	(tree_estimate_probability): Add noreturn exit edges; call
	bb_level_predictions; fix logic of return heuristics.
	(predict_paths_leading_to):  Rescuesce from old CVS version of
	process_note_prediction function.
	* predict.def (PRED_TREE_EARLY_RETURN): New predictor.

From-SVN: r87768
This commit is contained in:
Jan Hubicka 2004-09-20 20:43:30 +02:00 committed by Jan Hubicka
parent 348f5701fc
commit bb033fd806
3 changed files with 234 additions and 11 deletions
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11
gcc/ChangeLog
View File

@ -1,3 +1,14 @@
2004-09-20 Jan Hubicka <jh@suse.cz>
* predict.c (return_prediction): New function.
(apply_return_prediction): Likewise.
(tree_bb_level_predictions): Likewise.
(tree_estimate_probability): Add noreturn exit edges; call
bb_level_predictions; fix logic of return heuristics.
(predict_paths_leading_to): Rescuesce from old CVS version of
process_note_prediction function.
* predict.def (PRED_TREE_EARLY_RETURN): New predictor.
2004-09-20 Andreas Krebbel <krebbel1@de.ibm.com>
* config/s390/s390.c (s390_frame_info): Added alignment statement for

233
gcc/predict.c
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@ -77,6 +77,7 @@ static void estimate_loops_at_level (struct loop *loop);
static void propagate_freq (struct loop *);
static void estimate_bb_frequencies (struct loops *);
static int counts_to_freqs (void);
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);
@ -1119,6 +1120,152 @@ tree_predict_by_opcode (basic_block bb)
}
}
/* Try to guess whether the value of return means error code. */
static enum br_predictor
return_prediction (tree val, enum prediction *prediction)
{
/* VOID. */
if (!val)
return PRED_NO_PREDICTION;
/* Different heuristics for pointers and scalars. */
if (POINTER_TYPE_P (TREE_TYPE (val)))
{
/* NULL is usually not returned. */
if (integer_zerop (val))
{
*prediction = NOT_TAKEN;
return PRED_NULL_RETURN;
}
}
else if (INTEGRAL_TYPE_P (TREE_TYPE (val)))
{
/* Negative return values are often used to indicate
errors. */
if (TREE_CODE (val) == INTEGER_CST
&& tree_int_cst_sgn (val) < 0)
{
*prediction = NOT_TAKEN;
return PRED_NEGATIVE_RETURN;
}
/* Constant return values seems to be commonly taken.
Zero/one often represent booleans so exclude them from the
heuristics. */
if (TREE_CONSTANT (val)
&& (!integer_zerop (val) && !integer_onep (val)))
{
*prediction = TAKEN;
return PRED_NEGATIVE_RETURN;
}
}
return PRED_NO_PREDICTION;
}
/* Find the basic block with return expression and look up for possible
return value trying to apply RETURN_PREDICTION heuristics. */
static void
apply_return_prediction (int *heads)
{
tree return_stmt;
tree return_val;
edge e;
tree phi;
int phi_num_args, i;
enum br_predictor pred;
enum prediction direction;
for (e = EXIT_BLOCK_PTR->pred; e ; e = e->pred_next)
{
return_stmt = last_stmt (e->src);
if (TREE_CODE (return_stmt) == RETURN_EXPR)
break;
}
if (!e)
return;
return_val = TREE_OPERAND (return_stmt, 0);
if (!return_val)
return;
if (TREE_CODE (return_val) == MODIFY_EXPR)
return_val = TREE_OPERAND (return_val, 1);
if (TREE_CODE (return_val) != SSA_NAME
|| !SSA_NAME_DEF_STMT (return_val)
|| TREE_CODE (SSA_NAME_DEF_STMT (return_val)) != PHI_NODE)
return;
phi = SSA_NAME_DEF_STMT (return_val);
while (phi)
{
tree next = PHI_CHAIN (phi);
if (PHI_RESULT (phi) == return_val)
break;
phi = next;
}
if (!phi)
return;
phi_num_args = PHI_NUM_ARGS (phi);
pred = return_prediction (PHI_ARG_DEF (phi, 0), &direction);
/* Avoid the degenerate case where all return values form the function
belongs to same category (ie they are all positive constants)
so we can hardly say something about them. */
for (i = 1; i < phi_num_args; i++)
if (pred != return_prediction (PHI_ARG_DEF (phi, i), &direction))
break;
if (i != phi_num_args)
for (i = 0; i < phi_num_args; i++)
{
pred = return_prediction (PHI_ARG_DEF (phi, i), &direction);
if (pred != PRED_NO_PREDICTION)
predict_paths_leading_to (PHI_ARG_EDGE (phi, i)->src, heads, pred,
direction);
}
}
/* Look for basic block that contains unlikely to happen events
(such as noreturn calls) and mark all paths leading to execution
of this basic blocks as unlikely. */
static void
tree_bb_level_predictions (void)
{
basic_block bb;
int *heads;
heads = xmalloc (sizeof (int) * last_basic_block);
memset (heads, -1, sizeof (int) * last_basic_block);
heads[ENTRY_BLOCK_PTR->next_bb->index] = last_basic_block;
apply_return_prediction (heads);
FOR_EACH_BB (bb)
{
block_stmt_iterator bsi = bsi_last (bb);
for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
{
tree stmt = bsi_stmt (bsi);
switch (TREE_CODE (stmt))
{
case MODIFY_EXPR:
if (TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)
{
stmt = TREE_OPERAND (stmt, 1);
goto call_expr;
}
break;
case CALL_EXPR:
call_expr:;
if (call_expr_flags (stmt) & ECF_NORETURN)
predict_paths_leading_to (bb, heads, PRED_NORETURN,
NOT_TAKEN);
break;
default:
break;
}
}
}
free (heads);
}
/* Predict branch probabilities and estimate profile of the tree CFG. */
static void
tree_estimate_probability (void)
@ -1130,10 +1277,13 @@ tree_estimate_probability (void)
if (dump_file && (dump_flags & TDF_DETAILS))
flow_loops_dump (&loops_info, dump_file, NULL, 0);
add_noreturn_fake_exit_edges ();
connect_infinite_loops_to_exit ();
calculate_dominance_info (CDI_DOMINATORS);
calculate_dominance_info (CDI_POST_DOMINATORS);
tree_bb_level_predictions ();
predict_loops (&loops_info, false);
FOR_EACH_BB (bb)
@ -1143,18 +1293,23 @@ tree_estimate_probability (void)
for (e = bb->succ; e; e = e->succ_next)
{
/* Predict early returns to be probable, as we've already taken
care for error returns and other are often used for fast paths
trought function. */
if ((e->dest == EXIT_BLOCK_PTR
|| (e->dest->succ && !e->dest->succ->succ_next
&& e->dest->succ->dest == EXIT_BLOCK_PTR))
&& !predicted_by_p (bb, PRED_NULL_RETURN)
&& !predicted_by_p (bb, PRED_CONST_RETURN)
&& !predicted_by_p (bb, PRED_NEGATIVE_RETURN)
&& !last_basic_block_p (e->dest))
predict_edge_def (e, PRED_EARLY_RETURN, TAKEN);
care for error returns and other cases are often used for
fast paths trought function. */
if (e->dest == EXIT_BLOCK_PTR
&& TREE_CODE (last_stmt (bb)) == RETURN_EXPR
&& bb->pred && bb->pred->pred_next)
{
edge e1;
/* Look for block we are guarding (i.e. we dominate it,
for (e1 = bb->pred; e1; e1 = e1->pred_next)
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);
}
/* Look for block we are guarding (ie we dominate it,
but it doesn't postdominate us). */
if (e->dest != EXIT_BLOCK_PTR && e->dest != bb
&& dominated_by_p (CDI_DOMINATORS, e->dest, e->src)
@ -1287,6 +1442,62 @@ last_basic_block_p (basic_block bb)
&& bb->succ && !bb->succ->succ_next
&& bb->succ->dest->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
such that we do not post-dominate it) (but we fill this information
on demand, so -1 may be there in case this was not needed yet). */
static void
predict_paths_leading_to (basic_block bb, int *heads, enum br_predictor pred,
enum prediction taken)
{
edge e;
int y;
if (heads[bb->index] < 0)
{
/* This is first time we need this field in heads array; so
find first dominator that we do not post-dominate (we are
using already known members of heads array). */
basic_block ai = bb;
basic_block next_ai = get_immediate_dominator (CDI_DOMINATORS, bb);
int head;
while (heads[next_ai->index] < 0)
{
if (!dominated_by_p (CDI_POST_DOMINATORS, next_ai, bb))
break;
heads[next_ai->index] = ai->index;
ai = next_ai;
next_ai = get_immediate_dominator (CDI_DOMINATORS, next_ai);
}
if (!dominated_by_p (CDI_POST_DOMINATORS, next_ai, bb))
head = next_ai->index;
else
head = heads[next_ai->index];
while (next_ai != bb)
{
next_ai = ai;
if (heads[ai->index] == ENTRY_BLOCK)
ai = ENTRY_BLOCK_PTR;
else
ai = BASIC_BLOCK (heads[ai->index]);
heads[next_ai->index] = head;
}
}
y = heads[bb->index];
/* Now find the edge that leads to our branch and aply the prediction. */
if (y == last_basic_block)
return;
for (e = BASIC_BLOCK (y)->succ; e; e = e->succ_next)
if (e->dest->index >= 0
&& dominated_by_p (CDI_POST_DOMINATORS, e->dest, bb))
predict_edge_def (e, pred, taken);
}
/* This is used to carry information about basic blocks. It is
attached to the AUX field of the standard CFG block. */

1
gcc/predict.def
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@ -104,6 +104,7 @@ DEF_PREDICTOR (PRED_CALL, "call", HITRATE (70), 0)
/* Branch causing function to terminate is probably not taken. */
DEF_PREDICTOR (PRED_EARLY_RETURN, "early return", HITRATE (67), 0)
DEF_PREDICTOR (PRED_TREE_EARLY_RETURN, "early return (on trees)", HITRATE (67), 0)
/* Branch containing goto is probably not taken. */
DEF_PREDICTOR (PRED_GOTO, "goto", HITRATE (70), 0)