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);
}
}
+/* 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)
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)
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;
+
+ 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 (i.e. we dominate it,
+ /* 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)
&& 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);
+}
\f
/* This is used to carry information about basic blocks. It is
attached to the AUX field of the standard CFG block. */
projects / gcc.git / commitdiff