From: Jan Hubicka Date: Mon, 20 Sep 2004 18:43:30 +0000 (+0200) Subject: predict.c (return_prediction): New function. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=bb033fd8060e36e8bafdebec388e5fa91d073d61;p=gcc.git predict.c (return_prediction): New function. * 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 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 39dc5aabc70..1f0ddd6c6a3 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,14 @@ +2004-09-20 Jan Hubicka + + * 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 * config/s390/s390.c (s390_frame_info): Added alignment statement for diff --git a/gcc/predict.c b/gcc/predict.c index c0e7df2a972..7eaee34d2eb 100644 --- a/gcc/predict.c +++ b/gcc/predict.c @@ -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; + + 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) @@ -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. */ diff --git a/gcc/predict.def b/gcc/predict.def index 4b571630b3b..f469b34c4f8 100644 --- a/gcc/predict.def +++ b/gcc/predict.def @@ -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)