diff options
Diffstat (limited to 'gcc/predict.c')
| -rw-r--r-- | gcc/predict.c | 509 |
1 files changed, 432 insertions, 77 deletions
diff --git a/gcc/predict.c b/gcc/predict.c index 669760bf41f..271698bd2d1 100644 --- a/gcc/predict.c +++ b/gcc/predict.c @@ -53,6 +53,11 @@ Software Foundation, 59 Temple Place - Suite 330, Boston, MA #include "target.h" #include "loop.h" #include "cfgloop.h" +#include "tree-flow.h" +#include "ggc.h" +#include "tree-dump.h" +#include "tree-pass.h" +#include "timevar.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. */ @@ -65,9 +70,8 @@ static sreal real_zero, real_one, real_almost_one, real_br_prob_base, #define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY) #define PROB_ALWAYS (REG_BR_PROB_BASE) -static bool predicted_by_p (basic_block, enum br_predictor); static void combine_predictions_for_insn (rtx, basic_block); -static void dump_prediction (enum br_predictor, int, basic_block, int); +static void dump_prediction (FILE *, enum br_predictor, int, basic_block, int); static void estimate_loops_at_level (struct loop *loop); static void propagate_freq (struct loop *); static void estimate_bb_frequencies (struct loops *); @@ -148,8 +152,8 @@ probably_never_executed_bb_p (basic_block bb) /* Return true if the one of outgoing edges is already predicted by PREDICTOR. */ -static bool -predicted_by_p (basic_block bb, enum br_predictor predictor) +bool +rtl_predicted_by_p (basic_block bb, enum br_predictor predictor) { rtx note; if (!INSN_P (BB_END (bb))) @@ -161,6 +165,19 @@ predicted_by_p (basic_block bb, enum br_predictor predictor) return false; } +/* 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) +{ + struct edge_prediction *i = bb_ann (bb)->predictions; + for (i = bb_ann (bb)->predictions; i; i = i->next) + if (i->predictor == predictor) + return true; + return false; +} + void predict_insn (rtx insn, enum br_predictor predictor, int probability) { @@ -194,7 +211,7 @@ predict_insn_def (rtx insn, enum br_predictor predictor, /* Predict edge E with given probability if possible. */ void -predict_edge (edge e, enum br_predictor predictor, int probability) +rtl_predict_edge (edge e, enum br_predictor predictor, int probability) { rtx last_insn; last_insn = BB_END (e->src); @@ -211,6 +228,19 @@ predict_edge (edge e, enum br_predictor predictor, int probability) predict_insn (last_insn, predictor, probability); } +/* Predict edge E with the given PROBABILITY. */ +void +tree_predict_edge (edge e, enum br_predictor predictor, int probability) +{ + struct edge_prediction *i = ggc_alloc (sizeof (struct edge_prediction)); + + i->next = bb_ann (e->src)->predictions; + bb_ann (e->src)->predictions = i; + i->probability = probability; + i->predictor = predictor; + i->edge = e; +} + /* 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. */ @@ -255,34 +285,34 @@ invert_br_probabilities (rtx insn) /* Dump information about the branch prediction to the output file. */ static void -dump_prediction (enum br_predictor predictor, int probability, +dump_prediction (FILE *file, enum br_predictor predictor, int probability, basic_block bb, int used) { edge e = bb->succ; - if (!dump_file) + if (!file) return; while (e && (e->flags & EDGE_FALLTHRU)) e = e->succ_next; - fprintf (dump_file, " %s heuristics%s: %.1f%%", + fprintf (file, " %s heuristics%s: %.1f%%", predictor_info[predictor].name, used ? "" : " (ignored)", probability * 100.0 / REG_BR_PROB_BASE); if (bb->count) { - fprintf (dump_file, " exec "); - fprintf (dump_file, HOST_WIDEST_INT_PRINT_DEC, bb->count); + fprintf (file, " exec "); + fprintf (file, HOST_WIDEST_INT_PRINT_DEC, bb->count); if (e) { - fprintf (dump_file, " hit "); - fprintf (dump_file, HOST_WIDEST_INT_PRINT_DEC, e->count); - fprintf (dump_file, " (%.1f%%)", e->count * 100.0 / bb->count); + fprintf (file, " hit "); + fprintf (file, HOST_WIDEST_INT_PRINT_DEC, e->count); + fprintf (file, " (%.1f%%)", e->count * 100.0 / bb->count); } } - fprintf (dump_file, "\n"); + fprintf (file, "\n"); } /* Combine all REG_BR_PRED notes into single probability and attach REG_BR_PROB @@ -306,8 +336,7 @@ combine_predictions_for_insn (rtx insn, basic_block bb) bb->index); /* We implement "first match" heuristics and use probability guessed - by predictor with smallest index. In the future we will use better - probability combination techniques. */ + by predictor with smallest index. */ for (note = REG_NOTES (insn); note; note = XEXP (note, 1)) if (REG_NOTE_KIND (note) == REG_BR_PRED) { @@ -339,16 +368,19 @@ combine_predictions_for_insn (rtx insn, basic_block bb) first_match = true; if (!found) - dump_prediction (PRED_NO_PREDICTION, combined_probability, bb, true); + dump_prediction (dump_file, PRED_NO_PREDICTION, + combined_probability, bb, true); else { - dump_prediction (PRED_DS_THEORY, combined_probability, bb, !first_match); - dump_prediction (PRED_FIRST_MATCH, best_probability, bb, first_match); + dump_prediction (dump_file, PRED_DS_THEORY, combined_probability, + bb, !first_match); + dump_prediction (dump_file, PRED_FIRST_MATCH, best_probability, + bb, first_match); } if (first_match) combined_probability = best_probability; - dump_prediction (PRED_COMBINED, combined_probability, bb, true); + dump_prediction (dump_file, PRED_COMBINED, combined_probability, bb, true); while (*pnote) { @@ -357,7 +389,7 @@ combine_predictions_for_insn (rtx insn, basic_block bb) int predictor = INTVAL (XEXP (XEXP (*pnote, 0), 0)); int probability = INTVAL (XEXP (XEXP (*pnote, 0), 1)); - dump_prediction (predictor, probability, bb, + dump_prediction (dump_file, predictor, probability, bb, !first_match || best_predictor == predictor); *pnote = XEXP (*pnote, 1); } @@ -382,21 +414,126 @@ combine_predictions_for_insn (rtx insn, basic_block bb) } } -/* Statically estimate the probability that a branch will be taken. - ??? In the next revision there will be a number of other predictors added - from the above references. Further, each heuristic will be factored out - into its own function for clarity (and to facilitate the combination of - predictions). */ +/* Combine predictions into single probability and store them into CFG. + Remove now useless prediction entries. */ -void -estimate_probability (struct loops *loops_info) +static void +combine_predictions_for_bb (FILE *file, basic_block bb) { - basic_block bb; - unsigned i; + int best_probability = PROB_EVEN; + int best_predictor = END_PREDICTORS; + int combined_probability = REG_BR_PROB_BASE / 2; + int d; + bool first_match = false; + bool found = false; + struct edge_prediction *pred; + int nedges = 0; + edge e, first = NULL, second = NULL; - connect_infinite_loops_to_exit (); - calculate_dominance_info (CDI_DOMINATORS); - calculate_dominance_info (CDI_POST_DOMINATORS); + for (e = bb->succ; e; e = e->succ_next) + if (!(e->flags & (EDGE_EH | EDGE_FAKE))) + { + nedges ++; + if (first && !second) + second = e; + if (!first) + first = e; + } + + /* When there is no successor or only one choice, prediction is easy. + + We are lazy for now and predict only basic blocks with two outgoing + edges. It is possible to predict generic case too, but we have to + ignore first match heuristics and do more involved combining. Implement + this later. */ + if (nedges != 2) + { + for (e = bb->succ; e; e = e->succ_next) + if (!(e->flags & (EDGE_EH | EDGE_FAKE))) + e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges; + else + e->probability = 0; + bb_ann (bb)->predictions = NULL; + if (file) + fprintf (file, "%i edges in bb %i predicted to even probabilities\n", + nedges, bb->index); + return; + } + + if (file) + fprintf (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_ann (bb)->predictions; pred; pred = pred->next) + { + int predictor = pred->predictor; + int probability = pred->probability; + + if (pred->edge != first) + probability = REG_BR_PROB_BASE - probability; + + 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)); + + /* 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, + use no_prediction heuristic, in case we did match, use either + first match or Dempster-Shaffer theory depending on the flags. */ + + if (predictor_info [best_predictor].flags & PRED_FLAG_FIRST_MATCH) + first_match = true; + + if (!found) + dump_prediction (file, PRED_NO_PREDICTION, combined_probability, bb, true); + else + { + dump_prediction (file, PRED_DS_THEORY, combined_probability, bb, + !first_match); + dump_prediction (file, PRED_FIRST_MATCH, best_probability, bb, + first_match); + } + + if (first_match) + combined_probability = best_probability; + dump_prediction (file, PRED_COMBINED, combined_probability, bb, true); + + for (pred = bb_ann (bb)->predictions; pred; pred = pred->next) + { + int predictor = pred->predictor; + int probability = pred->probability; + + if (pred->edge != bb->succ) + probability = REG_BR_PROB_BASE - probability; + dump_prediction (file, predictor, probability, bb, + !first_match || best_predictor == predictor); + } + bb_ann (bb)->predictions = NULL; + + first->probability = combined_probability; + second->probability = REG_BR_PROB_BASE - combined_probability; +} + +/* Predict edge probabilities by exploiting loop structure. + When SIMPLELOOPS is set, attempt to count number of iterations by analyzing + RTL. */ +static void +predict_loops (struct loops *loops_info, bool simpleloops) +{ + unsigned i; /* Try to predict out blocks in a loop that are not part of a natural loop. */ @@ -412,27 +549,31 @@ estimate_probability (struct loops *loops_info) flow_loop_scan (loop, LOOP_EXIT_EDGES); exits = loop->num_exits; - iv_analysis_loop_init (loop); - find_simple_exit (loop, &desc); - - if (desc.simple_p && desc.const_iter) + if (simpleloops) { - int prob; - niter = desc.niter + 1; - if (niter == 0) /* We might overflow here. */ - niter = desc.niter; - - prob = (REG_BR_PROB_BASE - - (REG_BR_PROB_BASE + niter /2) / niter); - /* Branch prediction algorithm gives 0 frequency for everything - after the end of loop for loop having 0 probability to finish. */ - if (prob == REG_BR_PROB_BASE) - prob = REG_BR_PROB_BASE - 1; - predict_edge (desc.in_edge, PRED_LOOP_ITERATIONS, - prob); + iv_analysis_loop_init (loop); + find_simple_exit (loop, &desc); + + if (desc.simple_p && desc.const_iter) + { + int prob; + niter = desc.niter + 1; + if (niter == 0) /* We might overflow here. */ + niter = desc.niter; + + prob = (REG_BR_PROB_BASE + - (REG_BR_PROB_BASE + niter /2) / niter); + /* Branch prediction algorithm gives 0 frequency for everything + after the end of loop for loop having 0 probability to finish. */ + if (prob == REG_BR_PROB_BASE) + prob = REG_BR_PROB_BASE - 1; + predict_edge (desc.in_edge, PRED_LOOP_ITERATIONS, + prob); + } } bbs = get_loop_body (loop); + for (j = 0; j < loop->num_nodes; j++) { int header_found = 0; @@ -444,7 +585,7 @@ estimate_probability (struct loops *loops_info) statements construct loops via "non-loop" constructs in the source language and are better to be handled separately. */ - if (!can_predict_insn_p (BB_END (bb)) + if ((simpleloops && !can_predict_insn_p (BB_END (bb))) || predicted_by_p (bb, PRED_CONTINUE)) continue; @@ -474,6 +615,22 @@ estimate_probability (struct loops *loops_info) /* Free basic blocks from get_loop_body. */ free (bbs); } +} + +/* Statically estimate the probability that a branch will be taken and produce + estimated profile. When profile feedback is present never executed portions + of function gets estimated. */ + +void +estimate_probability (struct loops *loops_info) +{ + basic_block bb; + + connect_infinite_loops_to_exit (); + calculate_dominance_info (CDI_DOMINATORS); + calculate_dominance_info (CDI_POST_DOMINATORS); + + predict_loops (loops_info, true); iv_analysis_done (); @@ -622,10 +779,216 @@ estimate_probability (struct loops *loops_info) && bb->succ->succ_next != NULL) combine_predictions_for_insn (BB_END (bb), bb); + remove_fake_edges (); + /* Fill in the probability values in flowgraph based on the REG_BR_PROB + notes. */ + FOR_EACH_BB (bb) + { + rtx last_insn = BB_END (bb); + + if (!can_predict_insn_p (last_insn)) + { + /* We can predict only conditional jumps at the moment. + Expect each edge to be equally probable. + ?? In the future we want to make abnormal edges improbable. */ + int nedges = 0; + edge e; + + for (e = bb->succ; e; e = e->succ_next) + { + nedges++; + if (e->probability != 0) + break; + } + if (!e) + for (e = bb->succ; e; e = e->succ_next) + e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges; + } + } + estimate_bb_frequencies (loops_info); free_dominance_info (CDI_POST_DOMINATORS); +} + + +/* Predict using opcode of the last statement in basic block. */ +static void +tree_predict_by_opcode (basic_block bb) +{ + tree stmt = last_stmt (bb); + edge then_edge; + tree cond; + tree op0; + tree type; + + if (!stmt || TREE_CODE (stmt) != COND_EXPR) + return; + for (then_edge = bb->succ; then_edge; then_edge = then_edge->succ_next) + if (then_edge->flags & EDGE_TRUE_VALUE) + break; + cond = TREE_OPERAND (stmt, 0); + if (TREE_CODE_CLASS (TREE_CODE (cond)) != '<') + return; + op0 = TREE_OPERAND (cond, 0); + type = TREE_TYPE (op0); + /* Try "pointer heuristic." + A comparison ptr == 0 is predicted as false. + Similarly, a comparison ptr1 == ptr2 is predicted as false. */ + if (POINTER_TYPE_P (type)) + { + if (TREE_CODE (cond) == EQ_EXPR) + predict_edge_def (then_edge, PRED_TREE_POINTER, NOT_TAKEN); + else if (TREE_CODE (cond) == NE_EXPR) + predict_edge_def (then_edge, PRED_TREE_POINTER, TAKEN); + } + else + + /* Try "opcode heuristic." + EQ tests are usually false and NE tests are usually true. Also, + most quantities are positive, so we can make the appropriate guesses + about signed comparisons against zero. */ + switch (TREE_CODE (cond)) + { + case EQ_EXPR: + case UNEQ_EXPR: + /* Floating point comparisons appears to behave in a very + unpredictable way because of special role of = tests in + FP code. */ + if (FLOAT_TYPE_P (type)) + ; + /* Comparisons with 0 are often used for booleans and there is + nothing useful to predict about them. */ + else if (integer_zerop (op0) + || integer_zerop (TREE_OPERAND (cond, 1))) + ; + else + predict_edge_def (then_edge, PRED_TREE_OPCODE_NONEQUAL, NOT_TAKEN); + break; + + case NE_EXPR: + /* Floating point comparisons appears to behave in a very + unpredictable way because of special role of = tests in + FP code. */ + if (FLOAT_TYPE_P (type)) + ; + /* Comparisons with 0 are often used for booleans and there is + nothing useful to predict about them. */ + else if (integer_zerop (op0) + || integer_zerop (TREE_OPERAND (cond, 1))) + ; + else + predict_edge_def (then_edge, PRED_TREE_OPCODE_NONEQUAL, TAKEN); + break; + + case ORDERED_EXPR: + predict_edge_def (then_edge, PRED_TREE_FPOPCODE, TAKEN); + break; + + case UNORDERED_EXPR: + predict_edge_def (then_edge, PRED_TREE_FPOPCODE, NOT_TAKEN); + break; + + case LE_EXPR: + case LT_EXPR: + if (integer_zerop (TREE_OPERAND (cond, 1)) + || integer_onep (TREE_OPERAND (cond, 1)) + || integer_all_onesp (TREE_OPERAND (cond, 1)) + || real_zerop (TREE_OPERAND (cond, 1)) + || real_onep (TREE_OPERAND (cond, 1)) + || real_minus_onep (TREE_OPERAND (cond, 1))) + predict_edge_def (then_edge, PRED_TREE_OPCODE_POSITIVE, NOT_TAKEN); + break; + + case GE_EXPR: + case GT_EXPR: + if (integer_zerop (TREE_OPERAND (cond, 1)) + || integer_onep (TREE_OPERAND (cond, 1)) + || integer_all_onesp (TREE_OPERAND (cond, 1)) + || real_zerop (TREE_OPERAND (cond, 1)) + || real_onep (TREE_OPERAND (cond, 1)) + || real_minus_onep (TREE_OPERAND (cond, 1))) + predict_edge_def (then_edge, PRED_TREE_OPCODE_POSITIVE, TAKEN); + break; + + default: + break; + } +} + +/* Predict branch probabilities and estimate profile of the tree CFG. */ +static void +tree_estimate_probability (void) +{ + basic_block bb; + struct loops loops_info; + + flow_loops_find (&loops_info, LOOP_TREE); + if (dump_file && (dump_flags & TDF_DETAILS)) + flow_loops_dump (&loops_info, dump_file, NULL, 0); + + connect_infinite_loops_to_exit (); + calculate_dominance_info (CDI_DOMINATORS); + calculate_dominance_info (CDI_POST_DOMINATORS); + + predict_loops (&loops_info, false); + + FOR_EACH_BB (bb) + { + edge e; + + 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); + + /* 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) + && !dominated_by_p (CDI_POST_DOMINATORS, e->src, e->dest)) + { + block_stmt_iterator bi; + + /* The call heuristic claims that a guarded function call + is improbable. This is because such calls are often used + to signal exceptional situations such as printing error + messages. */ + for (bi = bsi_start (e->dest); !bsi_end_p (bi); + bsi_next (&bi)) + { + tree stmt = bsi_stmt (bi); + if ((TREE_CODE (stmt) == CALL_EXPR + || (TREE_CODE (stmt) == MODIFY_EXPR + && TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR)) + /* Constant and pure calls are hardly used to signalize + something exceptional. */ + && TREE_SIDE_EFFECTS (stmt)) + { + predict_edge_def (e, PRED_CALL, NOT_TAKEN); + break; + } + } + } + } + tree_predict_by_opcode (bb); + } + FOR_EACH_BB (bb) + combine_predictions_for_bb (dump_file, bb); + estimate_bb_frequencies (&loops_info); + free_dominance_info (CDI_POST_DOMINATORS); remove_fake_edges (); - estimate_bb_frequencies (loops_info); + flow_loops_free (&loops_info); + if (dump_file && (dump_flags & TDF_DETAILS)) + dump_tree_cfg (dump_file, dump_flags); } /* __builtin_expect dropped tokens into the insn stream describing expected @@ -1138,31 +1501,6 @@ estimate_bb_frequencies (struct loops *loops) } mark_dfs_back_edges (); - /* Fill in the probability values in flowgraph based on the REG_BR_PROB - notes. */ - FOR_EACH_BB (bb) - { - rtx last_insn = BB_END (bb); - - if (!can_predict_insn_p (last_insn)) - { - /* We can predict only conditional jumps at the moment. - Expect each edge to be equally probable. - ?? In the future we want to make abnormal edges improbable. */ - int nedges = 0; - edge e; - - for (e = bb->succ; e; e = e->succ_next) - { - nedges++; - if (e->probability != 0) - break; - } - if (!e) - for (e = bb->succ; e; e = e->succ_next) - e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges; - } - } ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE; @@ -1251,3 +1589,20 @@ choose_function_section (void) build_string (strlen (UNLIKELY_EXECUTED_TEXT_SECTION_NAME), UNLIKELY_EXECUTED_TEXT_SECTION_NAME); } + + +struct tree_opt_pass pass_profile = +{ + "profile", /* name */ + NULL, /* gate */ + tree_estimate_probability, /* execute */ + NULL, /* sub */ + NULL, /* next */ + 0, /* static_pass_number */ + TV_BRANCH_PROB, /* tv_id */ + PROP_cfg, /* properties_required */ + 0, /* properties_provided */ + 0, /* properties_destroyed */ + 0, /* todo_flags_start */ + TODO_ggc_collect | TODO_verify_ssa /* todo_flags_finish */ +}; |
