/* Branch prediction routines for the GNU compiler.
- Copyright (C) 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
+ Free Software Foundation, Inc.
This file is part of GCC.
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, 59 Temple Place - Suite 330, Boston, MA
-02111-1307, USA. */
+Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA. */
/* References:
#include "sreal.h"
#include "params.h"
#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"
+#include "tree-scalar-evolution.h"
+#include "cfgloop.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. */
real_inv_br_prob_base, real_one_half, real_bb_freq_max;
/* Random guesstimation given names. */
-#define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 10 - 1)
+#define PROB_VERY_UNLIKELY (REG_BR_PROB_BASE / 100 - 1)
#define PROB_EVEN (REG_BR_PROB_BASE / 2)
#define PROB_VERY_LIKELY (REG_BR_PROB_BASE - PROB_VERY_UNLIKELY)
#define PROB_ALWAYS (REG_BR_PROB_BASE)
static void combine_predictions_for_insn (rtx, basic_block);
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_loops_at_level (struct loop *, bitmap);
+static void propagate_freq (struct loop *, bitmap);
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);
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)
+ struct edge_prediction *i;
+ for (i = bb->predictions; i; i = i->ep_next)
+ if (i->ep_predictor == predictor)
return true;
return false;
}
-void
+static void
predict_insn (rtx insn, enum br_predictor predictor, int probability)
{
- if (!any_condjump_p (insn))
- abort ();
+ gcc_assert (any_condjump_p (insn));
if (!flag_guess_branch_prob)
return;
void
tree_predict_edge (edge e, enum br_predictor predictor, int probability)
{
- struct edge_prediction *i = ggc_alloc (sizeof (struct edge_prediction));
+ gcc_assert (profile_status != PROFILE_GUESSED);
+ 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));
+
+ i->ep_next = e->src->predictions;
+ e->src->predictions = i;
+ i->ep_probability = probability;
+ i->ep_predictor = predictor;
+ i->ep_edge = e;
+ }
+}
- i->next = bb_ann (e->src)->predictions;
- bb_ann (e->src)->predictions = i;
- i->probability = probability;
- i->predictor = predictor;
- i->edge = e;
+/* Remove all predictions on given basic block that are attached
+ to edge E. */
+void
+remove_predictions_associated_with_edge (edge e)
+{
+ if (e->src->predictions)
+ {
+ struct edge_prediction **prediction = &e->src->predictions;
+ while (*prediction)
+ {
+ if ((*prediction)->ep_edge == e)
+ *prediction = (*prediction)->ep_next;
+ else
+ prediction = &((*prediction)->ep_next);
+ }
+ }
}
/* Return true when we can store prediction on insn INSN.
{
return (JUMP_P (insn)
&& any_condjump_p (insn)
- && BLOCK_FOR_INSN (insn)->succ->succ_next);
+ && EDGE_COUNT (BLOCK_FOR_INSN (insn)->succs) >= 2);
}
/* Predict edge E by given predictor if possible. */
dump_prediction (FILE *file, enum br_predictor predictor, int probability,
basic_block bb, int used)
{
- edge e = bb->succ;
+ edge e;
+ edge_iterator ei;
if (!file)
return;
- while (e && (e->flags & EDGE_FALLTHRU))
- e = e->succ_next;
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ if (! (e->flags & EDGE_FALLTHRU))
+ break;
fprintf (file, " %s heuristics%s: %.1f%%",
predictor_info[predictor].name,
fprintf (file, "\n");
}
-/* We can not predict the probabilities of ougtoing edges of bb. Set them
+/* We can not predict the probabilities of outgoing edges of bb. Set them
evenly and hope for the best. */
static void
set_even_probabilities (basic_block bb)
{
int nedges = 0;
edge e;
+ edge_iterator ei;
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
nedges ++;
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
e->probability = (REG_BR_PROB_BASE + nedges / 2) / nedges;
else
/* Save the prediction into CFG in case we are seeing non-degenerated
conditional jump. */
- if (bb->succ->succ_next)
+ if (!single_succ_p (bb))
{
BRANCH_EDGE (bb)->probability = combined_probability;
FALLTHRU_EDGE (bb)->probability
= REG_BR_PROB_BASE - combined_probability;
}
}
+ else if (!single_succ_p (bb))
+ {
+ int prob = INTVAL (XEXP (prob_note, 0));
+
+ BRANCH_EDGE (bb)->probability = prob;
+ FALLTHRU_EDGE (bb)->probability = REG_BR_PROB_BASE - prob;
+ }
+ else
+ single_succ_edge (bb)->probability = REG_BR_PROB_BASE;
}
/* Combine predictions into single probability and store them into CFG.
Remove now useless prediction entries. */
static void
-combine_predictions_for_bb (FILE *file, basic_block bb)
+combine_predictions_for_bb (basic_block bb)
{
int best_probability = PROB_EVEN;
int best_predictor = END_PREDICTORS;
struct edge_prediction *pred;
int nedges = 0;
edge e, first = NULL, second = NULL;
+ edge_iterator ei;
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & (EDGE_EH | EDGE_FAKE)))
{
- nedges ++;
+ nedges ++;
if (first && !second)
second = e;
if (!first)
{
if (!bb->count)
set_even_probabilities (bb);
- bb_ann (bb)->predictions = NULL;
- if (file)
- fprintf (file, "%i edges in bb %i predicted to even probabilities\n",
+ bb->predictions = NULL;
+ if (dump_file)
+ fprintf (dump_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);
+ 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_ann (bb)->predictions; pred; pred = pred->next)
+ for (pred = bb->predictions; pred; pred = pred->ep_next)
{
- int predictor = pred->predictor;
- int probability = pred->probability;
+ int predictor = pred->ep_predictor;
+ int probability = pred->ep_probability;
- if (pred->edge != first)
+ if (pred->ep_edge != first)
probability = REG_BR_PROB_BASE - probability;
found = true;
first_match = true;
if (!found)
- dump_prediction (file, PRED_NO_PREDICTION, combined_probability, bb, true);
+ dump_prediction (dump_file, PRED_NO_PREDICTION, combined_probability, bb, true);
else
{
- dump_prediction (file, PRED_DS_THEORY, combined_probability, bb,
+ dump_prediction (dump_file, PRED_DS_THEORY, combined_probability, bb,
!first_match);
- dump_prediction (file, PRED_FIRST_MATCH, best_probability, bb,
+ dump_prediction (dump_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);
+ dump_prediction (dump_file, PRED_COMBINED, combined_probability, bb, true);
- for (pred = bb_ann (bb)->predictions; pred; pred = pred->next)
+ for (pred = bb->predictions; pred; pred = pred->ep_next)
{
- int predictor = pred->predictor;
- int probability = pred->probability;
+ int predictor = pred->ep_predictor;
+ int probability = pred->ep_probability;
- if (pred->edge != bb->succ)
+ if (pred->ep_edge != EDGE_SUCC (bb, 0))
probability = REG_BR_PROB_BASE - probability;
- dump_prediction (file, predictor, probability, bb,
+ dump_prediction (dump_file, predictor, probability, bb,
!first_match || best_predictor == predictor);
}
- bb_ann (bb)->predictions = NULL;
+ bb->predictions = NULL;
if (!bb->count)
{
}
/* Predict edge probabilities by exploiting loop structure.
- When SIMPLELOOPS is set, attempt to count number of iterations by analyzing
- RTL. */
+ When RTLSIMPLELOOPS is set, attempt to count number of iterations by analyzing
+ RTL otherwise use tree based approach. */
static void
-predict_loops (struct loops *loops_info, bool simpleloops)
+predict_loops (struct loops *loops_info, bool rtlsimpleloops)
{
unsigned i;
+ if (!rtlsimpleloops)
+ scev_initialize (loops_info);
+
/* Try to predict out blocks in a loop that are not part of a
natural loop. */
for (i = 1; i < loops_info->num; i++)
{
basic_block bb, *bbs;
unsigned j;
- int exits;
+ unsigned n_exits;
struct loop *loop = loops_info->parray[i];
struct niter_desc desc;
unsigned HOST_WIDE_INT niter;
+ edge *exits;
- flow_loop_scan (loop, LOOP_EXIT_EDGES);
- exits = loop->num_exits;
+ exits = get_loop_exit_edges (loop, &n_exits);
- if (simpleloops)
+ if (rtlsimpleloops)
{
iv_analysis_loop_init (loop);
find_simple_exit (loop, &desc);
niter = desc.niter + 1;
if (niter == 0) /* We might overflow here. */
niter = desc.niter;
+ if (niter
+ > (unsigned int) PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS))
+ niter = PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS);
prob = (REG_BR_PROB_BASE
- (REG_BR_PROB_BASE + niter /2) / niter);
prob);
}
}
+ else
+ {
+ struct tree_niter_desc niter_desc;
+
+ for (j = 0; j < n_exits; j++)
+ {
+ tree niter = NULL;
+
+ if (number_of_iterations_exit (loop, exits[j], &niter_desc, false))
+ niter = niter_desc.niter;
+ if (!niter || TREE_CODE (niter_desc.niter) != INTEGER_CST)
+ niter = loop_niter_by_eval (loop, exits[j]);
+
+ if (TREE_CODE (niter) == INTEGER_CST)
+ {
+ int probability;
+ int max = PARAM_VALUE (PARAM_MAX_PREDICTED_ITERATIONS);
+ if (host_integerp (niter, 1)
+ && tree_int_cst_lt (niter,
+ build_int_cstu (NULL_TREE, max - 1)))
+ {
+ HOST_WIDE_INT nitercst = tree_low_cst (niter, 1) + 1;
+ probability = ((REG_BR_PROB_BASE + nitercst / 2)
+ / nitercst);
+ }
+ else
+ probability = ((REG_BR_PROB_BASE + max / 2) / max);
+
+ predict_edge (exits[j], PRED_LOOP_ITERATIONS, probability);
+ }
+ }
+
+ }
+ free (exits);
bbs = get_loop_body (loop);
{
int header_found = 0;
edge e;
+ edge_iterator ei;
bb = bbs[j];
statements construct loops via "non-loop" constructs
in the source language and are better to be handled
separately. */
- if ((simpleloops && !can_predict_insn_p (BB_END (bb)))
+ if ((rtlsimpleloops && !can_predict_insn_p (BB_END (bb)))
|| predicted_by_p (bb, PRED_CONTINUE))
continue;
/* Loop branch heuristics - predict an edge back to a
loop's head as taken. */
- for (e = bb->succ; e; e = e->succ_next)
- if (e->dest == loop->header
- && e->src == loop->latch)
- {
- header_found = 1;
- predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
- }
+ if (bb == loop->latch)
+ {
+ e = find_edge (loop->latch, loop->header);
+ if (e)
+ {
+ header_found = 1;
+ predict_edge_def (e, PRED_LOOP_BRANCH, TAKEN);
+ }
+ }
/* Loop exit heuristics - predict an edge exiting the loop if the
conditional has no loop header successors as not taken. */
if (!header_found)
- for (e = bb->succ; e; e = e->succ_next)
- if (e->dest->index < 0
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ if (e->dest->index < NUM_FIXED_BLOCKS
|| !flow_bb_inside_loop_p (loop, e->dest))
predict_edge
(e, PRED_LOOP_EXIT,
(REG_BR_PROB_BASE
- predictor_info [(int) PRED_LOOP_EXIT].hitrate)
- / exits);
+ / n_exits);
}
/* Free basic blocks from get_loop_body. */
free (bbs);
}
+
+ if (!rtlsimpleloops)
+ {
+ scev_finalize ();
+ current_loops = NULL;
+ }
}
/* Attempt to predict probabilities of BB outgoing edges using local
}
}
-/* 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. */
-
+/* Set edge->probability for each successor edge of BB. */
void
-estimate_probability (struct loops *loops_info)
+guess_outgoing_edge_probabilities (basic_block bb)
{
- 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 ();
-
- /* Attempt to predict conditional jumps using a number of heuristics. */
- FOR_EACH_BB (bb)
+ bb_estimate_probability_locally (bb);
+ combine_predictions_for_insn (BB_END (bb), bb);
+}
+\f
+/* Return constant EXPR will likely have at execution time, NULL if unknown.
+ The function is used by builtin_expect branch predictor so the evidence
+ must come from this construct and additional possible constant folding.
+
+ We may want to implement more involved value guess (such as value range
+ propagation based prediction), but such tricks shall go to new
+ implementation. */
+
+static tree
+expr_expected_value (tree expr, bitmap visited)
+{
+ if (TREE_CONSTANT (expr))
+ return expr;
+ else if (TREE_CODE (expr) == SSA_NAME)
{
- rtx last_insn = BB_END (bb);
- edge e;
+ tree def = SSA_NAME_DEF_STMT (expr);
- if (! can_predict_insn_p (last_insn))
- continue;
+ /* If we were already here, break the infinite cycle. */
+ if (bitmap_bit_p (visited, SSA_NAME_VERSION (expr)))
+ return NULL;
+ bitmap_set_bit (visited, SSA_NAME_VERSION (expr));
- for (e = bb->succ; e; e = e->succ_next)
+ if (TREE_CODE (def) == PHI_NODE)
{
- /* 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);
+ /* All the arguments of the PHI node must have the same constant
+ length. */
+ int i;
+ tree val = NULL, new_val;
- /* 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))
+ for (i = 0; i < PHI_NUM_ARGS (def); i++)
{
- rtx insn;
-
- /* 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 (insn = BB_HEAD (e->dest); insn != NEXT_INSN (BB_END (e->dest));
- insn = NEXT_INSN (insn))
- if (CALL_P (insn)
- /* Constant and pure calls are hardly used to signalize
- something exceptional. */
- && ! CONST_OR_PURE_CALL_P (insn))
- {
- predict_edge_def (e, PRED_CALL, NOT_TAKEN);
- break;
- }
+ tree arg = PHI_ARG_DEF (def, i);
+
+ /* If this PHI has itself as an argument, we cannot
+ determine the string length of this argument. However,
+ if we can find an expected constant value for the other
+ PHI args then we can still be sure that this is
+ likely a constant. So be optimistic and just
+ continue with the next argument. */
+ if (arg == PHI_RESULT (def))
+ continue;
+
+ new_val = expr_expected_value (arg, visited);
+ if (!new_val)
+ return NULL;
+ if (!val)
+ val = new_val;
+ else if (!operand_equal_p (val, new_val, false))
+ return NULL;
}
+ return val;
}
- bb_estimate_probability_locally (bb);
+ if (TREE_CODE (def) != MODIFY_EXPR || TREE_OPERAND (def, 0) != expr)
+ return NULL;
+ return expr_expected_value (TREE_OPERAND (def, 1), visited);
}
-
- /* Attach the combined probability to each conditional jump. */
- FOR_EACH_BB (bb)
- if (JUMP_P (BB_END (bb))
- && any_condjump_p (BB_END (bb))
- && bb->succ->succ_next != NULL)
- combine_predictions_for_insn (BB_END (bb), bb);
-
- remove_fake_exit_edges ();
- /* Fill in the probability values in flowgraph based on the REG_BR_PROB
- notes. */
+ else if (TREE_CODE (expr) == CALL_EXPR)
+ {
+ tree decl = get_callee_fndecl (expr);
+ if (!decl)
+ return NULL;
+ 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 (TREE_CONSTANT (val))
+ return val;
+ return TREE_VALUE (TREE_CHAIN (TREE_OPERAND (expr, 1)));
+ }
+ }
+ if (BINARY_CLASS_P (expr) || COMPARISON_CLASS_P (expr))
+ {
+ tree op0, op1, res;
+ op0 = expr_expected_value (TREE_OPERAND (expr, 0), visited);
+ if (!op0)
+ return NULL;
+ op1 = expr_expected_value (TREE_OPERAND (expr, 1), visited);
+ if (!op1)
+ return NULL;
+ res = fold_build2 (TREE_CODE (expr), TREE_TYPE (expr), op0, op1);
+ if (TREE_CONSTANT (res))
+ return res;
+ return NULL;
+ }
+ if (UNARY_CLASS_P (expr))
+ {
+ tree op0, res;
+ op0 = expr_expected_value (TREE_OPERAND (expr, 0), visited);
+ if (!op0)
+ return NULL;
+ res = fold_build1 (TREE_CODE (expr), TREE_TYPE (expr), op0);
+ if (TREE_CONSTANT (res))
+ return res;
+ return NULL;
+ }
+ return NULL;
+}
+\f
+/* Get rid of all builtin_expect calls we no longer need. */
+static void
+strip_builtin_expect (void)
+{
+ basic_block bb;
FOR_EACH_BB (bb)
{
- rtx last_insn = BB_END (bb);
-
- if (!can_predict_insn_p (last_insn))
+ block_stmt_iterator bi;
+ for (bi = bsi_start (bb); !bsi_end_p (bi); bsi_next (&bi))
{
- /* 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)
+ tree stmt = bsi_stmt (bi);
+ tree fndecl;
+ tree arglist;
+
+ if (TREE_CODE (stmt) == MODIFY_EXPR
+ && TREE_CODE (TREE_OPERAND (stmt, 1)) == CALL_EXPR
+ && (fndecl = get_callee_fndecl (TREE_OPERAND (stmt, 1)))
+ && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL
+ && DECL_FUNCTION_CODE (fndecl) == BUILT_IN_EXPECT
+ && (arglist = TREE_OPERAND (TREE_OPERAND (stmt, 1), 1))
+ && TREE_CHAIN (arglist))
{
- nedges++;
- if (e->probability != 0)
- break;
+ TREE_OPERAND (stmt, 1) = TREE_VALUE (arglist);
+ update_stmt (stmt);
}
- 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);
- if (profile_status == PROFILE_ABSENT)
- profile_status = PROFILE_GUESSED;
-}
-
-/* Set edge->probability for each succestor edge of BB. */
-void
-guess_outgoing_edge_probabilities (basic_block bb)
-{
- bb_estimate_probability_locally (bb);
- combine_predictions_for_insn (BB_END (bb), bb);
}
\f
-
/* Predict using opcode of the last statement in basic block. */
static void
tree_predict_by_opcode (basic_block bb)
tree cond;
tree op0;
tree type;
+ tree val;
+ bitmap visited;
+ edge_iterator ei;
if (!stmt || TREE_CODE (stmt) != COND_EXPR)
return;
- for (then_edge = bb->succ; then_edge; then_edge = then_edge->succ_next)
+ FOR_EACH_EDGE (then_edge, ei, bb->succs)
if (then_edge->flags & EDGE_TRUE_VALUE)
- break;
+ break;
cond = TREE_OPERAND (stmt, 0);
- if (TREE_CODE_CLASS (TREE_CODE (cond)) != '<')
+ if (!COMPARISON_CLASS_P (cond))
return;
op0 = TREE_OPERAND (cond, 0);
type = TREE_TYPE (op0);
+ visited = BITMAP_ALLOC (NULL);
+ val = expr_expected_value (cond, visited);
+ BITMAP_FREE (visited);
+ if (val)
+ {
+ if (integer_zerop (val))
+ predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, NOT_TAKEN);
+ else
+ predict_edge_def (then_edge, PRED_BUILTIN_EXPECT, TAKEN);
+ return;
+ }
/* Try "pointer heuristic."
A comparison ptr == 0 is predicted as false.
Similarly, a comparison ptr1 == ptr2 is predicted as false. */
}
}
-/* Predict branch probabilities and estimate profile of the tree CFG. */
+/* 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 = NULL;
+ tree return_val;
+ edge e;
+ tree phi;
+ int phi_num_args, i;
+ enum br_predictor pred;
+ enum prediction direction;
+ edge_iterator ei;
+
+ FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
+ {
+ 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;
+ for (phi = SSA_NAME_DEF_STMT (return_val); phi; phi = PHI_CHAIN (phi))
+ if (PHI_RESULT (phi) == return_val)
+ break;
+ 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 = XNEWVEC (int, last_basic_block);
+ memset (heads, ENTRY_BLOCK, 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 unsigned int
tree_estimate_probability (void)
{
basic_block bb;
struct loops loops_info;
- flow_loops_find (&loops_info, LOOP_TREE);
+ flow_loops_find (&loops_info);
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 ();
+
+ mark_irreducible_loops (&loops_info);
predict_loops (&loops_info, false);
FOR_EACH_BB (bb)
{
edge e;
+ edge_iterator ei;
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
{
/* 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 through function. */
+ if (e->dest == EXIT_BLOCK_PTR
+ && TREE_CODE (last_stmt (bb)) == RETURN_EXPR
+ && !single_pred_p (bb))
+ {
+ 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);
+ }
/* Look for block we are guarding (ie we dominate it,
but it doesn't postdominate us). */
tree_predict_by_opcode (bb);
}
FOR_EACH_BB (bb)
- combine_predictions_for_bb (dump_file, bb);
+ combine_predictions_for_bb (bb);
+ strip_builtin_expect ();
estimate_bb_frequencies (&loops_info);
free_dominance_info (CDI_POST_DOMINATORS);
remove_fake_exit_edges ();
dump_tree_cfg (dump_file, dump_flags);
if (profile_status == PROFILE_ABSENT)
profile_status = PROFILE_GUESSED;
+ return 0;
}
\f
/* __builtin_expect dropped tokens into the insn stream describing expected
cond = simplify_rtx (cond);
/* Turn the condition into a scaled branch probability. */
- if (cond != const_true_rtx && cond != const0_rtx)
- abort ();
+ gcc_assert (cond == const_true_rtx || cond == const0_rtx);
predict_insn_def (insn, PRED_BUILTIN_EXPECT,
cond == const_true_rtx ? TAKEN : NOT_TAKEN);
}
return (bb->next_bb == EXIT_BLOCK_PTR
|| (bb->next_bb->next_bb == EXIT_BLOCK_PTR
- && bb->succ && !bb->succ->succ_next
- && bb->succ->dest->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
+ 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;
+ edge_iterator ei;
+ int y;
+
+ if (heads[bb->index] == ENTRY_BLOCK)
+ {
+ /* 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] == ENTRY_BLOCK)
+ {
+ 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;
+ 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_EACH_EDGE (e, ei, BASIC_BLOCK (y)->succs)
+ if (e->dest->index >= NUM_FIXED_BLOCKS
+ && 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
/* To keep queue of basic blocks to process. */
basic_block next;
- /* True if block needs to be visited in propagate_freq. */
- unsigned int tovisit:1;
-
/* Number of predecessors we need to visit first. */
int npredecessors;
} *block_info;
/* Similar information for edges. */
typedef struct edge_info_def
{
- /* In case edge is an loopback edge, the probability edge will be reached
+ /* In case edge is a loopback edge, the probability edge will be reached
in case header is. Estimated number of iterations of the loop can be
then computed as 1 / (1 - back_edge_prob). */
sreal back_edge_prob;
- /* True if the edge is an loopback edge in the natural loop. */
+ /* True if the edge is a loopback edge in the natural loop. */
unsigned int back_edge:1;
} *edge_info;
Propagate the frequencies for LOOP. */
static void
-propagate_freq (struct loop *loop)
+propagate_freq (struct loop *loop, bitmap tovisit)
{
basic_block head = loop->header;
basic_block bb;
basic_block last;
+ unsigned i;
edge e;
basic_block nextbb;
+ bitmap_iterator bi;
/* For each basic block we need to visit count number of his predecessors
we need to visit first. */
- FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
+ EXECUTE_IF_SET_IN_BITMAP (tovisit, 0, i, bi)
{
- if (BLOCK_INFO (bb)->tovisit)
+ edge_iterator ei;
+ int count = 0;
+
+ /* The outermost "loop" includes the exit block, which we can not
+ look up via BASIC_BLOCK. Detect this and use EXIT_BLOCK_PTR
+ directly. Do the same for the entry block. */
+ bb = BASIC_BLOCK (i);
+
+ FOR_EACH_EDGE (e, ei, bb->preds)
{
- int count = 0;
-
- for (e = bb->pred; e; e = e->pred_next)
- if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
- count++;
- else if (BLOCK_INFO (e->src)->tovisit
- && dump_file && !EDGE_INFO (e)->back_edge)
- fprintf (dump_file,
- "Irreducible region hit, ignoring edge to %i->%i\n",
- e->src->index, bb->index);
- BLOCK_INFO (bb)->npredecessors = count;
+ bool visit = bitmap_bit_p (tovisit, e->src->index);
+
+ if (visit && !(e->flags & EDGE_DFS_BACK))
+ count++;
+ else if (visit && dump_file && !EDGE_INFO (e)->back_edge)
+ fprintf (dump_file,
+ "Irreducible region hit, ignoring edge to %i->%i\n",
+ e->src->index, bb->index);
}
+ BLOCK_INFO (bb)->npredecessors = count;
}
memcpy (&BLOCK_INFO (head)->frequency, &real_one, sizeof (real_one));
last = head;
for (bb = head; bb; bb = nextbb)
{
+ edge_iterator ei;
sreal cyclic_probability, frequency;
memcpy (&cyclic_probability, &real_zero, sizeof (real_zero));
if (bb != head)
{
#ifdef ENABLE_CHECKING
- for (e = bb->pred; e; e = e->pred_next)
- if (BLOCK_INFO (e->src)->tovisit && !(e->flags & EDGE_DFS_BACK))
- abort ();
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ gcc_assert (!bitmap_bit_p (tovisit, e->src->index)
+ || (e->flags & EDGE_DFS_BACK));
#endif
- for (e = bb->pred; e; e = e->pred_next)
+ FOR_EACH_EDGE (e, ei, bb->preds)
if (EDGE_INFO (e)->back_edge)
{
sreal_add (&cyclic_probability, &cyclic_probability,
}
}
- BLOCK_INFO (bb)->tovisit = 0;
+ bitmap_clear_bit (tovisit, bb->index);
- /* Compute back edge frequencies. */
- for (e = bb->succ; e; e = e->succ_next)
- if (e->dest == head)
- {
- sreal tmp;
-
- /* EDGE_INFO (e)->back_edge_prob
- = ((e->probability * BLOCK_INFO (bb)->frequency)
- / REG_BR_PROB_BASE); */
-
- sreal_init (&tmp, e->probability, 0);
- sreal_mul (&tmp, &tmp, &BLOCK_INFO (bb)->frequency);
- sreal_mul (&EDGE_INFO (e)->back_edge_prob,
- &tmp, &real_inv_br_prob_base);
- }
+ e = find_edge (bb, head);
+ if (e)
+ {
+ sreal tmp;
+
+ /* EDGE_INFO (e)->back_edge_prob
+ = ((e->probability * BLOCK_INFO (bb)->frequency)
+ / REG_BR_PROB_BASE); */
+
+ sreal_init (&tmp, e->probability, 0);
+ sreal_mul (&tmp, &tmp, &BLOCK_INFO (bb)->frequency);
+ sreal_mul (&EDGE_INFO (e)->back_edge_prob,
+ &tmp, &real_inv_br_prob_base);
+ }
/* Propagate to successor blocks. */
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
if (!(e->flags & EDGE_DFS_BACK)
&& BLOCK_INFO (e->dest)->npredecessors)
{
nextbb = e->dest;
else
BLOCK_INFO (last)->next = e->dest;
-
+
last = e->dest;
}
- }
+ }
}
}
/* Estimate probabilities of loopback edges in loops at same nest level. */
static void
-estimate_loops_at_level (struct loop *first_loop)
+estimate_loops_at_level (struct loop *first_loop, bitmap tovisit)
{
struct loop *loop;
basic_block *bbs;
unsigned i;
- estimate_loops_at_level (loop->inner);
+ estimate_loops_at_level (loop->inner, tovisit);
- if (loop->latch->succ) /* Do not do this for dummy function loop. */
+ /* Do not do this for dummy function loop. */
+ if (EDGE_COUNT (loop->latch->succs) > 0)
{
/* Find current loop back edge and mark it. */
e = loop_latch_edge (loop);
bbs = get_loop_body (loop);
for (i = 0; i < loop->num_nodes; i++)
- BLOCK_INFO (bbs[i])->tovisit = 1;
+ bitmap_set_bit (tovisit, bbs[i]->index);
free (bbs);
- propagate_freq (loop);
+ propagate_freq (loop, tovisit);
}
}
/* Convert counts measured by profile driven feedback to frequencies.
Return nonzero iff there was any nonzero execution count. */
-static int
+int
counts_to_freqs (void)
{
gcov_type count_max, true_count_max = 0;
/* We can not compute accurately for large thresholds due to scaled
frequencies. */
- if (threshold > BB_FREQ_MAX)
- abort ();
+ gcc_assert (threshold <= BB_FREQ_MAX);
/* Frequencies are out of range. This either means that function contains
internal loop executing more than BB_FREQ_MAX times or profile feedback
if (!flag_branch_probabilities || !counts_to_freqs ())
{
static int real_values_initialized = 0;
+ bitmap tovisit;
if (!real_values_initialized)
{
mark_dfs_back_edges ();
- ENTRY_BLOCK_PTR->succ->probability = REG_BR_PROB_BASE;
+ single_succ_edge (ENTRY_BLOCK_PTR)->probability = REG_BR_PROB_BASE;
/* Set up block info for each basic block. */
+ tovisit = BITMAP_ALLOC (NULL);
alloc_aux_for_blocks (sizeof (struct block_info_def));
alloc_aux_for_edges (sizeof (struct edge_info_def));
FOR_BB_BETWEEN (bb, ENTRY_BLOCK_PTR, NULL, next_bb)
{
edge e;
+ edge_iterator ei;
- BLOCK_INFO (bb)->tovisit = 0;
- for (e = bb->succ; e; e = e->succ_next)
+ FOR_EACH_EDGE (e, ei, bb->succs)
{
sreal_init (&EDGE_INFO (e)->back_edge_prob, e->probability, 0);
sreal_mul (&EDGE_INFO (e)->back_edge_prob,
/* First compute probabilities locally for each loop from innermost
to outermost to examine probabilities for back edges. */
- estimate_loops_at_level (loops->tree_root);
+ estimate_loops_at_level (loops->tree_root, tovisit);
memcpy (&freq_max, &real_zero, sizeof (real_zero));
FOR_EACH_BB (bb)
free_aux_for_blocks ();
free_aux_for_edges ();
+ BITMAP_FREE (tovisit);
}
compute_function_frequency ();
if (flag_reorder_functions)
UNLIKELY_EXECUTED_TEXT_SECTION_NAME);
}
+static bool
+gate_estimate_probability (void)
+{
+ return flag_guess_branch_prob;
+}
struct tree_opt_pass pass_profile =
{
"profile", /* name */
- NULL, /* gate */
+ gate_estimate_probability, /* gate */
tree_estimate_probability, /* execute */
NULL, /* sub */
NULL, /* next */
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