Hi,
This patch adds an option. When the option is enabled, GCC will add a
record about it in an elf section called
".gnu.switches.text.branch.annotation" for every branch.
gcc/
2014-06-27 Yi Yang <ahyan...@google.com>
* auto-profile.c: Main comparison and reporting logic.
* cfg-flags.def: Add an extra flag representing an edge's
probability is predicted by annotations.
* predict.c: Set up the extra flag on an edge when appropriate.
* common.opt: Add an extra GCC option to turn on this report mechanism
diff --git a/gcc/auto-profile.c b/gcc/auto-profile.c
index 74d3d1d..f7698cd 100644
--- a/gcc/auto-profile.c
+++ b/gcc/auto-profile.c
@@ -40,6 +40,7 @@ along with GCC; see the file COPYING3. If not see
#include "opts.h" /* for in_fnames. */
#include "tree-pass.h" /* for ipa pass. */
#include "cfgloop.h" /* for loop_optimizer_init. */
+#include "md5.h" /* for hashing function names. */
#include "gimple.h"
#include "cgraph.h"
#include "tree-flow.h"
@@ -1367,6 +1368,80 @@ afdo_propagate (void)
}
}
+struct locus_information_t {
+ char filename[1024];
+ unsigned lineno;
+ unsigned function_lineno;
+ char function_hash[33];
+};
+
+static bool
+get_locus_information (location_t locus, locus_information_t* li) {
+ if (locus == UNKNOWN_LOCATION || !LOCATION_FILE(locus))
+ return false;
+ snprintf(li->filename, 1024, "%s", LOCATION_FILE(locus));
+ li->lineno = LOCATION_LINE(locus);
+
+ tree block = LOCATION_BLOCK (locus);
+ tree function_decl = current_function_decl;
+
+ if (block && TREE_CODE (block) == BLOCK)
+ {
+ for (block = BLOCK_SUPERCONTEXT (block);
+ block && (TREE_CODE (block) == BLOCK);
+ block = BLOCK_SUPERCONTEXT (block))
+ {
+ location_t tmp_locus = BLOCK_SOURCE_LOCATION (block);
+ if (LOCATION_LOCUS (tmp_locus) == UNKNOWN_LOCATION)
+ continue;
+
+ tree decl = get_function_decl_from_block (block);
+ function_decl = decl;
+ break;
+ }
+ }
+
+ if (!(function_decl && TREE_CODE (function_decl) == FUNCTION_DECL))
+ return false;
+ unsigned function_length = 0;
+ function *f = DECL_STRUCT_FUNCTION(function_decl);
+
+ li->function_lineno = LOCATION_LINE(DECL_SOURCE_LOCATION(function_decl));
+
+ if (f)
+ {
+ function_length = LOCATION_LINE(f->function_end_locus) -
+ li->function_lineno;
+ }
+
+ const char *fn_name = fndecl_name(function_decl);
+ unsigned char md5_result[16];
+
+ md5_ctx ctx;
+
+ md5_init_ctx(&ctx);
+ md5_process_bytes(fn_name, strlen(fn_name), &ctx);
+ md5_process_bytes(&function_length, sizeof(function_length), &ctx);
+ md5_finish_ctx(&ctx, md5_result);
+
+ for (int i = 0; i < 16; ++i)
+ {
+ sprintf(li->function_hash + i*2, "%02x", md5_result[i]);
+ }
+
+ return true;
+}
+
+void
+fill_invalid_locus_information(locus_information_t* li) {
+ snprintf(li->filename, 1024, "<unknown>");
+ li->lineno = 0;
+ li->function_lineno = 0;
+ for (int i = 0; i < 32; ++i)
+ li->function_hash[i] = '0';
+ li->function_hash[32] = '\0';
+}
+
/* Propagate counts on control flow graph and calculate branch
probabilities. */
@@ -1407,8 +1482,62 @@ afdo_calculate_branch_prob (void)
if (num_unknown_succ == 0 && total_count > 0)
{
FOR_EACH_EDGE (e, ei, bb->succs)
- e->probability =
- (double) e->count * REG_BR_PROB_BASE / total_count;
+ {
+ double probability =
+ (double) e->count * REG_BR_PROB_BASE / total_count;
+
+ if (flag_check_branch_annotation &&
+ bb->succs->length() == 2 &&
+ maybe_hot_count_p (cfun, bb->count) &&
+ bb->count >= 100)
+ {
+ gimple_stmt_iterator gsi;
+ gimple last = NULL;
+
+ for (gsi = gsi_last_nondebug_bb (bb);
+ !gsi_end_p (gsi);
+ gsi_prev_nondebug (&gsi))
+ {
+ last = gsi_stmt (gsi);
+
+ if (gimple_has_location (last))
+ break;
+ }
+
+ struct locus_information_t li;
+ bool annotated;
+
+ if (e->flags & EDGE_PREDICTED_BY_EXPECT)
+ annotated = true;
+ else
+ annotated = false;
+
+ if (get_locus_information(e->goto_locus, &li))
+ ;
+ else if (get_locus_information(gimple_location(last), &li))
+ ;
+ else
+ fill_invalid_locus_information(&li);
+
+ switch_to_section (get_section (
+ ".gnu.switches.text.branch.annotation",
+ SECTION_DEBUG | SECTION_MERGE |
+ SECTION_STRINGS | (SECTION_ENTSIZE & 1),
+ NULL));
+ char buf[1024];
+ snprintf (buf, 1024, "%s;%u;%d;"
+ HOST_WIDEST_INT_PRINT_DEC";%.6lf;%.6lf;%s;%u",
+ li.filename, li.lineno, bb->count, annotated?1:0,
+ probability/REG_BR_PROB_BASE,
+ e->probability/(double)REG_BR_PROB_BASE,
+ li.function_hash, li.function_lineno);
+ dw2_asm_output_nstring (buf, (size_t)-1, NULL);
+
+ break;
+ }
+
+ e->probability = probability;
+ }
}
}
FOR_ALL_BB (bb)
@@ -1417,8 +1546,11 @@ afdo_calculate_branch_prob (void)
edge_iterator ei;
FOR_EACH_EDGE (e, ei, bb->succs)
- e->count =
- (double) bb->count * e->probability / REG_BR_PROB_BASE;
+ {
+ e->count =
+ (double) bb->count * e->probability / REG_BR_PROB_BASE;
+ e->flags &= ~EDGE_PREDICTED_BY_EXPECT;
+ }
bb->aux = NULL;
}
@@ -1542,9 +1674,9 @@ afdo_annotate_cfg (const stmt_set &promoted_stmts)
afdo_source_profile->mark_annotated (cfun->function_end_locus);
if (max_count > 0)
{
+ profile_status = PROFILE_READ;
afdo_calculate_branch_prob ();
counts_to_freqs ();
- profile_status = PROFILE_READ;
}
if (flag_value_profile_transformations)
gimple_value_profile_transformations ();
diff --git a/gcc/cfg-flags.def b/gcc/cfg-flags.def
index 42a0473..5904d8d 100644
--- a/gcc/cfg-flags.def
+++ b/gcc/cfg-flags.def
@@ -186,6 +186,9 @@ DEF_EDGE_FLAG(TM_ABORT, 16)
/* Annotated during AutoFDO profile attribution. */
DEF_EDGE_FLAG(ANNOTATED, 17)
+/* Edge probability predicted by __builtin_expect. */
+DEF_EDGE_FLAG(PREDICTED_BY_EXPECT, 18)
+
#endif
/*
diff --git a/gcc/common.opt b/gcc/common.opt
index 4305c89..5ac159e 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -950,6 +950,10 @@ fauto-profile-record-coverage-in-elf
Common Report Var(flag_auto_profile_record_coverage_in_elf) Optimization
Whether to record annotation coverage info in elf.
+fcheck-branch-annotation
+Common Report Var(flag_check_branch_annotation)
+Record branch prediction information in elf.
+
; -fcheck-bounds causes gcc to generate array bounds checks.
; For C, C++ and ObjC: defaults off.
; For Java: defaults to on.
diff --git a/gcc/predict.c b/gcc/predict.c
index f27c58c..cecc801 100644
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -1014,6 +1014,11 @@ combine_predictions_for_bb (basic_block bb)
{
first->probability = combined_probability;
second->probability = REG_BR_PROB_BASE - combined_probability;
+ if (first_match && best_predictor == PRED_BUILTIN_EXPECT)
+ {
+ first->flags |= EDGE_PREDICTED_BY_EXPECT;
+ second->flags |= EDGE_PREDICTED_BY_EXPECT;
+ }
}
}
--
