> 2013-11-08 Teresa Johnson <tejohn...@google.com> > Jan Hubicka <j...@suse.cz> > > * predict.c (drop_profile): New function. > (handle_missing_profiles): Ditto. > (counts_to_freqs): Don't overwrite estimated frequencies > when function has no profile counts. > * predict.h (handle_missing_profiles): Declare. > * tree-inline.c (freqs_to_counts): New function. > (copy_cfg_body): Invoke freqs_to_counts as needed. > * tree-profile.c (tree_profiling): Invoke handle_missing_profiles. > > Index: predict.c > =================================================================== > --- predict.c (revision 204516) > +++ predict.c (working copy) > @@ -2765,6 +2765,107 @@ estimate_loops (void) > BITMAP_FREE (tovisit); > } > > +/* Drop the profile for NODE to guessed, and update its frequency based on > + whether it is expected to be HOT. */ > + > +static void > +drop_profile (struct cgraph_node *node, bool hot) > +{ > + struct function *fn = DECL_STRUCT_FUNCTION (node->decl); > + > + if (dump_file) > + fprintf (dump_file, > + "Dropping 0 profile for %s/%i. %s based on calls.\n", > + cgraph_node_name (node), node->order, > + hot ? "Function is hot" : "Function is normal"); > + /* We only expect to miss profiles for functions that are reached > + via non-zero call edges in cases where the function may have > + been linked from another module or library (COMDATs and extern > + templates). See the comments below for handle_missing_profiles. */ > + if (!DECL_COMDAT (node->decl) && !DECL_EXTERNAL (node->decl)) > + warning (0, > + "Missing counts for called function %s/%i", > + cgraph_node_name (node), node->order); > + > + profile_status_for_function (fn) > + = (flag_guess_branch_prob ? PROFILE_GUESSED : PROFILE_ABSENT); > + node->frequency > + = hot ? NODE_FREQUENCY_HOT : NODE_FREQUENCY_NORMAL; > +} > + > +/* In the case of COMDAT routines, multiple object files will contain the > same > + function and the linker will select one for the binary. In that case > + all the other copies from the profile instrument binary will be missing > + profile counts. Look for cases where this happened, due to non-zero > + call counts going to 0-count functions, and drop the profile to guessed > + so that we can use the estimated probabilities and avoid optimizing only > + for size. > + > + The other case where the profile may be missing is when the routine > + is not going to be emitted to the object file, e.g. for "extern template" > + class methods. Those will be marked DECL_EXTERNAL. Emit a warning in > + all other cases of non-zero calls to 0-count functions. */ > + > +void > +handle_missing_profiles (void) > +{ > + struct cgraph_node *node; > + int unlikely_count_fraction = PARAM_VALUE (UNLIKELY_BB_COUNT_FRACTION); > + vec<struct cgraph_node *> worklist; > + worklist.create (64); > + > + /* See if 0 count function has non-0 count callers. In this case we > + lost some profile. Drop its function profile to PROFILE_GUESSED. */ > + FOR_EACH_DEFINED_FUNCTION (node) > + { > + struct cgraph_edge *e; > + gcov_type call_count = 0; > + struct function *fn = DECL_STRUCT_FUNCTION (node->decl); > + > + if (node->count) > + continue; > + for (e = node->callers; e; e = e->next_caller) > + call_count += e->count; > + if (call_count > + && fn && fn->cfg > + && (call_count * unlikely_count_fraction >= profile_info->runs)) > + { > + bool maybe_hot = maybe_hot_count_p (NULL, call_count); > + > + drop_profile (node, maybe_hot); > + worklist.safe_push (node); > + }
Perhaps we should add an note/error on mishandled profile when function is not COMDAT? That way we may notice further bugs in this area. > + } > + > + /* Propagate the profile dropping to other 0-count COMDATs that are > + potentially called by COMDATs we already dropped the profile on. */ > + while (worklist.length () > 0) > + { > + struct cgraph_edge *e; > + > + node = worklist.pop (); > + for (e = node->callees; e; e = e->next_caller) > + { > + struct cgraph_node *callee = e->callee; > + struct function *fn = DECL_STRUCT_FUNCTION (callee->decl); > + > + if (callee->count > 0) > + continue; > + if (DECL_COMDAT (callee->decl) && fn && fn->cfg > + && profile_status_for_function (fn) == PROFILE_READ) Perhaps we can check here maybe_hot_bb_p for the caller and rely on profile estimate to give us false only for really known to be unlikely paths? (i.e. EH handling, noreturns etc.) > + { > + /* Since there are no non-0 call counts to this function, > + we don't know for sure whether it is hot. Indicate to > + the drop_profile routine that function should be marked > + normal, rather than hot. */ > + drop_profile (node, false); > + worklist.safe_push (callee); > + } > + } > + } > + worklist.release (); I would add a pointer set so we avoid duplicates in worklist. This is potentially quadratic for large programs. OK, with these changes. Honza