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Gather statistics about switch search depth results.

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compiler/switch_detection.m:
    Add conditionally-enabled code to gather statistics about
    what happens when a switch candidate has disjuncts left over,
    and we test whether these leftovers form a switch on another variable.
    (The results show that after 99.91% of switch candidates,
    there are *no* disjuncts left over.)

compiler/mercury_compile_main.m:
    Invoke the predicate that writes out any statistics we gathered.

tools/switch_depth:
    This new summarizes the results.
This commit is contained in:
Zoltan Somogyi
2026-01-15 10:45:35 +11:00
parent 5063ff4a98
commit 86b33fbd40
3 changed files with 127 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
compiler/mercury_compile_main.m
View File

@@ -2,7 +2,7 @@
% vim: ts=4 sw=4 et ft=mercury
%---------------------------------------------------------------------------%
% Copyright (C) 1994-2012 The University of Melbourne.
% Copyright (C) 2017-2025 The Mercury Team.
% Copyright (C) 2017-2026 The Mercury Team.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%---------------------------------------------------------------------------%
@@ -42,6 +42,8 @@
:- import_module backend_libs.
:- import_module backend_libs.compile_target_code.
:- import_module backend_libs.link_target_code.
:- import_module check_hlds.
:- import_module check_hlds.switch_detection.
:- import_module hlds.
:- import_module hlds.instmap.
:- import_module libs.check_libgrades.
@@ -130,6 +132,7 @@ real_main(!IO) :-
record_make_prereqs_cache_stats(!IO),
record_module_ext_cache_stats(!IO),
record_instmap_delta_restrict_stats(!IO),
record_switch_search_depth_results(!IO),
close_any_specific_compiler_streams(!IO).
%---------------------------------------------------------------------------%

90
compiler/switch_detection.m
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@@ -37,6 +37,8 @@
:- pred detect_switches_in_proc(switch_detect_info::in,
proc_info::in, proc_info::out) is det.
:- pred record_switch_search_depth_results(io::di, io::uo) is det.
%---------------------------------------------------------------------------%
%---------------------------------------------------------------------------%
@@ -87,6 +89,7 @@
:- import_module string.
:- import_module term.
:- import_module term_context.
:- import_module uint.
:- import_module unit.
:- import_module varset.
@@ -190,13 +193,13 @@ detect_switches_in_proc(Info, !ProcInfo) :-
Requant0 = do_not_need_to_requantify,
BodyDeletedCallCallees0 = set.init,
LocalInfo0 = local_switch_detect_info(VarTable, DisjunctionInfoMap,
ModuleInfo, Requant0, BodyDeletedCallCallees0),
0u, ModuleInfo, Requant0, BodyDeletedCallCallees0),
detect_switches_in_goal(InstMap0, nrsv, Goal0, Goal,
LocalInfo0, LocalInfo),
proc_info_set_goal(Goal, !ProcInfo),
LocalInfo = local_switch_detect_info(_VarTable, _DisjunctionInfoMap,
_ModuleInfo, Requant, BodyDeletedCallCallees),
_, _ModuleInfo, Requant, BodyDeletedCallCallees),
(
Requant = need_to_requantify,
requantify_proc_general(ord_nl_maybe_lambda, !ProcInfo)
@@ -217,7 +220,12 @@ detect_switches_in_proc(Info, !ProcInfo) :-
lsdi_disjunction_info_map :: disjunction_info_map,
% These fields are read-write.
%
% The depth matters only in detect_switches_in_disj predicate.
% It specifies the number of recursive calls to that predicate
% above the current invocation.
lsdi_depth :: uint,
% We update module_info when we enter a switch arm, and update
% the inst of the switched-on variable to record it being bound
% to one of the cons_ids that the switch arm is for.
@@ -270,6 +278,7 @@ detect_switches_in_goal(InstMap0, MaybeRequiredVar, Goal0, Goal, !LocalInfo) :-
GoalExpr = GoalExpr0
;
Disjuncts0 = [_ | _],
!LocalInfo ^ lsdi_depth := 0u,
detect_switches_in_disj(InstMap0, MaybeRequiredVar,
Disjuncts0, GoalInfo0, GoalExpr, !LocalInfo)
)
@@ -410,13 +419,20 @@ detect_switches_in_disj(InstMap0, MaybeRequiredVar, Disjuncts0, GoalInfo,
detect_switch_candidates_in_disj(!.LocalInfo, GoalInfo, Disjuncts0,
InstMap0, MaybeRequiredVar, VarsToTry,
no_candidate_switch, BestCandidateSoFar),
CurDepth = !.LocalInfo ^ lsdi_depth,
(
BestCandidateSoFar = no_candidate_switch,
trace [compile_time(flag("switch-detect-depth-stats")), io(!IO)] (
record_miss(CurDepth, !IO)
),
detect_sub_switches_in_disj(InstMap0, Disjuncts0, Disjuncts,
!LocalInfo),
GoalExpr = disj(Disjuncts)
;
BestCandidateSoFar = best_candidate_switch_so_far(BestCandidate),
trace [compile_time(flag("switch-detect-depth-stats")), io(!IO)] (
record_hit(CurDepth, !IO)
),
BestRank = BestCandidate ^ cs_rank,
(
BestRank = no_leftover_one_case,
@@ -448,6 +464,7 @@ detect_switches_in_disj(InstMap0, MaybeRequiredVar, Disjuncts0, GoalInfo,
GoalExpr = SwitchGoalExpr
;
LeftDisjuncts0 = [_ | _],
!LocalInfo ^ lsdi_depth := CurDepth + 1u,
detect_switches_in_disj(InstMap0, MaybeRequiredVar,
LeftDisjuncts0, GoalInfo, LeftGoal, !LocalInfo),
goal_to_disj_list(hlds_goal(LeftGoal, GoalInfo),
@@ -1084,6 +1101,73 @@ gather_smallest_context([Goal | Goals], !SmallestContext) :-
num_cases_in_table(cases_table(CasesMap, _)) = map.count(CasesMap).
%---------------------------------------------------------------------------%
:- type hit_and_miss
---> hit_and_miss(
ham_hit :: uint,
ham_miss :: uint
).
:- type hit_and_miss_map == map(uint, hit_and_miss).
:- mutable(ham_map, hit_and_miss_map, map.init, ground,
[untrailed, attach_to_io_state]).
:- pred record_hit(uint::in, io::di, io::uo) is det.
record_hit(Depth, !IO) :-
get_ham_map(HamMap0, !IO),
( if map.search(HamMap0, Depth, HitAndMiss0) then
HitAndMiss0 = hit_and_miss(Hit0, Miss0),
HitAndMiss = hit_and_miss(Hit0 + 1u, Miss0),
map.det_update(Depth, HitAndMiss, HamMap0, HamMap)
else
HitAndMiss = hit_and_miss(1u, 0u),
map.det_insert(Depth, HitAndMiss, HamMap0, HamMap)
),
set_ham_map(HamMap, !IO).
:- pred record_miss(uint::in, io::di, io::uo) is det.
record_miss(Depth, !IO) :-
get_ham_map(HamMap0, !IO),
( if map.search(HamMap0, Depth, HitAndMiss0) then
HitAndMiss0 = hit_and_miss(Hit0, Miss0),
HitAndMiss = hit_and_miss(Hit0, Miss0 + 1u),
map.det_update(Depth, HitAndMiss, HamMap0, HamMap)
else
HitAndMiss = hit_and_miss(0u, 1u),
map.det_insert(Depth, HitAndMiss, HamMap0, HamMap)
),
set_ham_map(HamMap, !IO).
record_switch_search_depth_results(!IO) :-
get_ham_map(HamMap, !IO),
map.to_assoc_list(HamMap, HamAL),
DescStrs = list.map(hit_and_miss_to_string, HamAL),
string.append_list(DescStrs, DescsStr),
( if DescsStr = "" then
% We should get here if the trace flag --switch-detect-depth-stats
% is not set.
true
else
io.open_append("/tmp/SWITCH_DEPTH_RESULTS", Result, !IO),
(
Result = error(_)
;
Result = ok(OutStream),
io.write_string(OutStream, DescsStr, !IO),
io.close_output(OutStream, !IO)
)
).
:- func hit_and_miss_to_string(pair(uint, hit_and_miss)) = string.
hit_and_miss_to_string(Depth - hit_and_miss(Hit, Miss)) = Str :-
string.format("depth %u hit %3u miss %3u\n",
[u(Depth), u(Hit), u(Miss)], Str).
%---------------------------------------------------------------------------%
:- end_module check_hlds.switch_detection.
%---------------------------------------------------------------------------%

36
tools/switch_depth Executable file
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@@ -0,0 +1,36 @@
#!/usr/bin/awk -f
# vim: ft=awk ts=4 sw=4 et
#
# This script summarizes the contents of the SWITCH_DEPTH_RESULTS files
# generated by the conditionally-enabled statistics-gathering code
# in switch_detection.m.
#
NF == 6 && $1 == "depth" {
depth = $2;
hit = $4;
miss = $6;
hits[depth] += hit;
hit_and_miss = hit + miss;
trials[depth] += hit_and_miss;
}
END {
max_depth = 0;
for (depth in trials) {
if (depth > max_depth) {
max_depth = depth;
}
hit_rate[depth] = (100 * hits[depth]) / trials[depth];
printf "depth %d: %5d trials, %5d hits, hit rate = %5.2f%%\n",
depth, trials[depth], hits[depth], hit_rate[depth];
}
i = 1;
while (i <= max_depth) {
leak_rate = (100 * trials[i]) / trials[i - 1];
printf "leak rate to depth %d: %5.2f%%\n", i, leak_rate;
i = i + 1;
}
}