llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Mark de Wever (mordante)
<details>
<summary>Changes</summary>
This changes the __output_buffer to a new structure. Since the other formatting
fucntions std::format_to, std::format_to_n, and std::formatted_size still use
the old codepaths the class is in a transition state. At the end of the series
the class should be in its final state.
write_double_comparison:
Before
----------------------------------------------------------------------------------------
Benchmark Time CPU
Iterations
----------------------------------------------------------------------------------------
BM_sprintf 197 ns 196 ns
3550000
BM_to_string 218 ns 218 ns
3214000
BM_to_chars 42.4 ns 42.3 ns
16575000
BM_to_chars_as_string 48.2 ns 48.1 ns
14542000
BM_format 175 ns 175 ns
4000000
BM_format_to_back_inserter<std::string> 175 ns 175
ns 3995000
BM_format_to_back_inserter<std::vector<char>> 207 ns
206 ns 3393000
BM_format_to_back_inserter<std::list<char>> 752 ns
750 ns 931000
BM_format_to_iterator/<std::array> 161 ns 161
ns 4345000
BM_format_to_iterator/<std::string> 161 ns 161
ns 4344000
BM_format_to_iterator/<std::vector> 162 ns 161
ns 4344000
After
----------------------------------------------------------------------------------------
Benchmark Time CPU
Iterations
----------------------------------------------------------------------------------------
BM_sprintf 197 ns 197 ns
3550000
BM_to_string 219 ns 219 ns
3199000
BM_to_chars 42.4 ns 42.4 ns
16554000
BM_to_chars_as_string 48.1 ns 48.1 ns
14569000
BM_format 167 ns 167 ns
4203000
BM_format_to_back_inserter<std::string> 179 ns 179
ns 3920000
BM_format_to_back_inserter<std::vector<char>> 214 ns
214 ns 3274000
BM_format_to_back_inserter<std::list<char>> 751 ns
751 ns 930000
BM_format_to_iterator/<std::array> 164 ns 164
ns 4258000
BM_format_to_iterator/<std::string> 165 ns 164
ns 4247000
BM_format_to_iterator/<std::vector> 165 ns 165
ns 4248000
Comparison
Benchmark Time
CPU Time Old Time New CPU Old CPU New
--------------------------------------------------------------------------------------------------------------------------------------------
BM_sprintf +0.0013
+0.0028 197 197 196 197
BM_to_string +0.0023
+0.0038 218 219 218 219
BM_to_chars +0.0014
+0.0030 42 42 42 42
BM_to_chars_as_string -0.0025
-0.0010 48 48 48 48
BM_format -0.0476
-0.0462 175 167 175 167
BM_format_to_back_inserter<std::string> +0.0190
+0.0205 175 179 175 179
BM_format_to_back_inserter<std::vector<char>>
+0.0348 +0.0363 207 214 206 214
BM_format_to_back_inserter<std::list<char>>
-0.0013 +0.0005 752 751 750 751
BM_format_to_iterator/<std::array> +0.0188
+0.0203 161 164 161 164
BM_format_to_iterator/<std::string> +0.0207
+0.0226 161 165 161 164
BM_format_to_iterator/<std::vector> +0.0197
+0.0212 162 165 161 165
OVERALL_GEOMEAN +0.0058
+0.0074 0 0 0 0
write_int_comparison:
Before
----------------------------------------------------------------------------------------
Benchmark Time CPU
Iterations
----------------------------------------------------------------------------------------
BM_sprintf 79.6 ns 79.5 ns
8739000
BM_to_string 14.9 ns 14.9 ns
46713000
BM_to_chars 5.68 ns 5.67 ns
120614000
BM_to_chars_as_string 14.2 ns 14.1 ns
49513000
BM_format 69.3 ns 69.2 ns
10105000
BM_format_to_back_inserter<std::string> 69.2 ns 69.1
ns 10138000
BM_format_to_back_inserter<std::vector<char>> 90.6 ns
90.5 ns 7728000
BM_format_to_back_inserter<std::list<char>> 234 ns
234 ns 2986000
BM_format_to_iterator/<std::array> 59.3 ns 59.3
ns 11805000
BM_format_to_iterator/<std::string> 58.7 ns 58.6
ns 11943000
BM_format_to_iterator/<std::vector> 60.1 ns 60.1
ns 11670000
After
----------------------------------------------------------------------------------------
Benchmark Time CPU
Iterations
----------------------------------------------------------------------------------------
BM_sprintf 80.2 ns 80.2 ns
8670000
BM_to_string 15.0 ns 15.0 ns
46559000
BM_to_chars 4.93 ns 4.93 ns
138016000
BM_to_chars_as_string 15.4 ns 15.4 ns
45415000
BM_format 62.1 ns 62.0 ns
11316000
BM_format_to_back_inserter<std::string> 70.2 ns 70.2
ns 9962000
BM_format_to_back_inserter<std::vector<char>> 92.8 ns
92.8 ns 7544000
BM_format_to_back_inserter<std::list<char>> 240 ns
240 ns 2917000
BM_format_to_iterator/<std::array> 60.5 ns 60.5
ns 11572000
BM_format_to_iterator/<std::string> 60.2 ns 60.2
ns 11653000
BM_format_to_iterator/<std::vector> 60.1 ns 60.1
ns 11659000
Comparison
Benchmark Time
CPU Time Old Time New CPU Old CPU New
--------------------------------------------------------------------------------------------------------------------------------------------
BM_sprintf +0.0072
+0.0081 80 80 80 80
BM_to_string +0.0043
+0.0053 15 15 15 15
BM_to_chars -0.1324
-0.1316 6 5 6 5
BM_to_chars_as_string +0.0895
+0.0906 14 15 14 15
BM_format -0.1047
-0.1040 69 62 69 62
BM_format_to_back_inserter<std::string> +0.0148
+0.0157 69 70 69 70
BM_format_to_back_inserter<std::vector<char>>
+0.0241 +0.0251 91 93 90 93
BM_format_to_back_inserter<std::list<char>>
+0.0222 +0.0232 234 240 234 240
BM_format_to_iterator/<std::array> +0.0196
+0.0205 59 60 59 60
BM_format_to_iterator/<std::string> +0.0266
+0.0275 59 60 59 60
BM_format_to_iterator/<std::vector> -0.0004
+0.0005 60 60 60 60
OVERALL_GEOMEAN -0.0045
-0.0036 0 0 0 0
write_string_comparison:
Before
---------------------------------------------------------------------------------------------------------------
Benchmark
Time CPU Iterations
---------------------------------------------------------------------------------------------------------------
BM_sprintf/C string len = 6 4.82
ns 4.82 ns 145548481
BM_format/C string len = 6 55.1
ns 55.1 ns 12713693
BM_format_to_back_inserter<std::string>/C string len = 6
55.1 ns 55.1 ns 12690821
BM_format_to_back_inserter<std::vector<char>>/C string len = 6
71.5 ns 71.5 ns 9805550
BM_format_to_back_inserter<std::deque<char>>/C string len = 6
154 ns 154 ns 4536256
BM_format_to_back_inserter<std::list<char>>/C string len = 6
130 ns 130 ns 5348845
BM_format_to_iterator/<std::array> C string len = 6
44.9 ns 44.9 ns 15556175
BM_format_to_iterator/<std::string> C string len = 6
45.8 ns 45.8 ns 15290662
BM_format_to_iterator/<std::vector> C string len = 6
44.4 ns 44.4 ns 15807704
BM_format_to_iterator/<std::deque> C string len = 6
50.0 ns 50.0 ns 13973893
BM_format/string len = 6 54.7
ns 54.7 ns 12793406
BM_format_to_back_inserter<std::string>/string len = 6
55.5 ns 55.5 ns 12620370
BM_format_to_back_inserter<std::vector<char>>/string len = 6
70.4 ns 70.4 ns 9936490
BM_format_to_back_inserter<std::deque<char>>/string len = 6
155 ns 155 ns 4521357
BM_format_to_back_inserter<std::list<char>>/string len = 6
135 ns 135 ns 5201519
BM_format_to_iterator/<std::array> string len = 6
44.6 ns 44.6 ns 15703872
BM_format_to_iterator/<std::string> string len = 6
45.0 ns 45.0 ns 15545182
BM_format_to_iterator/<std::vector> string len = 6
45.0 ns 45.0 ns 15539130
BM_format_to_iterator/<std::deque> string len = 6
50.5 ns 50.5 ns 13846916
BM_format/string_view len = 6 54.6
ns 54.6 ns 12821301
BM_format_to_back_inserter<std::string>/string_view len = 6
54.6 ns 54.6 ns 12827673
BM_format_to_back_inserter<std::vector<char>>/string_view len = 6
69.9 ns 69.9 ns 9958365
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6
157 ns 157 ns 4462445
BM_format_to_back_inserter<std::list<char>>/string_view len = 6
134 ns 134 ns 5232155
BM_format_to_iterator/<std::array> string_view len = 6
44.2 ns 44.2 ns 15871362
BM_format_to_iterator/<std::string> string_view len = 6
45.0 ns 45.0 ns 15582582
BM_format_to_iterator/<std::vector> string_view len = 6
45.1 ns 45.1 ns 15539906
BM_format_to_iterator/<std::deque> string_view len = 6
50.5 ns 50.5 ns 13896524
BM_sprintf/C string len = 60 4.15
ns 4.15 ns 168165776
BM_format/C string len = 60 73.8
ns 73.8 ns 9498291
BM_format_to_back_inserter<std::string>/C string len = 60
73.6 ns 73.6 ns 9535890
BM_format_to_back_inserter<std::vector<char>>/C string len = 60
83.1 ns 83.1 ns 8428154
BM_format_to_back_inserter<std::deque<char>>/C string len = 60
281 ns 281 ns 2490093
BM_format_to_back_inserter<std::list<char>>/C string len = 60
1157 ns 1157 ns 605227
BM_format_to_iterator/<std::array> C string len = 60
44.9 ns 44.9 ns 15604442
BM_format_to_iterator/<std::string> C string len = 60
45.8 ns 45.8 ns 15272196
BM_format_to_iterator/<std::vector> C string len = 60
44.6 ns 44.7 ns 15683193
BM_format_to_iterator/<std::deque> C string len = 60
50.6 ns 50.6 ns 13698382
BM_format/string len = 60 72.3
ns 72.3 ns 9648955
BM_format_to_back_inserter<std::string>/string len = 60
72.0 ns 72.0 ns 9738373
BM_format_to_back_inserter<std::vector<char>>/string len = 60
82.3 ns 82.3 ns 8517896
BM_format_to_back_inserter<std::deque<char>>/string len = 60
280 ns 280 ns 2496054
BM_format_to_back_inserter<std::list<char>>/string len = 60
1162 ns 1162 ns 602383
BM_format_to_iterator/<std::array> string len = 60
44.5 ns 44.5 ns 15727799
BM_format_to_iterator/<std::string> string len = 60
49.6 ns 49.6 ns 14096012
BM_format_to_iterator/<std::vector> string len = 60
49.8 ns 49.8 ns 14053734
BM_format_to_iterator/<std::deque> string len = 60
50.8 ns 50.8 ns 13801448
BM_format/string_view len = 60 72.5
ns 72.5 ns 9653638
BM_format_to_back_inserter<std::string>/string_view len = 60
72.7 ns 72.7 ns 9598203
BM_format_to_back_inserter<std::vector<char>>/string_view len = 60
81.9 ns 81.9 ns 8522306
BM_format_to_back_inserter<std::deque<char>>/string_view len = 60
283 ns 283 ns 2475014
BM_format_to_back_inserter<std::list<char>>/string_view len = 60
1162 ns 1162 ns 600924
BM_format_to_iterator/<std::array> string_view len = 60
44.1 ns 44.1 ns 15858951
BM_format_to_iterator/<std::string> string_view len = 60
44.9 ns 44.9 ns 15579340
BM_format_to_iterator/<std::vector> string_view len = 60
44.9 ns 44.9 ns 15586711
BM_format_to_iterator/<std::deque> string_view len = 60
50.0 ns 50.0 ns 13980804
BM_sprintf/C string len = 6000 116
ns 116 ns 6051541
BM_format/C string len = 6000 1000
ns 1000 ns 698647
BM_format_to_back_inserter<std::string>/C string len = 6000
1002 ns 1002 ns 701440
BM_format_to_back_inserter<std::vector<char>>/C string len = 6000
956 ns 956 ns 727585
BM_format_to_back_inserter<std::deque<char>>/C string len = 6000
14898 ns 14898 ns 46994
BM_format_to_back_inserter<std::list<char>>/C string len = 6000
114860 ns 114859 ns 6106
BM_format_to_iterator/<std::array> C string len = 6000
158 ns 158 ns 4425133
BM_format_to_iterator/<std::string> C string len = 6000
161 ns 161 ns 4335471
BM_format_to_iterator/<std::vector> C string len = 6000
157 ns 157 ns 4444174
BM_format_to_iterator/<std::deque> C string len = 6000
445 ns 445 ns 1574120
BM_format/string len = 6000 929
ns 929 ns 753630
BM_format_to_back_inserter<std::string>/string len = 6000
930 ns 930 ns 752888
BM_format_to_back_inserter<std::vector<char>>/string len = 6000
910 ns 910 ns 771111
BM_format_to_back_inserter<std::deque<char>>/string len = 6000
14875 ns 14876 ns 47221
BM_format_to_back_inserter<std::list<char>>/string len = 6000
114937 ns 114936 ns 6092
BM_format_to_iterator/<std::array> string len = 6000
118 ns 118 ns 5963643
BM_format_to_iterator/<std::string> string len = 6000
106 ns 106 ns 6584711
BM_format_to_iterator/<std::vector> string len = 6000
106 ns 106 ns 6583118
BM_format_to_iterator/<std::deque> string len = 6000
391 ns 391 ns 1790538
BM_format/string_view len = 6000 935
ns 935 ns 744348
BM_format_to_back_inserter<std::string>/string_view len = 6000
934 ns 934 ns 742039
BM_format_to_back_inserter<std::vector<char>>/string_view len =
6000 895 ns 895 ns 783527
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6000
14864 ns 14865 ns 47122
BM_format_to_back_inserter<std::list<char>>/string_view len = 6000
115042 ns 115044 ns 6091
BM_format_to_iterator/<std::array> string_view len = 6000
115 ns 115 ns 6070197
BM_format_to_iterator/<std::string> string_view len = 6000
116 ns 116 ns 6035109
BM_format_to_iterator/<std::vector> string_view len = 6000
115 ns 115 ns 6067683
BM_format_to_iterator/<std::deque> string_view len = 6000
387 ns 387 ns 1803466
After
---------------------------------------------------------------------------------------------------------------
Benchmark
Time CPU Iterations
---------------------------------------------------------------------------------------------------------------
BM_sprintf/C string len = 6 3.56
ns 3.56 ns 196337806
BM_format/C string len = 6 49.1
ns 49.1 ns 14241174
BM_format_to_back_inserter<std::string>/C string len = 6
56.8 ns 56.8 ns 12341483
BM_format_to_back_inserter<std::vector<char>>/C string len = 6
72.9 ns 72.9 ns 9610864
BM_format_to_back_inserter<std::deque<char>>/C string len = 6
155 ns 155 ns 4528719
BM_format_to_back_inserter<std::list<char>>/C string len = 6
137 ns 137 ns 5103340
BM_format_to_iterator/<std::array> C string len = 6
46.4 ns 46.4 ns 15081626
BM_format_to_iterator/<std::string> C string len = 6
47.0 ns 47.0 ns 14893458
BM_format_to_iterator/<std::vector> C string len = 6
45.9 ns 45.9 ns 15243762
BM_format_to_iterator/<std::deque> C string len = 6
52.6 ns 52.6 ns 13323560
BM_format/string len = 6 49.3
ns 49.3 ns 14181485
BM_format_to_back_inserter<std::string>/string len = 6
55.4 ns 55.4 ns 12644078
BM_format_to_back_inserter<std::vector<char>>/string len = 6
72.7 ns 72.7 ns 9618696
BM_format_to_back_inserter<std::deque<char>>/string len = 6
154 ns 154 ns 4540873
BM_format_to_back_inserter<std::list<char>>/string len = 6
134 ns 134 ns 5220153
BM_format_to_iterator/<std::array> string len = 6
46.5 ns 46.5 ns 15064445
BM_format_to_iterator/<std::string> string len = 6
47.3 ns 47.3 ns 14786851
BM_format_to_iterator/<std::vector> string len = 6
46.5 ns 46.5 ns 15069381
BM_format_to_iterator/<std::deque> string len = 6
52.9 ns 52.9 ns 13207437
BM_format/string_view len = 6 47.6
ns 47.6 ns 14688449
BM_format_to_back_inserter<std::string>/string_view len = 6
56.1 ns 56.1 ns 12514239
BM_format_to_back_inserter<std::vector<char>>/string_view len = 6
72.0 ns 72.0 ns 9705591
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6
152 ns 152 ns 4607470
BM_format_to_back_inserter<std::list<char>>/string_view len = 6
134 ns 134 ns 5233005
BM_format_to_iterator/<std::array> string_view len = 6
46.0 ns 46.0 ns 15205542
BM_format_to_iterator/<std::string> string_view len = 6
46.5 ns 46.5 ns 15067775
BM_format_to_iterator/<std::vector> string_view len = 6
46.5 ns 46.5 ns 15057288
BM_format_to_iterator/<std::deque> string_view len = 6
51.8 ns 51.8 ns 13564649
BM_sprintf/C string len = 60 4.83
ns 4.83 ns 145020116
BM_format/C string len = 60 72.3
ns 72.3 ns 9665555
BM_format_to_back_inserter<std::string>/C string len = 60
85.0 ns 85.0 ns 8249050
BM_format_to_back_inserter<std::vector<char>>/C string len = 60
94.7 ns 94.7 ns 7398143
BM_format_to_back_inserter<std::deque<char>>/C string len = 60
286 ns 286 ns 2452225
BM_format_to_back_inserter<std::list<char>>/C string len = 60
1179 ns 1179 ns 595011
BM_format_to_iterator/<std::array> C string len = 60
46.1 ns 46.1 ns 15157525
BM_format_to_iterator/<std::string> C string len = 60
47.0 ns 47.0 ns 14899863
BM_format_to_iterator/<std::vector> C string len = 60
45.8 ns 45.8 ns 15272542
BM_format_to_iterator/<std::deque> C string len = 60
58.7 ns 58.7 ns 11958910
BM_format/string len = 60 61.7
ns 61.7 ns 11308865
BM_format_to_back_inserter<std::string>/string len = 60
74.2 ns 74.2 ns 9401855
BM_format_to_back_inserter<std::vector<char>>/string len = 60
86.6 ns 86.6 ns 8079197
BM_format_to_back_inserter<std::deque<char>>/string len = 60
278 ns 278 ns 2519254
BM_format_to_back_inserter<std::list<char>>/string len = 60
1169 ns 1170 ns 597703
BM_format_to_iterator/<std::array> string len = 60
46.4 ns 46.4 ns 15074759
BM_format_to_iterator/<std::string> string len = 60
47.3 ns 47.3 ns 14801107
BM_format_to_iterator/<std::vector> string len = 60
46.3 ns 46.4 ns 15085548
BM_format_to_iterator/<std::deque> string len = 60
52.2 ns 52.2 ns 13331015
BM_format/string_view len = 60 65.0
ns 65.0 ns 10756847
BM_format_to_back_inserter<std::string>/string_view len = 60
78.5 ns 78.5 ns 9051370
BM_format_to_back_inserter<std::vector<char>>/string_view len = 60
87.9 ns 87.9 ns 7946825
BM_format_to_back_inserter<std::deque<char>>/string_view len = 60
280 ns 280 ns 2505999
BM_format_to_back_inserter<std::list<char>>/string_view len = 60
1174 ns 1174 ns 594829
BM_format_to_iterator/<std::array> string_view len = 60
46.3 ns 46.3 ns 15149785
BM_format_to_iterator/<std::string> string_view len = 60
46.7 ns 46.7 ns 15002678
BM_format_to_iterator/<std::vector> string_view len = 60
46.7 ns 46.7 ns 14996445
BM_format_to_iterator/<std::deque> string_view len = 60
52.6 ns 52.6 ns 13255470
BM_sprintf/C string len = 6000 77.1
ns 77.1 ns 9099121
BM_format/C string len = 6000 350
ns 350 ns 2013049
BM_format_to_back_inserter<std::string>/C string len = 6000
992 ns 992 ns 709093
BM_format_to_back_inserter<std::vector<char>>/C string len = 6000
1016 ns 1016 ns 694784
BM_format_to_back_inserter<std::deque<char>>/C string len = 6000
15158 ns 15159 ns 46125
BM_format_to_back_inserter<std::list<char>>/C string len = 6000
115703 ns 115705 ns 6055
BM_format_to_iterator/<std::array> C string len = 6000
166 ns 166 ns 4224749
BM_format_to_iterator/<std::string> C string len = 6000
153 ns 153 ns 4573034
BM_format_to_iterator/<std::vector> C string len = 6000
150 ns 150 ns 4678898
BM_format_to_iterator/<std::deque> C string len = 6000
465 ns 465 ns 1506323
BM_format/string len = 6000 281
ns 281 ns 2462572
BM_format_to_back_inserter<std::string>/string len = 6000
935 ns 935 ns 745376
BM_format_to_back_inserter<std::vector<char>>/string len = 6000
939 ns 939 ns 747498
BM_format_to_back_inserter<std::deque<char>>/string len = 6000
15069 ns 15069 ns 46429
BM_format_to_back_inserter<std::list<char>>/string len = 6000
115537 ns 115539 ns 6063
BM_format_to_iterator/<std::array> string len = 6000
120 ns 120 ns 5849159
BM_format_to_iterator/<std::string> string len = 6000
108 ns 108 ns 6482306
BM_format_to_iterator/<std::vector> string len = 6000
107 ns 107 ns 6547915
BM_format_to_iterator/<std::deque> string len = 6000
397 ns 397 ns 1763729
BM_format/string_view len = 6000 282
ns 282 ns 2490133
BM_format_to_back_inserter<std::string>/string_view len = 6000
927 ns 927 ns 750931
BM_format_to_back_inserter<std::vector<char>>/string_view len =
6000 946 ns 946 ns 735544
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6000
15028 ns 15029 ns 46612
BM_format_to_back_inserter<std::list<char>>/string_view len = 6000
115153 ns 115153 ns 6057
BM_format_to_iterator/<std::array> string_view len = 6000
122 ns 122 ns 5753940
BM_format_to_iterator/<std::string> string_view len = 6000
108 ns 108 ns 6507555
BM_format_to_iterator/<std::vector> string_view len = 6000
107 ns 107 ns 6510450
BM_format_to_iterator/<std::deque> string_view len = 6000
398 ns 398 ns 1762517
Comparison
Benchmark
Time CPU Time Old Time New CPU Old CPU
New
-------------------------------------------------------------------------------------------------------------------------------------------------------------------
BM_sprintf/C string len = 6
-0.2599 -0.2599 5 4 5
4
BM_format/C string len = 6
-0.1094 -0.1095 55 49 55
49
BM_format_to_back_inserter<std::string>/C string len = 6
+0.0316 +0.0316 55 57 55
57
BM_format_to_back_inserter<std::vector<char>>/C string len = 6
+0.0204 +0.0204 71 73
71 73
BM_format_to_back_inserter<std::deque<char>>/C string len = 6
+0.0023 +0.0023 154 155
154 155
BM_format_to_back_inserter<std::list<char>>/C string len = 6
+0.0521 +0.0520 130 137
130 137
BM_format_to_iterator/<std::array> C string len = 6
+0.0317 +0.0317 45 46 45
46
BM_format_to_iterator/<std::string> C string len = 6
+0.0265 +0.0265 46 47 46
47
BM_format_to_iterator/<std::vector> C string len = 6
+0.0345 +0.0345 44 46 44
46
BM_format_to_iterator/<std::deque> C string len = 6
+0.0511 +0.0511 50 53 50
53
BM_format/string len = 6
-0.0981 -0.0981 55 49 55
49
BM_format_to_back_inserter<std::string>/string len = 6
-0.0028 -0.0028 56 55 56
55
BM_format_to_back_inserter<std::vector<char>>/string len = 6
+0.0331 +0.0331 70 73
70 73
BM_format_to_back_inserter<std::deque<char>>/string len = 6
-0.0040 -0.0040 155 154
155 154
BM_format_to_back_inserter<std::list<char>>/string len = 6
-0.0019 -0.0019 135 134
135 134
BM_format_to_iterator/<std::array> string len = 6
+0.0427 +0.0427 45 46 45
46
BM_format_to_iterator/<std::string> string len = 6
+0.0515 +0.0515 45 47 45
47
BM_format_to_iterator/<std::vector> string len = 6
+0.0316 +0.0316 45 46 45
46
BM_format_to_iterator/<std::deque> string len = 6
+0.0475 +0.0475 51 53 51
53
BM_format/string_view len = 6
-0.1267 -0.1267 55 48 55
48
BM_format_to_back_inserter<std::string>/string_view len = 6
+0.0283 +0.0283 55 56 55
56
BM_format_to_back_inserter<std::vector<char>>/string_view len = 6
+0.0291 +0.0291 70 72
70 72
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6
-0.0305 -0.0306 157 152
157 152
BM_format_to_back_inserter<std::list<char>>/string_view len = 6
-0.0012 -0.0012 134 134
134 134
BM_format_to_iterator/<std::array> string_view len = 6
+0.0426 +0.0426 44 46 44
46
BM_format_to_iterator/<std::string> string_view len = 6
+0.0322 +0.0322 45 46 45
46
BM_format_to_iterator/<std::vector> string_view len = 6
+0.0309 +0.0309 45 46 45
46
BM_format_to_iterator/<std::deque> string_view len = 6
+0.0248 +0.0248 51 52 51
52
BM_sprintf/C string len = 60
+0.1633 +0.1633 4 5 4
5
BM_format/C string len = 60
-0.0203 -0.0203 74 72 74
72
BM_format_to_back_inserter<std::string>/C string len = 60
+0.1548 +0.1548 74 85 74
85
BM_format_to_back_inserter<std::vector<char>>/C string len = 60
+0.1395 +0.1395 83 95
83 95
BM_format_to_back_inserter<std::deque<char>>/C string len = 60
+0.0157 +0.0157 281 286
281 286
BM_format_to_back_inserter<std::list<char>>/C string len = 60
+0.0191 +0.0191 1157 1179
1157 1179
BM_format_to_iterator/<std::array> C string len = 60
+0.0283 +0.0283 45 46 45
46
BM_format_to_iterator/<std::string> C string len = 60
+0.0251 +0.0252 46 47 46
47
BM_format_to_iterator/<std::vector> C string len = 60
+0.0263 +0.0263 45 46 45
46
BM_format_to_iterator/<std::deque> C string len = 60
+0.1592 +0.1591 51 59 51
59
BM_format/string len = 60
-0.1466 -0.1466 72 62 72
62
BM_format_to_back_inserter<std::string>/string len = 60
+0.0299 +0.0299 72 74 72
74
BM_format_to_back_inserter<std::vector<char>>/string len = 60
+0.0522 +0.0522 82 87
82 87
BM_format_to_back_inserter<std::deque<char>>/string len = 60
-0.0099 -0.0099 280 278
280 278
BM_format_to_back_inserter<std::list<char>>/string len = 60
+0.0062 +0.0062 1162 1169
1162 1170
BM_format_to_iterator/<std::array> string len = 60
+0.0430 +0.0430 45 46 45
46
BM_format_to_iterator/<std::string> string len = 60
-0.0466 -0.0466 50 47 50
47
BM_format_to_iterator/<std::vector> string len = 60
-0.0693 -0.0693 50 46 50
46
BM_format_to_iterator/<std::deque> string len = 60
+0.0275 +0.0275 51 52 51
52
BM_format/string_view len = 60
-0.1034 -0.1034 73 65 73
65
BM_format_to_back_inserter<std::string>/string_view len = 60
+0.0790 +0.0790 73 78 73
78
BM_format_to_back_inserter<std::vector<char>>/string_view len = 60
+0.0735 +0.0735 82 88
82 88
BM_format_to_back_inserter<std::deque<char>>/string_view len = 60
-0.0103 -0.0104 283 280
283 280
BM_format_to_back_inserter<std::list<char>>/string_view len = 60
+0.0101 +0.0101 1162 1174
1162 1174
BM_format_to_iterator/<std::array> string_view len = 60
+0.0484 +0.0484 44 46 44
46
BM_format_to_iterator/<std::string> string_view len = 60
+0.0387 +0.0387 45 47 45
47
BM_format_to_iterator/<std::vector> string_view len = 60
+0.0402 +0.0402 45 47 45
47
BM_format_to_iterator/<std::deque> string_view len = 60
+0.0508 +0.0508 50 53 50
53
BM_sprintf/C string len = 6000
-0.3337 -0.3337 116 77 116
77
BM_format/C string len = 6000
-0.6500 -0.6500 1000 350 1000
350
BM_format_to_back_inserter<std::string>/C string len = 6000
-0.0104 -0.0105 1002 992 1002
992
BM_format_to_back_inserter<std::vector<char>>/C string len = 6000
+0.0630 +0.0630 956 1016
956 1016
BM_format_to_back_inserter<std::deque<char>>/C string len = 6000
+0.0175 +0.0175 14898 15158
14898 15159
BM_format_to_back_inserter<std::list<char>>/C string len = 6000
+0.0073 +0.0074 114860 115703
114859 115705
BM_format_to_iterator/<std::array> C string len = 6000
+0.0504 +0.0504 158 166 158
166
BM_format_to_iterator/<std::string> C string len = 6000
-0.0486 -0.0486 161 153 161
153
BM_format_to_iterator/<std::vector> C string len = 6000
-0.0483 -0.0483 157 150 157
150
BM_format_to_iterator/<std::deque> C string len = 6000
+0.0459 +0.0459 445 465 445
465
BM_format/string len = 6000
-0.6975 -0.6975 929 281 929
281
BM_format_to_back_inserter<std::string>/string len = 6000
+0.0050 +0.0050 930 935 930
935
BM_format_to_back_inserter<std::vector<char>>/string len = 6000
+0.0321 +0.0322 910 939
910 939
BM_format_to_back_inserter<std::deque<char>>/string len = 6000
+0.0130 +0.0130 14875 15069
14876 15069
BM_format_to_back_inserter<std::list<char>>/string len = 6000
+0.0052 +0.0052 114937 115537
114936 115539
BM_format_to_iterator/<std::array> string len = 6000
+0.0211 +0.0211 118 120 118
120
BM_format_to_iterator/<std::string> string len = 6000
+0.0146 +0.0146 106 108 106
108
BM_format_to_iterator/<std::vector> string len = 6000
+0.0048 +0.0048 106 107 106
107
BM_format_to_iterator/<std::deque> string len = 6000
+0.0150 +0.0150 391 397 391
397
BM_format/string_view len = 6000
-0.6989 -0.6989 935 282 935
282
BM_format_to_back_inserter<std::string>/string_view len = 6000
-0.0083 -0.0083 934 927 934
927
BM_format_to_back_inserter<std::vector<char>>/string_view len =
6000 +0.0566 +0.0566 895 946
895 946
BM_format_to_back_inserter<std::deque<char>>/string_view len = 6000
+0.0111 +0.0110 14864 15028
14865 15029
BM_format_to_back_inserter<std::list<char>>/string_view len = 6000
+0.0010 +0.0009 115042 115153
115044 115153
BM_format_to_iterator/<std::array> string_view len = 6000
+0.0560 +0.0560 115 122 115
122
BM_format_to_iterator/<std::string> string_view len = 6000
-0.0693 -0.0693 116 108 116
108
BM_format_to_iterator/<std::vector> string_view len = 6000
-0.0703 -0.0703 115 107 115
107
BM_format_to_iterator/<std::deque> string_view len = 6000
+0.0271 +0.0271 387 398 387
398
OVERALL_GEOMEAN
-0.0350 -0.0350 0 0 0
0
format:
Before
--------------------------------------------------------------------------------------------
Benchmark Time CPU Iterations
UserCounters...
--------------------------------------------------------------------------------------------
BM_format_string<char>/1 55.5 ns 55.5 ns
12463288 bytes_per_second=17.187Mi/s
BM_format_string<char>/2 27.6 ns 27.6 ns
25421994 bytes_per_second=69.1874Mi/s
BM_format_string<char>/4 14.0 ns 14.0 ns
49785656 bytes_per_second=271.524Mi/s
BM_format_string<char>/8 7.07 ns 7.07 ns
99247048 bytes_per_second=1.05444Gi/s
BM_format_string<char>/16 3.53 ns 3.53 ns
198072224 bytes_per_second=4.21726Gi/s
BM_format_string<char>/32 2.31 ns 2.31 ns
302771136 bytes_per_second=12.9138Gi/s
BM_format_string<char>/64 1.15 ns 1.15 ns
606646976 bytes_per_second=51.7527Gi/s
BM_format_string<char>/128 0.597 ns 0.597 ns
1172263936 bytes_per_second=199.688Gi/s
BM_format_string<char>/256 0.327 ns 0.327 ns
2148927744 bytes_per_second=728.678Gi/s
BM_format_string<char>/512 0.248 ns 0.248 ns
2821635584 bytes_per_second=1.8779Ti/s
BM_format_string<char>/1024 0.203 ns 0.203 ns
3433579520 bytes_per_second=4.57798Ti/s
BM_format_string<char>/2048 0.164 ns 0.164 ns
4277524480 bytes_per_second=11.3793Ti/s
BM_format_string<char>/4096 0.137 ns 0.137 ns
5122269184 bytes_per_second=27.2589Ti/s
BM_format_string<char>/8192 0.126 ns 0.126 ns
5564243968 bytes_per_second=59.2812Ti/s
BM_format_string<char>/16384 0.136 ns 0.136 ns
5153013760 bytes_per_second=109.492Ti/s
BM_format_string<char>/32768 0.135 ns 0.135 ns
5165088768 bytes_per_second=219.985Ti/s
BM_format_string<char>/65536 0.243 ns 0.242 ns
2930180096 bytes_per_second=246.57Ti/s
BM_format_string<char>/131072 0.490 ns 0.489 ns
1437990912 bytes_per_second=243.75Ti/s
BM_format_string<char>/262144 0.593 ns 0.592 ns
1183055872 bytes_per_second=402.931Ti/s
BM_format_string<char>/524288 0.643 ns 0.641 ns
1092616192 bytes_per_second=743.445Ti/s
BM_format_string<char>/1048576 0.669 ns 0.668 ns
1045430272 bytes_per_second=1.39478Pi/s
BM_format_string<wchar_t>/1 56.0 ns 55.9 ns
12511543 bytes_per_second=68.2628Mi/s
BM_format_string<wchar_t>/2 28.0 ns 27.9 ns
25062366 bytes_per_second=273.519Mi/s
BM_format_string<wchar_t>/4 14.0 ns 14.0 ns
50257068 bytes_per_second=1.06742Gi/s
BM_format_string<wchar_t>/8 9.24 ns 9.21 ns
76118616 bytes_per_second=3.23473Gi/s
BM_format_string<wchar_t>/16 4.66 ns 4.65 ns
151420352 bytes_per_second=12.8261Gi/s
BM_format_string<wchar_t>/32 2.35 ns 2.35 ns
298417600 bytes_per_second=50.7972Gi/s
BM_format_string<wchar_t>/64 1.35 ns 1.34 ns
521608704 bytes_per_second=177.502Gi/s
BM_format_string<wchar_t>/128 1.03 ns 1.03 ns
680946304 bytes_per_second=463.91Gi/s
BM_format_string<wchar_t>/256 0.849 ns 0.847 ns
825871104 bytes_per_second=1.09901Ti/s
BM_format_string<wchar_t>/512 0.681 ns 0.679 ns
1033245696 bytes_per_second=2.74383Ti/s
BM_format_string<wchar_t>/1024 0.576 ns 0.575 ns
1219777536 bytes_per_second=6.48343Ti/s
BM_format_string<wchar_t>/2048 0.515 ns 0.514 ns
1361629184 bytes_per_second=14.4881Ti/s
BM_format_string<wchar_t>/4096 0.546 ns 0.545 ns
1285427200 bytes_per_second=27.3342Ti/s
BM_format_string<wchar_t>/8192 0.550 ns 0.548 ns
1277042688 bytes_per_second=54.3343Ti/s
BM_format_string<wchar_t>/16384 0.583 ns 0.581 ns
1203879936 bytes_per_second=102.544Ti/s
BM_format_string<wchar_t>/32768 0.640 ns 0.638 ns
1095139328 bytes_per_second=186.82Ti/s
BM_format_string<wchar_t>/65536 0.642 ns 0.640 ns
1093337088 bytes_per_second=372.283Ti/s
BM_format_string<wchar_t>/131072 0.655 ns 0.654 ns
1070596096 bytes_per_second=729.428Ti/s
BM_format_string<wchar_t>/262144 2.68 ns 2.67 ns
262406144 bytes_per_second=357.446Ti/s
BM_format_string<wchar_t>/524288 2.13 ns 2.13 ns
330301440 bytes_per_second=897.574Ti/s
BM_format_string<wchar_t>/1048576 2.44 ns 2.43 ns
288358400 bytes_per_second=1.53149Pi/s
After
--------------------------------------------------------------------------------------------
Benchmark Time CPU Iterations
UserCounters...
--------------------------------------------------------------------------------------------
BM_format_string<char>/1 49.3 ns 49.1 ns
14230742 bytes_per_second=19.4054Mi/s
BM_format_string<char>/2 24.8 ns 24.8 ns
28253114 bytes_per_second=77.0465Mi/s
BM_format_string<char>/4 12.4 ns 12.4 ns
56381440 bytes_per_second=307.462Mi/s
BM_format_string<char>/8 6.23 ns 6.21 ns
112951232 bytes_per_second=1.19924Gi/s
BM_format_string<char>/16 3.10 ns 3.09 ns
225822496 bytes_per_second=4.81566Gi/s
BM_format_string<char>/32 1.98 ns 1.98 ns
354208192 bytes_per_second=15.0825Gi/s
BM_format_string<char>/64 0.990 ns 0.987 ns
714296384 bytes_per_second=60.3689Gi/s
BM_format_string<char>/128 0.504 ns 0.503 ns
1399988480 bytes_per_second=237.144Gi/s
BM_format_string<char>/256 0.335 ns 0.334 ns
2084828928 bytes_per_second=712.859Gi/s
BM_format_string<char>/512 0.187 ns 0.186 ns
3760082432 bytes_per_second=2.50102Ti/s
BM_format_string<char>/1024 0.109 ns 0.108 ns
6455339008 bytes_per_second=8.59552Ti/s
BM_format_string<char>/2048 0.080 ns 0.080 ns
8754006016 bytes_per_second=23.2731Ti/s
BM_format_string<char>/4096 0.051 ns 0.051 ns
13786701824 bytes_per_second=73.4088Ti/s
BM_format_string<char>/8192 0.042 ns 0.042 ns
16851435520 bytes_per_second=178.737Ti/s
BM_format_string<char>/16384 0.122 ns 0.122 ns
5746589696 bytes_per_second=122.029Ti/s
BM_format_string<char>/32768 0.107 ns 0.106 ns
6571687936 bytes_per_second=280.122Ti/s
BM_format_string<char>/65536 0.102 ns 0.102 ns
6876626944 bytes_per_second=584.381Ti/s
BM_format_string<char>/131072 0.106 ns 0.105 ns
6643122176 bytes_per_second=1.10413Pi/s
BM_format_string<char>/262144 0.589 ns 0.587 ns
1189609472 bytes_per_second=406.438Ti/s
BM_format_string<char>/524288 0.644 ns 0.642 ns
1088946176 bytes_per_second=743.064Ti/s
BM_format_string<char>/1048576 0.672 ns 0.670 ns
1039138816 bytes_per_second=1.38968Pi/s
BM_format_string<wchar_t>/1 48.7 ns 48.6 ns
14423178 bytes_per_second=78.5263Mi/s
BM_format_string<wchar_t>/2 24.4 ns 24.3 ns
28831748 bytes_per_second=313.869Mi/s
BM_format_string<wchar_t>/4 12.2 ns 12.2 ns
57661220 bytes_per_second=1.2253Gi/s
BM_format_string<wchar_t>/8 7.81 ns 7.79 ns
89887592 bytes_per_second=3.82675Gi/s
BM_format_string<wchar_t>/16 3.88 ns 3.87 ns
180450176 bytes_per_second=15.418Gi/s
BM_format_string<wchar_t>/32 1.98 ns 1.98 ns
354046112 bytes_per_second=60.3262Gi/s
BM_format_string<wchar_t>/64 1.02 ns 1.01 ns
689511680 bytes_per_second=234.906Gi/s
BM_format_string<wchar_t>/128 0.577 ns 0.576 ns
1215361408 bytes_per_second=828.297Gi/s
BM_format_string<wchar_t>/256 0.804 ns 0.802 ns
872249088 bytes_per_second=1.16111Ti/s
BM_format_string<wchar_t>/512 0.642 ns 0.641 ns
1093858304 bytes_per_second=2.90766Ti/s
BM_format_string<wchar_t>/1024 0.517 ns 0.516 ns
1354798080 bytes_per_second=7.21845Ti/s
BM_format_string<wchar_t>/2048 0.469 ns 0.467 ns
1491910656 bytes_per_second=15.9386Ti/s
BM_format_string<wchar_t>/4096 0.794 ns 0.792 ns
883822592 bytes_per_second=18.8156Ti/s
BM_format_string<wchar_t>/8192 0.722 ns 0.720 ns
971718656 bytes_per_second=41.3996Ti/s
BM_format_string<wchar_t>/16384 0.703 ns 0.701 ns
998031360 bytes_per_second=85.0369Ti/s
BM_format_string<wchar_t>/32768 0.724 ns 0.720 ns
971538432 bytes_per_second=165.467Ti/s
BM_format_string<wchar_t>/65536 0.745 ns 0.744 ns
941228032 bytes_per_second=320.665Ti/s
BM_format_string<wchar_t>/131072 0.742 ns 0.740 ns
945422336 bytes_per_second=644.032Ti/s
BM_format_string<wchar_t>/262144 2.99 ns 2.98 ns
234881024 bytes_per_second=319.75Ti/s
BM_format_string<wchar_t>/524288 3.31 ns 3.30 ns
212860928 bytes_per_second=578.085Ti/s
BM_format_string<wchar_t>/1048576 2.69 ns 2.68 ns
260046848 bytes_per_second=1.39081Pi/s
Comparison
Benchmark Time CPU
Time Old Time New CPU Old CPU New
--------------------------------------------------------------------------------------------------------------------------------
BM_format_string<char>/1 -0.1122 -0.1143
55 49 55 49
BM_format_string<char>/2 -0.0999 -0.1020
28 25 28 25
BM_format_string<char>/4 -0.1148 -0.1169
14 12 14 12
BM_format_string<char>/8 -0.1186 -0.1207
7 6 7 6
BM_format_string<char>/16 -0.1222 -0.1243
4 3 4 3
BM_format_string<char>/32 -0.1417 -0.1438
2 2 2 2
BM_format_string<char>/64 -0.1407 -0.1427
1 1 1 1
BM_format_string<char>/128 -0.1559 -0.1579
1 1 1 1
BM_format_string<char>/256 +0.0249 +0.0222
0 0 0 0
BM_format_string<char>/512 -0.2473 -0.2491
0 0 0 0
BM_format_string<char>/1024 -0.4661 -0.4674
0 0 0 0
BM_format_string<char>/2048 -0.5096 -0.5111
0 0 0 0
BM_format_string<char>/4096 -0.6278 -0.6287
0 0 0 0
BM_format_string<char>/8192 -0.6674 -0.6683
0 0 0 0
BM_format_string<char>/16384 -0.1005 -0.1027
0 0 0 0
BM_format_string<char>/32768 -0.2127 -0.2147
0 0 0 0
BM_format_string<char>/65536 -0.5796 -0.5781
0 0 0 0
BM_format_string<char>/131072 -0.7844 -0.7844
0 0 0 0
BM_format_string<char>/262144 -0.0073 -0.0086
1 1 1 1
BM_format_string<char>/524288 +0.0017 +0.0005
1 1 1 1
BM_format_string<char>/1048576 +0.0039 +0.0037
1 1 1 1
BM_format_string<wchar_t>/1 -0.1304 -0.1307
56 49 56 49
BM_format_string<wchar_t>/2 -0.1285 -0.1286
28 24 28 24
BM_format_string<wchar_t>/4 -0.1288 -0.1288
14 12 14 12
BM_format_string<wchar_t>/8 -0.1547 -0.1547
9 8 9 8
BM_format_string<wchar_t>/16 -0.1681 -0.1681
5 4 5 4
BM_format_string<wchar_t>/32 -0.1579 -0.1580
2 2 2 2
BM_format_string<wchar_t>/64 -0.2443 -0.2444
1 1 1 1
BM_format_string<wchar_t>/128 -0.4400 -0.4399
1 1 1 1
BM_format_string<wchar_t>/256 -0.0535 -0.0535
1 1 1 1
BM_format_string<wchar_t>/512 -0.0563 -0.0563
1 1 1 1
BM_format_string<wchar_t>/1024 -0.1018 -0.1018
1 1 1 1
BM_format_string<wchar_t>/2048 -0.0910 -0.0910
1 0 1 0
BM_format_string<wchar_t>/4096 +0.4528 +0.4527
1 1 1 1
BM_format_string<wchar_t>/8192 +0.3121 +0.3124
1 1 1 1
BM_format_string<wchar_t>/16384 +0.2059 +0.2059
1 1 1 1
BM_format_string<wchar_t>/32768 +0.1316 +0.1290
1 1 1 1
BM_format_string<wchar_t>/65536 +0.1604 +0.1610
1 1 1 1
BM_format_string<wchar_t>/131072 +0.1326 +0.1326
1 1 1 1
BM_format_string<wchar_t>/262144 +0.1181 +0.1179
3 3 3 3
BM_format_string<wchar_t>/524288 +0.5515 +0.5527
2 3 2 3
BM_format_string<wchar_t>/1048576 +0.1007 +0.1011
2 3 2 3
OVERALL_GEOMEAN -0.1685 -0.1693
0 0 0 0
---
Full diff: https://github.com/llvm/llvm-project/pull/101817.diff
2 Files Affected:
- (modified) libcxx/include/__format/buffer.h (+237-18)
- (modified) libcxx/include/__format/format_functions.h (+12-12)
``````````diff
diff --git a/libcxx/include/__format/buffer.h b/libcxx/include/__format/buffer.h
index 8598f0a1c0395..1f26bfa923a6a 100644
--- a/libcxx/include/__format/buffer.h
+++ b/libcxx/include/__format/buffer.h
@@ -58,23 +58,156 @@ namespace __format {
/// This helper is used together with the @ref back_insert_iterator to offer
/// type-erasure for the formatting functions. This reduces the number to
/// template instantiations.
+///
+/// The design of the class is being changed to improve performance and do some
+/// code cleanups.
+/// The original design (as shipped up to LLVM-19) uses the following design:
+/// - There is an external object that connects the buffer to the output.
+/// - The class constructor stores a function pointer to a grow function and a
+/// type-erased pointer to the object that does the grow.
+/// - When writing data to the buffer would exceed the external buffer's
+/// capacity it requests the external buffer to flush its contents.
+///
+/// The new design tries to solve some issues with the current design:
+/// - The buffer used is a fixed-size buffer, benchmarking shows that using a
+/// dynamic allocated buffer has performance benefits.
+/// - Implementing P3107R5 "Permit an efficient implementation of std::print"
+/// is not trivial with the current buffers. Using the code from this series
+/// makes it trivial.
+///
+/// This class is ABI-tagged, still the new design does not change the size of
+/// objects of this class.
+///
+/// The new design contains information regarding format_to_n changes, these
+/// will be implemented in follow-up patch.
+///
+/// The new design is the following.
+/// - There is an external object that connects the buffer to the output.
+/// - This buffer object:
+/// - inherits publicly from this class.
+/// - has a static or dynamic buffer.
+/// - has a static member function to make space in its buffer write
+/// operations. This can be done by increasing the size of the internal
+/// buffer or by writing the contents of the buffer to the output iterator.
+///
+/// This member function is a constructor argument, so its name is not
+/// fixed. The code uses the name __prepare_write.
+/// - The number of output code units can be limited by a __max_output_size
+/// object. This is used in format_to_n This object:
+/// - Contains the maximum number of code units to be written.
+/// - Contains the number of code units that are requested to be written.
+/// This number is returned to the user of format_to_n.
+/// - The write functions call objects __request_write member function.
+/// This function:
+/// - Updates the number of code units that are requested to be written.
+/// - Returns the number of code units that can be written without
+/// exceeding the maximum number of code units to be written.
+///
+/// Documentation for the buffer usage members:
+/// - __ptr_ the start of the buffer.
+/// - __capacity_ the number of code units that can be written.
+/// This means [__ptr_, __ptr_ + __capacity_) is a valid range to write to.
+/// - __size_ the number of code units written in the buffer. The next code
+/// unit will be written at __ptr_ + __size_. This __size_ may NOT contain
+/// the total number of code units written by the __output_buffer. Whether or
+/// not it does depends on the sub-class used. Typically the total number of
+/// code units written is not interesting. It is interesting for format_to_n
+/// which has its own way to track this number.
+///
+/// Documentation for the buffer changes function:
+/// The subclasses have a function with the following signature:
+///
+/// static void __prepare_write(
+/// __output_buffer<_CharT>& __buffer, size_t __code_units);
+///
+/// This function is called when a write function writes more code units than
+/// the buffer' available space. When an __max_output_size object is provided
+/// the number of code units is the number of code units returned from
+/// __max_output_size::__request_write function.
+///
+/// - The __buffer contains *this. Since the class containing this function
+/// inherits from __output_buffer it's save to cast it to the subclass being
+/// used.
+/// - The __code_units is the number of code units the caller will write + 1.
+/// - This value does not take the avaiable space of the buffer into account.
+/// - The push_back function is more efficient when writing before resizing,
+/// this means the buffer should always have room for one code unit. Hence
+/// the + 1 is the size.
+/// - When the function returns there is room for at least one code unit. There
+/// is no requirement there is room for __code_units code units:
+/// - The class has some "bulk" operations. For example, __copy which copies
+/// the contents of a basic_string_view to the output. If the sub-class has
+/// a fixed size buffer the size of the basic_string_view may be larger
+/// than the buffer. In that case it's impossible to honor the requested
+/// size.
+/// - The at least one code unit makes sure the entire output can be written.
+/// (Obviously making room one code unit at a time is slow and
+/// it's recommended to return a larger available space.)
+/// - When the buffer has room for at least one code unit the function may be
+/// a no-op.
+/// - When the function makes space for more code units it uses one for these
+/// functions to signal the change:
+/// - __buffer_flushed()
+/// - This function is typically used for a fixed sized buffer.
+/// - The current contents of [__ptr_, __ptr_ + __size_) have been
+/// processed.
+/// - __ptr_ remains unchanged.
+/// - __capacity_ remains unchanged.
+/// - __size_ will be set to 0.
+/// - __buffer_moved(_CharT* __ptr, size_t __capacity)
+/// - This function is typically used for a dynamic sized buffer. There the
+/// location of the buffer changes due to reallocations.
+/// - __ptr_ will be set to __ptr. (This value may be the old value of
+/// __ptr_).
+/// - __capacity_ will be set to __capacity. (This value may be the old
+/// value of __capacity_).
+/// - __size_ remains unchanged,
+/// - The range [__ptr, __ptr + __size_) contains the original data of the
+/// range [__ptr_, __ptr_ + __size_).
+///
+/// The push_back function expects a valid buffer and a capacity of at least 1.
+/// This means:
+/// - The class is constructed with a valid buffer,
+/// - __buffer_moved is called with a valid buffer is used before the first
+/// write operation,
+/// - no write function is ever called, or
+/// - the class is constructed with a __max_output_size object with __max_size
0.
+///
+/// The latter option allows formatted_size to use the output buffer without
+/// ever writing anything to the buffer.
template <__fmt_char_type _CharT>
class _LIBCPP_TEMPLATE_VIS __output_buffer {
public:
- using value_type = _CharT;
+ using value_type = _CharT;
+ using __prepare_write_type = void (*)(__output_buffer<_CharT>&, size_t);
- template <class _Tp>
+ template <class _Tp> // Deprecated LLVM-19 function.
_LIBCPP_HIDE_FROM_ABI explicit __output_buffer(_CharT* __ptr, size_t
__capacity, _Tp* __obj)
: __ptr_(__ptr),
__capacity_(__capacity),
__flush_([](_CharT* __p, size_t __n, void* __o) {
static_cast<_Tp*>(__o)->__flush(__p, __n); }),
__obj_(__obj) {}
+ // New LLVM-20 function.
+ [[nodiscard]]
+ _LIBCPP_HIDE_FROM_ABI explicit __output_buffer(_CharT* __ptr, size_t
__capacity, __prepare_write_type __prepare_write)
+ : __ptr_(__ptr), __capacity_(__capacity),
__prepare_write_(__prepare_write), __obj_(nullptr) {}
+
+ // Deprecated LLVM-19 function.
_LIBCPP_HIDE_FROM_ABI void __reset(_CharT* __ptr, size_t __capacity) {
__ptr_ = __ptr;
__capacity_ = __capacity;
}
+ // New LLVM-20 function.
+ _LIBCPP_HIDE_FROM_ABI void __buffer_flused() { __size_ = 0; }
+
+ // New LLVM-20 function.
+ _LIBCPP_HIDE_FROM_ABI void __buffer_moved(_CharT* __ptr, size_t __capacity) {
+ __ptr_ = __ptr;
+ __capacity_ = __capacity;
+ }
+
_LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return
std::back_insert_iterator{*this}; }
// Used in std::back_insert_iterator.
@@ -84,7 +217,7 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
// Profiling showed flushing after adding is more efficient than flushing
// when entering the function.
if (__size_ == __capacity_)
- __flush();
+ __flush(0);
}
/// Copies the input __str to the buffer.
@@ -107,7 +240,7 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
size_t __n = __str.size();
__flush_on_overflow(__n);
- if (__n < __capacity_) { // push_back requires the buffer to have room
for at least one character (so use <).
+ if (__n < __capacity_) { // push_back requires the buffer to have room for
at least one character (so use <).
std::copy_n(__str.data(), __n, std::addressof(__ptr_[__size_]));
__size_ += __n;
return;
@@ -118,12 +251,12 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
_LIBCPP_ASSERT_INTERNAL(__size_ == 0, "the buffer should be flushed by
__flush_on_overflow");
const _InCharT* __first = __str.data();
do {
- size_t __chunk = std::min(__n, __capacity_);
+ size_t __chunk = std::min(__n, __capacity_ - __size_);
std::copy_n(__first, __chunk, std::addressof(__ptr_[__size_]));
__size_ = __chunk;
__first += __chunk;
__n -= __chunk;
- __flush();
+ __flush(__n);
} while (__n);
}
@@ -148,12 +281,12 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
// Transform the data in "__capacity_" sized chunks.
_LIBCPP_ASSERT_INTERNAL(__size_ == 0, "the buffer should be flushed by
__flush_on_overflow");
do {
- size_t __chunk = std::min(__n, __capacity_);
+ size_t __chunk = std::min(__n, __capacity_ - __size_);
std::transform(__first, __first + __chunk,
std::addressof(__ptr_[__size_]), __operation);
__size_ = __chunk;
__first += __chunk;
__n -= __chunk;
- __flush();
+ __flush(__n);
} while (__n);
}
@@ -174,20 +307,36 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
std::fill_n(std::addressof(__ptr_[__size_]), __chunk, __value);
__size_ = __chunk;
__n -= __chunk;
- __flush();
+ __flush(__n);
} while (__n);
}
- _LIBCPP_HIDE_FROM_ABI void __flush() {
- __flush_(__ptr_, __size_, __obj_);
- __size_ = 0;
+ _LIBCPP_HIDE_FROM_ABI void __flush(size_t __size_hint) {
+ if (__obj_) {
+ // LLVM-19 code path
+ __flush_(__ptr_, __size_, __obj_);
+ __size_ = 0;
+ } else {
+ // LLVM-20 code path
+ __prepare_write_(*this, __size_hint + 1); // + 1 to always have space
for the next time
+ }
}
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t __capacity() const { return
__capacity_; }
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t __size() const { return __size_; }
+
private:
_CharT* __ptr_;
size_t __capacity_;
size_t __size_{0};
- void (*__flush_)(_CharT*, size_t, void*);
+ union {
+ // LLVM-19 member
+ void (*__flush_)(_CharT*, size_t, void*);
+ // LLVM-20 member
+ void (*__prepare_write_)(__output_buffer<_CharT>&, size_t);
+ };
+ static_assert(sizeof(__flush_) == sizeof(__prepare_write_), "The union is an
ABI break.");
+ static_assert(alignof(decltype(__flush_)) ==
alignof(decltype(__prepare_write_)), "The union is an ABI break.");
void* __obj_;
/// Flushes the buffer when the output operation would overflow the buffer.
@@ -224,11 +373,14 @@ class _LIBCPP_TEMPLATE_VIS __output_buffer {
/// the buffers. This would make the code more complex and \ref format_to_n
is
/// not the most common use case. Therefore the optimization isn't done.
_LIBCPP_HIDE_FROM_ABI void __flush_on_overflow(size_t __n) {
- if (__size_ + __n >= __capacity_)
- __flush();
+ __n += __size_;
+ if (__n >= __capacity_)
+ __flush(__n - __capacity_ + 1);
}
};
+// ***** ***** ***** LLVM-19 classes ***** ***** *****
+
/// A storage using an internal buffer.
///
/// This storage is used when writing a single element to the output iterator
@@ -373,7 +525,7 @@ class _LIBCPP_TEMPLATE_VIS __format_buffer {
_LIBCPP_HIDE_FROM_ABI void __flush(_CharT* __ptr, size_t __n) {
__writer_.__flush(__ptr, __n); }
_LIBCPP_HIDE_FROM_ABI _OutIt __out_it() && {
- __output_.__flush();
+ __output_.__flush(0);
return std::move(__writer_).__out_it();
}
@@ -395,7 +547,7 @@ class _LIBCPP_TEMPLATE_VIS __formatted_size_buffer {
_LIBCPP_HIDE_FROM_ABI void __flush(const _CharT*, size_t __n) { __size_ +=
__n; }
_LIBCPP_HIDE_FROM_ABI size_t __result() && {
- __output_.__flush();
+ __output_.__flush(0);
return __size_;
}
@@ -499,11 +651,78 @@ struct _LIBCPP_TEMPLATE_VIS __format_to_n_buffer final
_LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return
this->__output_.__make_output_iterator(); }
_LIBCPP_HIDE_FROM_ABI format_to_n_result<_OutIt> __result() && {
- this->__output_.__flush();
+ this->__output_.__flush(0);
return {std::move(this->__writer_).__out_it(), this->__size_};
}
};
+// ***** ***** ***** LLVM-20 classes ***** ***** *****
+
+// A dynamically growing buffer.
+template <__fmt_char_type _CharT>
+class _LIBCPP_TEMPLATE_VIS __allocating_buffer : public
__output_buffer<_CharT> {
+public:
+ __allocating_buffer(const __allocating_buffer&) = delete;
+ __allocating_buffer& operator=(const __allocating_buffer&) = delete;
+
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI __allocating_buffer()
+ : __output_buffer<_CharT>{__buffer_, __buffer_size_, __prepare_write} {}
+
+ _LIBCPP_HIDE_FROM_ABI ~__allocating_buffer() {
+ if (__ptr_ != __buffer_) {
+ ranges::destroy_n(__ptr_, this->__size());
+ allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_,
this->__capacity());
+ }
+ }
+
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI basic_string_view<_CharT> __view() {
return {__ptr_, this->__size()}; }
+
+private:
+ // At the moment the allocator is hard-code. There might be reasons to have
+ // an allocator trait in the future. This ensures forward compatibility.
+ using _Alloc = allocator<_CharT>;
+ _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
+
+ // Since allocating is expensive the class has a small internal buffer. When
+ // its capacity is exceeded a dynamic buffer will be allocated.
+ static constexpr size_t __buffer_size_ = 256;
+ _CharT __buffer_[__buffer_size_];
+ _CharT* __ptr_{__buffer_};
+
+ _LIBCPP_HIDE_FROM_ABI void __grow_buffer(size_t __capacity) {
+ if (__capacity < __buffer_size_)
+ return;
+
+ _LIBCPP_ASSERT_INTERNAL(__capacity > this->__capacity(), "the buffer must
grow");
+ auto __result = std::__allocate_at_least(__alloc_, __capacity);
+ auto __guard = std::__make_exception_guard([&] {
+ allocator_traits<_Alloc>::deallocate(__alloc_, __result.ptr,
__result.count);
+ });
+ // This shouldn't throw, but just to be safe. Note that at -O1 this
+ // guard is optimized away so there is no runtime overhead.
+ new (__result.ptr) _CharT[__result.count];
+ std::copy_n(__ptr_, this->__size(), __result.ptr);
+ __guard.__complete();
+ if (__ptr_ != __buffer_) {
+ ranges::destroy_n(__ptr_, this->__capacity());
+ allocator_traits<_Alloc>::deallocate(__alloc_, __ptr_,
this->__capacity());
+ }
+
+ __ptr_ = __result.ptr;
+ this->__buffer_moved(__ptr_, __result.count);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI void __prepare_write(size_t __size_hint) {
+ __grow_buffer(std::max<size_t>(this->__capacity() + __size_hint,
this->__capacity() * 1.6));
+ }
+
+ _LIBCPP_HIDE_FROM_ABI static void __prepare_write(__output_buffer<_CharT>&
__buffer, size_t __size_hint) {
+
static_cast<__allocating_buffer<_CharT>&>(__buffer).__prepare_write(__size_hint);
+ }
+};
+
+// ***** ***** ***** LLVM-19 and LLVM-20 class ***** ***** *****
+
// A dynamically growing buffer intended to be used for retargeting a context.
//
// P2286 Formatting ranges adds range formatting support. It allows the user to
diff --git a/libcxx/include/__format/format_functions.h
b/libcxx/include/__format/format_functions.h
index d14b49aff1495..a5c63bd4db70f 100644
--- a/libcxx/include/__format/format_functions.h
+++ b/libcxx/include/__format/format_functions.h
@@ -452,9 +452,9 @@ format_to(_OutIt __out_it, wformat_string<_Args...> __fmt,
_Args&&... __args) {
// fires too eagerly, see http://llvm.org/PR61563.
template <class = void>
[[nodiscard]] _LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI string
vformat(string_view __fmt, format_args __args) {
- string __res;
- std::vformat_to(std::back_inserter(__res), __fmt, __args);
- return __res;
+ __format::__allocating_buffer<char> __buffer;
+ std::vformat_to(__buffer.__make_output_iterator(), __fmt, __args);
+ return string{__buffer.__view()};
}
# ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
@@ -463,9 +463,9 @@ template <class = void>
template <class = void>
[[nodiscard]] _LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI wstring
vformat(wstring_view __fmt, wformat_args __args) {
- wstring __res;
- std::vformat_to(std::back_inserter(__res), __fmt, __args);
- return __res;
+ __format::__allocating_buffer<wchar_t> __buffer;
+ std::vformat_to(__buffer.__make_output_iterator(), __fmt, __args);
+ return wstring{__buffer.__view()};
}
# endif
@@ -585,9 +585,9 @@ format_to(_OutIt __out_it, locale __loc,
wformat_string<_Args...> __fmt, _Args&&
template <class = void>
[[nodiscard]] _LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI string
vformat(locale __loc, string_view __fmt, format_args __args) {
- string __res;
- std::vformat_to(std::back_inserter(__res), std::move(__loc), __fmt, __args);
- return __res;
+ __format::__allocating_buffer<char> __buffer;
+ std::vformat_to(__buffer.__make_output_iterator(), std::move(__loc), __fmt,
__args);
+ return string{__buffer.__view()};
}
# ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
@@ -596,9 +596,9 @@ vformat(locale __loc, string_view __fmt, format_args
__args) {
template <class = void>
[[nodiscard]] _LIBCPP_ALWAYS_INLINE inline _LIBCPP_HIDE_FROM_ABI wstring
vformat(locale __loc, wstring_view __fmt, wformat_args __args) {
- wstring __res;
- std::vformat_to(std::back_inserter(__res), std::move(__loc), __fmt, __args);
- return __res;
+ __format::__allocating_buffer<wchar_t> __buffer;
+ std::vformat_to(__buffer.__make_output_iterator(), std::move(__loc), __fmt,
__args);
+ return wstring{__buffer.__view()};
}
# endif
``````````
</details>
https://github.com/llvm/llvm-project/pull/101817
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