[libcxx-commits] [PATCH] D101752: Speedup to_string for integers using zero-copy.

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone requested changes to this revision.
Quuxplusone added a comment.
This revision now requires changes to proceed.

@Roman-Koshelev: By "benchmark," I think we mean putting it in the diff proper. Here's the patch I was about to suggest... https://pastebin.com/raw/Jg2htyVG ...except that then I //ran// that benchmark (with and without the patch to src/) and was unable to detect any performance improvement. Changing the first `resize` to `__resize_default_init` helped, but not enough.

  $ bin/clang++ -O2 ../libcxx/benchmarks/to_string.bench.cpp lib/libc++.a lib/libc++abi.a -I ../libcxx/utils/google-benchmark/include/ -L /usr/local/lib -lbenchmark -o new.exe
  $ ./new.exe
  2021-05-08T11:16:51-04:00
  Running ./new.exe
  Run on (8 X 2200 MHz CPU s)
  CPU Caches:
    L1 Data 32 KiB (x4)
    L1 Instruction 32 KiB (x4)
    L2 Unified 256 KiB (x4)
    L3 Unified 6144 KiB (x1)
  Load Average: 1.72, 2.07, 2.17
  ----------------------------------------------------------
  Benchmark                Time             CPU   Iterations
  ----------------------------------------------------------
  BM_ToString/1         9156 ns         9152 ns        74252
  BM_ToString/2         9207 ns         9203 ns        74929
  BM_ToString/3        10199 ns        10192 ns        67968
  BM_ToString/4        10034 ns        10027 ns        68924
  BM_ToString/5        11141 ns        11118 ns        63743
  BM_ToString/6        11534 ns        11485 ns        62568
  BM_ToString/7        11926 ns        11925 ns        58581
  BM_ToString/8        12282 ns        12257 ns        52108
  BM_ToString/9        13072 ns        13033 ns        51947
  BM_ToString/10       13010 ns        12994 ns        53775
  BM_ToWstring/1        6809 ns         6808 ns       101851
  BM_ToWstring/2        7863 ns         7849 ns        88482
  BM_ToWstring/3        8748 ns         8735 ns        77942
  BM_ToWstring/4        9448 ns         9409 ns        77254
  BM_ToWstring/5       88436 ns        88398 ns         7768
  BM_ToWstring/6       88524 ns        88499 ns         7703
  BM_ToWstring/7       90242 ns        90205 ns         7622
  BM_ToWstring/8       92892 ns        92575 ns         7279
  BM_ToWstring/9       90693 ns        90591 ns         7435
  BM_ToWstring/10      93344 ns        93128 ns         7646
  $ git checkout main -- ../libcxx/src/string.cpp
  $ ninja cxx ; ninja cxx ; ninja cxx
  [5/5] Creating library symlink lib/libc++.1.dylib lib/libc++.dylib
  [1/1] Linking CXX static library lib/libc++.a
  ninja: no work to do.
  $ bin/clang++ -O2 ../libcxx/benchmarks/to_string.bench.cpp lib/libc++.a lib/libc++abi.a -I ../libcxx/utils/google-benchmark/include/ -L /usr/local/lib -lbenchmark -o old.exe
  $ ./old.exe
  2021-05-08T11:18:56-04:00
  Running ./old.exe
  Run on (8 X 2200 MHz CPU s)
  CPU Caches:
    L1 Data 32 KiB (x4)
    L1 Instruction 32 KiB (x4)
    L2 Unified 256 KiB (x4)
    L3 Unified 6144 KiB (x1)
  Load Average: 2.54, 2.45, 2.31
  ----------------------------------------------------------
  Benchmark                Time             CPU   Iterations
  ----------------------------------------------------------
  BM_ToString/1         8390 ns         8386 ns        79859
  BM_ToString/2         9494 ns         9488 ns        72932
  BM_ToString/3        10157 ns        10152 ns        67160
  BM_ToString/4        10708 ns        10691 ns        66018
  BM_ToString/5        12084 ns        12068 ns        57079
  BM_ToString/6        12080 ns        12074 ns        56325
  BM_ToString/7        13303 ns        13295 ns        51666
  BM_ToString/8        12070 ns        12062 ns        56550
  BM_ToString/9        12610 ns        12605 ns        55151
  BM_ToString/10       12362 ns        12357 ns        55914
  BM_ToWstring/1        6791 ns         6787 ns       101672
  BM_ToWstring/2        7698 ns         7696 ns        89471
  BM_ToWstring/3        8682 ns         8672 ns        79495
  BM_ToWstring/4        9499 ns         9466 ns        76316
  BM_ToWstring/5       93702 ns        93611 ns         7603
  BM_ToWstring/6       95741 ns        95541 ns         7602
  BM_ToWstring/7       98949 ns        98798 ns         6976
  BM_ToWstring/8       94875 ns        94835 ns         7649
  BM_ToWstring/9       94720 ns        94675 ns         7441
  BM_ToWstring/10      94846 ns        94802 ns         7011


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101752/new/

https://reviews.llvm.org/D101752