[libcxx-commits] [PATCH] D75211: Partially inline basic_string::operator=(const basic_string&)

[Martijn Vels via Phabricator via libcxx-commits]

mvels created this revision.
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mvels added reviewers: EricWF, ldionne.
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mvels updated this revision to Diff 246823.
mvels added a comment.

Fix left behind comment


This change partially inlines operator=(const basic_string&) where both the input and current instance are short strings, making the assignment a fixed length inlined memcpy.

Assignments where either of the strings are long are delegate to __assign_no_alias<__is_short>(), which is templated for the long / short branch already observed in the caller.

Stable:

  --------------------------------------------------------------------------------
  Benchmark                                     Time             CPU   Iterations
  --------------------------------------------------------------------------------
  BM_StringAssignStr_Empty_Opaque            2.65 ns         2.66 ns    263745536
  BM_StringAssignStr_Empty_Transparent       2.95 ns         2.96 ns    236494848
  BM_StringAssignStr_Small_Opaque            2.93 ns         2.94 ns    237301760
  BM_StringAssignStr_Small_Transparent       2.69 ns         2.69 ns    265809920
  BM_StringAssignStr_Large_Opaque            19.6 ns         19.6 ns     35573760
  BM_StringAssignStr_Large_Transparent       19.1 ns         19.1 ns     36716544
  BM_StringAssignStr_Huge_Opaque             1901 ns         1901 ns       364544
  BM_StringAssignStr_Huge_Transparent        1889 ns         1889 ns       360448

Unstable

  --------------------------------------------------------------------------------
  Benchmark                                     Time             CPU   Iterations
  --------------------------------------------------------------------------------
  BM_StringAssignStr_Empty_Opaque            1.29 ns         1.29 ns    540454912
  BM_StringAssignStr_Empty_Transparent       1.11 ns         1.12 ns    628482048
  BM_StringAssignStr_Small_Opaque            1.29 ns         1.29 ns    541216768
  BM_StringAssignStr_Small_Transparent       1.11 ns         1.11 ns    629469184
  BM_StringAssignStr_Large_Opaque            15.6 ns         15.6 ns     44945408
  BM_StringAssignStr_Large_Transparent       14.9 ns         14.9 ns     46764032
  BM_StringAssignStr_Huge_Opaque             1713 ns         1713 ns       401408
  BM_StringAssignStr_Huge_Transparent        1704 ns         1704 ns       397312


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75211

Files:
  libcxx/__string
  libcxx/include/__string
  libcxx/include/string
  libcxx/string

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