[libcxx-commits] [PATCH] D72986: Removed pathological case

[Martijn Vels via Phabricator via libcxx-commits]

mvels created this revision.
Herald added subscribers: libcxx-commits, christof.
Herald added a project: libc++.

Merge branch 'master' into string-optimize-assign-string

Add basic_string::__assign_str_noalias_external(const value_type* s, size_type n)

This change introduces the `__assign_str_noalias_external` which is invoked on the slow path from basic_string::operator=(const basic_string&).

The function is optimized for the source never aliassing the destination, the size always being inside the max_size, and have well predicted branches for non pathological assignments, i.e.: short --> long.

Merge branch 'master' into string-optimize-assign-string

Add basic_string::__string_assign_str_noalias_external

This changes adds the `__string_assign_str_noalias_external` function which is now used by the `operator=(const basic_string&)` method as a slow path if either of the strings is a long string.

`__string_assign_str_noalias_external` is optimized for being called from the operator= method: no alias into `this`, input has terminating zero as s[n], and size does not exceed max size. The branch in the external instantiated code should be well predicted.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72986

Files:
  libcxx/include/__string
  libcxx/include/string
  libcxx/src/string.cpp

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