commit acefe88a4997c8109994c8aa249c077a55e8e4eb
author Wyatt Hepler <hepler@google.com> Fri Nov 19 09:51:51 2021 -0800
committer CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Nov 19 23:36:31 2021 +0000
tree 78754f4b74f6ae84ff657573744ce565aebe6452
parent b19d586c06e3b9eef13a99092a231f060b90bc26

pw_function: Size optimizations

Three size optimizations, ordered from most to least impactful:

- Remove the template parameters for NullFunctionTarget.

  The NullFunctionTarget is the same for all instantiations of
  pw::Function. Since it was a template, though, every unique
  pw::Function instantiation created new copies of the
  NullFunctionTarget virtual functions.

  This change drops the NullFunctionTarget template parameters. It uses
  a single FunctionTarget<void> implementation for all pw::Function
  instantiations. This does mean that the operator() function is called
  with extra arguments -- but it's illegal to call a null function
  anyway. MoveInitializeTo() and IsNull() functions are moved to a
  common base class shared by all pw::Function instantiations.

- Provide default implementation of the IsNull() virtual function. It is
  false for all derived classes except NullFunctionTarget, so the
  implementation can be shared across pw::Function instantiations.

- Forward arguments to operator(). In theory this can avoid unnecessary
  copies of the arguments, though the compiler should be able to
  optimize this. This has a very small size savings on optimized builds.

Change-Id: I4cc8caccc52d899d1a0f46cdf9f367e552f3e6e0
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/70160
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>