[cfe-dev] libc++ clean-up

[Howard Hinnant]

On Sep 4, 2014, at 4:01 PM, Marshall Clow <mclow.lists at gmail.com> wrote:

> 
> On Sep 4, 2014, at 5:36 AM, C. Bergström <cbergstrom at pathscale.com> wrote:
> 
>> 
>> Hi
>> 
>> Would patches for cleaning up unnecessary #include for libc++ be accepted? In general it seems like it has followed the rather poorly designed GNU STL rather than being more strict.
>> 
>> A simple preprocessed hello world which only #include <iostream>
>> 
>> CC -E hello.cxx -std=c++11  > hello-libcxx.e.cxx
>> 
>> du -sh *.e.cxx
>> 532K    hello-stdcxx.e.cxx
>> 1.3M    hello-libcxx.e.cxx
>> 
>> The effects of this cascade into being a measurable performance difference later on in the compiler. (My numbers may not be exactly llvm upstream though - ymmv) Basically the Module size and other things are larger as a result.
> 
> Note that libc++ contains a lot of stuff that libstdc++ does not (all of the C++14 additions, for example).
> 
> However, I’d be interested in suggestions/proposals for making the compile-time burden smaller.

Adding #includes to <__config>, such as <unistd.h> and <errno.h> contributes to poor compile times.

Howard