RFC - Remove support for PCH post 4.8

Chris Lattner clattner@apple.com
Tue Nov 27 19:20:00 GMT 2012

On Nov 27, 2012, at 8:00 AM, Diego Novillo <dnovillo@google.com> wrote:
> I admit that I'm partly fishing here, but my proposal is based on the following:
> * The implementation of PCH in GCC is atrocious and hard to maintain.
> * The next C++ standard is likely to define modules
> (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3347.pdf)
> * The user-base for PCH is negligibly small (here's where I'm mostly guessing).
> * PCH is absolutely useless for C.

PCH is used extensively in Objective-C code and many C++ applications that also build for windows.  I'm not sure how important these communities are though...


> Removing PCH will give us more implementation freedom for the memory
> management project
> (http://gcc.gnu.org/wiki/cxx-conversion/gc-alternatives).
> With some effort, we could revive the streaming work done in the PPH
> branch and re-implement PCH with it (when we abandoned the branch, we
> were probably 80% complete as a PCH replacement). If we could at least
> remove support for C, then I can see a streaming-based PCH for the 4.9
> release.
> Thoughts?
> Are there any big PCH users out there?
> Thanks.  Diego.

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