[PATCH] D51544: [OpenCL] Split opencl-c.h header

[Andrew Savonichev via Phabricator via cfe-commits]

asavonic added a comment.

In https://reviews.llvm.org/D51544#1224730, @Anastasia wrote:

> It seems generally good to partition this big header but I am trying to understand what problem is it trying to solve now?


Main motivation is to reduce memory footprint by factoring out everything that is 'common' between PCHs compiled for different targets (CL1.2/2.0 and spir/spir64).

> So if we want to add these 2 devices, we now need 4*2 different PCHs,
>  since every combination of -cl-std and -triple must be compiled twice
>  with different OpenCL extensions defines.
> 
> Size of each PCH is 2.5M, so we need ~20M of memory to store our
>  PCHs. If we want to add more devices or support another OpenCL C
>  version, the size will double.

This also allows to do 'partial' pre-compilation, where 'common' part is pre-compiled into a single target independent PCH, and plain header is used for all target-specific things.
In this case, you no longer need to maintain different target-specific PCHs and this greatly simplifies the whole process.

> opencl-c-platform.h (5K LOC) must still be pre-compiled for each
>  supported combination, but since it is a lot smaller (~0.5M vs
>  original 2.5M), it is not that bad. Or we can sacrifice some
>  performance and leave this header without pre-compilation: large
>  portion of opencl-c-platform.h contains vendor extensions, so it will
>  be removed by preprocessor anyway.


Repository:
  rC Clang

https://reviews.llvm.org/D51544