[PATCH] D77923: OpenCL: Fix some missing predefined macros

Mon Apr 13 11:18:10 PDT 2020

scott.linder added a comment.

In D77923#1978261 <https://reviews.llvm.org/D77923#1978261>, @arsenm wrote:

> In D77923#1978172 <https://reviews.llvm.org/D77923#1978172>, @scott.linder wrote:
>
> > https://www.khronos.org/registry/OpenCL/sdk/2.0/docs/man/xhtml/preprocessorDirectives.html describes `__OPENCL_VERSION__` as "an integer reflecting the version number of the OpenCL supported by the OpenCL device." as contrasted with `__OPENCL_C_VERSION__` which is described as "an integer reflecting the OpenCL C version specified by the -cl-std build option to clBuildProgram or clCompileProgram. If the -cl-std build option is not specified, the OpenCL C version supported by the compiler for this OpenCL device will be used."
> >
> > But I don't see where the correct use of these is defined? How should the user decide which to use? It does seem like `__OPENCL_VERSION__` and `__OPENCL_C_VERSION__` can differ, e.g. if you compile for a device supporting 2.0 with `-cl-std=1.2`, but why would `__OPENCL_VERSION__` ever be referenced then?
>
>
> I don't know why you would ever use this; but the standard says it should be defined, so I guess we have to define it

Right, I just want to understand the actual semantics and it doesn't seem clear. I agree that I don't see a use for `__OPENCL_VERSION__` but we define it so I'm sure people are using it, so likely we need to be careful that this patch preserves the existing behavior of the runtime.

In D77923#1976497 <https://reviews.llvm.org/D77923#1976497>, @jvesely wrote:

> OPENCL_VERSION is something that should be really set by the opencl driver rather than the compiler.
>  coarse-grained SVM can be done without FEATURE_FLAT_ADDRESS_SPACE, so those gpus can get over 1.2, while the compiler can be used in an implementation that doesn't go above 1.2 even for gfx700+

I don't know why this would imply we can't just have a static `__OPENCL_VERSION__` for each device in Clang? I don't see anything in the standard that says you are not allowed to have (going with your example) `__OPENCL_VERSION__=200` and `__OPENCL_C_VERSION=120` at the same time.

It seems like we should be able to just have `__OPENCL_VERSION__` defined in Clang, and let the runtime control setting `__OPENCL_C_VERSION__` via `-cl-std=`. If the current patch sets `__OPENCL_VERSION__` differently than the runtime does then it seems like we should make it match, but I'm not sure how best to confirm that.

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  https://reviews.llvm.org/D77923/new/

https://reviews.llvm.org/D77923