[PATCH] D75917: Expose llvm fence instruction as clang intrinsic

Mon Mar 16 17:31:07 PDT 2020

sameerds added a comment.

In D75917#1917296 <https://reviews.llvm.org/D75917#1917296>, @JonChesterfield wrote:

> In D75917#1916972 <https://reviews.llvm.org/D75917#1916972>, @sameerds wrote:
>
> > Well, there is a problem: The LangRef says that scopes are target-defined. This change says that scopes are defined by the high-level language and further assumes that OpenCL scopes make sense in all languages. Besides conflicting with the LangRef, this not seem to work with C++, which has no scopes and nor with CUDA or HIP, whose scopes are not represented in any AtomicScopeModel.
>
>
> I don't follow. IR has a fence instruction. This builtin maps directly to it, passing whatever integer arguments were given to the intrinsic along unchanged. It's exactly as valid, or invalid, as said fence instruction.

Is it really? The scope argument of the IR fence is a target-specific string:
http://llvm.org/docs/LangRef.html#syncscope

The change that I see here is assuming a numerical argument, and also assuming that the numbers used must conform to the OpenCL enum. That would certainly make the builtin quite different from the IR fence.

Repository:
  rC Clang

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  https://reviews.llvm.org/D75917/new/

https://reviews.llvm.org/D75917