[PATCH] D92277: [OpenCL] Refactor of targets OpenCL option settings

[Anton Zabaznov via Phabricator via cfe-commits]

azabaznov added inline comments.


================
Comment at: clang/lib/Basic/TargetInfo.cpp:360
+    // Set core features based on OpenCL version
+    for (auto CoreExt : clang::getCoreFeatures(Opts))
+      getTargetOpts().OpenCLFeaturesMap[CoreExt] = true;
----------------
Anastasia wrote:
> azabaznov wrote:
> > Anastasia wrote:
> > > I still think the target map should be immutable and especially we should not change it silently based on the language compiled even if we have done it before but that caused incorrect behavior i.e. successfully compiling for the architectures that didn't support the features.
> > > 
> > > If I look at existing targets they already set most of the core features apart from 3d image writes. Perhaps it is reasonable to just drop this code? I don't think it makes the issue worse, in fact, I think it will make the behavior slightly better because now a diagnostic will occur if there is an attempt to use the unsupported feature although the diagnostic won't be the optimal one.  After all it will still remain the responsibility of the user to get the right combination of a language version and a target.
> > > 
> > > It would be reasonable however to introduce a diagnostic that would report a mismatch between the language version and the hardware support available. We report similar diagnostics in `CompilerInvocation` already. But I don't think we have to do it in this patch because it doesn't introduce any regression. We already have a bug although the behavior of this bug will change. And perhaps if we add `OpenCLOptions` as a part of `LangOpts` at some point this will become straightforward to diagnose. However, I suggest we add information about this issue in a FIXME or perhaps this deserves a clang bug!
> > > I still think the target map should be immutable and especially we should not change it silently based on the language compiled
> > 
> > I'm confused. I think we have agreed to unconditionally support core features for a specific language version. Did I miss something?
> > 
> > > successfully compiling for the architectures that didn't support the features.
> > 
> > I like idea providing diagnostics in that case. Something like: "Warning: r600 target doesn't support 
> > cl_khr_3d_image_writes which is core in OpenCL C 2.0, consider using OpenCL C 3.0". I also think this should be done in a separate commit.
> > 
> > > If I look at existing targets they already set most of the core features apart from 3d image writes. Perhaps it is reasonable to just drop this code?
> > 
> > Oh, I haven't noticed that target set core features. For example //cl_khr_global_int32_base_atomics// is being set by NVPTX and AMDGPU, so I agree that this should be removed from target settings.
> It is correct that the core features should be set unconditionally but not in the `TargetInfo`. If core features are used for targets that don't support them then it should not succeed silently as it does now i.e. this means we need to know what is supported by the targets.
> 
> Setting target features in `TargetInfo` is correct and should stay.  We should not change them here though because the language version doesn't change the target capabilities. It can either expose or hide them from the user but it should not modify targets. This is why `TargetInfo` is immutable after its creation and this is how it should stay. I think it's better if we remove the code here completely and introduce a diagnostic in the subsequent patches that would just check that the features required in the language version are supported by the target.
> 
> If we do this then during the parsing we will only use feature information from `OpenCLOptions` not the targets, but we will know that the target have support of all the features because the check has been performed earlier.
I'm not generally against of removing core features set up, but I do have some questions and arguments:

> It is correct that the core features should be set unconditionally but not in the TargetInfo

Just to make sure: where do you mean core features should be set unconditionally? 

> Setting target features in TargetInfo is correct and should stay. We should not change them here though because the language version doesn't change the target capabilities. It can either expose or hide them from the user but it should not modify targets. This is why TargetInfo is immutable after its creation and this is how it should stay

I agree that `TargetInfo `should stay immutable during parsing, but for example here, in `TargetInfo::adjust`, current design already allows to change target capabilities based on language options, so I don't see what is conceptually wrong here.

> If core features are used for targets that don't support them then it should not succeed silently as it does now i.e. this means we need to know what is supported by the targets.

My main point in proposed design is that it is closer to specification: if target reports support for OpenCL C 2.0 then there is no need to extra checking for support of //core// features such as 3d image writes (we could also set for example generic address space  and pipes as supported unconditionally later) as it is core in OpenCL C 2.0. Of course this should not be done silently; some diagnostics like fatal error "OpenCL C 2.0 is not supported in this target" or warning "core feature cl_khr_3d_image_writes is not supported in this target".



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  https://reviews.llvm.org/D92277/new/

https://reviews.llvm.org/D92277