[PATCH] D69952: [OPENMP50]Generalize handling of context matching/scoring.

[Johannes Doerfert via Phabricator via cfe-commits]

jdoerfert added inline comments.


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Comment at: clang/include/clang/Basic/Attr.td:3310
+    VariadicUnsignedArgument<"CtxSelectorSets">,
+    VariadicUnsignedArgument<"CtxSelectors">,
     VariadicStringArgument<"ImplVendors">
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ABataev wrote:
> jdoerfert wrote:
> > Is it possible to have a `VariadicObject` type here to represent the hierarchy and the connection between scores, selector sets, and selectors in a more explicit way?
> Nope, attributes td supports only limited number of possible constructs,mostly because of the serialization/deserialization problem.
That is what I was afraid of.


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Comment at: clang/include/clang/Basic/OpenMPKinds.def:226
+// OpenMP context selectors.
+OPENMP_CONTEXT_SELECTOR(vendor)
 
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ABataev wrote:
> jdoerfert wrote:
> > Can we add this into `llvm/include/llvm/IR/OpenMPKinds.def` from the very beginning?
> When we have it in trunk, sure.
Let's get it in then :)


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Comment at: clang/include/clang/Basic/OpenMPKinds.h:43
+/// Struct to store the context selectors info.
+template <typename T, typename VectorType = llvm::ArrayRef<T>>
+struct OpenMPCtxSelectorData {
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ABataev wrote:
> jdoerfert wrote:
> > I feel uneasy about using an ArrayRef for storage as it can easily lead to UB when the underlying values go out of scope.
> This structure is used in 2 ways: 1. Store the data befoere creating the attribute (which will store all the data). 2. Generalize data later atthe codegen phase without allocating new memory (the data is alredy stored in the attribute and don't need to allocate it several times).
That might all be true but it does not address my comments. I argue that this is easy to be misused not that it will not work right now. For me this is a potentially misused performance improvement, a combination we should not introduce.

You could, for example, remove the ArrayRef default parameter and make it explicit at the instantiation sites. Though, I'd actually prefer owning the data here, e.g., in a SmallVector.


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Comment at: clang/include/clang/Basic/OpenMPKinds.h:52
+                                 VectorType &&Names)
+      : CtxSet(CtxSet), Ctx(Ctx), Names(Names) {}
+  template <typename U>
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ABataev wrote:
> jdoerfert wrote:
> > This constructor, together with the default vector type (ArrayRef), will most certainly lead to problems when used. Given that Names is an xvalue, it is basically at the end of its lifetime. If the user did not change the ArrayRef to sth that owns the data, Names will contain stale references.
> No, mostly it will point to the data stored in the attribute, which exist all the time the function it is attached to exists.
See above.


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Comment at: clang/include/clang/Basic/OpenMPKinds.h:56
+                                 OpenMPContextSelectorKind Ctx, const U &Names)
+      : CtxSet(CtxSet), Ctx(Ctx), Names(Names.begin(), Names.end()) {}
+};
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ABataev wrote:
> jdoerfert wrote:
> > Why do you need a second template version here?
> To construct the object when the container Names cannot be created dieectly using the first constructor (SmallVector and UniqueVector are not quite compatible in this sence, for example)
That can be addressed by changing the first constructor. Why is it an xvalue there and why is the container not const?


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Comment at: clang/include/clang/Basic/OpenMPKinds.h:57
+      : CtxSet(CtxSet), Ctx(Ctx), Names(Names.begin(), Names.end()) {}
+};
+
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ABataev wrote:
> jdoerfert wrote:
> > It seems we always associate a scope with this class (even if the type of the scope varies), right? If so we can add it into this class to simplify the interfaces and tie them together in a nicer way.
> What scope are you ralking about?
"scope" was me thinking about the above issues while I was writing this comment about the "score":

It seems we always associate a score with this class (even if the type of the score varies), right? If so we can add it into this class to simplify the interfaces and tie them together in a nicer way.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D69952/new/

https://reviews.llvm.org/D69952