[clang] [llvm] [NFC][Clang][OpenMP] Add a util to implicitly map attach-ptr-exprs on `target`, when applicable. (PR #161294)

[Abhinav Gaba via llvm-commits]

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@@ -9247,6 +9284,156 @@ class MappableExprsHandler {
     }
   }
 
+  /// On a target construct, if there's an implicit map on a struct, or that of
+  /// this[:], and an explicit map with a member of that struct/class as the
+  /// base-pointer, we need to make sure that base-pointer is implicitly mapped,
+  /// to make sure we don't map the full struct/class. For example:
+  ///
+  /// \code
+  ///   struct S {
+  ///     int dummy[10000];
+  ///     int *p;
+  ///     void f1() {
+  ///       #pragma omp target map(p[0:1])
+  ///       (void)this;
+  ///     }
+  ///   }; S s;
+  ///
+  ///   void f2() {
+  ///     #pragma omp target map(s.p[0:10])
+  ///     (void)s;
+  ///   }
+  /// \endcode
+  ///
+  /// Only `this-p` and `s.p` should be mapped in the two cases above.
+  //
+  // OpenMP 6.0: 7.9.6 map clause, pg 285
+  // If a list item with an implicitly determined data-mapping attribute does
+  // not have any corresponding storage in the device data environment prior to
+  // a task encountering the construct associated with the map clause, and one
+  // or more contiguous parts of the original storage are either list items or
+  // base pointers to list items that are explicitly mapped on the construct,
+  // only those parts of the original storage will have corresponding storage in
+  // the device data environment as a result of the map clauses on the
+  // construct.
+  void addImplicitMapForAttachPtrBaseIfMemberOfCapturedVD(
+      const ValueDecl *CapturedVD, MapDataArrayTy &DeclComponentLists,
+      SmallVectorImpl<
+          SmallVector<OMPClauseMappableExprCommon::MappableComponent, 8>>
+          &ComponentVectorStorage) const {
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abhinavgaba wrote:

This PR was created after receiving feedback that it would be good to break the parent PR #153684 into smaller patches that can be merged independently. This is one such smaller patch. The NFC tag can be removed that causes concern/confusion.

There is no change in the output IR with this change alone. The parent PR is needed to change the output IR.

https://github.com/llvm/llvm-project/pull/161294