[PATCH] D19770: Add FixedSizeStorage to TrailingObjects; NFC

[Hubert Tong via llvm-commits]

hubert.reinterpretcast created this revision.
hubert.reinterpretcast added reviewers: rsmith, faisalv, aaron.ballman.
hubert.reinterpretcast added subscribers: nwilson, cfe-commits, llvm-commits.

This change introduces two types, `FixedSizeStorage` and `FixedSizeStorageOwner`, which can be used to provide stack-allocated objects with trailing objects.

http://reviews.llvm.org/D19770

Files:
  include/llvm/Support/TrailingObjects.h

Index: include/llvm/Support/TrailingObjects.h
===================================================================
--- include/llvm/Support/TrailingObjects.h
+++ include/llvm/Support/TrailingObjects.h
@@ -342,6 +342,38 @@
                        TrailingTys, size_t>::type... Counts) {
     return sizeof(BaseTy) + ParentType::additionalSizeToAllocImpl(0, Counts...);
   }
+
+  /// A type where its ::_ template member is suitable for use as
+  /// uninitialized storage of an object if it were allocated with the given
+  /// trailing object counts. The template arguments are similar to those of
+  /// additionalSizeToAlloc.
+  template <typename... Tys> struct FixedSizeStorage {
+    template <size_t... Counts>
+    using _ =
+        llvm::AlignedCharArray<trailing_objects_internal::AlignmentCalcHelper<
+                                   BaseTy, TrailingTys...>::Alignment,
+                               totalSizeToAlloc<Tys...>(Counts...)>;
+  };
+
+  /// A type that acts as the owner for an object placed into fixed storage.
+  class FixedSizeStorageOwner {
+  public:
+    FixedSizeStorageOwner(BaseTy *p) : p(p) {}
+    ~FixedSizeStorageOwner() {
+      assert(p && "FixedSizeStorageOwner owns null?");
+      p->~BaseTy();
+    }
+
+    BaseTy *get() { return p; }
+
+  private:
+    FixedSizeStorageOwner(const FixedSizeStorageOwner &) = delete;
+    FixedSizeStorageOwner(FixedSizeStorageOwner &&) = delete;
+    FixedSizeStorageOwner &operator=(const FixedSizeStorageOwner &) = delete;
+    FixedSizeStorageOwner &operator=(FixedSizeStorageOwner &&) = delete;
+
+    BaseTy *const p;
+  };
 };
 
 } // end namespace llvm


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