[PATCH] D12455: [IR] Teach `llvm::User` to co-allocate a descriptor.

[Joseph Tremoulet via llvm-commits]

JosephTremoulet added inline comments.

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Comment at: include/llvm/IR/User.h:49-54
@@ -48,6 +48,8 @@
 
-  /// Allocate a User with the operands co-allocated.
+  /// Allocate a User with the operands co-allocated.  If DescBytes is non-zero
+  /// then allocate an additional DescBytes bytes before the operands. These
+  /// bytes can be accessed by calling getDescriptor.
   ///
   /// This is used for subclasses which have a fixed number of operands.
-  void *operator new(size_t Size, unsigned Us);
+  void *operator new(size_t Size, unsigned Us, unsigned DescBytes = 0);
 
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I wonder what sort of alignment guarantees this should make / what sort of alignment expectations it should set.  The end of this allocation will always be 4 bytes before a pointer-aligned address, correct?  Maybe just note that in the comment so that callers can figure out how to get pointer alignment if they want it?


http://reviews.llvm.org/D12455