[PATCH] D21453: Add support for attribute "overallocated"

[Akira Hatanaka via cfe-commits]

ahatanak created this revision.
ahatanak added reviewers: rsmith, george.burgess.iv, aaron.ballman.
ahatanak added subscribers: cfe-commits, dexonsmith, hfinkel.

This patch adds support for attribute "overallocated", which will be used to indicate a union or struct is over-allocated. This is needed to have __builtin_object_size correctly compute the size of an object when malloc allocates extra space at the end of a struct or union. For example,

struct S {
   int a;
   char s[32];
};

void *p = malloc(sizeof(S) + 64);
unsigned s = builtin_object_size(((struct S*)p)->s, 1); // "s" should be 32+64=96, not 32.

The link to the relevant discussion on cfe-dev is here:

http://lists.llvm.org/pipermail/cfe-dev/2016-March/047782.html

http://reviews.llvm.org/D21453

Files:
  include/clang/Basic/Attr.td
  include/clang/Basic/AttrDocs.td
  lib/AST/ExprConstant.cpp
  lib/Sema/SemaDeclAttr.cpp
  test/CodeGen/object-size.c
  test/CodeGen/object-size.cpp

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