[PATCH] [PATCH/RFC] Use a BumpAllocator for DIEs

[Frederic Riss]

This update removes the limitation to a fixed maximum number of
attributes per DIE. The patch is very similar to the first one that
I sent for discussion. It only adds a pointer to a vector of DIEs
as arguement to DIE::addValue(). If a DIE overflows its inline storage
for attributes, it is added to the vector. The vector is then iterated
just before the BumpPtrAllocator is destroyed to call the destructors
of all these DIEs.

This approach gives the most flexibilty as it doesn't impose the
memory management upon the user (for example DIEHashTest.cpp continues
to use stack allocated DIEs and it works fine).

I've been playing with this for the last few days, and I have quite
a few different implementations lying around (for example using
std::vectors with a custom stateful allocator). They are all more
complicated and don't perform as well as this patch.

There's one point that I'd like to mention: the patch unifies the
existing bookkeeping of the DIEBlock and DIELoc objects and treats
them the same as standard DIEs. This means that we will call ~DIE
on DIEBlock and DIELoc objects which will result in a 'partial'
destruction (DIEBlock inherits both from DIEValue and from DIE).
I think this is fine. It should do exactly what we want and just
call the destructors of the SmallVectors in the DIE part of the
object, but I wanted to mention it in case someone thinks its not
legal to do that.


http://reviews.llvm.org/D7072

Files:
  include/llvm/CodeGen/DIE.h
  lib/CodeGen/AsmPrinter/DIE.cpp
  lib/CodeGen/AsmPrinter/DIEHash.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
  lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  lib/CodeGen/AsmPrinter/DwarfFile.cpp
  lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  lib/CodeGen/AsmPrinter/DwarfUnit.h
  unittests/CodeGen/DIEHashTest.cpp

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