Comment 4 for bug 910363

Compiling the attached preprocessed file with this:
g++-4.5 -Os -fPIC -g -pedantic -Wno-long-long -fno-exceptions -o Type2.cpp.o -c Type2.ii

Results in writing 32 bits to a 24-bit bitfield, overwriting the first byte of the next member variable.

These two members of class Type are (on x86_64) at offset 0x8:
  TypeID ID : 8;
  unsigned SubclassData : 24;

When setSubclassData() isn't inlined, it's called (from StructType::setBody() and PointerType's constructor) with the address of 'SubclassData' in %rdi...:

   0x00007ffff76d684f <+71>: lea 0x9(%rdi),%r12
   0x00007ffff76d6853 <+75>: or $0x1,%esi
   0x00007ffff76d6856 <+78>: mov %r12,%rdi
   0x00007ffff76d6859 <+81>: callq 0x7ffff76d6774 <llvm::Type::setSubclassData(unsigned int)>

...but then, setSubclassData writes more than 24 bits to that address:

   0x00007ffff76d6774 <+0>: mov %esi,%eax
   0x00007ffff76d6776 <+2>: sub $0x8,%rsp
   0x00007ffff76d677a <+6>: and $0xffffff,%eax
   0x00007ffff76d677f <+11>: cmp %esi,%eax
   0x00007ffff76d6781 <+13>: mov %eax,(%rdi) # corruption