[LLVMdev] TargetData::getPreferredAlignment(const GlobalVariable *GV) is strange ...

[Fabian Scheler]

Hello everybody,

I am somewhat confused by the following method within the LLVM,
especially the lines
"confusion starts" -> "confusion ends" are hard to follow. Maybe the
idea is that if there
are such big data structures one does not waste much memory anyway if
they are aligned
 to a 16-byte boundary. However, my assembler complains here because
it only supports
 1-, 2-, 4- and 8-byte boundaries :-(

I checked the svn log but I didn't find any explanation, the doxygen
docu is not very helpful
here, too. So, any help on this issue is highly appreciated.

Thanks in advance!

Ciao, Fabian

unsigned TargetData::getPreferredAlignment(const GlobalVariable *GV) const {
  const Type *ElemType = GV->getType()->getElementType();
  unsigned Alignment = getPrefTypeAlignment(ElemType);
  if (GV->getAlignment() > Alignment)
    Alignment = GV->getAlignment();

==================== confusion starts ========================
  if (GV->hasInitializer()) {
    if (Alignment < 16) {
      // If the global is not external, see if it is large.  If so, give it a
      // larger alignment.
      if (getTypeSizeInBits(ElemType) > 128)
        Alignment = 16;    // 16-byte alignment.
    }
  }
==================== confusion ends =========================

  return Alignment;
}