Roman Zippel wrote: > Hi, > > On Wed, 20 Jun 2007, Kenneth Zadeck wrote: > > >>> I don't understand, wouldn't the consertive approach be that the value >>> simply doesn't survive? >>> >>> >> No, the conservative is that we do not know anything. it could be >> destroyed and it could not be destroyed. >> > > What is the value of this? If we don't know anything, we can't use the > value anymore, since it may be destroyed, so effectively we have to > assume the value is destroyed. > > If we add the dead note there we are asserting that the value is modified by the caller. however it might not be and someone could write a piece of asm right after the call to use that reg if the person knew that the reg was not modified by that particular call.
having the dead note there is asserting to the register allocator that they are free to use that reg after the calll in any way that it wants and there is a (small) possibility that is wrong.