Roman Zippel wrote: > Hi, > > On Wed, 20 Jun 2007, Kenneth Zadeck wrote: > > >> For certain regs, the subroutine may or may not modify the value. The >> better information alluded to is information that one might get by doing >> interprocedural analysis. Without such information you have to assume >> that the value may or may not survive. The treatment of these vars is >> thus conservative, but correct. >> > > I don't understand, wouldn't the consertive approach be that the value > simply doesn't survive? > > bye, Roman > No, the conservative is that we do not know anything. it could be destroyed and it could not be destroyed.
Better information would tell us definitively that it there was one of two possible outcomes, the value is destroyed by the call or was not destroyed and passes thru unscathed. When we do forwards analysis around a call, the may def does kill the value, i.e. we cannot reliably use the value after the call.
