------- Comment #16 from dberlin at gcc dot gnu dot org 2006-07-18 17:03 ------- Subject: Re: [4.0/4.1/4.2 Regression] Tree loop optimizer does worse job than RTL loop optimizer
anemo at mba dot ocn dot ne dot jp wrote: > ------- Comment #15 from anemo at mba dot ocn dot ne dot jp 2006-07-18 16:53 > ------- > (In reply to comment #14) >> This is because it's an incoming parameter, and as a result, this >> doesn't look at all like an array access, but just a random pointer access. >> >> I have no plans to make the alias analysis algorithm reconstruct array >> indexes from random pointer arithmetic. > > I do not think reconstructing array indexes are needed, > but is it hard to tell that *(a+0) never be an alias of *(a+1) ? We already do say this when we know the offsets. The point is that without reconstructing the array indexes, we'd have to follow use-def chains for *every single pointer access* on *every single operand update*, in order to attempt to get the offsets and disambiguate them. This is incredibly slow. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20643
