[PATCH] D20695: Floating Point SCEV Analysis

[silviu.baranga@arm.com via llvm-commits]

sbaranga added a comment.

In http://reviews.llvm.org/D20695#447451, @sanjoy wrote:

> In http://reviews.llvm.org/D20695#446877, @sbaranga wrote:
>
> > > float x = init;
> >
> > > 
> >
> > >   for (int i=0;i<N;i++){
> >
> > >     A[i] = x;
> >
> > >     x += fp_inc; // Loop invariant variable or constant
> >
> > >   }
> >
> >
> >
>
>
>
>
> > If this is correct with fast-math, we should be able to use this to
>
> >  get the backedge taken count - which would be a good reason for doing
>
> >  this in SCEV.
>
>
> Shouldn't SCEV //today// be able to compute the backedge taken count of
>  the above loop (since the controlling induction variable is
>  integral)?


Hi Sanjoy,

For that loop, yes, SCEV should be able to figure out the backedge taken count today.

But using that reasoning I think we should be able to get the backedge taken count for the following loop (again, I don't know if this is actually correct):

float i = 0.f;
for (; i < N; i+=fp_inc) {}

This was something previously raised by Michael on the llvm-dev thread.


Repository:
  rL LLVM

http://reviews.llvm.org/D20695