loop unroll question

loop unroll question

[Revital Eres]

Hello,

For mainline on power-pc 4 with the option -O3 -funroll-loops, 
the following loop is not unrolled, but in GCC 3.4 it is. 
Also for mainline the bct is not inserted, but again in GCC 3.4 
it is.

void
example_new(int a[],int b[],int c[], int j) 
{
    int i;

    for(i=0 ; i<=j ; i++) 
       {
          c[i]=a[i]+b[i];
       }
    return;
}

If the condition is changed to < (instead of <=) the unrolling is 
done as expected and bct is inserted.

Thanks,
Revital

Re: loop unroll question

[Zdenek Dvorak]

Hello,

> For mainline on power-pc 4 with the option -O3 -funroll-loops, 
> the following loop is not unrolled, but in GCC 3.4 it is. 
> Also for mainline the bct is not inserted, but again in GCC 3.4 
> it is.
> 
> void
> example_new(int a[],int b[],int c[], int j) 
> {
>     int i;
> 
>     for(i=0 ; i<=j ; i++) 
>        {
>           c[i]=a[i]+b[i];
>        }
>     return;
> }

as for inserting bct -- it was wrong to do this, since the loop could
be the infinite one (not really, since we work in a signed arithmetics
for that the overflow has an undefined behavior, but we cannot
verify this on rtl level).

As for unrolling, we are too conservative here; I will send a patch
for this soon.

Zdenek

> If the condition is changed to < (instead of <=) the unrolling is 
> done as expected and bct is inserted.
> 
> Thanks,
> Revital