On April 27, 2017 8:47:18 PM GMT+02:00, Steve Ellcey <sell...@cavium.com> wrote:
>I have a question about the GCC loop structure. I am trying to
>identify the
>induction variable for a for loop and I don't see how to do that.
>
>For example, if I have:
>
> int foo(int *a, int *b, int *c, int *d, int *e, int *f, int n)
> {
> int i;
> for (i = 0; i < n; i++) {
> a[i] = b[i] + c[i];
> d[i] = e[i] * f[i];
> }
> }
>
>I basically want to identify 'i' as the IV and look at its uses inside
>the
>loop.
>
>I can look at the control_ivs in the loop structure and I see:
>
>base is:
><integer_cst 0x7f1d0d29d090 type <integer_type 0x7f1d0d2985e8 int>
>constant 1>
>step is:
><integer_cst 0x7f1d0d29d090 type <integer_type 0x7f1d0d2985e8 int>
>constant 1>
>
>But it doesn't say what is being set to base or what is being increased
>by
>step in each loop iteration. (I am also not sure why base is 1 and not
>0.)
>
>Does this refer to a psuedo-IV or something instead of a real SSA
>variable
>that appears in the tree? How would I identify 'i' as the IV for this
>loop? Do I need to look at the loop header and latch and see what the
>header sets and what the latch checks to identify the variable?
I think you want to look at all loop header PHIs. The PHI results that satisfy
simple_iv should be those you are interested in.
Richard.
>Steve Ellcey
>sell...@cavium.com
