[loopy.match] Targeting reduction expression in an instruction

[kaushikcfd]

In the following kernel:

knl = lp.make_kernel(
    ["{[i]: 0<=i<8}",
     "{[j]: 8<=j<10}"],
    """
    out = sum(i, x[i]) + sum(j, x[j])
    """)

It seems that there's no way to prefetch x in the sum-reduce over i. The root of the problem seems to be that the IR does not allow tagging reduction expressions.

[inducer]

From my perspective, the idea is that you turn any subexpression you would like to tag into a substitution rule (using, e.g. extract_subst).

To be fair, no other type of subexpression can be individually tagged either.

[kaushikcfd]

There's no way to target the individual reduction nodes from the extract_subst either. On applying: lp.extract_subst(knl, "subst", "x[arg0]", parameters=("arg0", )) both the reductions are converted to a substitution.

[inducer]

I think it could be taught.

extract_subst(knl, "sum(i, *)")