Re: reassociation pass and built-in functions

["Daniel Berlin" <dberlin at dberlin dot org>]

On 2/20/07, Revital1 Eres <ERES@il.ibm.com> wrote:
> Hello,
>
> We saw that the reassociation pass does not operate on built-in functions,
> for example:
>
> vp3 = vec_madd (vp1, vp2, vp3);
>
> In the RTL level the function is expanded to regular insn:
>
> (insn 87 91 88 9 (set (reg/v:V4SF 217 [ vp3 ])
>         (plus:V4SF (mult:V4SF (reg/v:V4SF 219 [ vp1 ])
>                 (reg/v:V4SF 218 [ vp2 ]))
>             (reg/v:V4SF 217 [ vp3 ]))) -1 (nil)
>     (nil))
>
>
> The reassociation could open opportunity for the variable expansion
> optimization to be applied when vec_madd is in a loop.
> (this is what the reassociation pass do for similar accumulation
> instruction that is not in built-in function)
> Currently MVE fails as it expects the pattern:
>
> x = x + something
>
> while it finds:
>
> x = something + x
>
> I could fix this in the MVE code, but I was wondering about the
> relations of reassociation pass and built-in functions in general.

If you find builtin functions you want to reassociate, this is
generally a good sign they should have been expanded to trees rather
than kept as builtins.
If you expanded them, they would have been reassociated (or at least,
they should be. I think we reassociate vector calculations, but it's
been a while since i looked).