On Fri, 8 Nov 2024 20:25:23 GMT, Vladimir Ivanov <vliva...@openjdk.org> wrote:
> In the latest version you added new Ideal nodes (`MulIVL` and `MulUIVL`). I > don't see a compelling reason to do so. IMO matcher functionality is more > than enough to cover `VPMULDQ` case. `MulIVL` is equivalent to `MulVL` + > `has_int_inputs()` predicate. For `MulUIVL` you additionally do input > rewiring (using `forward_masked_input`), but (1) `AndV src (Replicate > 0xFFFFFFFF))` operands can be easily detected on matcher side (with an extra > AD instruction); and (2) such optimization is limited because it is valid > only for `0xFFFFFFFF` case while `has_uint_inputs() == true` for `C <= > 0xFFFFFFFF`. > > So, IMO `MulIVL` and `MulUIVL` nodes just add noise in Ideal graph without > improving situation during matching. Hi Vladimir, Problem occurs if AndV gets shared, in such case matcher will not be able to absorb the masking pattern. Specialized IR overrules any such limitations and shields pattern it represents from downstream optimizations. ------------- PR Comment: https://git.openjdk.org/jdk/pull/21244#issuecomment-2466624605
