RFR: 8341137: Optimize long vector multiplication using x86 VPMUL[U]DQ instruction

[Vladimir Ivanov]

On Fri, 18 Oct 2024 05:05:16 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

> The issue is that a node is not immutable.

I don't see any issues with mutability here. `MulVLNode::_mult_lower_double_word` is constant, so you have to allocate new node if you want to change its value. (And that's exactly what `MulVLNode::Ideal()` does.) But I agree with you that  a dedicated ideal node type (e.g., `MulVI2L`) is much cleaner than `MulVLNode::_mult_lower_double_word`. Still, I'd prefer to see the logic confined in matcher-related code instead.

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PR Comment: https://git.openjdk.org/jdk/pull/21244#issuecomment-2421412061