[llvm] [DAG] SDPatternMatch m_Zero/m_One/m_AllOnes have inconsistent undef h… (PR #147044)

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woruyu wrote:

> @woruyu do you have the `add(psadbw(X,0),psadbw(Y,0)) -> psadbw(add(X,Y),0)` patch somewhere?

I originally added the SDPattern for add(psadbw(X,0), psadbw(Y,0)) -> psadbw(add(X,Y),0) in commit [e71c622](https://github.com/llvm/llvm-project/commit/e71c622fa858f5562947774a4a5110ba48f03bf7), but removed it during a force-push in [229ec28](https://github.com/llvm/llvm-project/commit/229ec2822e5c5d959f287eb8f93fbce0007e3b13) based on review feedback. It’s not included in the final PR.

https://github.com/llvm/llvm-project/pull/147044