[llvm] Fold (select_cc (select cond, x, y), x, a, b, eq) to (select cond, a, b) (PR #199688)

[via llvm-commits]

AZero13 wrote:

> Can this be done more cleanly with sd_match patterns?

if (sd_match(N0, m_SetCC(m_Value(LHS), m_Value(RHS),
                         m_CondCode(CCNode))))
                         
Is not cleaner.

https://github.com/llvm/llvm-project/pull/199688