The passthru operand is a tuple. We need to extract the correct field vector from it. Existing tests only handled the undef passthru case which accidentally worked. Possibly due to IMPLICIT_DEF being converted to noreg. Fixes #172628.
llvm.fma.f16
llvm.fsh[l|r].*
PHINode::removeIncomingValueIf()
PHINode::removeIncomingValue()