llvm dev - Feb 2019 - Clearing the NoPHIs MF property

Hi,

we discovered (with expensive checks) in the SystemZ backend that while 
expanding an isel pseudo involving creating a PHI, the NoPHIs attributes 
must be reset in case the function had no PHIs to begin with. Therefore 
this is done in SystemZISelLowering.cpp with an explicit call.

It seems however that this is probably needed in more cases (like in 
AArch64TargetLowering::EmitF128CSEL?), so maybe there ought to be some 
mechanism (in MachineInstrBuilder?) to do this upon creating a PHI 
instruction?

/Jonas