GlobalISel: Make legalizer/regbankselect clear NoPHIs property

[arsenm]

Summary

If no phi existed in the original MIR and these introduced one, the
verifier would fail.

[qcolombet]

We should really just compute this property at some point (same for novregs), but that's for another day :).
LGTM.

[arsenm]

r354813

include/llvm/CodeGen/GlobalISel/Legalizer.h

return MachineFunctionProperties().set(
         MachineFunctionProperties::Property::IsSSA);
   }
 
   MachineFunctionProperties getSetProperties() const override {
     return MachineFunctionProperties().set(
         MachineFunctionProperties::Property::Legalized);
   }
 
+  MachineFunctionProperties getClearedProperties() const override {
+    return MachineFunctionProperties()
+      .set(MachineFunctionProperties::Property::NoPHIs);
+  }
+
   bool combineExtracts(MachineInstr &MI, MachineRegisterInfo &MRI,
                        const TargetInstrInfo &TII);
 
   bool runOnMachineFunction(MachineFunction &MF) override;
 };
 } // End namespace llvm.
 
 #endif

include/llvm/CodeGen/GlobalISel/RegBankSelect.h

return MachineFunctionProperties()
         .set(MachineFunctionProperties::Property::Legalized);
   }
 
   MachineFunctionProperties getSetProperties() const override {
     return MachineFunctionProperties().set(
         MachineFunctionProperties::Property::RegBankSelected);
   }
 
+  MachineFunctionProperties getClearedProperties() const override {
+    return MachineFunctionProperties()
+      .set(MachineFunctionProperties::Property::NoPHIs);
+  }
+
   /// Walk through \p MF and assign a register bank to every virtual register
   /// that are still mapped to nothing.
   /// The target needs to provide a RegisterBankInfo and in particular
   /// override RegisterBankInfo::getInstrMapping.
   ///
   /// Simplified algo:
   /// \code
   ///   RBI = MF.subtarget.getRegBankInfo()