[GISel]: Add a getConstantFPVRegVal utility

[aditya_nandakumar]

Summary

This might be useful across various GISel passes.

[qcolombet]

LGTM

[aditya_nandakumar]

committed in r302964

include/llvm/CodeGen/GlobalISel/Utils.h

 class MachineOptimizationRemarkMissed;
 class MachineRegisterInfo;
 class MCInstrDesc;
 class RegisterBankInfo;
 class TargetInstrInfo;
 class TargetPassConfig;
 class TargetRegisterInfo;
 class Twine;
+class ConstantFP;
 
 /// Try to constrain Reg so that it is usable by argument OpIdx of the
 /// provided MCInstrDesc \p II. If this fails, create a new virtual
 /// register in the correct class and insert a COPY before \p InsertPt.
 /// The debug location of \p InsertPt is used for the new copy.
 ///
 /// \return The virtual register constrained to the right register class.
 unsigned constrainOperandRegClass(const MachineFunction &MF,

 
 void reportGISelFailure(MachineFunction &MF, const TargetPassConfig &TPC,
                         MachineOptimizationRemarkEmitter &MORE,
                         const char *PassName, StringRef Msg,
                         const MachineInstr &MI);
 
 Optional<int64_t> getConstantVRegVal(unsigned VReg,
                                      const MachineRegisterInfo &MRI);
+const ConstantFP* getConstantFPVRegVal(unsigned VReg,
+                                       const MachineRegisterInfo &MRI);
 
 } // End namespace llvm.
 #endif

lib/CodeGen/GlobalISel/Utils.cpp

if (MI->getOperand(1).isImm())
     return MI->getOperand(1).getImm();
 
   if (MI->getOperand(1).isCImm() &&
       MI->getOperand(1).getCImm()->getBitWidth() <= 64)
     return MI->getOperand(1).getCImm()->getSExtValue();
 
   return None;
 }
+
+const llvm::ConstantFP* llvm::getConstantFPVRegVal(unsigned VReg,
+                                       const MachineRegisterInfo &MRI) {
+  MachineInstr *MI = MRI.getVRegDef(VReg);
+  if (TargetOpcode::G_FCONSTANT != MI->getOpcode())
+    return nullptr;
+  return MI->getOperand(1).getFPImm();
+}