[X86] Use 'llvm_unreachable' instead of nullptr in unreachable code to

avoid static check fail

RegClassOrBank is an object of RegClassOrRegBank, which is defined as
using llvm::RegClassOrRegBank = typedef PointerUnion<const
TargetRegisterClass *, const RegisterBank *>
so control flow can not get here. Use ""llvm_unreachable" here to avoid
"null pointer" confusion.

Patch by Shengchen Kan (skan)

Differential Revision: https://reviews.llvm.org/D62006

Signed-off-by: pengfei <[email protected]>
llvm-svn: 361912

Author: phoebewang

llvm/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp

@@ -91,7 +91,9 @@ RegisterBankInfo::getRegBank(unsigned Reg, const MachineRegisterInfo &MRI,
     return RB;
   if (auto *RC = RegClassOrBank.dyn_cast<const TargetRegisterClass *>())
     return &getRegBankFromRegClass(*RC);
-  return nullptr;
+
+  llvm_unreachable("RegClassOrBank is either a const RegisterBank* or "
+                   "a const TargetRegisterClass*");
 }
 
 const TargetRegisterClass &

llvm/lib/Target/X86/X86InstructionSelector.cpp

@@ -1610,8 +1610,8 @@ bool X86InstructionSelector::selectDivRem(MachineInstr &I,
   assert(RegTy == MRI.getType(Op1Reg) && RegTy == MRI.getType(Op2Reg) &&
          "Arguments and return value types must match");
 
-  const RegisterBank *RegRB = RBI.getRegBank(DstReg, MRI, TRI);
-  if (!RegRB || RegRB->getID() != X86::GPRRegBankID)
+  const RegisterBank &RegRB = *RBI.getRegBank(DstReg, MRI, TRI);
+  if (RegRB.getID() != X86::GPRRegBankID)
     return false;
 
   const static unsigned NumTypes = 4; // i8, i16, i32, i64
@@ -1709,7 +1709,7 @@ bool X86InstructionSelector::selectDivRem(MachineInstr &I,
   const DivRemEntry &TypeEntry = *OpEntryIt;
   const DivRemEntry::DivRemResult &OpEntry = TypeEntry.ResultTable[OpIndex];
 
-  const TargetRegisterClass *RegRC = getRegClass(RegTy, *RegRB);
+  const TargetRegisterClass *RegRC = getRegClass(RegTy, RegRB);
   if (!RBI.constrainGenericRegister(Op1Reg, *RegRC, MRI) ||
       !RBI.constrainGenericRegister(Op2Reg, *RegRC, MRI) ||
       !RBI.constrainGenericRegister(DstReg, *RegRC, MRI)) {