Simplify a bunch of isVirtualRegister() and isPhysicalRegister() logic.

These functions not longer assert when passed 0, but simply return false instead.

No functional change intended.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123155 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/DeadMachineInstructionElim.cpp b/lib/CodeGen/DeadMachineInstructionElim.cpp
index 32040e5..fdc1d91 100644
--- a/lib/CodeGen/DeadMachineInstructionElim.cpp
+++ b/lib/CodeGen/DeadMachineInstructionElim.cpp
@@ -159,7 +159,7 @@
         const MachineOperand &MO = MI->getOperand(i);
         if (MO.isReg() && MO.isDef()) {
           unsigned Reg = MO.getReg();
-          if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
+          if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
             LivePhysRegs.reset(Reg);
             // Check the subreg set, not the alias set, because a def
             // of a super-register may still be partially live after
@@ -176,7 +176,7 @@
         const MachineOperand &MO = MI->getOperand(i);
         if (MO.isReg() && MO.isUse()) {
           unsigned Reg = MO.getReg();
-          if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg)) {
+          if (TargetRegisterInfo::isPhysicalRegister(Reg)) {
             LivePhysRegs.set(Reg);
             for (const unsigned *AliasSet = TRI->getAliasSet(Reg);
                  *AliasSet; ++AliasSet)