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/SelectionDAG/InstrEmitter.cpp b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index d7bf6c1..e309def 100644
--- a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -703,7 +703,7 @@
         for (unsigned i = 0, e = F->getNumOperands(); i != e; ++i)
           if (RegisterSDNode *R = dyn_cast<RegisterSDNode>(F->getOperand(i))) {
             unsigned Reg = R->getReg();
-            if (Reg != 0 && TargetRegisterInfo::isPhysicalRegister(Reg))
+            if (TargetRegisterInfo::isPhysicalRegister(Reg))
               UsedRegs.push_back(Reg);
           }
       }