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/LiveDebugVariables.cpp b/lib/CodeGen/LiveDebugVariables.cpp
index ac95e73..da4b017 100644
--- a/lib/CodeGen/LiveDebugVariables.cpp
+++ b/lib/CodeGen/LiveDebugVariables.cpp
@@ -359,7 +359,7 @@
   // If the location is a virtual register, make sure it is mapped.
   if (MI->getOperand(0).isReg()) {
     unsigned Reg = MI->getOperand(0).getReg();
-    if (Reg && TargetRegisterInfo::isVirtualRegister(Reg))
+    if (TargetRegisterInfo::isVirtualRegister(Reg))
       mapVirtReg(Reg, UV);
   }