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/AllocationOrder.cpp b/lib/CodeGen/AllocationOrder.cpp
index 26d4cd4..20c7625 100644
--- a/lib/CodeGen/AllocationOrder.cpp
+++ b/lib/CodeGen/AllocationOrder.cpp
@@ -33,7 +33,7 @@
   Hint = HintPair.second;
 
   // Translate to physreg, or 0 if not assigned yet.
-  if (Hint && TargetRegisterInfo::isVirtualRegister(Hint))
+  if (TargetRegisterInfo::isVirtualRegister(Hint))
     Hint = VRM.getPhys(Hint);
 
   // The remaining allocation order may depend on the hint.