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/RegAllocLinearScan.cpp b/lib/CodeGen/RegAllocLinearScan.cpp
index bbff424..14f6726 100644
--- a/lib/CodeGen/RegAllocLinearScan.cpp
+++ b/lib/CodeGen/RegAllocLinearScan.cpp
@@ -1421,8 +1421,7 @@
   std::pair<unsigned, unsigned> Hint = mri_->getRegAllocationHint(cur->reg);
   // Resolve second part of the hint (if possible) given the current allocation.
   unsigned physReg = Hint.second;
-  if (physReg &&
-      TargetRegisterInfo::isVirtualRegister(physReg) && vrm_->hasPhys(physReg))
+  if (TargetRegisterInfo::isVirtualRegister(physReg) && vrm_->hasPhys(physReg))
     physReg = vrm_->getPhys(physReg);
 
   TargetRegisterClass::iterator I, E;