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/PeepholeOptimizer.cpp b/lib/CodeGen/PeepholeOptimizer.cpp
index 54466ef..5f6ee30 100644
--- a/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/lib/CodeGen/PeepholeOptimizer.cpp
@@ -295,7 +295,7 @@
     if (!MO.isReg() || MO.isDef())
       continue;
     unsigned Reg = MO.getReg();
-    if (!Reg || TargetRegisterInfo::isPhysicalRegister(Reg))
+    if (!TargetRegisterInfo::isVirtualRegister(Reg))
       continue;
     if (ImmDefRegs.count(Reg) == 0)
       continue;