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.

llvm-svn: 123155
diff --git a/llvm/lib/CodeGen/PeepholeOptimizer.cpp b/llvm/lib/CodeGen/PeepholeOptimizer.cpp
index 54466ef..5f6ee30 100644
--- a/llvm/lib/CodeGen/PeepholeOptimizer.cpp
+++ b/llvm/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;