Subzero: Fix a couple of debugging tools.

src/IceTargetLoweringMIPS32.cpp

Index: src/IceTargetLoweringMIPS32.cpp
diff --git a/src/IceTargetLoweringMIPS32.cpp b/src/IceTargetLoweringMIPS32.cpp
index b634306a989f700c2b71ac9ca7e1dcf041bd1a03..22c37435e0d2a45cce4bc4509df8c6342c0205a0 100644
--- a/src/IceTargetLoweringMIPS32.cpp
+++ b/src/IceTargetLoweringMIPS32.cpp
@@ -243,12 +243,12 @@ Variable *TargetMIPS32::getPhysicalRegister(SizeT RegNum, Type Ty) {
     Reg = Func->makeVariable(Ty);
     Reg->setRegNum(RegNum);
     PhysicalRegisters[Ty][RegNum] = Reg;
-    // Specially mark SP as an "argument" so that it is considered live upon
-    // function entry.
-    if (RegNum == RegMIPS32::Reg_SP || RegNum == RegMIPS32::Reg_RA) {
-      Func->addImplicitArg(Reg);
-      Reg->setIgnoreLiveness();
-    }
+    // Specially mark a named physical register as an "argument" so that it is
+    // considered live upon function entry.  Otherwise it's possible to get
+    // liveness validation errors for saving callee-save registers.
+    Func->addImplicitArg(Reg);
+    // Don't bother tracking the live range of a named physical register.
+    Reg->setIgnoreLiveness();
   }
   return Reg;
 }