[CodeGen] Always use `printReg` to print registers in both MIR and debug
output

As part of the unification of the debug format and the MIR format,
always use `printReg` to print all kinds of registers.

Updated the tests using '_' instead of '%noreg' until we decide which
one we want to be the default one.

Differential Revision: https://reviews.llvm.org/D40421

llvm-svn: 319445
diff --git a/llvm/lib/CodeGen/RegAllocBasic.cpp b/llvm/lib/CodeGen/RegAllocBasic.cpp
index b38373d..3d60f31 100644
--- a/llvm/lib/CodeGen/RegAllocBasic.cpp
+++ b/llvm/lib/CodeGen/RegAllocBasic.cpp
@@ -219,8 +219,8 @@
       Intfs.push_back(Intf);
     }
   }
-  DEBUG(dbgs() << "spilling " << TRI->getName(PhysReg) <<
-        " interferences with " << VirtReg << "\n");
+  DEBUG(dbgs() << "spilling " << printReg(PhysReg, TRI)
+               << " interferences with " << VirtReg << "\n");
   assert(!Intfs.empty() && "expected interference");
 
   // Spill each interfering vreg allocated to PhysReg or an alias.