[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/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index 9da8810..f26f43d 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -813,7 +813,7 @@
 void RegAllocFast::dumpState() {
   for (unsigned Reg = 1, E = TRI->getNumRegs(); Reg != E; ++Reg) {
     if (PhysRegState[Reg] == regDisabled) continue;
-    dbgs() << " " << TRI->getName(Reg);
+    dbgs() << " " << printReg(Reg, TRI);
     switch(PhysRegState[Reg]) {
     case regFree:
       break;