Pass DebugLoc and SDLoc by const ref.

This used to be free, copying and moving DebugLocs became expensive
after the metadata rewrite. Passing by reference eliminates a ton of
track/untrack operations. No functionality change intended.

llvm-svn: 272512
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 8920d20..a90ce05 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -169,7 +169,7 @@
     Locs.push_back(Loc);
 }
 
-void CodeViewDebug::maybeRecordLocation(DebugLoc DL,
+void CodeViewDebug::maybeRecordLocation(const DebugLoc &DL,
                                         const MachineFunction *MF) {
   // Skip this instruction if it has the same location as the previous one.
   if (DL == CurFn->LastLoc)