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/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index 25c4e96..23ec5bc 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1435,7 +1435,8 @@
 
 /// Emit an unconditional branch to the given block, unless it is the immediate
 /// (fall-through) successor, and update the CFG.
-void FastISel::fastEmitBranch(MachineBasicBlock *MSucc, DebugLoc DbgLoc) {
+void FastISel::fastEmitBranch(MachineBasicBlock *MSucc,
+                              const DebugLoc &DbgLoc) {
   if (FuncInfo.MBB->getBasicBlock()->size() > 1 &&
       FuncInfo.MBB->isLayoutSuccessor(MSucc)) {
     // For more accurate line information if this is the only instruction