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/Target/Mips/MipsSEISelDAGToDAG.cpp b/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
index 7de8641..8ea35f1 100644
--- a/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
+++ b/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
@@ -237,8 +237,8 @@
 }
 
 void MipsSEDAGToDAGISel::selectAddESubE(unsigned MOp, SDValue InFlag,
-                                           SDValue CmpLHS, SDLoc DL,
-                                           SDNode *Node) const {
+                                        SDValue CmpLHS, const SDLoc &DL,
+                                        SDNode *Node) const {
   unsigned Opc = InFlag.getOpcode(); (void)Opc;
 
   assert(((Opc == ISD::ADDC || Opc == ISD::ADDE) ||