MachineFunctionPrinterPass: Declare SlotIndexes as used if available;…

… NFC

This makes print-machineinstrs print the slot indexes in more
situations. NFC for normal compilation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344004 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineFunctionPrinterPass.cpp

@@ -39,6 +39,7 @@ struct MachineFunctionPrinterPass : public MachineFunctionPass {
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.setPreservesAll();
+    AU.addUsedIfAvailable<SlotIndexes>();
     MachineFunctionPass::getAnalysisUsage(AU);
   }