[NFC][LTO] Directly create default AA pipeline

[aeubanks]

Summary

I believe the comment was supposed to only apply to runNewPMCustomPasses().

[aeubanks]

https://reviews.llvm.org/D96553

llvm/lib/LTO/LTOBackend.cpp

else if (Conf.RunCSIRInstr) {
     PGOOpt = PGOOptions(Conf.CSIRProfile, "", Conf.ProfileRemapping,
                         PGOOptions::IRUse, PGOOptions::CSIRUse);
   }
 
   PassInstrumentationCallbacks PIC;
   StandardInstrumentations SI(Conf.DebugPassManager);
   SI.registerCallbacks(PIC);
   PassBuilder PB(Conf.DebugPassManager, TM, Conf.PTO, PGOOpt, &PIC);
-  AAManager AA;
-
-  // Parse a custom AA pipeline if asked to.
-  if (auto Err = PB.parseAAPipeline(AA, "default"))
-    report_fatal_error("Error parsing default AA pipeline");
 
   RegisterPassPlugins(Conf.PassPlugins, PB);
 
   LoopAnalysisManager LAM(Conf.DebugPassManager);
   FunctionAnalysisManager FAM(Conf.DebugPassManager);
   CGSCCAnalysisManager CGAM(Conf.DebugPassManager);
   ModuleAnalysisManager MAM(Conf.DebugPassManager);
 
   std::unique_ptr<TargetLibraryInfoImpl> TLII(
       new TargetLibraryInfoImpl(Triple(TM->getTargetTriple())));
   if (Conf.Freestanding)
     TLII->disableAllFunctions();
   FAM.registerPass([&] { return TargetLibraryAnalysis(*TLII); });
 
+  AAManager AA = PB.buildDefaultAAPipeline();
   // Register the AA manager first so that our version is the one used.
   FAM.registerPass([&] { return std::move(AA); });
 
   // Register all the basic analyses with the managers.
   PB.registerModuleAnalyses(MAM);
   PB.registerCGSCCAnalyses(CGAM);
   PB.registerFunctionAnalyses(FAM);
   PB.registerLoopAnalyses(LAM);