[MemorySSA] Set LoopSimplify to preserve MemorySSA in the NPM, if analysis exists.

[asbirlea]

Summary

LoopSimplify is preserved in the legacy pass manager, but not in the new pass manager.
Update LoopSimplify to preserve MemorySSA conditionally when the analysis is available (same behavior as the legacy pass manager).

[chandlerc]

lib/Transforms/Utils/LoopSimplify.cpp

863

If it doesn't cause too much churn in tests, I'd prefer to make this conditional as well.

[asbirlea]

Address comment.

[chandlerc]

LGTM

lib/Transforms/Utils/LoopSimplify.cpp

 
 PreservedAnalyses LoopSimplifyPass::run(Function &F,
                                         FunctionAnalysisManager &AM) {
   bool Changed = false;
   LoopInfo *LI = &AM.getResult<LoopAnalysis>(F);
   DominatorTree *DT = &AM.getResult<DominatorTreeAnalysis>(F);
   ScalarEvolution *SE = AM.getCachedResult<ScalarEvolutionAnalysis>(F);
   AssumptionCache *AC = &AM.getResult<AssumptionAnalysis>(F);
+  auto *MSSAAnalysis = AM.getCachedResult<MemorySSAAnalysis>(F);
+  std::unique_ptr<MemorySSAUpdater> MSSAU;
+  if (MSSAAnalysis) {
+    auto *MSSA = &MSSAAnalysis->getMSSA();
+    MSSAU = make_unique<MemorySSAUpdater>(MSSA);
+  }
+
 
   // Note that we don't preserve LCSSA in the new PM, if you need it run LCSSA
-  // after simplifying the loops. MemorySSA is not preserved either.
+  // after simplifying the loops. MemorySSA is preserved if it exists.
   for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
     Changed |=
-        simplifyLoop(*I, DT, LI, SE, AC, nullptr, /*PreserveLCSSA*/ false);
+        simplifyLoop(*I, DT, LI, SE, AC, MSSAU.get(), /*PreserveLCSSA*/ false);
 
   if (!Changed)
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
   PA.preserve<DominatorTreeAnalysis>();
   PA.preserve<LoopAnalysis>();
   PA.preserve<BasicAA>();
   PA.preserve<GlobalsAA>();
   PA.preserve<SCEVAA>();
   PA.preserve<ScalarEvolutionAnalysis>();
   PA.preserve<DependenceAnalysis>();
+  PA.preserve<MemorySSAAnalysis>();
   // BPI maps conditional terminators to probabilities, LoopSimplify can insert
   // blocks, but it does so only by splitting existing blocks and edges. This
   // results in the interesting property that all new terminators inserted are
   // unconditional branches which do not appear in BPI. All deletions are
   // handled via ValueHandle callbacks w/in BPI.
   PA.preserve<BranchProbabilityAnalysis>();
   return PA;
 }

unittests/Transforms/Scalar/LoopPassManagerTest.cpp

LoopPassManagerTest()
 
     // We need DominatorTreeAnalysis for LoopAnalysis.
     FAM.registerPass([&] { return DominatorTreeAnalysis(); });
     FAM.registerPass([&] { return LoopAnalysis(); });
     // We also allow loop passes to assume a set of other analyses and so need
     // those.
     FAM.registerPass([&] { return AAManager(); });
     FAM.registerPass([&] { return AssumptionAnalysis(); });
-    if (EnableMSSALoopDependency)
-      FAM.registerPass([&] { return MemorySSAAnalysis(); });
     FAM.registerPass([&] { return ScalarEvolutionAnalysis(); });
     FAM.registerPass([&] { return TargetLibraryAnalysis(); });
     FAM.registerPass([&] { return TargetIRAnalysis(); });
 
     // Register required pass instrumentation analysis.
     LAM.registerPass([&] { return PassInstrumentationAnalysis(); });
     FAM.registerPass([&] { return PassInstrumentationAnalysis(); });
     MAM.registerPass([&] { return PassInstrumentationAnalysis(); });