[LICM] NFC. Remove AST caching infrastructure

[DaniilSuchkov]

Summary

Since (once D73081 is landed) LICM doesn't use AST caching any more, this infrastructure is now obsolete and we can remove it.
This patch will to be landed at least a day or two after D73081 to ensure everything's fine without AST cache.

[asbirlea]

Thank you!

llvm/lib/Transforms/Scalar/LICM.cpp

static void eraseInstruction(Instruction &I, ICFLoopSafetyInfo &SafetyInfo,
                              AliasSetTracker *AST, MemorySSAUpdater *MSSAU);
 
 static void moveInstructionBefore(Instruction &I, Instruction &Dest,
                                   ICFLoopSafetyInfo &SafetyInfo,
                                   MemorySSAUpdater *MSSAU, ScalarEvolution *SE);
 
 namespace {
 struct LoopInvariantCodeMotion {
-  using ASTrackerMapTy = DenseMap<Loop *, std::unique_ptr<AliasSetTracker>>;
   bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
                  TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
                  ScalarEvolution *SE, MemorySSA *MSSA,
-                 OptimizationRemarkEmitter *ORE, bool DeleteAST);
+                 OptimizationRemarkEmitter *ORE);
 
-  ASTrackerMapTy &getLoopToAliasSetMap() { return LoopToAliasSetMap; }
   LoopInvariantCodeMotion(unsigned LicmMssaOptCap,
                           unsigned LicmMssaNoAccForPromotionCap)
       : LicmMssaOptCap(LicmMssaOptCap),
         LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
 
 private:
-  ASTrackerMapTy LoopToAliasSetMap;
   unsigned LicmMssaOptCap;
   unsigned LicmMssaNoAccForPromotionCap;
 
   std::unique_ptr<AliasSetTracker>
   collectAliasInfoForLoop(Loop *L, LoopInfo *LI, AliasAnalysis *AA);
   std::unique_ptr<AliasSetTracker>
   collectAliasInfoForLoopWithMSSA(Loop *L, AliasAnalysis *AA,
                                   MemorySSAUpdater *MSSAU);
 };
 
 struct LegacyLICMPass : public LoopPass {
   static char ID; // Pass identification, replacement for typeid
   LegacyLICMPass(
       unsigned LicmMssaOptCap = SetLicmMssaOptCap,
       unsigned LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap)
       : LoopPass(ID), LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap) {
     initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
-    if (skipLoop(L)) {
-      // If we have run LICM on a previous loop but now we are skipping
-      // (because we've hit the opt-bisect limit), we need to clear the
-      // loop alias information.
-      LICM.getLoopToAliasSetMap().clear();
+    if (skipLoop(L))
       return false;
-    }
 
     auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
     MemorySSA *MSSA = EnableMSSALoopDependency
                           ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA())
                           : nullptr;
     // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
     // pass.  Function analyses need to be preserved across loop transformations
     // but ORE cannot be preserved (see comment before the pass definition).
     OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
     return LICM.runOnLoop(L,
                           &getAnalysis<AAResultsWrapperPass>().getAAResults(),
                           &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
                           &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
                           &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
                               *L->getHeader()->getParent()),
                           &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
                               *L->getHeader()->getParent()),
-                          SE ? &SE->getSE() : nullptr, MSSA, &ORE, true);
+                          SE ? &SE->getSE() : nullptr, MSSA, &ORE);
   }
 
   /// This transformation requires natural loop information & requires that
   /// loop preheaders be inserted into the CFG...
   ///
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     if (EnableMSSALoopDependency) {
       AU.addRequired<MemorySSAWrapperPass>();
       AU.addPreserved<MemorySSAWrapperPass>();
     }
     AU.addRequired<TargetTransformInfoWrapperPass>();
     getLoopAnalysisUsage(AU);
   }
 
-  using llvm::Pass::doFinalization;
-
-  bool doFinalization() override {
-    auto &AliasSetMap = LICM.getLoopToAliasSetMap();
-    // All loops in the AliasSetMap should be cleaned up already. The only case
-    // where we fail to do so is if an outer loop gets deleted before LICM
-    // visits it.
-    assert(all_of(AliasSetMap,
-                  [](LoopInvariantCodeMotion::ASTrackerMapTy::value_type &KV) {
-                    return !KV.first->getParentLoop();
-                  }) &&
-           "Didn't free loop alias sets");
-    AliasSetMap.clear();
-    return false;
-  }
-
 private:
   LoopInvariantCodeMotion LICM;
-
-  /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
-  void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
-                               Loop *L) override;
-
-  /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
-  /// set.
-  void deleteAnalysisValue(Value *V, Loop *L) override;
-
-  /// Simple Analysis hook. Delete loop L from alias set map.
-  void deleteAnalysisLoop(Loop *L) override;
 };
 } // namespace
 
 PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
                                 LoopStandardAnalysisResults &AR, LPMUpdater &) {
   const auto &FAM =
       AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
   Function *F = L.getHeader()->getParent();
 
   auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F);
   // FIXME: This should probably be optional rather than required.
   if (!ORE)
     report_fatal_error("LICM: OptimizationRemarkEmitterAnalysis not "
                        "cached at a higher level");
 
   LoopInvariantCodeMotion LICM(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
   if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.TTI, &AR.SE,
-                      AR.MSSA, ORE, true))
+                      AR.MSSA, ORE))
     return PreservedAnalyses::all();
 
   auto PA = getLoopPassPreservedAnalyses();
 
   PA.preserve<DominatorTreeAnalysis>();
   PA.preserve<LoopAnalysis>();
   if (AR.MSSA)
     PA.preserve<MemorySSAAnalysis>();

 Pass *llvm::createLICMPass(unsigned LicmMssaOptCap,
                            unsigned LicmMssaNoAccForPromotionCap) {
   return new LegacyLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);
 }
 
 /// Hoist expressions out of the specified loop. Note, alias info for inner
 /// loop is not preserved so it is not a good idea to run LICM multiple
 /// times on one loop.
-/// We should delete AST for inner loops in the new pass manager to avoid
-/// memory leak.
-///
 bool LoopInvariantCodeMotion::runOnLoop(
     Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
     TargetLibraryInfo *TLI, TargetTransformInfo *TTI, ScalarEvolution *SE,
-    MemorySSA *MSSA, OptimizationRemarkEmitter *ORE, bool DeleteAST) {
+    MemorySSA *MSSA, OptimizationRemarkEmitter *ORE) {
   bool Changed = false;
 
   assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
 
   // If this loop has metadata indicating that LICM is not to be performed then
   // just exit.
   if (hasDisableLICMTransformsHint(L)) {
     return false;
bool LoopInvariantCodeMotion::runOnLoop(
 
   // Check that neither this loop nor its parent have had LCSSA broken. LICM is
   // specifically moving instructions across the loop boundary and so it is
   // especially in need of sanity checking here.
   assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!");
   assert((!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) &&
          "Parent loop not left in LCSSA form after LICM!");
 
-  // If this loop is nested inside of another one, save the alias information
-  // for when we process the outer loop.
-  if (!MSSAU.get() && CurAST.get() && L->getParentLoop() && !DeleteAST)
-    LoopToAliasSetMap[L] = std::move(CurAST);
-
   if (MSSAU.get() && VerifyMemorySSA)
     MSSAU->getMemorySSA()->verifyMemorySSA();
 
   if (Changed && SE)
     SE->forgetLoopDispositions(L);
   return Changed;
 }
 
bool llvm::promoteLoopAccessesToScalars(
   if (PreheaderLoad->use_empty())
     eraseInstruction(*PreheaderLoad, *SafetyInfo, CurAST, MSSAU);
 
   return true;
 }
 
 /// Returns an owning pointer to an alias set which incorporates aliasing info
 /// from L and all subloops of L.
-/// FIXME: In new pass manager, there is no helper function to handle loop
-/// analysis such as cloneBasicBlockAnalysis, so the AST needs to be recomputed
-/// from scratch for every loop. Hook up with the helper functions when
-/// available in the new pass manager to avoid redundant computation.
 std::unique_ptr<AliasSetTracker>
 LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
                                                  AliasAnalysis *AA) {
-  std::unique_ptr<AliasSetTracker> CurAST;
-  SmallVector<Loop *, 4> RecomputeLoops;
-  for (Loop *InnerL : L->getSubLoops()) {
-    auto MapI = LoopToAliasSetMap.find(InnerL);
-    // If the AST for this inner loop is missing it may have been merged into
-    // some other loop's AST and then that loop unrolled, and so we need to
-    // recompute it.
-    if (MapI == LoopToAliasSetMap.end()) {
-      RecomputeLoops.push_back(InnerL);
-      continue;
-    }
-    std::unique_ptr<AliasSetTracker> InnerAST = std::move(MapI->second);
+  auto CurAST = std::make_unique<AliasSetTracker>(*AA);
 
-    if (CurAST) {
-      // What if InnerLoop was modified by other passes ?
-      // Once we've incorporated the inner loop's AST into ours, we don't need
-      // the subloop's anymore.
-      CurAST->add(*InnerAST);
-    } else {
-      CurAST = std::move(InnerAST);
-    }
-    LoopToAliasSetMap.erase(MapI);
-  }
-  if (!CurAST)
-    CurAST = std::make_unique<AliasSetTracker>(*AA);
-
-  // Add everything from the sub loops that are no longer directly available.
-  for (Loop *InnerL : RecomputeLoops)
+  // Add everything from all the sub loops.
+  for (Loop *InnerL : L->getSubLoops())
     for (BasicBlock *BB : InnerL->blocks())
       CurAST->add(*BB);
 
   // And merge in this loop (without anything from inner loops).
   for (BasicBlock *BB : L->blocks())
     if (LI->getLoopFor(BB) == L)
       CurAST->add(*BB);
 
   return CurAST;
 }
 
 std::unique_ptr<AliasSetTracker>
 LoopInvariantCodeMotion::collectAliasInfoForLoopWithMSSA(
     Loop *L, AliasAnalysis *AA, MemorySSAUpdater *MSSAU) {
   auto *MSSA = MSSAU->getMemorySSA();
   auto CurAST = std::make_unique<AliasSetTracker>(*AA, MSSA, L);
   CurAST->addAllInstructionsInLoopUsingMSSA();
   return CurAST;
 }
 
-/// Simple analysis hook. Clone alias set info.
-///
-void LegacyLICMPass::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
-                                             Loop *L) {
-  auto ASTIt = LICM.getLoopToAliasSetMap().find(L);
-  if (ASTIt == LICM.getLoopToAliasSetMap().end())
-    return;
-
-  ASTIt->second->copyValue(From, To);
-}
-
-/// Simple Analysis hook. Delete value V from alias set
-///
-void LegacyLICMPass::deleteAnalysisValue(Value *V, Loop *L) {
-  auto ASTIt = LICM.getLoopToAliasSetMap().find(L);
-  if (ASTIt == LICM.getLoopToAliasSetMap().end())
-    return;
-
-  ASTIt->second->deleteValue(V);
-}
-
-/// Simple Analysis hook. Delete value L from alias set map.
-///
-void LegacyLICMPass::deleteAnalysisLoop(Loop *L) {
-  if (!LICM.getLoopToAliasSetMap().count(L))
-    return;
-
-  LICM.getLoopToAliasSetMap().erase(L);
-}
-
 static bool pointerInvalidatedByLoop(MemoryLocation MemLoc,
                                      AliasSetTracker *CurAST, Loop *CurLoop,
                                      AliasAnalysis *AA) {
   // First check to see if any of the basic blocks in CurLoop invalidate *V.
   bool isInvalidatedAccordingToAST = CurAST->getAliasSetFor(MemLoc).isMod();
 
   if (!isInvalidatedAccordingToAST || !LICMN2Theshold)
     return isInvalidatedAccordingToAST;