[ADCE] Remove the need of DomTree

[NutshellySima]

Summary

ADCE doesn't need to query domtree.

[kuhar]

lib/Transforms/Scalar/ADCE.cpp

675

Can you add a comment explaining that you only get DT to preserve it, and only when it's already available?

702

Same as above

[NutshellySima]

Address comments.

[brzycki]

LGTM if you have done a full test-suite correctness test on this patch.

lib/Transforms/Scalar/ADCE.cpp

struct BlockInfoType {
   bool terminatorIsLive() const { return TerminatorLiveInfo->Live; }
 };
 
 class AggressiveDeadCodeElimination {
   Function &F;
 
   // ADCE does not use DominatorTree per se, but it updates it to preserve the
   // analysis.
-  DominatorTree &DT;
+  DominatorTree *DT;
   PostDominatorTree &PDT;
 
   /// Mapping of blocks to associated information, an element in BlockInfoVec.
   /// Use MapVector to get deterministic iteration order.
   MapVector<BasicBlock *, BlockInfoType> BlockInfo;
   bool isLive(BasicBlock *BB) { return BlockInfo[BB].Live; }
 
   /// Mapping of instructions to associated information.
class AggressiveDeadCodeElimination {
   /// Set the BlockInfo::PostOrder field based on a post-order
   /// numbering of the reverse control flow graph.
   void computeReversePostOrder();
 
   /// Make the terminator of this block an unconditional branch to \p Target.
   void makeUnconditional(BasicBlock *BB, BasicBlock *Target);
 
 public:
-  AggressiveDeadCodeElimination(Function &F, DominatorTree &DT,
+  AggressiveDeadCodeElimination(Function &F, DominatorTree *DT,
                                 PostDominatorTree &PDT)
       : F(F), DT(DT), PDT(PDT) {}
 
   bool performDeadCodeElimination();
 };
 
 } // end anonymous namespace
 
for (auto *Succ : RemovedSuccessors) {
       if (Succ != PreferredSucc->BB) {
         LLVM_DEBUG(dbgs() << "ADCE: (Post)DomTree edge enqueued for deletion"
                           << BB->getName() << " -> " << Succ->getName()
                           << "\n");
         DeletedEdges.push_back({DominatorTree::Delete, BB, Succ});
       }
     }
 
-    DomTreeUpdater(DT, PDT, DomTreeUpdater::UpdateStrategy::Eager)
+    DomTreeUpdater(DT, &PDT, DomTreeUpdater::UpdateStrategy::Eager)
         .applyUpdates(DeletedEdges);
 
     NumBranchesRemoved += 1;
   }
 }
 
 // reverse top-sort order
 void AggressiveDeadCodeElimination::computeReversePostOrder() {

 }
 
 //===----------------------------------------------------------------------===//
 //
 // Pass Manager integration code
 //
 //===----------------------------------------------------------------------===//
 PreservedAnalyses ADCEPass::run(Function &F, FunctionAnalysisManager &FAM) {
-  auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
+  auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(F);
   auto &PDT = FAM.getResult<PostDominatorTreeAnalysis>(F);
   if (!AggressiveDeadCodeElimination(F, DT, PDT).performDeadCodeElimination())
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
   PA.preserveSet<CFGAnalyses>();
   PA.preserve<GlobalsAA>();
   PA.preserve<DominatorTreeAnalysis>();
struct ADCELegacyPass : public FunctionPass {
   ADCELegacyPass() : FunctionPass(ID) {
     initializeADCELegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
 
-    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+    auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
     auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
     return AggressiveDeadCodeElimination(F, DT, PDT)
         .performDeadCodeElimination();
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    // We require DominatorTree here only to update and thus preserve it.
-    AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<PostDominatorTreeWrapperPass>();
     if (!RemoveControlFlowFlag)
       AU.setPreservesCFG();
     else {
       AU.addPreserved<DominatorTreeWrapperPass>();
       AU.addPreserved<PostDominatorTreeWrapperPass>();
     }
     AU.addPreserved<GlobalsAAWrapperPass>();
   }
 };
 
 } // end anonymous namespace
 
 char ADCELegacyPass::ID = 0;
 
 INITIALIZE_PASS_BEGIN(ADCELegacyPass, "adce",
                       "Aggressive Dead Code Elimination", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
 INITIALIZE_PASS_END(ADCELegacyPass, "adce", "Aggressive Dead Code Elimination",
                     false, false)
 
 FunctionPass *llvm::createAggressiveDCEPass() { return new ADCELegacyPass(); }

test/Transforms/LoopRotate/pr35210.ll

 ;RUN: opt %s -passes='adce,loop(rotate),adce' -S -debug-pass-manager -debug-only=loop-rotate 2>&1 | FileCheck %s
 ;REQUIRES: asserts
 
 ; This test is to make sure we invalidate the post dominator pass after loop rotate simplifies the loop latch.
 ; The adce passes are here to make sure post dominator analysis is required.
 
 ; CHECK: Starting llvm::Function pass manager run.
 ; CHECK-NEXT: Running pass: ADCEPass on f
-; CHECK-NEXT: Running analysis: DominatorTreeAnalysis on f
 ; CHECK-NEXT: Running analysis: PostDominatorTreeAnalysis on f
 ; CHECK-NEXT: Running pass: FunctionToLoopPassAdaptor{{.*}} on f
 ; CHECK-NEXT: Starting llvm::Function pass manager run.
 ; CHECK-NEXT: Running pass: LoopSimplifyPass on f
 ; CHECK-NEXT: Running analysis: LoopAnalysis on f
+; CHECK-NEXT: Running analysis: DominatorTreeAnalysis on f
 ; CHECK-NEXT: Running analysis: AssumptionAnalysis on f
 ; CHECK-NEXT: Running pass: LCSSAPass on f
 ; CHECK-NEXT: Finished llvm::Function pass manager run.
 ; CHECK-NEXT: Running analysis: AAManager on f
 ; CHECK-NEXT: Running analysis: TargetLibraryAnalysis on f
 ; CHECK-NEXT: Running analysis: ScalarEvolutionAnalysis on f
 ; CHECK-NEXT: Running analysis: TargetIRAnalysis on f
 ; CHECK-NEXT: Running analysis: InnerAnalysisManagerProxy{{.*}} on f