Revert "[ADCE][Dominators] Teach ADCE to preserve dominators"

This reverts commit r311039. The patch caused the
`test/Bindings/OCaml/Output/scalar_opts.ml` to fail.

llvm-svn: 311049

Author: kuhar

llvm/include/llvm/Support/GenericDomTreeConstruction.h

@@ -914,12 +914,7 @@ struct SemiNCAInfo {
     if (!FromTN) return;
 
     const TreeNodePtr ToTN = DT.getNode(To);
-    if (!ToTN) {
-      DEBUG(dbgs() << "\tTo (" << BlockNamePrinter(To)
-                   << ") already unreachable -- there is no edge to delete\n");
-      return;
-    }
-
+    assert(ToTN && "To already unreachable -- there is no edge to delete");
     const NodePtr NCDBlock = DT.findNearestCommonDominator(From, To);
     const TreeNodePtr NCD = DT.getNode(NCDBlock);
 

llvm/lib/Transforms/Scalar/ADCE.cpp

@@ -27,7 +27,6 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/DebugInfoMetadata.h"
-#include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instructions.h"
@@ -90,10 +89,6 @@ struct BlockInfoType {
 
 class AggressiveDeadCodeElimination {
   Function &F;
-
-  // ADCE does not use DominatorTree per se, but it updates it to preserve the
-  // analysis.
-  DominatorTree &DT;
   PostDominatorTree &PDT;
 
   /// Mapping of blocks to associated information, an element in BlockInfoVec.
@@ -162,10 +157,9 @@ class AggressiveDeadCodeElimination {
   void makeUnconditional(BasicBlock *BB, BasicBlock *Target);
 
 public:
- AggressiveDeadCodeElimination(Function &F, DominatorTree &DT,
-                               PostDominatorTree &PDT)
-     : F(F), DT(DT), PDT(PDT) {}
- bool performDeadCodeElimination();
+  AggressiveDeadCodeElimination(Function &F, PostDominatorTree &PDT)
+      : F(F), PDT(PDT) {}
+  bool performDeadCodeElimination();
 };
 }
 
@@ -563,31 +557,14 @@ void AggressiveDeadCodeElimination::updateDeadRegions() {
     }
     assert((PreferredSucc && PreferredSucc->PostOrder > 0) &&
            "Failed to find safe successor for dead branch");
-
-    // Collect removed successors to update the (Post)DominatorTrees.
-    SmallPtrSet<BasicBlock *, 4> RemovedSuccessors;
     bool First = true;
     for (auto *Succ : successors(BB)) {
-      if (!First || Succ != PreferredSucc->BB) {
+      if (!First || Succ != PreferredSucc->BB)
         Succ->removePredecessor(BB);
-        RemovedSuccessors.insert(Succ);
-      } else
+      else
         First = false;
     }
     makeUnconditional(BB, PreferredSucc->BB);
-
-    // Inform the dominators about the deleted CFG edges.
-    for (auto *Succ : RemovedSuccessors) {
-      // It might have happened that the same successor appeared multiple times
-      // and the CFG edge wasn't really removed.
-      if (Succ != PreferredSucc->BB) {
-        DEBUG(dbgs() << "ADCE: Removing (Post)DomTree edge " << BB->getName()
-                     << " -> " << Succ->getName() << "\n");
-        DT.deleteEdge(BB, Succ);
-        PDT.deleteEdge(BB, Succ);
-      }
-    }
-
     NumBranchesRemoved += 1;
   }
 }
@@ -632,9 +609,6 @@ void AggressiveDeadCodeElimination::makeUnconditional(BasicBlock *BB,
   InstInfo[NewTerm].Live = true;
   if (const DILocation *DL = PredTerm->getDebugLoc())
     NewTerm->setDebugLoc(DL);
-
-  InstInfo.erase(PredTerm);
-  PredTerm->eraseFromParent();
 }
 
 //===----------------------------------------------------------------------===//
@@ -643,16 +617,13 @@ void AggressiveDeadCodeElimination::makeUnconditional(BasicBlock *BB,
 //
 //===----------------------------------------------------------------------===//
 PreservedAnalyses ADCEPass::run(Function &F, FunctionAnalysisManager &FAM) {
-  auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
   auto &PDT = FAM.getResult<PostDominatorTreeAnalysis>(F);
-  if (!AggressiveDeadCodeElimination(F, DT, PDT).performDeadCodeElimination())
+  if (!AggressiveDeadCodeElimination(F, PDT).performDeadCodeElimination())
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
   PA.preserveSet<CFGAnalyses>();
   PA.preserve<GlobalsAA>();
-  PA.preserve<DominatorTreeAnalysis>();
-  PA.preserve<PostDominatorTreeAnalysis>();
   return PA;
 }
 
@@ -666,22 +637,15 @@ struct ADCELegacyPass : public FunctionPass {
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
-
-    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
     auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
-    return AggressiveDeadCodeElimination(F, DT, PDT)
-        .performDeadCodeElimination();
+    return AggressiveDeadCodeElimination(F, 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();
     AU.addPreserved<GlobalsAAWrapperPass>();
-    AU.addPreserved<DominatorTreeWrapperPass>();
-    AU.addPreserved<PostDominatorTreeWrapperPass>();
   }
 };
 }