[DominatorTree] Simplify ChildrenGetter.

Summary:
Simplify ChildrenGetter to a simple wrapper around a GraphDiff call.
GraphDiff already handles nullptr in children, so the special casing in
clang can also be removed.

Reviewers: kuhar, dblaikie

Subscribers: llvm-commits, cfe-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D84713

clang/include/clang/Analysis/Analyses/Dominators.h

@@ -273,76 +273,6 @@ public:
 
 namespace llvm {
 
-/// Clang's CFG contains nullpointers for unreachable succesors, e.g. when an
-/// if statement's condition is always false, it's 'then' branch is represented
-/// with a nullptr. This however will result in a nullpointer derefernece for
-/// dominator tree calculation.
-///
-/// To circumvent this, let's just crudely specialize the children getters
-/// used in LLVM's dominator tree builder.
-namespace DomTreeBuilder {
-
-using ClangCFGDomChildrenGetter =
-SemiNCAInfo<clang::CFGDomTree::DominatorTreeBase>::ChildrenGetter<
-                                                             /*Inverse=*/false>;
-
-template <>
-template <>
-inline ClangCFGDomChildrenGetter::ResultTy ClangCFGDomChildrenGetter::Get(
-    clang::CFGBlock *N, std::integral_constant<bool, /*Inverse=*/false>) {
-  auto RChildren = reverse(children<NodePtr>(N));
-  ResultTy Ret(RChildren.begin(), RChildren.end());
-  Ret.erase(std::remove(Ret.begin(), Ret.end(), nullptr), Ret.end());
-  return Ret;
-}
-
-using ClangCFGDomReverseChildrenGetter =
-SemiNCAInfo<clang::CFGDomTree::DominatorTreeBase>::ChildrenGetter<
-                                                              /*Inverse=*/true>;
-
-template <>
-template <>
-inline ClangCFGDomReverseChildrenGetter::ResultTy
-ClangCFGDomReverseChildrenGetter::Get(
-    clang::CFGBlock *N, std::integral_constant<bool, /*Inverse=*/true>) {
-  auto IChildren = inverse_children<NodePtr>(N);
-  ResultTy Ret(IChildren.begin(), IChildren.end());
-  Ret.erase(std::remove(Ret.begin(), Ret.end(), nullptr), Ret.end());
-  return Ret;
-}
-
-using ClangCFGPostDomChildrenGetter =
-SemiNCAInfo<clang::CFGPostDomTree::DominatorTreeBase>::ChildrenGetter<
-                                                             /*Inverse=*/false>;
-
-template <>
-template <>
-inline ClangCFGPostDomChildrenGetter::ResultTy
-ClangCFGPostDomChildrenGetter::Get(
-    clang::CFGBlock *N, std::integral_constant<bool, /*Inverse=*/false>) {
-  auto RChildren = reverse(children<NodePtr>(N));
-  ResultTy Ret(RChildren.begin(), RChildren.end());
-  Ret.erase(std::remove(Ret.begin(), Ret.end(), nullptr), Ret.end());
-  return Ret;
-}
-
-using ClangCFGPostDomReverseChildrenGetter =
-SemiNCAInfo<clang::CFGPostDomTree::DominatorTreeBase>::ChildrenGetter<
-                                                              /*Inverse=*/true>;
-
-template <>
-template <>
-inline ClangCFGPostDomReverseChildrenGetter::ResultTy
-ClangCFGPostDomReverseChildrenGetter::Get(
-    clang::CFGBlock *N, std::integral_constant<bool, /*Inverse=*/true>) {
-  auto IChildren = inverse_children<NodePtr>(N);
-  ResultTy Ret(IChildren.begin(), IChildren.end());
-  Ret.erase(std::remove(Ret.begin(), Ret.end(), nullptr), Ret.end());
-  return Ret;
-}
-
-} // end of namespace DomTreeBuilder
-
 //===-------------------------------------
 /// DominatorTree GraphTraits specialization so the DominatorTree can be
 /// iterable by generic graph iterators.

llvm/include/llvm/Support/GenericDomTreeConstruction.h

@@ -103,31 +103,13 @@ struct SemiNCAInfo {
     // in progress, we need this information to continue it.
   }
 
-  template <bool Inversed> struct ChildrenGetter {
+  template <bool Inversed>
-    using ResultTy = SmallVector<NodePtr, 8>;
+  static SmallVector<NodePtr, 8> getChildren(NodePtr N, BatchUpdatePtr BUI) {
-
+    if (BUI)
-    static ResultTy Get(NodePtr N, std::integral_constant<bool, false>) {
-      auto RChildren = reverse(children<NodePtr>(N));
-      return ResultTy(RChildren.begin(), RChildren.end());
-    }
-
-    static ResultTy Get(NodePtr N, std::integral_constant<bool, true>) {
-      auto IChildren = inverse_children<NodePtr>(N);
-      return ResultTy(IChildren.begin(), IChildren.end());
-    }
-
-    using Tag = std::integral_constant<bool, Inversed>;
-
-    // The function below is the core part of the batch updater. It allows the
-    // Depth Based Search algorithm to perform incremental updates in lockstep
-    // with updates to the CFG. We emulated lockstep CFG updates by getting its
-    // next snapshots by reverse-applying future updates.
-    static ResultTy Get(NodePtr N, BatchUpdatePtr BUI) {
-      if (!BUI)
-        return Get(N, Tag());
       return BUI->PreViewCFG.template getChildren<Inversed>(N);
-    }
+    GraphDiffT GD;
-  };
+    return GD.template getChildren<Inversed>(N);
+  }
 
   NodePtr getIDom(NodePtr BB) const {
     auto InfoIt = NodeToInfo.find(BB);
@@ -194,8 +176,7 @@ struct SemiNCAInfo {
       NumToNode.push_back(BB);
 
       constexpr bool Direction = IsReverse != IsPostDom;  // XOR.
-      for (const NodePtr Succ :
+      for (const NodePtr Succ : getChildren<Direction>(BB, BatchUpdates)) {
-           ChildrenGetter<Direction>::Get(BB, BatchUpdates)) {
         const auto SIT = NodeToInfo.find(Succ);
         // Don't visit nodes more than once but remember to collect
         // ReverseChildren.
@@ -330,7 +311,7 @@ struct SemiNCAInfo {
   // to CFG nodes within infinite loops.
   static bool HasForwardSuccessors(const NodePtr N, BatchUpdatePtr BUI) {
     assert(N && "N must be a valid node");
-    return !ChildrenGetter<false>::Get(N, BUI).empty();
+    return !getChildren<false>(N, BUI).empty();
   }
 
   static NodePtr GetEntryNode(const DomTreeT &DT) {
@@ -748,8 +729,7 @@ struct SemiNCAInfo {
         //
         // Invariant: there is an optimal path from `To` to TN with the minimum
         // depth being CurrentLevel.
-        for (const NodePtr Succ :
+        for (const NodePtr Succ : getChildren<IsPostDom>(TN->getBlock(), BUI)) {
-             ChildrenGetter<IsPostDom>::Get(TN->getBlock(), BUI)) {
           const TreeNodePtr SuccTN = DT.getNode(Succ);
           assert(SuccTN &&
                  "Unreachable successor found at reachable insertion");
@@ -879,7 +859,7 @@ struct SemiNCAInfo {
     // the DomTree about it.
     // The check is O(N), so run it only in debug configuration.
     auto IsSuccessor = [BUI](const NodePtr SuccCandidate, const NodePtr Of) {
-      auto Successors = ChildrenGetter<IsPostDom>::Get(Of, BUI);
+      auto Successors = getChildren<IsPostDom>(Of, BUI);
       return llvm::find(Successors, SuccCandidate) != Successors.end();
     };
     (void)IsSuccessor;
@@ -967,7 +947,7 @@ struct SemiNCAInfo {
     LLVM_DEBUG(dbgs() << "IsReachableFromIDom " << BlockNamePrinter(TN)
                       << "\n");
     auto TNB = TN->getBlock();
-    for (const NodePtr Pred : ChildrenGetter<!IsPostDom>::Get(TNB, BUI)) {
+    for (const NodePtr Pred : getChildren<!IsPostDom>(TNB, BUI)) {
       LLVM_DEBUG(dbgs() << "\tPred " << BlockNamePrinter(Pred) << "\n");
       if (!DT.getNode(Pred)) continue;