Template-ize more of the DomTree internal implementation details. Only the calculate() methods for DomTree and PostDomTree remain to be merged/template-ized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42476 91177308-0d34-0410-b5e6-96231b3b80d8
2025-07-25 13:24:46 +00:00 · 2007-09-30 04:17:16 +00:00
parent c28476f1d9
commit ab528fe0fb
5 changed files with 145 additions and 156 deletions
--- a/include/llvm/Analysis/DominatorInternals.h
+++ b/include/llvm/Analysis/DominatorInternals.h
@@ -6,17 +6,31 @@
 // the University of Illinois Open Source License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-//
-// This file defines shared implementation details of dominator and
-// postdominator calculation.  This file SHOULD NOT BE INCLUDED outside
-// of the dominator and postdominator implementation files.
-//
-//===----------------------------------------------------------------------===//

 #ifndef LLVM_ANALYSIS_DOMINATOR_INTERNALS_H
 #define LLVM_ANALYSIS_DOMINATOR_INTERNALS_H

 #include "llvm/Analysis/Dominators.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+//===----------------------------------------------------------------------===//
+//
+// DominatorTree construction - This pass constructs immediate dominator
+// information for a flow-graph based on the algorithm described in this
+// document:
+//
+//   A Fast Algorithm for Finding Dominators in a Flowgraph
+//   T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
+//
+// This implements both the O(n*ack(n)) and the O(n*log(n)) versions of EVAL and
+// LINK, but it turns out that the theoretically slower O(n*log(n))
+// implementation is actually faster than the "efficient" algorithm (even for
+// large CFGs) because the constant overheads are substantially smaller.  The
+// lower-complexity version can be enabled with the following #define:
+//
+#define BALANCE_IDOM_TREE 0
+//
+//===----------------------------------------------------------------------===//

 namespace llvm {

@@ -85,6 +99,115 @@ unsigned DFSPass(DominatorTreeBase& DT, typename GraphT::NodeType* V,
    return N;
 }

+template<class GraphT>
+void Compress(DominatorTreeBase& DT, typename GraphT::NodeType *VIn) {
+  std::vector<typename GraphT::NodeType*> Work;
+  SmallPtrSet<typename GraphT::NodeType*, 32> Visited;
+  typename GraphT::NodeType* VInAncestor = DT.Info[VIn].Ancestor;
+  DominatorTreeBase::InfoRec &VInVAInfo = DT.Info[VInAncestor];
+
+  if (VInVAInfo.Ancestor != 0)
+    Work.push_back(VIn);
+  
+  while (!Work.empty()) {
+    typename GraphT::NodeType* V = Work.back();
+    DominatorTree::InfoRec &VInfo = DT.Info[V];
+    typename GraphT::NodeType* VAncestor = VInfo.Ancestor;
+    DominatorTreeBase::InfoRec &VAInfo = DT.Info[VAncestor];
+
+    // Process Ancestor first
+    if (Visited.insert(VAncestor) &&
+        VAInfo.Ancestor != 0) {
+      Work.push_back(VAncestor);
+      continue;
+    } 
+    Work.pop_back(); 
+
+    // Update VInfo based on Ancestor info
+    if (VAInfo.Ancestor == 0)
+      continue;
+    typename GraphT::NodeType* VAncestorLabel = VAInfo.Label;
+    typename GraphT::NodeType* VLabel = VInfo.Label;
+    if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
+      VInfo.Label = VAncestorLabel;
+    VInfo.Ancestor = VAInfo.Ancestor;
+  }
+}
+
+template<class GraphT>
+typename GraphT::NodeType* Eval(DominatorTreeBase& DT,
+                                typename GraphT::NodeType *V) {
+  DominatorTreeBase::InfoRec &VInfo = DT.Info[V];
+#if !BALANCE_IDOM_TREE
+  // Higher-complexity but faster implementation
+  if (VInfo.Ancestor == 0)
+    return V;
+  Compress<GraphT>(DT, V);
+  return VInfo.Label;
+#else
+  // Lower-complexity but slower implementation
+  if (VInfo.Ancestor == 0)
+    return VInfo.Label;
+  Compress<GraphT>(DT, V);
+  GraphT::NodeType* VLabel = VInfo.Label;
+
+  GraphT::NodeType* VAncestorLabel = DT.Info[VInfo.Ancestor].Label;
+  if (DT.Info[VAncestorLabel].Semi >= DT.Info[VLabel].Semi)
+    return VLabel;
+  else
+    return VAncestorLabel;
+#endif
+}
+
+template<class GraphT>
+void Link(DominatorTreeBase& DT, typename GraphT::NodeType* V,
+          typename GraphT::NodeType* W, DominatorTreeBase::InfoRec &WInfo) {
+#if !BALANCE_IDOM_TREE
+  // Higher-complexity but faster implementation
+  WInfo.Ancestor = V;
+#else
+  // Lower-complexity but slower implementation
+  GraphT::NodeType* WLabel = WInfo.Label;
+  unsigned WLabelSemi = DT.Info[WLabel].Semi;
+  GraphT::NodeType* S = W;
+  InfoRec *SInfo = &DT.Info[S];
+
+  GraphT::NodeType* SChild = SInfo->Child;
+  InfoRec *SChildInfo = &DT.Info[SChild];
+
+  while (WLabelSemi < DT.Info[SChildInfo->Label].Semi) {
+    GraphT::NodeType* SChildChild = SChildInfo->Child;
+    if (SInfo->Size+DT.Info[SChildChild].Size >= 2*SChildInfo->Size) {
+      SChildInfo->Ancestor = S;
+      SInfo->Child = SChild = SChildChild;
+      SChildInfo = &DT.Info[SChild];
+    } else {
+      SChildInfo->Size = SInfo->Size;
+      S = SInfo->Ancestor = SChild;
+      SInfo = SChildInfo;
+      SChild = SChildChild;
+      SChildInfo = &DT.Info[SChild];
+    }
+  }
+
+  DominatorTreeBase::InfoRec &VInfo = DT.Info[V];
+  SInfo->Label = WLabel;
+
+  assert(V != W && "The optimization here will not work in this case!");
+  unsigned WSize = WInfo.Size;
+  unsigned VSize = (VInfo.Size += WSize);
+
+  if (VSize < 2*WSize)
+    std::swap(S, VInfo.Child);
+
+  while (S) {
+    SInfo = &DT.Info[S];
+    SInfo->Ancestor = V;
+    S = SInfo->Child;
+  }
+#endif
+}
+
 }

 #endif