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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50659 91177308-0d34-0410-b5e6-96231b3b80d8
364 lines
13 KiB
C++
364 lines
13 KiB
C++
//=== llvm/Analysis/DominatorInternals.h - Dominator Calculation -*- C++ -*-==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_DOMINATOR_INTERNALS_H
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#define LLVM_ANALYSIS_DOMINATOR_INTERNALS_H
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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//===----------------------------------------------------------------------===//
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//
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// DominatorTree construction - This pass constructs immediate dominator
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// information for a flow-graph based on the algorithm described in this
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// document:
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//
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// A Fast Algorithm for Finding Dominators in a Flowgraph
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// T. Lengauer & R. Tarjan, ACM TOPLAS July 1979, pgs 121-141.
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//
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// This implements both the O(n*ack(n)) and the O(n*log(n)) versions of EVAL and
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// LINK, but it turns out that the theoretically slower O(n*log(n))
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// implementation is actually faster than the "efficient" algorithm (even for
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// large CFGs) because the constant overheads are substantially smaller. The
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// lower-complexity version can be enabled with the following #define:
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//
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#define BALANCE_IDOM_TREE 0
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//
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//===----------------------------------------------------------------------===//
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namespace llvm {
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template<class GraphT>
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unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
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typename GraphT::NodeType* V, unsigned N) {
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// This is more understandable as a recursive algorithm, but we can't use the
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// recursive algorithm due to stack depth issues. Keep it here for
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// documentation purposes.
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#if 0
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InfoRec &VInfo = DT.Info[DT.Roots[i]];
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VInfo.DFSNum = VInfo.Semi = ++N;
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VInfo.Label = V;
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Vertex.push_back(V); // Vertex[n] = V;
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//Info[V].Ancestor = 0; // Ancestor[n] = 0
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//Info[V].Child = 0; // Child[v] = 0
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VInfo.Size = 1; // Size[v] = 1
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for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
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InfoRec &SuccVInfo = DT.Info[*SI];
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if (SuccVInfo.Semi == 0) {
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SuccVInfo.Parent = V;
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N = DTDFSPass(DT, *SI, N);
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}
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}
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#else
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bool IsChilOfArtificialExit = (N != 0);
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std::vector<std::pair<typename GraphT::NodeType*,
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typename GraphT::ChildIteratorType> > Worklist;
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Worklist.push_back(std::make_pair(V, GraphT::child_begin(V)));
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while (!Worklist.empty()) {
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typename GraphT::NodeType* BB = Worklist.back().first;
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typename GraphT::ChildIteratorType NextSucc = Worklist.back().second;
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &BBInfo =
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DT.Info[BB];
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// First time we visited this BB?
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if (NextSucc == GraphT::child_begin(BB)) {
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BBInfo.DFSNum = BBInfo.Semi = ++N;
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BBInfo.Label = BB;
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DT.Vertex.push_back(BB); // Vertex[n] = V;
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//BBInfo[V].Ancestor = 0; // Ancestor[n] = 0
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//BBInfo[V].Child = 0; // Child[v] = 0
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BBInfo.Size = 1; // Size[v] = 1
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if (IsChilOfArtificialExit)
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BBInfo.Parent = 1;
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IsChilOfArtificialExit = false;
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}
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// store the DFS number of the current BB - the reference to BBInfo might
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// get invalidated when processing the successors.
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unsigned BBDFSNum = BBInfo.DFSNum;
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// If we are done with this block, remove it from the worklist.
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if (NextSucc == GraphT::child_end(BB)) {
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Worklist.pop_back();
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continue;
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}
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// Increment the successor number for the next time we get to it.
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++Worklist.back().second;
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// Visit the successor next, if it isn't already visited.
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typename GraphT::NodeType* Succ = *NextSucc;
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &SuccVInfo =
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DT.Info[Succ];
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if (SuccVInfo.Semi == 0) {
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SuccVInfo.Parent = BBDFSNum;
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Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
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}
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}
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#endif
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return N;
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}
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template<class GraphT>
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void Compress(DominatorTreeBase<typename GraphT::NodeType>& DT,
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typename GraphT::NodeType *VIn) {
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std::vector<typename GraphT::NodeType*> Work;
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SmallPtrSet<typename GraphT::NodeType*, 32> Visited;
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInVAInfo =
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DT.Info[DT.Vertex[DT.Info[VIn].Ancestor]];
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if (VInVAInfo.Ancestor != 0)
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Work.push_back(VIn);
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while (!Work.empty()) {
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typename GraphT::NodeType* V = Work.back();
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInfo =
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DT.Info[V];
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typename GraphT::NodeType* VAncestor = DT.Vertex[VInfo.Ancestor];
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VAInfo =
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DT.Info[VAncestor];
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// Process Ancestor first
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if (Visited.insert(VAncestor) &&
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VAInfo.Ancestor != 0) {
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Work.push_back(VAncestor);
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continue;
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}
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Work.pop_back();
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// Update VInfo based on Ancestor info
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if (VAInfo.Ancestor == 0)
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continue;
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typename GraphT::NodeType* VAncestorLabel = VAInfo.Label;
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typename GraphT::NodeType* VLabel = VInfo.Label;
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if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
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VInfo.Label = VAncestorLabel;
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VInfo.Ancestor = VAInfo.Ancestor;
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}
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}
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template<class GraphT>
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typename GraphT::NodeType* Eval(DominatorTreeBase<typename GraphT::NodeType>& DT,
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typename GraphT::NodeType *V) {
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInfo =
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DT.Info[V];
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#if !BALANCE_IDOM_TREE
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// Higher-complexity but faster implementation
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if (VInfo.Ancestor == 0)
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return V;
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Compress<GraphT>(DT, V);
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return VInfo.Label;
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#else
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// Lower-complexity but slower implementation
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if (VInfo.Ancestor == 0)
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return VInfo.Label;
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Compress<GraphT>(DT, V);
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GraphT::NodeType* VLabel = VInfo.Label;
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GraphT::NodeType* VAncestorLabel = DT.Info[VInfo.Ancestor].Label;
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if (DT.Info[VAncestorLabel].Semi >= DT.Info[VLabel].Semi)
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return VLabel;
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else
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return VAncestorLabel;
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#endif
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}
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template<class GraphT>
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void Link(DominatorTreeBase<typename GraphT::NodeType>& DT,
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unsigned DFSNumV, typename GraphT::NodeType* W,
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &WInfo) {
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#if !BALANCE_IDOM_TREE
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// Higher-complexity but faster implementation
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WInfo.Ancestor = DFSNumV;
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#else
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// Lower-complexity but slower implementation
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GraphT::NodeType* WLabel = WInfo.Label;
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unsigned WLabelSemi = DT.Info[WLabel].Semi;
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GraphT::NodeType* S = W;
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InfoRec *SInfo = &DT.Info[S];
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GraphT::NodeType* SChild = SInfo->Child;
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InfoRec *SChildInfo = &DT.Info[SChild];
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while (WLabelSemi < DT.Info[SChildInfo->Label].Semi) {
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GraphT::NodeType* SChildChild = SChildInfo->Child;
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if (SInfo->Size+DT.Info[SChildChild].Size >= 2*SChildInfo->Size) {
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SChildInfo->Ancestor = S;
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SInfo->Child = SChild = SChildChild;
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SChildInfo = &DT.Info[SChild];
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} else {
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SChildInfo->Size = SInfo->Size;
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S = SInfo->Ancestor = SChild;
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SInfo = SChildInfo;
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SChild = SChildChild;
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SChildInfo = &DT.Info[SChild];
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}
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}
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DominatorTreeBase::InfoRec &VInfo = DT.Info[V];
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SInfo->Label = WLabel;
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assert(V != W && "The optimization here will not work in this case!");
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unsigned WSize = WInfo.Size;
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unsigned VSize = (VInfo.Size += WSize);
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if (VSize < 2*WSize)
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std::swap(S, VInfo.Child);
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while (S) {
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SInfo = &DT.Info[S];
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SInfo->Ancestor = V;
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S = SInfo->Child;
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}
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#endif
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}
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template<class FuncT, class NodeT>
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void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
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FuncT& F) {
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typedef GraphTraits<NodeT> GraphT;
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unsigned N = 0;
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bool MultipleRoots = (DT.Roots.size() > 1);
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if (MultipleRoots) {
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &BBInfo =
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DT.Info[NULL];
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BBInfo.DFSNum = BBInfo.Semi = ++N;
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BBInfo.Label = NULL;
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DT.Vertex.push_back(NULL); // Vertex[n] = V;
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//BBInfo[V].Ancestor = 0; // Ancestor[n] = 0
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//BBInfo[V].Child = 0; // Child[v] = 0
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BBInfo.Size = 1; // Size[v] = 1
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}
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// Step #1: Number blocks in depth-first order and initialize variables used
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// in later stages of the algorithm.
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for (unsigned i = 0, e = static_cast<unsigned>(DT.Roots.size());
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i != e; ++i)
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N = DFSPass<GraphT>(DT, DT.Roots[i], N);
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// it might be that some blocks did not get a DFS number (e.g., blocks of
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// infinite loops). In these cases an artificial exit node is required.
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MultipleRoots |= (DT.isPostDominator() && N != F.size());
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for (unsigned i = N; i >= 2; --i) {
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typename GraphT::NodeType* W = DT.Vertex[i];
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &WInfo =
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DT.Info[W];
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// Step #2: Calculate the semidominators of all vertices
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bool HasChildOutsideDFS = false;
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// initialize the semi dominator to point to the parent node
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WInfo.Semi = WInfo.Parent;
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for (typename GraphTraits<Inverse<NodeT> >::ChildIteratorType CI =
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GraphTraits<Inverse<NodeT> >::child_begin(W),
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E = GraphTraits<Inverse<NodeT> >::child_end(W); CI != E; ++CI) {
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if (DT.Info.count(*CI)) { // Only if this predecessor is reachable!
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unsigned SemiU = DT.Info[Eval<GraphT>(DT, *CI)].Semi;
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if (SemiU < WInfo.Semi)
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WInfo.Semi = SemiU;
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}
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else {
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// if the child has no DFS number it is not post-dominated by any exit,
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// and so is the current block.
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HasChildOutsideDFS = true;
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}
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}
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// if some child has no DFS number it is not post-dominated by any exit,
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// and so is the current block.
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if (DT.isPostDominator() && HasChildOutsideDFS)
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WInfo.Semi = 0;
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DT.Info[DT.Vertex[WInfo.Semi]].Bucket.push_back(W);
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typename GraphT::NodeType* WParent = DT.Vertex[WInfo.Parent];
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Link<GraphT>(DT, WInfo.Parent, W, WInfo);
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// Step #3: Implicitly define the immediate dominator of vertices
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std::vector<typename GraphT::NodeType*> &WParentBucket =
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DT.Info[WParent].Bucket;
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while (!WParentBucket.empty()) {
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typename GraphT::NodeType* V = WParentBucket.back();
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WParentBucket.pop_back();
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typename GraphT::NodeType* U = Eval<GraphT>(DT, V);
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DT.IDoms[V] = DT.Info[U].Semi < DT.Info[V].Semi ? U : WParent;
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}
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}
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// Step #4: Explicitly define the immediate dominator of each vertex
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for (unsigned i = 2; i <= N; ++i) {
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typename GraphT::NodeType* W = DT.Vertex[i];
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typename GraphT::NodeType*& WIDom = DT.IDoms[W];
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if (WIDom != DT.Vertex[DT.Info[W].Semi])
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WIDom = DT.IDoms[WIDom];
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}
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if (DT.Roots.empty()) return;
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// Add a node for the root. This node might be the actual root, if there is
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// one exit block, or it may be the virtual exit (denoted by (BasicBlock *)0)
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// which postdominates all real exits if there are multiple exit blocks, or
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// an infinite loop.
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typename GraphT::NodeType* Root = !MultipleRoots ? DT.Roots[0] : 0;
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DT.DomTreeNodes[Root] = DT.RootNode =
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new DomTreeNodeBase<typename GraphT::NodeType>(Root, 0);
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// Loop over all of the reachable blocks in the function...
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for (unsigned i = 2; i <= N; ++i) {
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typename GraphT::NodeType* W = DT.Vertex[i];
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DomTreeNodeBase<typename GraphT::NodeType> *BBNode = DT.DomTreeNodes[W];
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if (BBNode) continue; // Haven't calculated this node yet?
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typename GraphT::NodeType* ImmDom = DT.getIDom(W);
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assert(ImmDom || DT.DomTreeNodes[NULL]);
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// Get or calculate the node for the immediate dominator
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DomTreeNodeBase<typename GraphT::NodeType> *IDomNode =
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DT.getNodeForBlock(ImmDom);
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// Add a new tree node for this BasicBlock, and link it as a child of
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// IDomNode
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DomTreeNodeBase<typename GraphT::NodeType> *C =
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new DomTreeNodeBase<typename GraphT::NodeType>(W, IDomNode);
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DT.DomTreeNodes[W] = IDomNode->addChild(C);
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}
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// Free temporary memory used to construct idom's
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DT.IDoms.clear();
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DT.Info.clear();
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std::vector<typename GraphT::NodeType*>().swap(DT.Vertex);
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// FIXME: This does not work on PostDomTrees. It seems likely that this is
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// due to an error in the algorithm for post-dominators. This really should
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// be investigated and fixed at some point.
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// DT.updateDFSNumbers();
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// Start out with the DFS numbers being invalid. Let them be computed if
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// demanded.
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DT.DFSInfoValid = false;
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}
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}
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#endif
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