//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Owen Anderson and is distributed under
-// 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.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#define LLVM_ANALYSIS_DOMINATOR_INTERNALS_H
#include "llvm/Analysis/Dominators.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 {
template<class GraphT>
-unsigned DFSPass(DominatorTreeBase& DT, typename GraphT::NodeType* V,
- unsigned N) {
+unsigned DFSPass(DominatorTreeBase<typename GraphT::NodeType>& DT,
+ typename GraphT::NodeType* V, unsigned N) {
// This is more understandable as a recursive algorithm, but we can't use the
// recursive algorithm due to stack depth issues. Keep it here for
// documentation purposes.
#if 0
InfoRec &VInfo = DT.Info[DT.Roots[i]];
- VInfo.Semi = ++N;
+ VInfo.DFSNum = VInfo.Semi = ++N;
VInfo.Label = V;
Vertex.push_back(V); // Vertex[n] = V;
}
}
#else
+ bool IsChilOfArtificialExit = (N != 0);
+
std::vector<std::pair<typename GraphT::NodeType*,
typename GraphT::ChildIteratorType> > Worklist;
Worklist.push_back(std::make_pair(V, GraphT::child_begin(V)));
typename GraphT::NodeType* BB = Worklist.back().first;
typename GraphT::ChildIteratorType NextSucc = Worklist.back().second;
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &BBInfo =
+ DT.Info[BB];
+
// First time we visited this BB?
if (NextSucc == GraphT::child_begin(BB)) {
- DominatorTree::InfoRec &BBInfo = DT.Info[BB];
- BBInfo.Semi = ++N;
+ BBInfo.DFSNum = BBInfo.Semi = ++N;
BBInfo.Label = BB;
DT.Vertex.push_back(BB); // Vertex[n] = V;
//BBInfo[V].Ancestor = 0; // Ancestor[n] = 0
//BBInfo[V].Child = 0; // Child[v] = 0
BBInfo.Size = 1; // Size[v] = 1
+
+ if (IsChilOfArtificialExit)
+ BBInfo.Parent = 1;
+
+ IsChilOfArtificialExit = false;
}
-
+
+ // store the DFS number of the current BB - the reference to BBInfo might
+ // get invalidated when processing the successors.
+ unsigned BBDFSNum = BBInfo.DFSNum;
+
// If we are done with this block, remove it from the worklist.
if (NextSucc == GraphT::child_end(BB)) {
Worklist.pop_back();
// Visit the successor next, if it isn't already visited.
typename GraphT::NodeType* Succ = *NextSucc;
- DominatorTree::InfoRec &SuccVInfo = DT.Info[Succ];
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &SuccVInfo =
+ DT.Info[Succ];
if (SuccVInfo.Semi == 0) {
- SuccVInfo.Parent = BB;
+ SuccVInfo.Parent = BBDFSNum;
Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
}
}
return N;
}
+template<class GraphT>
+void Compress(DominatorTreeBase<typename GraphT::NodeType>& DT,
+ typename GraphT::NodeType *VIn) {
+ SmallVector<typename GraphT::NodeType*, 32> Work;
+ SmallPtrSet<typename GraphT::NodeType*, 32> Visited;
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInVAInfo =
+ DT.Info[DT.Vertex[DT.Info[VIn].Ancestor]];
+
+ if (VInVAInfo.Ancestor != 0)
+ Work.push_back(VIn);
+
+ while (!Work.empty()) {
+ typename GraphT::NodeType* V = Work.back();
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInfo =
+ DT.Info[V];
+ typename GraphT::NodeType* VAncestor = DT.Vertex[VInfo.Ancestor];
+ typename DominatorTreeBase<typename GraphT::NodeType>::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<typename GraphT::NodeType>& DT,
+ typename GraphT::NodeType *V) {
+ typename DominatorTreeBase<typename GraphT::NodeType>::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<typename GraphT::NodeType>& DT,
+ unsigned DFSNumV, typename GraphT::NodeType* W,
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &WInfo) {
+#if !BALANCE_IDOM_TREE
+ // Higher-complexity but faster implementation
+ WInfo.Ancestor = DFSNumV;
+#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
+}
+
+template<class FuncT, class NodeT>
+void Calculate(DominatorTreeBase<typename GraphTraits<NodeT>::NodeType>& DT,
+ FuncT& F) {
+ typedef GraphTraits<NodeT> GraphT;
+
+ unsigned N = 0;
+ bool MultipleRoots = (DT.Roots.size() > 1);
+ if (MultipleRoots) {
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &BBInfo =
+ DT.Info[NULL];
+ BBInfo.DFSNum = BBInfo.Semi = ++N;
+ BBInfo.Label = NULL;
+
+ DT.Vertex.push_back(NULL); // Vertex[n] = V;
+ //BBInfo[V].Ancestor = 0; // Ancestor[n] = 0
+ //BBInfo[V].Child = 0; // Child[v] = 0
+ BBInfo.Size = 1; // Size[v] = 1
+ }
+
+ // Step #1: Number blocks in depth-first order and initialize variables used
+ // in later stages of the algorithm.
+ for (unsigned i = 0, e = static_cast<unsigned>(DT.Roots.size());
+ i != e; ++i)
+ N = DFSPass<GraphT>(DT, DT.Roots[i], N);
+
+ // it might be that some blocks did not get a DFS number (e.g., blocks of
+ // infinite loops). In these cases an artificial exit node is required.
+ MultipleRoots |= (DT.isPostDominator() && N != F.size());
+
+ for (unsigned i = N; i >= 2; --i) {
+ typename GraphT::NodeType* W = DT.Vertex[i];
+ typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &WInfo =
+ DT.Info[W];
+
+ // Step #2: Calculate the semidominators of all vertices
+
+ // initialize the semi dominator to point to the parent node
+ WInfo.Semi = WInfo.Parent;
+ typedef GraphTraits<Inverse<NodeT> > InvTraits;
+ for (typename InvTraits::ChildIteratorType CI =
+ InvTraits::child_begin(W),
+ E = InvTraits::child_end(W); CI != E; ++CI) {
+ typename InvTraits::NodeType *N = *CI;
+ if (DT.Info.count(N)) { // Only if this predecessor is reachable!
+ unsigned SemiU = DT.Info[Eval<GraphT>(DT, N)].Semi;
+ if (SemiU < WInfo.Semi)
+ WInfo.Semi = SemiU;
+ }
+ }
+
+ DT.Info[DT.Vertex[WInfo.Semi]].Bucket.push_back(W);
+
+ typename GraphT::NodeType* WParent = DT.Vertex[WInfo.Parent];
+ Link<GraphT>(DT, WInfo.Parent, W, WInfo);
+
+ // Step #3: Implicitly define the immediate dominator of vertices
+ std::vector<typename GraphT::NodeType*> &WParentBucket =
+ DT.Info[WParent].Bucket;
+ while (!WParentBucket.empty()) {
+ typename GraphT::NodeType* V = WParentBucket.back();
+ WParentBucket.pop_back();
+ typename GraphT::NodeType* U = Eval<GraphT>(DT, V);
+ DT.IDoms[V] = DT.Info[U].Semi < DT.Info[V].Semi ? U : WParent;
+ }
+ }
+
+ // Step #4: Explicitly define the immediate dominator of each vertex
+ for (unsigned i = 2; i <= N; ++i) {
+ typename GraphT::NodeType* W = DT.Vertex[i];
+ typename GraphT::NodeType*& WIDom = DT.IDoms[W];
+ if (WIDom != DT.Vertex[DT.Info[W].Semi])
+ WIDom = DT.IDoms[WIDom];
+ }
+
+ if (DT.Roots.empty()) return;
+
+ // Add a node for the root. This node might be the actual root, if there is
+ // one exit block, or it may be the virtual exit (denoted by (BasicBlock *)0)
+ // which postdominates all real exits if there are multiple exit blocks, or
+ // an infinite loop.
+ typename GraphT::NodeType* Root = !MultipleRoots ? DT.Roots[0] : 0;
+
+ DT.DomTreeNodes[Root] = DT.RootNode =
+ new DomTreeNodeBase<typename GraphT::NodeType>(Root, 0);
+
+ // Loop over all of the reachable blocks in the function...
+ for (unsigned i = 2; i <= N; ++i) {
+ typename GraphT::NodeType* W = DT.Vertex[i];
+
+ DomTreeNodeBase<typename GraphT::NodeType> *BBNode = DT.DomTreeNodes[W];
+ if (BBNode) continue; // Haven't calculated this node yet?
+
+ typename GraphT::NodeType* ImmDom = DT.getIDom(W);
+
+ assert(ImmDom || DT.DomTreeNodes[NULL]);
+
+ // Get or calculate the node for the immediate dominator
+ DomTreeNodeBase<typename GraphT::NodeType> *IDomNode =
+ DT.getNodeForBlock(ImmDom);
+
+ // Add a new tree node for this BasicBlock, and link it as a child of
+ // IDomNode
+ DomTreeNodeBase<typename GraphT::NodeType> *C =
+ new DomTreeNodeBase<typename GraphT::NodeType>(W, IDomNode);
+ DT.DomTreeNodes[W] = IDomNode->addChild(C);
+ }
+
+ // Free temporary memory used to construct idom's
+ DT.IDoms.clear();
+ DT.Info.clear();
+ std::vector<typename GraphT::NodeType*>().swap(DT.Vertex);
+
+ DT.updateDFSNumbers();
+}
+
}
#endif
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