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4ade012dd0
I haven't looked closely at exactly why the side effect is required, but this seems better than not mentioning it at all. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226030 91177308-0d34-0410-b5e6-96231b3b80d8
294 lines
10 KiB
C++
294 lines
10 KiB
C++
//===- GenericDomTreeConstruction.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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/// \file
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///
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/// Generic dominator tree construction - This file provides routines to
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/// construct immediate dominator information for a flow-graph based on the
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/// algorithm described in this 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 the O(n*log(n)) versions of EVAL and LINK, because it turns
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/// out that the theoretically slower O(n*log(n)) implementation is actually
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/// faster than the almost-linear O(n*alpha(n)) version, even for large CFGs.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
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#define LLVM_SUPPORT_GENERICDOMTREECONSTRUCTION_H
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Support/GenericDomTree.h"
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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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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 IsChildOfArtificialExit = (N != 0);
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SmallVector<std::pair<typename GraphT::NodeType*,
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typename GraphT::ChildIteratorType>, 32> 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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if (IsChildOfArtificialExit)
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BBInfo.Parent = 1;
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IsChildOfArtificialExit = 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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typename GraphT::NodeType*
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Eval(DominatorTreeBase<typename GraphT::NodeType>& DT,
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typename GraphT::NodeType *VIn, unsigned LastLinked) {
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VInInfo =
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DT.Info[VIn];
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if (VInInfo.DFSNum < LastLinked)
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return VIn;
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SmallVector<typename GraphT::NodeType*, 32> Work;
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SmallPtrSet<typename GraphT::NodeType*, 32> Visited;
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if (VInInfo.Parent >= LastLinked)
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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.Parent];
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// Process Ancestor first
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if (Visited.insert(VAncestor).second && VInfo.Parent >= LastLinked) {
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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 (VInfo.Parent < LastLinked)
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continue;
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typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &VAInfo =
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DT.Info[VAncestor];
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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.Parent = VAInfo.Parent;
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}
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return VInInfo.Label;
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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[nullptr];
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BBInfo.DFSNum = BBInfo.Semi = ++N;
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BBInfo.Label = nullptr;
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DT.Vertex.push_back(nullptr); // Vertex[n] = V;
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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 != GraphTraits<FuncT*>::size(&F));
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// When naively implemented, the Lengauer-Tarjan algorithm requires a separate
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// bucket for each vertex. However, this is unnecessary, because each vertex
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// is only placed into a single bucket (that of its semidominator), and each
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// vertex's bucket is processed before it is added to any bucket itself.
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//
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// Instead of using a bucket per vertex, we use a single array Buckets that
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// has two purposes. Before the vertex V with preorder number i is processed,
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// Buckets[i] stores the index of the first element in V's bucket. After V's
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// bucket is processed, Buckets[i] stores the index of the next element in the
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// bucket containing V, if any.
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SmallVector<unsigned, 32> Buckets;
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Buckets.resize(N + 1);
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for (unsigned i = 1; i <= N; ++i)
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Buckets[i] = i;
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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: Implicitly define the immediate dominator of vertices
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for (unsigned j = i; Buckets[j] != i; j = Buckets[j]) {
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typename GraphT::NodeType* V = DT.Vertex[Buckets[j]];
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typename GraphT::NodeType* U = Eval<GraphT>(DT, V, i + 1);
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DT.IDoms[V] = DT.Info[U].Semi < i ? U : W;
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}
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// Step #3: Calculate the semidominators of all vertices
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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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typedef GraphTraits<Inverse<NodeT> > InvTraits;
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for (typename InvTraits::ChildIteratorType CI =
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InvTraits::child_begin(W),
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E = InvTraits::child_end(W); CI != E; ++CI) {
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typename InvTraits::NodeType *N = *CI;
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if (DT.Info.count(N)) { // Only if this predecessor is reachable!
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unsigned SemiU = DT.Info[Eval<GraphT>(DT, N, i + 1)].Semi;
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if (SemiU < WInfo.Semi)
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WInfo.Semi = SemiU;
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}
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}
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// If V is a non-root vertex and sdom(V) = parent(V), then idom(V) is
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// necessarily parent(V). In this case, set idom(V) here and avoid placing
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// V into a bucket.
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if (WInfo.Semi == WInfo.Parent) {
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DT.IDoms[W] = DT.Vertex[WInfo.Parent];
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} else {
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Buckets[i] = Buckets[WInfo.Semi];
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Buckets[WInfo.Semi] = i;
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}
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}
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if (N >= 1) {
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typename GraphT::NodeType* Root = DT.Vertex[1];
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for (unsigned j = 1; Buckets[j] != 1; j = Buckets[j]) {
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typename GraphT::NodeType* V = DT.Vertex[Buckets[j]];
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DT.IDoms[V] = Root;
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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] : nullptr;
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DT.RootNode =
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(DT.DomTreeNodes[Root] =
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llvm::make_unique<DomTreeNodeBase<typename GraphT::NodeType>>(
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Root, nullptr)).get();
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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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// Don't replace this with 'count', the insertion side effect is important
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if (DT.DomTreeNodes[W])
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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[nullptr]);
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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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DT.DomTreeNodes[W] = IDomNode->addChild(
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llvm::make_unique<DomTreeNodeBase<typename GraphT::NodeType>>(
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W, IDomNode));
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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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DT.Vertex.clear();
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DT.Vertex.shrink_to_fit();
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DT.updateDFSNumbers();
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}
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}
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#endif
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