llvm-6502/include/llvm/Analysis/DominatorInternals.h
2009-01-05 17:59:02 +00:00

364 lines
13 KiB
C++

//=== llvm/Analysis/DominatorInternals.h - Dominator Calculation -*- C++ -*-==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_DOMINATOR_INTERNALS_H
#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<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.DFSNum = VInfo.Semi = ++N;
VInfo.Label = V;
Vertex.push_back(V); // Vertex[n] = V;
//Info[V].Ancestor = 0; // Ancestor[n] = 0
//Info[V].Child = 0; // Child[v] = 0
VInfo.Size = 1; // Size[v] = 1
for (succ_iterator SI = succ_begin(V), E = succ_end(V); SI != E; ++SI) {
InfoRec &SuccVInfo = DT.Info[*SI];
if (SuccVInfo.Semi == 0) {
SuccVInfo.Parent = V;
N = DTDFSPass(DT, *SI, N);
}
}
#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)));
while (!Worklist.empty()) {
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)) {
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();
continue;
}
// Increment the successor number for the next time we get to it.
++Worklist.back().second;
// Visit the successor next, if it isn't already visited.
typename GraphT::NodeType* Succ = *NextSucc;
typename DominatorTreeBase<typename GraphT::NodeType>::InfoRec &SuccVInfo =
DT.Info[Succ];
if (SuccVInfo.Semi == 0) {
SuccVInfo.Parent = BBDFSNum;
Worklist.push_back(std::make_pair(Succ, GraphT::child_begin(Succ)));
}
}
#endif
return N;
}
template<class GraphT>
void Compress(DominatorTreeBase<typename GraphT::NodeType>& DT,
typename GraphT::NodeType *VIn) {
std::vector<typename GraphT::NodeType*> 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
bool HasChildOutsideDFS = false;
// initialize the semi dominator to point to the parent node
WInfo.Semi = WInfo.Parent;
for (typename GraphTraits<Inverse<NodeT> >::ChildIteratorType CI =
GraphTraits<Inverse<NodeT> >::child_begin(W),
E = GraphTraits<Inverse<NodeT> >::child_end(W); CI != E; ++CI) {
if (DT.Info.count(*CI)) { // Only if this predecessor is reachable!
unsigned SemiU = DT.Info[Eval<GraphT>(DT, *CI)].Semi;
if (SemiU < WInfo.Semi)
WInfo.Semi = SemiU;
}
else {
// if the child has no DFS number it is not post-dominated by any exit,
// and so is the current block.
HasChildOutsideDFS = true;
}
}
// if some child has no DFS number it is not post-dominated by any exit,
// and so is the current block.
if (DT.isPostDominator() && HasChildOutsideDFS)
WInfo.Semi = 0;
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);
// FIXME: This does not work on PostDomTrees. It seems likely that this is
// due to an error in the algorithm for post-dominators. This really should
// be investigated and fixed at some point.
// DT.updateDFSNumbers();
// Start out with the DFS numbers being invalid. Let them be computed if
// demanded.
DT.DFSInfoValid = false;
}
}
#endif