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//==- llvm/VMCore/DominatorCalculation.h - Dominator Calculation -*- C++ -*-==//
//
// 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.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_VMCORE_DOMINATOR_CALCULATION_H
#define LLVM_VMCORE_DOMINATOR_CALCULATION_H
#include "llvm/Analysis/Dominators.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 {
void DTCompress(DominatorTree& DT, BasicBlock *VIn) {
std::vector<BasicBlock *> Work;
SmallPtrSet<BasicBlock *, 32> Visited;
BasicBlock *VInAncestor = DT.Info[VIn].Ancestor;
DominatorTree::InfoRec &VInVAInfo = DT.Info[VInAncestor];
if (VInVAInfo.Ancestor != 0)
Work.push_back(VIn);
while (!Work.empty()) {
BasicBlock *V = Work.back();
DominatorTree::InfoRec &VInfo = DT.Info[V];
BasicBlock *VAncestor = VInfo.Ancestor;
DominatorTree::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;
BasicBlock *VAncestorLabel = VAInfo.Label;
BasicBlock *VLabel = VInfo.Label;
if (DT.Info[VAncestorLabel].Semi < DT.Info[VLabel].Semi)
VInfo.Label = VAncestorLabel;
VInfo.Ancestor = VAInfo.Ancestor;
}
}
BasicBlock *DTEval(DominatorTree& DT, BasicBlock *V) {
DominatorTree::InfoRec &VInfo = DT.Info[V];
#if !BALANCE_IDOM_TREE
// Higher-complexity but faster implementation
if (VInfo.Ancestor == 0)
return V;
DTCompress(DT, V);
return VInfo.Label;
#else
// Lower-complexity but slower implementation
if (VInfo.Ancestor == 0)
return VInfo.Label;
DTCompress(DT, V);
BasicBlock *VLabel = VInfo.Label;
BasicBlock *VAncestorLabel = DT.Info[VInfo.Ancestor].Label;
if (DT.Info[VAncestorLabel].Semi >= DT.Info[VLabel].Semi)
return VLabel;
else
return VAncestorLabel;
#endif
}
void DTLink(DominatorTree& DT, BasicBlock *V, BasicBlock *W,
DominatorTree::InfoRec &WInfo) {
#if !BALANCE_IDOM_TREE
// Higher-complexity but faster implementation
WInfo.Ancestor = V;
#else
// Lower-complexity but slower implementation
BasicBlock *WLabel = WInfo.Label;
unsigned WLabelSemi = Info[WLabel].Semi;
BasicBlock *S = W;
InfoRec *SInfo = &Info[S];
BasicBlock *SChild = SInfo->Child;
InfoRec *SChildInfo = &Info[SChild];
while (WLabelSemi < Info[SChildInfo->Label].Semi) {
BasicBlock *SChildChild = SChildInfo->Child;
if (SInfo->Size+Info[SChildChild].Size >= 2*SChildInfo->Size) {
SChildInfo->Ancestor = S;
SInfo->Child = SChild = SChildChild;
SChildInfo = &Info[SChild];
} else {
SChildInfo->Size = SInfo->Size;
S = SInfo->Ancestor = SChild;
SInfo = SChildInfo;
SChild = SChildChild;
SChildInfo = &Info[SChild];
}
}
InfoRec &VInfo = 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 = &Info[S];
SInfo->Ancestor = V;
S = SInfo->Child;
}
#endif
}
void DTcalculate(DominatorTree& DT, Function &F) {
BasicBlock* Root = DT.Roots[0];
// Add a node for the root...
DT.DomTreeNodes[Root] = DT.RootNode = new DomTreeNode(Root, 0);
DT.Vertex.push_back(0);
// Step #1: Number blocks in depth-first order and initialize variables used
// in later stages of the algorithm.
unsigned N = DT.DFSPass(Root, 0);
for (unsigned i = N; i >= 2; --i) {
BasicBlock *W = DT.Vertex[i];
DominatorTree::InfoRec &WInfo = DT.Info[W];
// Step #2: Calculate the semidominators of all vertices
for (pred_iterator PI = pred_begin(W), E = pred_end(W); PI != E; ++PI)
if (DT.Info.count(*PI)) { // Only if this predecessor is reachable!
unsigned SemiU = DT.Info[DTEval(DT, *PI)].Semi;
if (SemiU < WInfo.Semi)
WInfo.Semi = SemiU;
}
DT.Info[DT.Vertex[WInfo.Semi]].Bucket.push_back(W);
BasicBlock *WParent = WInfo.Parent;
DTLink(DT, WParent, W, WInfo);
// Step #3: Implicitly define the immediate dominator of vertices
std::vector<BasicBlock*> &WParentBucket = DT.Info[WParent].Bucket;
while (!WParentBucket.empty()) {
BasicBlock *V = WParentBucket.back();
WParentBucket.pop_back();
BasicBlock *U = DTEval(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) {
BasicBlock *W = DT.Vertex[i];
BasicBlock *&WIDom = DT.IDoms[W];
if (WIDom != DT.Vertex[DT.Info[W].Semi])
WIDom = DT.IDoms[WIDom];
}
// Loop over all of the reachable blocks in the function...
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
if (BasicBlock *ImmDom = DT.getIDom(I)) { // Reachable block.
DomTreeNode *BBNode = DT.DomTreeNodes[I];
if (BBNode) continue; // Haven't calculated this node yet?
// Get or calculate the node for the immediate dominator
DomTreeNode *IDomNode = DT.getNodeForBlock(ImmDom);
// Add a new tree node for this BasicBlock, and link it as a child of
// IDomNode
DomTreeNode *C = new DomTreeNode(I, IDomNode);
DT.DomTreeNodes[I] = IDomNode->addChild(C);
}
// Free temporary memory used to construct idom's
DT.Info.clear();
DT.IDoms.clear();
std::vector<BasicBlock*>().swap(DT.Vertex);
DT.updateDFSNumbers();
}
}
#endif
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