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109 lines
3.8 KiB
C++
109 lines
3.8 KiB
C++
//==- DominatorCalculation.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 was developed by Owen Anderson and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_VMCORE_DOMINATOR_CALCULATION_H
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#define LLVM_VMCORE_DOMINATOR_CALCULATION_H
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/DominatorInternals.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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void DTcalculate(DominatorTree& DT, Function &F) {
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BasicBlock* Root = DT.Roots[0];
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// Add a node for the root...
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DT.DomTreeNodes[Root] = DT.RootNode = new DomTreeNode(Root, 0);
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DT.Vertex.push_back(0);
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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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unsigned N = DFSPass<GraphTraits<BasicBlock*> >(DT, Root, 0);
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for (unsigned i = N; i >= 2; --i) {
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BasicBlock *W = DT.Vertex[i];
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DominatorTree::InfoRec &WInfo = DT.Info[W];
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// Step #2: Calculate the semidominators of all vertices
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for (pred_iterator PI = pred_begin(W), E = pred_end(W); PI != E; ++PI)
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if (DT.Info.count(*PI)) { // Only if this predecessor is reachable!
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unsigned SemiU = DT.Info[Eval(DT, *PI)].Semi;
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if (SemiU < WInfo.Semi)
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WInfo.Semi = SemiU;
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}
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DT.Info[DT.Vertex[WInfo.Semi]].Bucket.push_back(W);
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BasicBlock *WParent = WInfo.Parent;
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Link(DT, WParent, W, WInfo);
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// Step #3: Implicitly define the immediate dominator of vertices
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std::vector<BasicBlock*> &WParentBucket = DT.Info[WParent].Bucket;
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while (!WParentBucket.empty()) {
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BasicBlock *V = WParentBucket.back();
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WParentBucket.pop_back();
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BasicBlock *U = Eval(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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BasicBlock *W = DT.Vertex[i];
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BasicBlock *&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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// Loop over all of the reachable blocks in the function...
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for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
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if (BasicBlock *ImmDom = DT.getIDom(I)) { // Reachable block.
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DomTreeNode *BBNode = DT.DomTreeNodes[I];
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if (BBNode) continue; // Haven't calculated this node yet?
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// Get or calculate the node for the immediate dominator
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DomTreeNode *IDomNode = 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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DomTreeNode *C = new DomTreeNode(I, IDomNode);
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DT.DomTreeNodes[I] = IDomNode->addChild(C);
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}
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// Free temporary memory used to construct idom's
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DT.Info.clear();
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DT.IDoms.clear();
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std::vector<BasicBlock*>().swap(DT.Vertex);
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DT.updateDFSNumbers();
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}
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}
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#endif
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