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Convert ImmediateDominators::DFSPass from being recursive to being iterative.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@35815 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-04-09 06:44:42 +00:00
parent 5694b6e90e
commit a9f120bd9f
1 changed files with 43 additions and 1 deletions
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44
lib/VMCore/Dominators.cpp
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@ -50,12 +50,16 @@ C("idom", "Immediate Dominators Construction", true);
unsigned ImmediateDominators::DFSPass(BasicBlock *V, InfoRec &VInfo,
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
VInfo.Semi = ++N;
VInfo.Label = V;
Vertex.push_back(V); // Vertex[n] = V;
//Info[V].Ancestor = 0; // Ancestor[n] = 0
//Child[V] = 0; // Child[v] = 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) {
@ -65,6 +69,44 @@ unsigned ImmediateDominators::DFSPass(BasicBlock *V, InfoRec &VInfo,
N = DFSPass(*SI, SuccVInfo, N);
}
}
#else
std::vector<std::pair<BasicBlock*, unsigned> > Worklist;
Worklist.push_back(std::make_pair(V, 0U));
while (!Worklist.empty()) {
BasicBlock *BB = Worklist.back().first;
unsigned NextSucc = Worklist.back().second;
// First time we visited this BB?
if (NextSucc == 0) {
InfoRec &BBInfo = Info[BB];
BBInfo.Semi = ++N;
BBInfo.Label = BB;
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 we are done with this block, remove it from the worklist.
if (NextSucc == BB->getTerminator()->getNumSuccessors()) {
Worklist.pop_back();
continue;
}
// Otherwise, 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.
BasicBlock *Succ = BB->getTerminator()->getSuccessor(NextSucc);
InfoRec &SuccVInfo = Info[Succ];
if (SuccVInfo.Semi == 0) {
SuccVInfo.Parent = BB;
Worklist.push_back(std::make_pair(Succ, 0U));
}
}
#endif
return N;
}