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Remove the #ifdef'd code for balancing the eval-link data structure. It doesn't

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compile, and everyone's tests have shown it to be slower in practice, even for
quite large graphs.

I also hope to do an optimization that is only correct with the simpler data
structure, which would break this even further.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122684 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Cameron Zwarich 2011-01-02 07:53:49 +00:00
parent 6b04160dd8
commit c9e152b778
1 changed files with 3 additions and 65 deletions
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68
include/llvm/Analysis/DominatorInternals.h
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@ -22,13 +22,9 @@
// 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
// This implements the O(n*log(n)) versions of EVAL and LINK, because it turns
// out that the theoretically slower O(n*log(n)) implementation is actually
// faster than the almost-linear O(n*alpha(n)) version, even for large CFGs.
//
//===----------------------------------------------------------------------===//
@ -157,75 +153,17 @@ 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>