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//===- MaximumSpanningTree.cpp - LLVM Pass to estimate profile info -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This module privides means for calculating a maximum spanning tree for the
// CFG of a function according to a given profile. The tree does not contain
// leaf edges, since they are needed for optimal edge profiling.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "maximum-spanning-tree"
#include "MaximumSpanningTree.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
using namespace llvm;
namespace {
// compare two weighted edges
struct VISIBILITY_HIDDEN EdgeWeightCompare {
bool operator()(const ProfileInfo::EdgeWeight X,
const ProfileInfo::EdgeWeight Y) const {
if (X.second > Y.second) return true;
if (X.second < Y.second) return false;
// It would be enough to just compare the weights of the edges and be
// done. With edges of the same weight this may lead to a different MST
// each time the MST is created. To have more stable sorting (and thus
// more stable MSTs) furhter sort the edges.
if (X.first.first != 0 && Y.first.first == 0) return true;
if (X.first.first == 0 && Y.first.first != 0) return false;
if (X.first.first == 0 && Y.first.first == 0) return false;
if (X.first.first->size() > Y.first.first->size()) return true;
if (X.first.first->size() < Y.first.first->size()) return false;
if (X.first.second != 0 && Y.first.second == 0) return true;
if (X.first.second == 0 && Y.first.second != 0) return false;
if (X.first.second == 0 && Y.first.second == 0) return false;
if (X.first.second->size() > Y.first.second->size()) return true;
if (X.first.second->size() < Y.first.second->size()) return false;
return false;
}
};
}
static void inline printMSTEdge(ProfileInfo::EdgeWeight E,
const char *M) {
DEBUG(errs() << "--Edge " << E.first
<<" (Weight "<< format("%g",E.second) << ") "
<< (M) << "\n");
}
// MaximumSpanningTree() - Takes a function and returns a spanning tree
// according to the currently active profiling information, the leaf edges are
// NOT in the MST. MaximumSpanningTree uses the algorithm of Kruskal.
MaximumSpanningTree::MaximumSpanningTree(std::vector<ProfileInfo::EdgeWeight>
&EdgeVector) {
std::sort(EdgeVector.begin(), EdgeVector.end(), EdgeWeightCompare());
// Create spanning tree, Forest contains a special data structure
// that makes checking if two nodes are already in a common (sub-)tree
// fast and cheap.
EquivalenceClasses<const BasicBlock*> Forest;
for (std::vector<ProfileInfo::EdgeWeight>::iterator bbi = EdgeVector.begin(),
bbe = EdgeVector.end(); bbi != bbe; ++bbi) {
Forest.insert(bbi->first.first);
Forest.insert(bbi->first.second);
}
Forest.insert(0);
// Iterate over the sorted edges, biggest first.
for (std::vector<ProfileInfo::EdgeWeight>::iterator bbi = EdgeVector.begin(),
bbe = EdgeVector.end(); bbi != bbe; ++bbi) {
ProfileInfo::Edge e = (*bbi).first;
if (Forest.findLeader(e.first) != Forest.findLeader(e.second)) {
Forest.unionSets(e.first, e.second);
// So we know now that the edge is not already in a subtree (and not
// (0,entry)), so we push the edge to the MST if it has some successors.
MST.push_back(e);
printMSTEdge(*bbi,"in MST");
} else {
// This edge is either (0,entry) or (BB,0) or would create a circle in a
// subtree.
printMSTEdge(*bbi,"*not* in MST");
}
}
// Sort the MST edges.
std::stable_sort(MST.begin(),MST.end());
}
MaximumSpanningTree::MaxSpanTree::iterator MaximumSpanningTree::begin() {
return MST.begin();
}
MaximumSpanningTree::MaxSpanTree::iterator MaximumSpanningTree::end() {
return MST.end();
}
void MaximumSpanningTree::dump() {
errs()<<"{";
for ( MaxSpanTree::iterator ei = MST.begin(), ee = MST.end();
ei!=ee; ++ei ) {
errs()<<"("<<((*ei).first?(*ei).first->getNameStr():"0")<<",";
errs()<<(*ei).second->getNameStr()<<")";
}
errs()<<"}\n";
}
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