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//===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
//
// This file defines the LoopInfo class that is used to identify natural loops
// and determine the loop depth of various nodes of the CFG. Note that the
// loops identified may actually be several natural loops that share the same
// header node... not just a single natural loop.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h"
#include "Support/DepthFirstIterator.h"
#include <algorithm>
AnalysisID cfg::LoopInfo::ID(AnalysisID::create<cfg::LoopInfo>());
//===----------------------------------------------------------------------===//
// cfg::Loop implementation
//
bool cfg::Loop::contains(const BasicBlock *BB) const {
return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
}
//===----------------------------------------------------------------------===//
// cfg::LoopInfo implementation
//
bool cfg::LoopInfo::runOnMethod(Method *M) {
BBMap.clear(); // Reset internal state of analysis
TopLevelLoops.clear();
Calculate(getAnalysis<DominatorSet>()); // Update
return false;
}
void cfg::LoopInfo::Calculate(const DominatorSet &DS) {
const BasicBlock *RootNode = DS.getRoot();
for (df_iterator<const BasicBlock*> NI = df_begin(RootNode),
NE = df_end(RootNode); NI != NE; ++NI)
if (Loop *L = ConsiderForLoop(*NI, DS))
TopLevelLoops.push_back(L);
for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
TopLevelLoops[i]->setLoopDepth(1);
}
void cfg::LoopInfo::getAnalysisUsageInfo(Pass::AnalysisSet &Required,
Pass::AnalysisSet &Destroyed,
Pass::AnalysisSet &Provided) {
Required.push_back(DominatorSet::ID);
Provided.push_back(ID);
}
cfg::Loop *cfg::LoopInfo::ConsiderForLoop(const BasicBlock *BB,
const DominatorSet &DS) {
if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
std::vector<const BasicBlock *> TodoStack;
// Scan the predecessors of BB, checking to see if BB dominates any of
// them.
for (pred_const_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
TodoStack.push_back(*I);
if (TodoStack.empty()) return 0; // Doesn't dominate any predecessors...
// Create a new loop to represent this basic block...
Loop *L = new Loop(BB);
BBMap[BB] = L;
while (!TodoStack.empty()) { // Process all the nodes in the loop
const BasicBlock *X = TodoStack.back();
TodoStack.pop_back();
if (!L->contains(X)) { // As of yet unprocessed??
L->Blocks.push_back(X);
// Add all of the predecessors of X to the end of the work stack...
TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
}
}
// Add the basic blocks that comprise this loop to the BBMap so that this
// loop can be found for them. Also check subsidary basic blocks to see if
// they start subloops of their own.
//
for (std::vector<const BasicBlock*>::reverse_iterator I = L->Blocks.rbegin(),
E = L->Blocks.rend(); I != E; ++I) {
// Check to see if this block starts a new loop
if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
L->SubLoops.push_back(NewLoop);
NewLoop->ParentLoop = L;
}
if (BBMap.find(*I) == BBMap.end())
BBMap.insert(std::make_pair(*I, L));
}
return L;
}
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