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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 "llvm/Assembly/Writer.h"
#include "Support/DepthFirstIterator.h"
#include <algorithm>
static RegisterAnalysis<LoopInfo>
X("loops", "Natural Loop Construction", true);
//===----------------------------------------------------------------------===//
// Loop implementation
//
bool Loop::contains(const BasicBlock *BB) const {
return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
}
void Loop::print(std::ostream &OS) const {
OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
for (unsigned i = 0; i < getBlocks().size(); ++i) {
if (i) OS << ",";
WriteAsOperand(OS, (const Value*)getBlocks()[i]);
}
OS << "\n";
std::copy(getSubLoops().begin(), getSubLoops().end(),
std::ostream_iterator<const Loop*>(OS, "\n"));
}
//===----------------------------------------------------------------------===//
// LoopInfo implementation
//
void LoopInfo::stub() {}
bool LoopInfo::runOnFunction(Function &) {
releaseMemory();
Calculate(getAnalysis<DominatorSet>()); // Update
return false;
}
void LoopInfo::releaseMemory() {
for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
E = TopLevelLoops.end(); I != E; ++I)
delete *I; // Delete all of the loops...
BBMap.clear(); // Reset internal state of analysis
TopLevelLoops.clear();
}
void LoopInfo::Calculate(const DominatorSet &DS) {
BasicBlock *RootNode = DS.getRoot();
for (df_iterator<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 LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<DominatorSet>();
}
void LoopInfo::print(std::ostream &OS) const {
for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
TopLevelLoops[i]->print(OS);
}
Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
std::vector<BasicBlock *> TodoStack;
// Scan the predecessors of BB, checking to see if BB dominates any of
// them.
for (pred_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
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<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;
}
/// getLoopPreheader - If there is a preheader for this loop, return it. A
/// loop has a preheader if there is only one edge to the header of the loop
/// from outside of the loop. If this is the case, the block branching to the
/// header of the loop is the preheader node. The "preheaders" pass can be
/// "Required" to ensure that there is always a preheader node for every loop.
///
/// This method returns null if there is no preheader for the loop (either
/// because the loop is dead or because multiple blocks branch to the header
/// node of this loop).
///
BasicBlock *Loop::getLoopPreheader() const {
// Keep track of nodes outside the loop branching to the header...
BasicBlock *Out = 0;
// Loop over the predecessors of the header node...
BasicBlock *Header = getHeader();
for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
PI != PE; ++PI)
if (!contains(*PI)) { // If the block is not in the loop...
if (Out) return 0; // Multiple predecessors outside the loop
Out = *PI;
}
// If there is exactly one preheader, return it. If there was zero, then Out
// is still null.
return Out;
}
/// addBasicBlockToLoop - This function is used by other analyses to update loop
/// information. NewBB is set to be a new member of the current loop. Because
/// of this, it is added as a member of all parent loops, and is added to the
/// specified LoopInfo object as being in the current basic block. It is not
/// valid to replace the loop header with this method.
///
void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!");
assert(NewBB && "Cannot add a null basic block to the loop!");
assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
// Add the loop mapping to the LoopInfo object...
LI.BBMap[NewBB] = this;
// Add the basic block to this loop and all parent loops...
Loop *L = this;
while (L) {
L->Blocks.push_back(NewBB);
L = L->getParentLoop();
}
}
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