-//===- LoopInfo.cpp - Natural Loop Calculator -------------------------------=//
+//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
//
// 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
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/BasicBlock.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Assembly/Writer.h"
#include "Support/DepthFirstIterator.h"
#include <algorithm>
-bool cfg::Loop::contains(const BasicBlock *BB) const {
+namespace llvm {
+
+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();
}
-cfg::LoopInfo::LoopInfo(const DominatorSet &DS) {
- const BasicBlock *RootNode = DS.getRoot();
+bool Loop::isLoopExit(const BasicBlock *BB) const {
+ for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
+ SI != SE; ++SI) {
+ if (!contains(*SI))
+ return true;
+ }
+ return false;
+}
+
+/// getNumBackEdges - Calculate the number of back edges to the loop header.
+///
+unsigned Loop::getNumBackEdges() const {
+ unsigned NumBackEdges = 0;
+ BasicBlock *H = getHeader();
- for (df_iterator<const BasicBlock*> NI = df_begin(RootNode),
+ for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
+ if (contains(*I))
+ ++NumBackEdges;
+
+ return NumBackEdges;
+}
+
+void Loop::print(std::ostream &OS, unsigned Depth) const {
+ OS << std::string(Depth*2, ' ') << "Loop Containing: ";
+
+ for (unsigned i = 0; i < getBlocks().size(); ++i) {
+ if (i) OS << ",";
+ WriteAsOperand(OS, getBlocks()[i], false);
+ }
+ if (!ExitBlocks.empty()) {
+ OS << "\tExitBlocks: ";
+ for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
+ if (i) OS << ",";
+ WriteAsOperand(OS, getExitBlocks()[i], false);
+ }
+ }
+
+ OS << "\n";
+
+ for (iterator I = begin(), E = end(); I != E; ++I)
+ (*I)->print(OS, Depth+2);
+}
+
+void Loop::dump() const {
+ print(std::cerr);
+}
+
+
+//===----------------------------------------------------------------------===//
+// 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);
TopLevelLoops[i]->setLoopDepth(1);
}
-cfg::Loop *cfg::LoopInfo::ConsiderForLoop(const BasicBlock *BB,
- const DominatorSet &DS) {
- if (BBMap.find(BB) != BBMap.end()) return 0; // Havn't processed this node?
+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);
+#if 0
+ for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
+ E = BBMap.end(); I != E; ++I)
+ OS << "BB '" << I->first->getName() << "' level = "
+ << I->second->LoopDepth << "\n";
+#endif
+}
+
+static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
+ if (SubLoop == 0) return true;
+ if (SubLoop == ParentLoop) return false;
+ return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
+}
- std::vector<const BasicBlock *> TodoStack;
+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 (BasicBlock::pred_const_iterator I = BB->pred_begin(),
- E = BB->pred_end(); I != E; ++I)
+ // them. This identifies backedges which target this node...
+ 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...
+ if (TodoStack.empty()) return 0; // No backedges to this block...
// Create a new loop to represent this basic block...
Loop *L = new Loop(BB);
BBMap[BB] = L;
+ BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
+
while (!TodoStack.empty()) { // Process all the nodes in the loop
- const BasicBlock *X = TodoStack.back();
+ BasicBlock *X = TodoStack.back();
TodoStack.pop_back();
- if (!L->contains(X)) { // As of yet unprocessed??
- L->Blocks.push_back(X);
+ if (!L->contains(X) && // As of yet unprocessed??
+ DS.dominates(EntryBlock, X)) { // X is reachable from entry block?
+ // Check to see if this block already belongs to a loop. If this occurs
+ // then we have a case where a loop that is supposed to be a child of the
+ // current loop was processed before the current loop. When this occurs,
+ // this child loop gets added to a part of the current loop, making it a
+ // sibling to the current loop. We have to reparent this loop.
+ if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
+ if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
+ // Remove the subloop from it's current parent...
+ assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
+ Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
+ std::vector<Loop*>::iterator I =
+ std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
+ assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
+ SLP->SubLoops.erase(I); // Remove from parent...
+
+ // Add the subloop to THIS loop...
+ SubLoop->ParentLoop = L;
+ L->SubLoops.push_back(SubLoop);
+ }
+ // Normal case, add the block to our loop...
+ L->Blocks.push_back(X);
+
// Add all of the predecessors of X to the end of the work stack...
- TodoStack.insert(TodoStack.end(), X->pred_begin(), X->pred_end());
+ 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 there are any loops nested within this loop, create them now!
+ for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
+ E = L->Blocks.end(); I != E; ++I)
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));
+
+ // Add the basic blocks that comprise this loop to the BBMap so that this
+ // loop can be found for them.
+ //
+ for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
+ E = L->Blocks.end(); I != E; ++I) {
+ std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
+ if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
+ BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
}
+ // Now that we have a list of all of the child loops of this loop, check to
+ // see if any of them should actually be nested inside of each other. We can
+ // accidentally pull loops our of their parents, so we must make sure to
+ // organize the loop nests correctly now.
+ {
+ std::map<BasicBlock*, Loop*> ContainingLoops;
+ for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
+ Loop *Child = L->SubLoops[i];
+ assert(Child->getParentLoop() == L && "Not proper child loop?");
+
+ if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
+ // If there is already a loop which contains this loop, move this loop
+ // into the containing loop.
+ MoveSiblingLoopInto(Child, ContainingLoop);
+ --i; // The loop got removed from the SubLoops list.
+ } else {
+ // This is currently considered to be a top-level loop. Check to see if
+ // any of the contained blocks are loop headers for subloops we have
+ // already processed.
+ for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
+ Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
+ if (BlockLoop == 0) { // Child block not processed yet...
+ BlockLoop = Child;
+ } else if (BlockLoop != Child) {
+ Loop *SubLoop = BlockLoop;
+ // Reparent all of the blocks which used to belong to BlockLoops
+ for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
+ ContainingLoops[SubLoop->Blocks[j]] = Child;
+
+ // There is already a loop which contains this block, that means
+ // that we should reparent the loop which the block is currently
+ // considered to belong to to be a child of this loop.
+ MoveSiblingLoopInto(SubLoop, Child);
+ --i; // We just shrunk the SubLoops list.
+ }
+ }
+ }
+ }
+ }
+
+ // Now that we know all of the blocks that make up this loop, see if there are
+ // any branches to outside of the loop... building the ExitBlocks list.
+ for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
+ BE = L->Blocks.end(); BI != BE; ++BI)
+ for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
+ if (!L->contains(*I)) // Not in current loop?
+ L->ExitBlocks.push_back(*I); // It must be an exit block...
+
return L;
}
+
+/// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
+/// the NewParent Loop, instead of being a sibling of it.
+void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
+ Loop *OldParent = NewChild->getParentLoop();
+ assert(OldParent && OldParent == NewParent->getParentLoop() &&
+ NewChild != NewParent && "Not sibling loops!");
+
+ // Remove NewChild from being a child of OldParent
+ std::vector<Loop*>::iterator I =
+ std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
+ assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
+ OldParent->SubLoops.erase(I); // Remove from parent's subloops list
+ NewChild->ParentLoop = 0;
+
+ InsertLoopInto(NewChild, NewParent);
+}
+
+/// InsertLoopInto - This inserts loop L into the specified parent loop. If the
+/// parent loop contains a loop which should contain L, the loop gets inserted
+/// into L instead.
+void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
+ BasicBlock *LHeader = L->getHeader();
+ assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
+
+ // Check to see if it belongs in a child loop...
+ for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
+ if (Parent->SubLoops[i]->contains(LHeader)) {
+ InsertLoopInto(L, Parent->SubLoops[i]);
+ return;
+ }
+
+ // If not, insert it here!
+ Parent->SubLoops.push_back(L);
+ L->ParentLoop = Parent;
+}
+
+
+
+/// 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 && Out != *PI)
+ return 0; // Multiple predecessors outside the loop
+ Out = *PI;
+ }
+
+ // Make sure there is only one exit out of the preheader...
+ succ_iterator SI = succ_begin(Out);
+ ++SI;
+ if (SI != succ_end(Out))
+ return 0; // Multiple exits from the block, must not be a preheader.
+
+
+ // 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();
+ }
+}
+
+/// changeExitBlock - This method is used to update loop information. All
+/// instances of the specified Old basic block are removed from the exit list
+/// and replaced with New.
+///
+void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
+ assert(Old != New && "Cannot changeExitBlock to the same thing!");
+ assert(Old && New && "Cannot changeExitBlock to or from a null node!");
+ assert(hasExitBlock(Old) && "Old exit block not found!");
+ std::vector<BasicBlock*>::iterator
+ I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
+ while (I != ExitBlocks.end()) {
+ *I = New;
+ I = std::find(I+1, ExitBlocks.end(), Old);
+ }
+}
+
+} // End llvm namespace