-//===- 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/Constants.h"
+#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Support/CFG.h"
#include "llvm/Assembly/Writer.h"
+#include "llvm/Support/CFG.h"
#include "Support/DepthFirstIterator.h"
#include <algorithm>
+#include <iostream>
+
+using namespace llvm;
static RegisterAnalysis<LoopInfo>
X("loops", "Natural Loop Construction", true);
}
bool Loop::isLoopExit(const BasicBlock *BB) const {
- for (BasicBlock::succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
+ 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 (std::vector<BasicBlock*>::const_iterator I = Blocks.begin(),
- E = Blocks.end(); I != E; ++I)
- for (BasicBlock::succ_iterator SI = succ_begin(*I), SE = succ_end(*I);
- SI != SE; ++SI)
- if (*SI == H)
- ++NumBackEdges;
-
+ 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) const {
- OS << std::string(getLoopDepth()*2, ' ') << "Loop Containing: ";
+/// isLoopInvariant - Return true if the specified value is loop invariant
+///
+bool Loop::isLoopInvariant(Value *V) const {
+ if (Instruction *I = dyn_cast<Instruction>(V))
+ return !contains(I->getParent());
+ return true; // All non-instructions are loop invariant
+}
+
+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 (unsigned i = 0, e = getSubLoops().size(); i != e; ++i)
- getSubLoops()[i]->print(OS);
+ for (iterator I = begin(), E = end(); I != E; ++I)
+ (*I)->print(OS, Depth+2);
}
void Loop::dump() const {
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 {
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";
+ << I->second->getLoopDepth() << "\n";
#endif
}
Loop *L = new Loop(BB);
BBMap[BB] = L;
+ BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
+
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??
+ 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,
NewLoop->ParentLoop = L;
}
-
// Add the basic blocks that comprise this loop to the BBMap so that this
// loop can be found for them.
//
BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
}
- // 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...
+ // 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.
+ }
+ }
+ }
+ }
+ }
+
+ 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;
+}
+
+/// changeLoopFor - Change the top-level loop that contains BB to the
+/// specified loop. This should be used by transformations that restructure
+/// the loop hierarchy tree.
+void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) {
+ Loop *&OldLoop = BBMap[BB];
+ assert(OldLoop && "Block not in a loop yet!");
+ OldLoop = L;
+}
+
+/// changeTopLevelLoop - Replace the specified loop in the top-level loops
+/// list with the indicated loop.
+void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
+ std::vector<Loop*>::iterator I = std::find(TopLevelLoops.begin(),
+ TopLevelLoops.end(), OldLoop);
+ assert(I != TopLevelLoops.end() && "Old loop not at top level!");
+ *I = NewLoop;
+ assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
+ "Loops already embedded into a subloop!");
+}
+
+/// removeLoop - This removes the specified top-level loop from this loop info
+/// object. The loop is not deleted, as it will presumably be inserted into
+/// another loop.
+Loop *LoopInfo::removeLoop(iterator I) {
+ assert(I != end() && "Cannot remove end iterator!");
+ Loop *L = *I;
+ assert(L->getParentLoop() == 0 && "Not a top-level loop!");
+ TopLevelLoops.erase(TopLevelLoops.begin() + (I-begin()));
return L;
}
+/// removeBlock - This method completely removes BB from all data structures,
+/// including all of the Loop objects it is nested in and our mapping from
+/// BasicBlocks to loops.
+void LoopInfo::removeBlock(BasicBlock *BB) {
+ std::map<BasicBlock *, Loop*>::iterator I = BBMap.find(BB);
+ if (I != BBMap.end()) {
+ for (Loop *L = I->second; L; L = L->getParentLoop())
+ L->removeBlockFromLoop(BB);
+
+ BBMap.erase(I);
+ }
+}
+
+
+//===----------------------------------------------------------------------===//
+// APIs for simple analysis of the loop.
+//
+
+/// getExitBlocks - Return all of the successor blocks of this loop. These
+/// are the blocks _outside of the current loop_ which are branched to.
+///
+void Loop::getExitBlocks(std::vector<BasicBlock*> &ExitBlocks) const {
+ for (std::vector<BasicBlock*>::const_iterator BI = Blocks.begin(),
+ BE = Blocks.end(); BI != BE; ++BI)
+ for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
+ if (!contains(*I)) // Not in current loop?
+ ExitBlocks.push_back(*I); // It must be an exit block...
+}
+
+
/// 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.
+/// header of the loop is the preheader node.
///
-/// 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).
+/// This method returns null if there is no preheader for the loop.
///
BasicBlock *Loop::getLoopPreheader() const {
// Keep track of nodes outside the loop branching to the header...
return Out;
}
+/// getCanonicalInductionVariable - Check to see if the loop has a canonical
+/// induction variable: an integer recurrence that starts at 0 and increments by
+/// one each time through the loop. If so, return the phi node that corresponds
+/// to it.
+///
+PHINode *Loop::getCanonicalInductionVariable() const {
+ BasicBlock *H = getHeader();
+
+ BasicBlock *Incoming = 0, *Backedge = 0;
+ pred_iterator PI = pred_begin(H);
+ assert(PI != pred_end(H) && "Loop must have at least one backedge!");
+ Backedge = *PI++;
+ if (PI == pred_end(H)) return 0; // dead loop
+ Incoming = *PI++;
+ if (PI != pred_end(H)) return 0; // multiple backedges?
+
+ if (contains(Incoming)) {
+ if (contains(Backedge))
+ return 0;
+ std::swap(Incoming, Backedge);
+ } else if (!contains(Backedge))
+ return 0;
+
+ // Loop over all of the PHI nodes, looking for a canonical indvar.
+ for (BasicBlock::iterator I = H->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ if (Instruction *Inc =
+ dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
+ if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
+ if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
+ if (CI->equalsInt(1))
+ return PN;
+
+ return 0;
+}
+
+/// getCanonicalInductionVariableIncrement - Return the LLVM value that holds
+/// the canonical induction variable value for the "next" iteration of the loop.
+/// This always succeeds if getCanonicalInductionVariable succeeds.
+///
+Instruction *Loop::getCanonicalInductionVariableIncrement() const {
+ if (PHINode *PN = getCanonicalInductionVariable()) {
+ bool P1InLoop = contains(PN->getIncomingBlock(1));
+ return cast<Instruction>(PN->getIncomingValue(P1InLoop));
+ }
+ return 0;
+}
+
+/// getTripCount - Return a loop-invariant LLVM value indicating the number of
+/// times the loop will be executed. Note that this means that the backedge of
+/// the loop executes N-1 times. If the trip-count cannot be determined, this
+/// returns null.
+///
+Value *Loop::getTripCount() const {
+ // Canonical loops will end with a 'setne I, V', where I is the incremented
+ // canonical induction variable and V is the trip count of the loop.
+ Instruction *Inc = getCanonicalInductionVariableIncrement();
+ if (Inc == 0) return 0;
+ PHINode *IV = cast<PHINode>(Inc->getOperand(0));
+
+ BasicBlock *BackedgeBlock =
+ IV->getIncomingBlock(contains(IV->getIncomingBlock(1)));
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(BackedgeBlock->getTerminator()))
+ if (BI->isConditional())
+ if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
+ if (SCI->getOperand(0) == Inc)
+ if (BI->getSuccessor(0) == getHeader()) {
+ if (SCI->getOpcode() == Instruction::SetNE)
+ return SCI->getOperand(1);
+ } else if (SCI->getOpcode() == Instruction::SetEQ) {
+ return SCI->getOperand(1);
+ }
+
+ return 0;
+}
+
+
+//===-------------------------------------------------------------------===//
+// APIs for updating loop information after changing the CFG
+//
+
/// 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
/// 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((Blocks.empty() || 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!");
}
}
-/// 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.
+/// replaceChildLoopWith - This is used when splitting loops up. It replaces
+/// the OldChild entry in our children list with NewChild, and updates the
+/// parent pointers of the two loops as appropriate.
+void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
+ assert(OldChild->ParentLoop == this && "This loop is already broken!");
+ assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
+ std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
+ OldChild);
+ assert(I != SubLoops.end() && "OldChild not in loop!");
+ *I = NewChild;
+ OldChild->ParentLoop = 0;
+ NewChild->ParentLoop = this;
+}
+
+/// addChildLoop - Add the specified loop to be a child of this loop.
///
-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);
- }
+void Loop::addChildLoop(Loop *NewChild) {
+ assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
+ NewChild->ParentLoop = this;
+ SubLoops.push_back(NewChild);
+}
+
+template<typename T>
+static void RemoveFromVector(std::vector<T*> &V, T *N) {
+ typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
+ assert(I != V.end() && "N is not in this list!");
+ V.erase(I);
+}
+
+/// removeChildLoop - This removes the specified child from being a subloop of
+/// this loop. The loop is not deleted, as it will presumably be inserted
+/// into another loop.
+Loop *Loop::removeChildLoop(iterator I) {
+ assert(I != SubLoops.end() && "Cannot remove end iterator!");
+ Loop *Child = *I;
+ assert(Child->ParentLoop == this && "Child is not a child of this loop!");
+ SubLoops.erase(SubLoops.begin()+(I-begin()));
+ Child->ParentLoop = 0;
+ return Child;
+}
+
+
+/// removeBlockFromLoop - This removes the specified basic block from the
+/// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
+/// does not update the mapping in the LoopInfo class.
+void Loop::removeBlockFromLoop(BasicBlock *BB) {
+ RemoveFromVector(Blocks, BB);
}
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