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llvm-project/llvm/lib/Analysis/LoopInfo.cpp

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//===- 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
// 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/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include <algorithm>
#include <iostream>
using namespace llvm;
static RegisterAnalysis<LoopInfo>
X("loops", "Natural Loop Construction", true);
//===----------------------------------------------------------------------===//
// Loop implementation
//
bool Loop::contains(const BasicBlock *BB) const {
return std::find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
}
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 (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
if (contains(*I))
++NumBackEdges;
return NumBackEdges;
}
/// 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);
}
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
//
bool LoopInfo::runOnFunction(Function &) {
releaseMemory();
Calculate(getAnalysis<ETForest>()); // 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(ETForest &EF) {
BasicBlock *RootNode = EF.getRoot();
for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
NE = df_end(RootNode); NI != NE; ++NI)
if (Loop *L = ConsiderForLoop(*NI, EF))
TopLevelLoops.push_back(L);
}
void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<ETForest>();
}
void LoopInfo::print(std::ostream &OS, const Module* ) 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->getLoopDepth() << "\n";
#endif
}
static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
if (SubLoop == 0) return true;
if (SubLoop == ParentLoop) return false;
return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
}
Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, ETForest &EF) {
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. This identifies backedges which target this node...
for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
if (EF.dominates(BB, *I)) // If BB dominates it's predecessor...
TodoStack.push_back(*I);
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
BasicBlock *X = TodoStack.back();
TodoStack.pop_back();
if (!L->contains(X) && // As of yet unprocessed??
EF.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(), pred_begin(X), pred_end(X));
}
}
// 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, EF)) {
L->SubLoops.push_back(NewLoop);
NewLoop->ParentLoop = 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.
}
}
}
}
}
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.
///
/// 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...
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.
assert(Out && "Header of loop has no predecessors from outside loop?");
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;
}
/// getLoopLatch - If there is a latch block for this loop, return it. A
/// latch block is the canonical backedge for a loop. A loop header in normal
/// form has two edges into it: one from a preheader and one from a latch
/// block.
BasicBlock *Loop::getLoopLatch() const {
BasicBlock *Header = getHeader();
pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
if (PI == PE) return 0; // no preds?
BasicBlock *Latch = 0;
if (contains(*PI))
Latch = *PI;
++PI;
if (PI == PE) return 0; // only one pred?
if (contains(*PI)) {
if (Latch) return 0; // multiple backedges
Latch = *PI;
}
++PI;
if (PI != PE) return 0; // more than two preds
return Latch;
}
/// 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(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(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;
}
/// isLCSSAForm - Return true if the Loop is in LCSSA form
bool Loop::isLCSSAForm() const {
for (Loop::block_iterator BB = block_begin(), E = block_end();
BB != E; ++BB) {
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
++UI) {
BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
if (PHINode* p = dyn_cast<PHINode>(*UI)) {
unsigned OperandNo = UI.getOperandNo();
UserBB = p->getIncomingBlock(OperandNo/2);
}
if (!contains(UserBB)) {
return false;
}
}
}
return true;
}
//===-------------------------------------------------------------------===//
// 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
/// 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((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!");
// 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();
}
}
/// 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::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);
}
// Ensure this file gets linked when LoopInfo.h is used.
DEFINING_FILE_FOR(LoopInfo)
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