llvm-6502/include/llvm/Analysis/LoopInfoImpl.h
2012-09-05 17:55:46 +00:00

570 lines
21 KiB
C++

//===- llvm/Analysis/LoopInfoImpl.h - Natural Loop Calculator ---*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This is the generic implementation of LoopInfo used for both Loops and
// MachineLoops.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_LOOP_INFO_IMPL_H
#define LLVM_ANALYSIS_LOOP_INFO_IMPL_H
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/ADT/PostOrderIterator.h"
namespace llvm {
//===----------------------------------------------------------------------===//
// APIs for simple analysis of the loop. See header notes.
/// getExitingBlocks - Return all blocks inside the loop that have successors
/// outside of the loop. These are the blocks _inside of the current loop_
/// which branch out. The returned list is always unique.
///
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::
getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const {
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
std::sort(LoopBBs.begin(), LoopBBs.end());
typedef GraphTraits<BlockT*> BlockTraits;
for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI)
for (typename BlockTraits::ChildIteratorType I =
BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
I != E; ++I)
if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I)) {
// Not in current loop? It must be an exit block.
ExitingBlocks.push_back(*BI);
break;
}
}
/// getExitingBlock - If getExitingBlocks would return exactly one block,
/// return that block. Otherwise return null.
template<class BlockT, class LoopT>
BlockT *LoopBase<BlockT, LoopT>::getExitingBlock() const {
SmallVector<BlockT*, 8> ExitingBlocks;
getExitingBlocks(ExitingBlocks);
if (ExitingBlocks.size() == 1)
return ExitingBlocks[0];
return 0;
}
/// getExitBlocks - Return all of the successor blocks of this loop. These
/// are the blocks _outside of the current loop_ which are branched to.
///
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::
getExitBlocks(SmallVectorImpl<BlockT*> &ExitBlocks) const {
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
std::sort(LoopBBs.begin(), LoopBBs.end());
typedef GraphTraits<BlockT*> BlockTraits;
for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI)
for (typename BlockTraits::ChildIteratorType I =
BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
I != E; ++I)
if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
// Not in current loop? It must be an exit block.
ExitBlocks.push_back(*I);
}
/// getExitBlock - If getExitBlocks would return exactly one block,
/// return that block. Otherwise return null.
template<class BlockT, class LoopT>
BlockT *LoopBase<BlockT, LoopT>::getExitBlock() const {
SmallVector<BlockT*, 8> ExitBlocks;
getExitBlocks(ExitBlocks);
if (ExitBlocks.size() == 1)
return ExitBlocks[0];
return 0;
}
/// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::
getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const {
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
array_pod_sort(LoopBBs.begin(), LoopBBs.end());
typedef GraphTraits<BlockT*> BlockTraits;
for (block_iterator BI = block_begin(), BE = block_end(); BI != BE; ++BI)
for (typename BlockTraits::ChildIteratorType I =
BlockTraits::child_begin(*BI), E = BlockTraits::child_end(*BI);
I != E; ++I)
if (!std::binary_search(LoopBBs.begin(), LoopBBs.end(), *I))
// Not in current loop? It must be an exit block.
ExitEdges.push_back(Edge(*BI, *I));
}
/// 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.
///
template<class BlockT, class LoopT>
BlockT *LoopBase<BlockT, LoopT>::getLoopPreheader() const {
// Keep track of nodes outside the loop branching to the header...
BlockT *Out = getLoopPredecessor();
if (!Out) return 0;
// Make sure there is only one exit out of the preheader.
typedef GraphTraits<BlockT*> BlockTraits;
typename BlockTraits::ChildIteratorType SI = BlockTraits::child_begin(Out);
++SI;
if (SI != BlockTraits::child_end(Out))
return 0; // Multiple exits from the block, must not be a preheader.
// The predecessor has exactly one successor, so it is a preheader.
return Out;
}
/// getLoopPredecessor - If the given loop's header has exactly one unique
/// predecessor outside the loop, return it. Otherwise return null.
/// This is less strict that the loop "preheader" concept, which requires
/// the predecessor to have exactly one successor.
///
template<class BlockT, class LoopT>
BlockT *LoopBase<BlockT, LoopT>::getLoopPredecessor() const {
// Keep track of nodes outside the loop branching to the header...
BlockT *Out = 0;
// Loop over the predecessors of the header node...
BlockT *Header = getHeader();
typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
for (typename InvBlockTraits::ChildIteratorType PI =
InvBlockTraits::child_begin(Header),
PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) {
typename InvBlockTraits::NodeType *N = *PI;
if (!contains(N)) { // If the block is not in the loop...
if (Out && Out != N)
return 0; // Multiple predecessors outside the loop
Out = N;
}
}
// Make sure there is only one exit out of the preheader.
assert(Out && "Header of loop has no predecessors from outside loop?");
return Out;
}
/// getLoopLatch - If there is a single latch block for this loop, return it.
/// A latch block is a block that contains a branch back to the header.
template<class BlockT, class LoopT>
BlockT *LoopBase<BlockT, LoopT>::getLoopLatch() const {
BlockT *Header = getHeader();
typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
typename InvBlockTraits::ChildIteratorType PI =
InvBlockTraits::child_begin(Header);
typename InvBlockTraits::ChildIteratorType PE =
InvBlockTraits::child_end(Header);
BlockT *Latch = 0;
for (; PI != PE; ++PI) {
typename InvBlockTraits::NodeType *N = *PI;
if (contains(N)) {
if (Latch) return 0;
Latch = N;
}
}
return Latch;
}
//===----------------------------------------------------------------------===//
// APIs for updating loop information after changing the CFG
//
/// addBasicBlockToLoop - This method 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.
///
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::
addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LIB) {
assert((Blocks.empty() || LIB[getHeader()] == this) &&
"Incorrect LI specified for this loop!");
assert(NewBB && "Cannot add a null basic block to the loop!");
assert(LIB[NewBB] == 0 && "BasicBlock already in the loop!");
LoopT *L = static_cast<LoopT *>(this);
// Add the loop mapping to the LoopInfo object...
LIB.BBMap[NewBB] = L;
// Add the basic block to this loop and all parent loops...
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 pointer of OldChild to be null and the NewChild to be this loop.
/// This updates the loop depth of the new child.
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::
replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild) {
assert(OldChild->ParentLoop == this && "This loop is already broken!");
assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
typename std::vector<LoopT *>::iterator I =
std::find(SubLoops.begin(), SubLoops.end(), OldChild);
assert(I != SubLoops.end() && "OldChild not in loop!");
*I = NewChild;
OldChild->ParentLoop = 0;
NewChild->ParentLoop = static_cast<LoopT *>(this);
}
/// verifyLoop - Verify loop structure
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::verifyLoop() const {
#ifndef NDEBUG
assert(!Blocks.empty() && "Loop header is missing");
// Setup for using a depth-first iterator to visit every block in the loop.
SmallVector<BlockT*, 8> ExitBBs;
getExitBlocks(ExitBBs);
llvm::SmallPtrSet<BlockT*, 8> VisitSet;
VisitSet.insert(ExitBBs.begin(), ExitBBs.end());
df_ext_iterator<BlockT*, llvm::SmallPtrSet<BlockT*, 8> >
BI = df_ext_begin(getHeader(), VisitSet),
BE = df_ext_end(getHeader(), VisitSet);
// Keep track of the number of BBs visited.
unsigned NumVisited = 0;
// Sort the blocks vector so that we can use binary search to do quick
// lookups.
SmallVector<BlockT*, 128> LoopBBs(block_begin(), block_end());
std::sort(LoopBBs.begin(), LoopBBs.end());
// Check the individual blocks.
for ( ; BI != BE; ++BI) {
BlockT *BB = *BI;
bool HasInsideLoopSuccs = false;
bool HasInsideLoopPreds = false;
SmallVector<BlockT *, 2> OutsideLoopPreds;
typedef GraphTraits<BlockT*> BlockTraits;
for (typename BlockTraits::ChildIteratorType SI =
BlockTraits::child_begin(BB), SE = BlockTraits::child_end(BB);
SI != SE; ++SI)
if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), *SI)) {
HasInsideLoopSuccs = true;
break;
}
typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
for (typename InvBlockTraits::ChildIteratorType PI =
InvBlockTraits::child_begin(BB), PE = InvBlockTraits::child_end(BB);
PI != PE; ++PI) {
BlockT *N = *PI;
if (std::binary_search(LoopBBs.begin(), LoopBBs.end(), N))
HasInsideLoopPreds = true;
else
OutsideLoopPreds.push_back(N);
}
if (BB == getHeader()) {
assert(!OutsideLoopPreds.empty() && "Loop is unreachable!");
} else if (!OutsideLoopPreds.empty()) {
// A non-header loop shouldn't be reachable from outside the loop,
// though it is permitted if the predecessor is not itself actually
// reachable.
BlockT *EntryBB = BB->getParent()->begin();
for (df_iterator<BlockT *> NI = df_begin(EntryBB),
NE = df_end(EntryBB); NI != NE; ++NI)
for (unsigned i = 0, e = OutsideLoopPreds.size(); i != e; ++i)
assert(*NI != OutsideLoopPreds[i] &&
"Loop has multiple entry points!");
}
assert(HasInsideLoopPreds && "Loop block has no in-loop predecessors!");
assert(HasInsideLoopSuccs && "Loop block has no in-loop successors!");
assert(BB != getHeader()->getParent()->begin() &&
"Loop contains function entry block!");
NumVisited++;
}
assert(NumVisited == getNumBlocks() && "Unreachable block in loop");
// Check the subloops.
for (iterator I = begin(), E = end(); I != E; ++I)
// Each block in each subloop should be contained within this loop.
for (block_iterator BI = (*I)->block_begin(), BE = (*I)->block_end();
BI != BE; ++BI) {
assert(std::binary_search(LoopBBs.begin(), LoopBBs.end(), *BI) &&
"Loop does not contain all the blocks of a subloop!");
}
// Check the parent loop pointer.
if (ParentLoop) {
assert(std::find(ParentLoop->begin(), ParentLoop->end(), this) !=
ParentLoop->end() &&
"Loop is not a subloop of its parent!");
}
#endif
}
/// verifyLoop - Verify loop structure of this loop and all nested loops.
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::verifyLoopNest(
DenseSet<const LoopT*> *Loops) const {
Loops->insert(static_cast<const LoopT *>(this));
// Verify this loop.
verifyLoop();
// Verify the subloops.
for (iterator I = begin(), E = end(); I != E; ++I)
(*I)->verifyLoopNest(Loops);
}
template<class BlockT, class LoopT>
void LoopBase<BlockT, LoopT>::print(raw_ostream &OS, unsigned Depth) const {
OS.indent(Depth*2) << "Loop at depth " << getLoopDepth()
<< " containing: ";
for (unsigned i = 0; i < getBlocks().size(); ++i) {
if (i) OS << ",";
BlockT *BB = getBlocks()[i];
WriteAsOperand(OS, BB, false);
if (BB == getHeader()) OS << "<header>";
if (BB == getLoopLatch()) OS << "<latch>";
if (isLoopExiting(BB)) OS << "<exiting>";
}
OS << "\n";
for (iterator I = begin(), E = end(); I != E; ++I)
(*I)->print(OS, Depth+2);
}
//===----------------------------------------------------------------------===//
/// Stable LoopInfo Analysis - Build a loop tree using stable iterators so the
/// result does / not depend on use list (block predecessor) order.
///
/// Discover a subloop with the specified backedges such that: All blocks within
/// this loop are mapped to this loop or a subloop. And all subloops within this
/// loop have their parent loop set to this loop or a subloop.
template<class BlockT, class LoopT>
static void discoverAndMapSubloop(LoopT *L, ArrayRef<BlockT*> Backedges,
LoopInfoBase<BlockT, LoopT> *LI,
DominatorTreeBase<BlockT> &DomTree) {
typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
unsigned NumBlocks = 0;
unsigned NumSubloops = 0;
// Perform a backward CFG traversal using a worklist.
std::vector<BlockT *> ReverseCFGWorklist(Backedges.begin(), Backedges.end());
while (!ReverseCFGWorklist.empty()) {
BlockT *PredBB = ReverseCFGWorklist.back();
ReverseCFGWorklist.pop_back();
LoopT *Subloop = LI->getLoopFor(PredBB);
if (!Subloop) {
if (!DomTree.isReachableFromEntry(PredBB))
continue;
// This is an undiscovered block. Map it to the current loop.
LI->changeLoopFor(PredBB, L);
++NumBlocks;
if (PredBB == L->getHeader())
continue;
// Push all block predecessors on the worklist.
ReverseCFGWorklist.insert(ReverseCFGWorklist.end(),
InvBlockTraits::child_begin(PredBB),
InvBlockTraits::child_end(PredBB));
}
else {
// This is a discovered block. Find its outermost discovered loop.
while (LoopT *Parent = Subloop->getParentLoop())
Subloop = Parent;
// If it is already discovered to be a subloop of this loop, continue.
if (Subloop == L)
continue;
// Discover a subloop of this loop.
Subloop->setParentLoop(L);
++NumSubloops;
NumBlocks += Subloop->getBlocks().capacity();
PredBB = Subloop->getHeader();
// Continue traversal along predecessors that are not loop-back edges from
// within this subloop tree itself. Note that a predecessor may directly
// reach another subloop that is not yet discovered to be a subloop of
// this loop, which we must traverse.
for (typename InvBlockTraits::ChildIteratorType PI =
InvBlockTraits::child_begin(PredBB),
PE = InvBlockTraits::child_end(PredBB); PI != PE; ++PI) {
if (LI->getLoopFor(*PI) != Subloop)
ReverseCFGWorklist.push_back(*PI);
}
}
}
L->getSubLoopsVector().reserve(NumSubloops);
L->getBlocksVector().reserve(NumBlocks);
}
namespace {
/// Populate all loop data in a stable order during a single forward DFS.
template<class BlockT, class LoopT>
class PopulateLoopsDFS {
typedef GraphTraits<BlockT*> BlockTraits;
typedef typename BlockTraits::ChildIteratorType SuccIterTy;
LoopInfoBase<BlockT, LoopT> *LI;
DenseSet<const BlockT *> VisitedBlocks;
std::vector<std::pair<BlockT*, SuccIterTy> > DFSStack;
public:
PopulateLoopsDFS(LoopInfoBase<BlockT, LoopT> *li):
LI(li) {}
void traverse(BlockT *EntryBlock);
protected:
void insertIntoLoop(BlockT *Block);
BlockT *dfsSource() { return DFSStack.back().first; }
SuccIterTy &dfsSucc() { return DFSStack.back().second; }
SuccIterTy dfsSuccEnd() { return BlockTraits::child_end(dfsSource()); }
void pushBlock(BlockT *Block) {
DFSStack.push_back(std::make_pair(Block, BlockTraits::child_begin(Block)));
}
};
} // anonymous
/// Top-level driver for the forward DFS within the loop.
template<class BlockT, class LoopT>
void PopulateLoopsDFS<BlockT, LoopT>::traverse(BlockT *EntryBlock) {
pushBlock(EntryBlock);
VisitedBlocks.insert(EntryBlock);
while (!DFSStack.empty()) {
// Traverse the leftmost path as far as possible.
while (dfsSucc() != dfsSuccEnd()) {
BlockT *BB = *dfsSucc();
++dfsSucc();
if (!VisitedBlocks.insert(BB).second)
continue;
// Push the next DFS successor onto the stack.
pushBlock(BB);
}
// Visit the top of the stack in postorder and backtrack.
insertIntoLoop(dfsSource());
DFSStack.pop_back();
}
}
/// Add a single Block to its ancestor loops in PostOrder. If the block is a
/// subloop header, add the subloop to its parent in PostOrder, then reverse the
/// Block and Subloop vectors of the now complete subloop to achieve RPO.
template<class BlockT, class LoopT>
void PopulateLoopsDFS<BlockT, LoopT>::insertIntoLoop(BlockT *Block) {
LoopT *Subloop = LI->getLoopFor(Block);
if (Subloop && Block == Subloop->getHeader()) {
// We reach this point once per subloop after processing all the blocks in
// the subloop.
if (Subloop->getParentLoop())
Subloop->getParentLoop()->getSubLoopsVector().push_back(Subloop);
else
LI->addTopLevelLoop(Subloop);
// For convenience, Blocks and Subloops are inserted in postorder. Reverse
// the lists, except for the loop header, which is always at the beginning.
std::reverse(Subloop->getBlocksVector().begin()+1,
Subloop->getBlocksVector().end());
std::reverse(Subloop->getSubLoopsVector().begin(),
Subloop->getSubLoopsVector().end());
Subloop = Subloop->getParentLoop();
}
for (; Subloop; Subloop = Subloop->getParentLoop())
Subloop->getBlocksVector().push_back(Block);
}
/// Analyze LoopInfo discovers loops during a postorder DominatorTree traversal
/// interleaved with backward CFG traversals within each subloop
/// (discoverAndMapSubloop). The backward traversal skips inner subloops, so
/// this part of the algorithm is linear in the number of CFG edges. Subloop and
/// Block vectors are then populated during a single forward CFG traversal
/// (PopulateLoopDFS).
///
/// During the two CFG traversals each block is seen three times:
/// 1) Discovered and mapped by a reverse CFG traversal.
/// 2) Visited during a forward DFS CFG traversal.
/// 3) Reverse-inserted in the loop in postorder following forward DFS.
///
/// The Block vectors are inclusive, so step 3 requires loop-depth number of
/// insertions per block.
template<class BlockT, class LoopT>
void LoopInfoBase<BlockT, LoopT>::
Analyze(DominatorTreeBase<BlockT> &DomTree) {
// Postorder traversal of the dominator tree.
DomTreeNodeBase<BlockT>* DomRoot = DomTree.getRootNode();
for (po_iterator<DomTreeNodeBase<BlockT>*> DomIter = po_begin(DomRoot),
DomEnd = po_end(DomRoot); DomIter != DomEnd; ++DomIter) {
BlockT *Header = DomIter->getBlock();
SmallVector<BlockT *, 4> Backedges;
// Check each predecessor of the potential loop header.
typedef GraphTraits<Inverse<BlockT*> > InvBlockTraits;
for (typename InvBlockTraits::ChildIteratorType PI =
InvBlockTraits::child_begin(Header),
PE = InvBlockTraits::child_end(Header); PI != PE; ++PI) {
BlockT *Backedge = *PI;
// If Header dominates predBB, this is a new loop. Collect the backedges.
if (DomTree.dominates(Header, Backedge)
&& DomTree.isReachableFromEntry(Backedge)) {
Backedges.push_back(Backedge);
}
}
// Perform a backward CFG traversal to discover and map blocks in this loop.
if (!Backedges.empty()) {
LoopT *L = new LoopT(Header);
discoverAndMapSubloop(L, ArrayRef<BlockT*>(Backedges), this, DomTree);
}
}
// Perform a single forward CFG traversal to populate block and subloop
// vectors for all loops.
PopulateLoopsDFS<BlockT, LoopT> DFS(this);
DFS.traverse(DomRoot->getBlock());
}
// Debugging
template<class BlockT, class LoopT>
void LoopInfoBase<BlockT, LoopT>::print(raw_ostream &OS) const {
for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
TopLevelLoops[i]->print(OS);
#if 0
for (DenseMap<BasicBlock*, LoopT*>::const_iterator I = BBMap.begin(),
E = BBMap.end(); I != E; ++I)
OS << "BB '" << I->first->getName() << "' level = "
<< I->second->getLoopDepth() << "\n";
#endif
}
} // End llvm namespace
#endif