1 //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the LoopInfo class that is used to identify natural loops
11 // and determine the loop depth of various nodes of the CFG. A natural loop
12 // has exactly one entry-point, which is called the header. Note that natural
13 // loops may actually be several loops that share the same header node.
15 // This analysis calculates the nesting structure of loops in a function. For
16 // each natural loop identified, this analysis identifies natural loops
17 // contained entirely within the loop and the basic blocks the make up the loop.
19 // It can calculate on the fly various bits of information, for example:
21 // * whether there is a preheader for the loop
22 // * the number of back edges to the header
23 // * whether or not a particular block branches out of the loop
24 // * the successor blocks of the loop
28 // Note that this analysis specifically identifies *Loops* not cycles or SCCs
29 // in the CFG. There can be strongly connected components in the CFG which
30 // this analysis will not recognize and that will not be represented by a Loop
31 // instance. In particular, a Loop might be inside such a non-loop SCC, or a
32 // non-loop SCC might contain a sub-SCC which is a Loop.
34 //===----------------------------------------------------------------------===//
36 #ifndef LLVM_ANALYSIS_LOOPINFO_H
37 #define LLVM_ANALYSIS_LOOPINFO_H
39 #include "llvm/ADT/DenseMap.h"
40 #include "llvm/ADT/DenseSet.h"
41 #include "llvm/ADT/GraphTraits.h"
42 #include "llvm/ADT/SmallPtrSet.h"
43 #include "llvm/ADT/SmallVector.h"
44 #include "llvm/IR/CFG.h"
45 #include "llvm/IR/Instruction.h"
46 #include "llvm/IR/Instructions.h"
47 #include "llvm/IR/PassManager.h"
48 #include "llvm/Pass.h"
49 #include "llvm/Support/Allocator.h"
61 template <class N, bool IsPostDom> class DominatorTreeBase;
62 template <class N, class M> class LoopInfoBase;
63 template <class N, class M> class LoopBase;
65 //===----------------------------------------------------------------------===//
66 /// Instances of this class are used to represent loops that are detected in the
69 template <class BlockT, class LoopT> class LoopBase {
71 // Loops contained entirely within this one.
72 std::vector<LoopT *> SubLoops;
74 // The list of blocks in this loop. First entry is the header node.
75 std::vector<BlockT *> Blocks;
77 SmallPtrSet<const BlockT *, 8> DenseBlockSet;
79 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
80 /// Indicator that this loop is no longer a valid loop.
81 bool IsInvalid = false;
84 LoopBase(const LoopBase<BlockT, LoopT> &) = delete;
85 const LoopBase<BlockT, LoopT> &
86 operator=(const LoopBase<BlockT, LoopT> &) = delete;
89 /// Return the nesting level of this loop. An outer-most loop has depth 1,
90 /// for consistency with loop depth values used for basic blocks, where depth
91 /// 0 is used for blocks not inside any loops.
92 unsigned getLoopDepth() const {
93 assert(!isInvalid() && "Loop not in a valid state!");
95 for (const LoopT *CurLoop = ParentLoop; CurLoop;
96 CurLoop = CurLoop->ParentLoop)
100 BlockT *getHeader() const { return getBlocks().front(); }
101 LoopT *getParentLoop() const { return ParentLoop; }
103 /// This is a raw interface for bypassing addChildLoop.
104 void setParentLoop(LoopT *L) {
105 assert(!isInvalid() && "Loop not in a valid state!");
109 /// Return true if the specified loop is contained within in this loop.
110 bool contains(const LoopT *L) const {
111 assert(!isInvalid() && "Loop not in a valid state!");
116 return contains(L->getParentLoop());
119 /// Return true if the specified basic block is in this loop.
120 bool contains(const BlockT *BB) const {
121 assert(!isInvalid() && "Loop not in a valid state!");
122 return DenseBlockSet.count(BB);
125 /// Return true if the specified instruction is in this loop.
126 template <class InstT> bool contains(const InstT *Inst) const {
127 return contains(Inst->getParent());
130 /// Return the loops contained entirely within this loop.
131 const std::vector<LoopT *> &getSubLoops() const {
132 assert(!isInvalid() && "Loop not in a valid state!");
135 std::vector<LoopT *> &getSubLoopsVector() {
136 assert(!isInvalid() && "Loop not in a valid state!");
139 typedef typename std::vector<LoopT *>::const_iterator iterator;
141 typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
142 iterator begin() const { return getSubLoops().begin(); }
143 iterator end() const { return getSubLoops().end(); }
144 reverse_iterator rbegin() const { return getSubLoops().rbegin(); }
145 reverse_iterator rend() const { return getSubLoops().rend(); }
146 bool empty() const { return getSubLoops().empty(); }
148 /// Get a list of the basic blocks which make up this loop.
149 ArrayRef<BlockT *> getBlocks() const {
150 assert(!isInvalid() && "Loop not in a valid state!");
153 typedef typename ArrayRef<BlockT *>::const_iterator block_iterator;
154 block_iterator block_begin() const { return getBlocks().begin(); }
155 block_iterator block_end() const { return getBlocks().end(); }
156 inline iterator_range<block_iterator> blocks() const {
157 assert(!isInvalid() && "Loop not in a valid state!");
158 return make_range(block_begin(), block_end());
161 /// Get the number of blocks in this loop in constant time.
162 /// Invalidate the loop, indicating that it is no longer a loop.
163 unsigned getNumBlocks() const {
164 assert(!isInvalid() && "Loop not in a valid state!");
165 return Blocks.size();
168 /// Return a direct, mutable handle to the blocks vector so that we can
169 /// mutate it efficiently with techniques like `std::remove`.
170 std::vector<BlockT *> &getBlocksVector() {
171 assert(!isInvalid() && "Loop not in a valid state!");
174 /// Return a direct, mutable handle to the blocks set so that we can
175 /// mutate it efficiently.
176 SmallPtrSetImpl<const BlockT *> &getBlocksSet() {
177 assert(!isInvalid() && "Loop not in a valid state!");
178 return DenseBlockSet;
181 /// Return a direct, immutable handle to the blocks set.
182 const SmallPtrSetImpl<const BlockT *> &getBlocksSet() const {
183 assert(!isInvalid() && "Loop not in a valid state!");
184 return DenseBlockSet;
187 /// Return true if this loop is no longer valid. The only valid use of this
188 /// helper is "assert(L.isInvalid())" or equivalent, since IsInvalid is set to
189 /// true by the destructor. In other words, if this accessor returns true,
190 /// the caller has already triggered UB by calling this accessor; and so it
191 /// can only be called in a context where a return value of true indicates a
192 /// programmer error.
193 bool isInvalid() const {
194 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
201 /// True if terminator in the block can branch to another block that is
202 /// outside of the current loop.
203 bool isLoopExiting(const BlockT *BB) const {
204 assert(!isInvalid() && "Loop not in a valid state!");
205 for (const auto &Succ : children<const BlockT *>(BB)) {
212 /// Returns true if \p BB is a loop-latch.
213 /// A latch block is a block that contains a branch back to the header.
214 /// This function is useful when there are multiple latches in a loop
215 /// because \fn getLoopLatch will return nullptr in that case.
216 bool isLoopLatch(const BlockT *BB) const {
217 assert(!isInvalid() && "Loop not in a valid state!");
218 assert(contains(BB) && "block does not belong to the loop");
220 BlockT *Header = getHeader();
221 auto PredBegin = GraphTraits<Inverse<BlockT *>>::child_begin(Header);
222 auto PredEnd = GraphTraits<Inverse<BlockT *>>::child_end(Header);
223 return std::find(PredBegin, PredEnd, BB) != PredEnd;
226 /// Calculate the number of back edges to the loop header.
227 unsigned getNumBackEdges() const {
228 assert(!isInvalid() && "Loop not in a valid state!");
229 unsigned NumBackEdges = 0;
230 BlockT *H = getHeader();
232 for (const auto Pred : children<Inverse<BlockT *>>(H))
239 //===--------------------------------------------------------------------===//
240 // APIs for simple analysis of the loop.
242 // Note that all of these methods can fail on general loops (ie, there may not
243 // be a preheader, etc). For best success, the loop simplification and
244 // induction variable canonicalization pass should be used to normalize loops
245 // for easy analysis. These methods assume canonical loops.
247 /// Return all blocks inside the loop that have successors outside of the
248 /// loop. These are the blocks _inside of the current loop_ which branch out.
249 /// The returned list is always unique.
250 void getExitingBlocks(SmallVectorImpl<BlockT *> &ExitingBlocks) const;
252 /// If getExitingBlocks would return exactly one block, return that block.
253 /// Otherwise return null.
254 BlockT *getExitingBlock() const;
256 /// Return all of the successor blocks of this loop. These are the blocks
257 /// _outside of the current loop_ which are branched to.
258 void getExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
260 /// If getExitBlocks would return exactly one block, return that block.
261 /// Otherwise return null.
262 BlockT *getExitBlock() const;
264 /// Return true if no exit block for the loop has a predecessor that is
265 /// outside the loop.
266 bool hasDedicatedExits() const;
268 /// Return all unique successor blocks of this loop.
269 /// These are the blocks _outside of the current loop_ which are branched to.
270 /// This assumes that loop exits are in canonical form, i.e. all exits are
272 void getUniqueExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
274 /// If getUniqueExitBlocks would return exactly one block, return that block.
275 /// Otherwise return null.
276 BlockT *getUniqueExitBlock() const;
279 typedef std::pair<const BlockT *, const BlockT *> Edge;
281 /// Return all pairs of (_inside_block_,_outside_block_).
282 void getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const;
284 /// If there is a preheader for this loop, return it. A loop has a preheader
285 /// if there is only one edge to the header of the loop from outside of the
286 /// loop. If this is the case, the block branching to the header of the loop
287 /// is the preheader node.
289 /// This method returns null if there is no preheader for the loop.
290 BlockT *getLoopPreheader() const;
292 /// If the given loop's header has exactly one unique predecessor outside the
293 /// loop, return it. Otherwise return null.
294 /// This is less strict that the loop "preheader" concept, which requires
295 /// the predecessor to have exactly one successor.
296 BlockT *getLoopPredecessor() const;
298 /// If there is a single latch block for this loop, return it.
299 /// A latch block is a block that contains a branch back to the header.
300 BlockT *getLoopLatch() const;
302 /// Return all loop latch blocks of this loop. A latch block is a block that
303 /// contains a branch back to the header.
304 void getLoopLatches(SmallVectorImpl<BlockT *> &LoopLatches) const {
305 assert(!isInvalid() && "Loop not in a valid state!");
306 BlockT *H = getHeader();
307 for (const auto Pred : children<Inverse<BlockT *>>(H))
309 LoopLatches.push_back(Pred);
312 //===--------------------------------------------------------------------===//
313 // APIs for updating loop information after changing the CFG
316 /// This method is used by other analyses to update loop information.
317 /// NewBB is set to be a new member of the current loop.
318 /// Because of this, it is added as a member of all parent loops, and is added
319 /// to the specified LoopInfo object as being in the current basic block. It
320 /// is not valid to replace the loop header with this method.
321 void addBasicBlockToLoop(BlockT *NewBB, LoopInfoBase<BlockT, LoopT> &LI);
323 /// This is used when splitting loops up. It replaces the OldChild entry in
324 /// our children list with NewChild, and updates the parent pointer of
325 /// OldChild to be null and the NewChild to be this loop.
326 /// This updates the loop depth of the new child.
327 void replaceChildLoopWith(LoopT *OldChild, LoopT *NewChild);
329 /// Add the specified loop to be a child of this loop.
330 /// This updates the loop depth of the new child.
331 void addChildLoop(LoopT *NewChild) {
332 assert(!isInvalid() && "Loop not in a valid state!");
333 assert(!NewChild->ParentLoop && "NewChild already has a parent!");
334 NewChild->ParentLoop = static_cast<LoopT *>(this);
335 SubLoops.push_back(NewChild);
338 /// This removes the specified child from being a subloop of this loop. The
339 /// loop is not deleted, as it will presumably be inserted into another loop.
340 LoopT *removeChildLoop(iterator I) {
341 assert(!isInvalid() && "Loop not in a valid state!");
342 assert(I != SubLoops.end() && "Cannot remove end iterator!");
344 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
345 SubLoops.erase(SubLoops.begin() + (I - begin()));
346 Child->ParentLoop = nullptr;
350 /// This removes the specified child from being a subloop of this loop. The
351 /// loop is not deleted, as it will presumably be inserted into another loop.
352 LoopT *removeChildLoop(LoopT *Child) {
353 return removeChildLoop(llvm::find(*this, Child));
356 /// This adds a basic block directly to the basic block list.
357 /// This should only be used by transformations that create new loops. Other
358 /// transformations should use addBasicBlockToLoop.
359 void addBlockEntry(BlockT *BB) {
360 assert(!isInvalid() && "Loop not in a valid state!");
361 Blocks.push_back(BB);
362 DenseBlockSet.insert(BB);
365 /// interface to reverse Blocks[from, end of loop] in this loop
366 void reverseBlock(unsigned from) {
367 assert(!isInvalid() && "Loop not in a valid state!");
368 std::reverse(Blocks.begin() + from, Blocks.end());
371 /// interface to do reserve() for Blocks
372 void reserveBlocks(unsigned size) {
373 assert(!isInvalid() && "Loop not in a valid state!");
374 Blocks.reserve(size);
377 /// This method is used to move BB (which must be part of this loop) to be the
378 /// loop header of the loop (the block that dominates all others).
379 void moveToHeader(BlockT *BB) {
380 assert(!isInvalid() && "Loop not in a valid state!");
383 for (unsigned i = 0;; ++i) {
384 assert(i != Blocks.size() && "Loop does not contain BB!");
385 if (Blocks[i] == BB) {
386 Blocks[i] = Blocks[0];
393 /// This removes the specified basic block from the current loop, updating the
394 /// Blocks as appropriate. This does not update the mapping in the LoopInfo
396 void removeBlockFromLoop(BlockT *BB) {
397 assert(!isInvalid() && "Loop not in a valid state!");
398 auto I = find(Blocks, BB);
399 assert(I != Blocks.end() && "N is not in this list!");
402 DenseBlockSet.erase(BB);
405 /// Verify loop structure
406 void verifyLoop() const;
408 /// Verify loop structure of this loop and all nested loops.
409 void verifyLoopNest(DenseSet<const LoopT *> *Loops) const;
411 /// Print loop with all the BBs inside it.
412 void print(raw_ostream &OS, unsigned Depth = 0, bool Verbose = false) const;
415 friend class LoopInfoBase<BlockT, LoopT>;
417 /// This creates an empty loop.
418 LoopBase() : ParentLoop(nullptr) {}
420 explicit LoopBase(BlockT *BB) : ParentLoop(nullptr) {
421 Blocks.push_back(BB);
422 DenseBlockSet.insert(BB);
425 // Since loop passes like SCEV are allowed to key analysis results off of
426 // `Loop` pointers, we cannot re-use pointers within a loop pass manager.
427 // This means loop passes should not be `delete` ing `Loop` objects directly
428 // (and risk a later `Loop` allocation re-using the address of a previous one)
429 // but should be using LoopInfo::markAsRemoved, which keeps around the `Loop`
430 // pointer till the end of the lifetime of the `LoopInfo` object.
432 // To make it easier to follow this rule, we mark the destructor as
435 for (auto *SubLoop : SubLoops)
438 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
443 DenseBlockSet.clear();
444 ParentLoop = nullptr;
448 template <class BlockT, class LoopT>
449 raw_ostream &operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) {
454 // Implementation in LoopInfoImpl.h
455 extern template class LoopBase<BasicBlock, Loop>;
457 /// Represents a single loop in the control flow graph. Note that not all SCCs
458 /// in the CFG are necessarily loops.
459 class Loop : public LoopBase<BasicBlock, Loop> {
461 /// A range representing the start and end location of a loop.
468 LocRange(DebugLoc Start) : Start(std::move(Start)), End(std::move(Start)) {}
469 LocRange(DebugLoc Start, DebugLoc End)
470 : Start(std::move(Start)), End(std::move(End)) {}
472 const DebugLoc &getStart() const { return Start; }
473 const DebugLoc &getEnd() const { return End; }
477 explicit operator bool() const { return Start && End; }
480 /// Return true if the specified value is loop invariant.
481 bool isLoopInvariant(const Value *V) const;
483 /// Return true if all the operands of the specified instruction are loop
485 bool hasLoopInvariantOperands(const Instruction *I) const;
487 /// If the given value is an instruction inside of the loop and it can be
488 /// hoisted, do so to make it trivially loop-invariant.
489 /// Return true if the value after any hoisting is loop invariant. This
490 /// function can be used as a slightly more aggressive replacement for
493 /// If InsertPt is specified, it is the point to hoist instructions to.
494 /// If null, the terminator of the loop preheader is used.
495 bool makeLoopInvariant(Value *V, bool &Changed,
496 Instruction *InsertPt = nullptr) const;
498 /// If the given instruction is inside of the loop and it can be hoisted, do
499 /// so to make it trivially loop-invariant.
500 /// Return true if the instruction after any hoisting is loop invariant. This
501 /// function can be used as a slightly more aggressive replacement for
504 /// If InsertPt is specified, it is the point to hoist instructions to.
505 /// If null, the terminator of the loop preheader is used.
507 bool makeLoopInvariant(Instruction *I, bool &Changed,
508 Instruction *InsertPt = nullptr) const;
510 /// Check to see if the loop has a canonical induction variable: an integer
511 /// recurrence that starts at 0 and increments by one each time through the
512 /// loop. If so, return the phi node that corresponds to it.
514 /// The IndVarSimplify pass transforms loops to have a canonical induction
517 PHINode *getCanonicalInductionVariable() const;
519 /// Return true if the Loop is in LCSSA form.
520 bool isLCSSAForm(DominatorTree &DT) const;
522 /// Return true if this Loop and all inner subloops are in LCSSA form.
523 bool isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const;
525 /// Return true if the Loop is in the form that the LoopSimplify form
526 /// transforms loops to, which is sometimes called normal form.
527 bool isLoopSimplifyForm() const;
529 /// Return true if the loop body is safe to clone in practice.
530 bool isSafeToClone() const;
532 /// Returns true if the loop is annotated parallel.
534 /// A parallel loop can be assumed to not contain any dependencies between
535 /// iterations by the compiler. That is, any loop-carried dependency checking
536 /// can be skipped completely when parallelizing the loop on the target
537 /// machine. Thus, if the parallel loop information originates from the
538 /// programmer, e.g. via the OpenMP parallel for pragma, it is the
539 /// programmer's responsibility to ensure there are no loop-carried
540 /// dependencies. The final execution order of the instructions across
541 /// iterations is not guaranteed, thus, the end result might or might not
542 /// implement actual concurrent execution of instructions across multiple
544 bool isAnnotatedParallel() const;
546 /// Return the llvm.loop loop id metadata node for this loop if it is present.
548 /// If this loop contains the same llvm.loop metadata on each branch to the
549 /// header then the node is returned. If any latch instruction does not
550 /// contain llvm.loop or if multiple latches contain different nodes then
552 MDNode *getLoopID() const;
553 /// Set the llvm.loop loop id metadata for this loop.
555 /// The LoopID metadata node will be added to each terminator instruction in
556 /// the loop that branches to the loop header.
558 /// The LoopID metadata node should have one or more operands and the first
559 /// operand should be the node itself.
560 void setLoopID(MDNode *LoopID) const;
562 /// Add llvm.loop.unroll.disable to this loop's loop id metadata.
564 /// Remove existing unroll metadata and add unroll disable metadata to
565 /// indicate the loop has already been unrolled. This prevents a loop
566 /// from being unrolled more than is directed by a pragma if the loop
567 /// unrolling pass is run more than once (which it generally is).
568 void setLoopAlreadyUnrolled();
571 void dumpVerbose() const;
573 /// Return the debug location of the start of this loop.
574 /// This looks for a BB terminating instruction with a known debug
575 /// location by looking at the preheader and header blocks. If it
576 /// cannot find a terminating instruction with location information,
577 /// it returns an unknown location.
578 DebugLoc getStartLoc() const;
580 /// Return the source code span of the loop.
581 LocRange getLocRange() const;
583 StringRef getName() const {
584 if (BasicBlock *Header = getHeader())
585 if (Header->hasName())
586 return Header->getName();
587 return "<unnamed loop>";
593 friend class LoopInfoBase<BasicBlock, Loop>;
594 friend class LoopBase<BasicBlock, Loop>;
595 explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {}
599 //===----------------------------------------------------------------------===//
600 /// This class builds and contains all of the top-level loop
601 /// structures in the specified function.
604 template <class BlockT, class LoopT> class LoopInfoBase {
605 // BBMap - Mapping of basic blocks to the inner most loop they occur in
606 DenseMap<const BlockT *, LoopT *> BBMap;
607 std::vector<LoopT *> TopLevelLoops;
608 BumpPtrAllocator LoopAllocator;
610 friend class LoopBase<BlockT, LoopT>;
611 friend class LoopInfo;
613 void operator=(const LoopInfoBase &) = delete;
614 LoopInfoBase(const LoopInfoBase &) = delete;
618 ~LoopInfoBase() { releaseMemory(); }
620 LoopInfoBase(LoopInfoBase &&Arg)
621 : BBMap(std::move(Arg.BBMap)),
622 TopLevelLoops(std::move(Arg.TopLevelLoops)),
623 LoopAllocator(std::move(Arg.LoopAllocator)) {
624 // We have to clear the arguments top level loops as we've taken ownership.
625 Arg.TopLevelLoops.clear();
627 LoopInfoBase &operator=(LoopInfoBase &&RHS) {
628 BBMap = std::move(RHS.BBMap);
630 for (auto *L : TopLevelLoops)
633 TopLevelLoops = std::move(RHS.TopLevelLoops);
634 LoopAllocator = std::move(RHS.LoopAllocator);
635 RHS.TopLevelLoops.clear();
639 void releaseMemory() {
642 for (auto *L : TopLevelLoops)
644 TopLevelLoops.clear();
645 LoopAllocator.Reset();
648 template <typename... ArgsTy> LoopT *AllocateLoop(ArgsTy &&... Args) {
649 LoopT *Storage = LoopAllocator.Allocate<LoopT>();
650 return new (Storage) LoopT(std::forward<ArgsTy>(Args)...);
653 /// iterator/begin/end - The interface to the top-level loops in the current
656 typedef typename std::vector<LoopT *>::const_iterator iterator;
658 typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
659 iterator begin() const { return TopLevelLoops.begin(); }
660 iterator end() const { return TopLevelLoops.end(); }
661 reverse_iterator rbegin() const { return TopLevelLoops.rbegin(); }
662 reverse_iterator rend() const { return TopLevelLoops.rend(); }
663 bool empty() const { return TopLevelLoops.empty(); }
665 /// Return all of the loops in the function in preorder across the loop
666 /// nests, with siblings in forward program order.
668 /// Note that because loops form a forest of trees, preorder is equivalent to
669 /// reverse postorder.
670 SmallVector<LoopT *, 4> getLoopsInPreorder();
672 /// Return all of the loops in the function in preorder across the loop
673 /// nests, with siblings in *reverse* program order.
675 /// Note that because loops form a forest of trees, preorder is equivalent to
676 /// reverse postorder.
678 /// Also note that this is *not* a reverse preorder. Only the siblings are in
679 /// reverse program order.
680 SmallVector<LoopT *, 4> getLoopsInReverseSiblingPreorder();
682 /// Return the inner most loop that BB lives in. If a basic block is in no
683 /// loop (for example the entry node), null is returned.
684 LoopT *getLoopFor(const BlockT *BB) const { return BBMap.lookup(BB); }
686 /// Same as getLoopFor.
687 const LoopT *operator[](const BlockT *BB) const { return getLoopFor(BB); }
689 /// Return the loop nesting level of the specified block. A depth of 0 means
690 /// the block is not inside any loop.
691 unsigned getLoopDepth(const BlockT *BB) const {
692 const LoopT *L = getLoopFor(BB);
693 return L ? L->getLoopDepth() : 0;
696 // True if the block is a loop header node
697 bool isLoopHeader(const BlockT *BB) const {
698 const LoopT *L = getLoopFor(BB);
699 return L && L->getHeader() == BB;
702 /// This removes the specified top-level loop from this loop info object.
703 /// The loop is not deleted, as it will presumably be inserted into
705 LoopT *removeLoop(iterator I) {
706 assert(I != end() && "Cannot remove end iterator!");
708 assert(!L->getParentLoop() && "Not a top-level loop!");
709 TopLevelLoops.erase(TopLevelLoops.begin() + (I - begin()));
713 /// Change the top-level loop that contains BB to the specified loop.
714 /// This should be used by transformations that restructure the loop hierarchy
716 void changeLoopFor(BlockT *BB, LoopT *L) {
724 /// Replace the specified loop in the top-level loops list with the indicated
726 void changeTopLevelLoop(LoopT *OldLoop, LoopT *NewLoop) {
727 auto I = find(TopLevelLoops, OldLoop);
728 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
730 assert(!NewLoop->ParentLoop && !OldLoop->ParentLoop &&
731 "Loops already embedded into a subloop!");
734 /// This adds the specified loop to the collection of top-level loops.
735 void addTopLevelLoop(LoopT *New) {
736 assert(!New->getParentLoop() && "Loop already in subloop!");
737 TopLevelLoops.push_back(New);
740 /// This method completely removes BB from all data structures,
741 /// including all of the Loop objects it is nested in and our mapping from
742 /// BasicBlocks to loops.
743 void removeBlock(BlockT *BB) {
744 auto I = BBMap.find(BB);
745 if (I != BBMap.end()) {
746 for (LoopT *L = I->second; L; L = L->getParentLoop())
747 L->removeBlockFromLoop(BB);
755 static bool isNotAlreadyContainedIn(const LoopT *SubLoop,
756 const LoopT *ParentLoop) {
759 if (SubLoop == ParentLoop)
761 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
764 /// Create the loop forest using a stable algorithm.
765 void analyze(const DominatorTreeBase<BlockT, false> &DomTree);
768 void print(raw_ostream &OS) const;
770 void verify(const DominatorTreeBase<BlockT, false> &DomTree) const;
772 /// Destroy a loop that has been removed from the `LoopInfo` nest.
774 /// This runs the destructor of the loop object making it invalid to
775 /// reference afterward. The memory is retained so that the *pointer* to the
776 /// loop remains valid.
778 /// The caller is responsible for removing this loop from the loop nest and
779 /// otherwise disconnecting it from the broader `LoopInfo` data structures.
780 /// Callers that don't naturally handle this themselves should probably call
782 void destroy(LoopT *L) {
785 // Since LoopAllocator is a BumpPtrAllocator, this Deallocate only poisons
786 // \c L, but the pointer remains valid for non-dereferencing uses.
787 LoopAllocator.Deallocate(L);
791 // Implementation in LoopInfoImpl.h
792 extern template class LoopInfoBase<BasicBlock, Loop>;
794 class LoopInfo : public LoopInfoBase<BasicBlock, Loop> {
795 typedef LoopInfoBase<BasicBlock, Loop> BaseT;
797 friend class LoopBase<BasicBlock, Loop>;
799 void operator=(const LoopInfo &) = delete;
800 LoopInfo(const LoopInfo &) = delete;
804 explicit LoopInfo(const DominatorTreeBase<BasicBlock, false> &DomTree);
806 LoopInfo(LoopInfo &&Arg) : BaseT(std::move(static_cast<BaseT &>(Arg))) {}
807 LoopInfo &operator=(LoopInfo &&RHS) {
808 BaseT::operator=(std::move(static_cast<BaseT &>(RHS)));
812 /// Handle invalidation explicitly.
813 bool invalidate(Function &F, const PreservedAnalyses &PA,
814 FunctionAnalysisManager::Invalidator &);
816 // Most of the public interface is provided via LoopInfoBase.
818 /// Update LoopInfo after removing the last backedge from a loop. This updates
819 /// the loop forest and parent loops for each block so that \c L is no longer
820 /// referenced, but does not actually delete \c L immediately. The pointer
821 /// will remain valid until this LoopInfo's memory is released.
824 /// Returns true if replacing From with To everywhere is guaranteed to
825 /// preserve LCSSA form.
826 bool replacementPreservesLCSSAForm(Instruction *From, Value *To) {
827 // Preserving LCSSA form is only problematic if the replacing value is an
829 Instruction *I = dyn_cast<Instruction>(To);
832 // If both instructions are defined in the same basic block then replacement
833 // cannot break LCSSA form.
834 if (I->getParent() == From->getParent())
836 // If the instruction is not defined in a loop then it can safely replace
838 Loop *ToLoop = getLoopFor(I->getParent());
841 // If the replacing instruction is defined in the same loop as the original
842 // instruction, or in a loop that contains it as an inner loop, then using
843 // it as a replacement will not break LCSSA form.
844 return ToLoop->contains(getLoopFor(From->getParent()));
847 /// Checks if moving a specific instruction can break LCSSA in any loop.
849 /// Return true if moving \p Inst to before \p NewLoc will break LCSSA,
850 /// assuming that the function containing \p Inst and \p NewLoc is currently
852 bool movementPreservesLCSSAForm(Instruction *Inst, Instruction *NewLoc) {
853 assert(Inst->getFunction() == NewLoc->getFunction() &&
854 "Can't reason about IPO!");
856 auto *OldBB = Inst->getParent();
857 auto *NewBB = NewLoc->getParent();
859 // Movement within the same loop does not break LCSSA (the equality check is
860 // to avoid doing a hashtable lookup in case of intra-block movement).
864 auto *OldLoop = getLoopFor(OldBB);
865 auto *NewLoop = getLoopFor(NewBB);
867 if (OldLoop == NewLoop)
870 // Check if Outer contains Inner; with the null loop counting as the
872 auto Contains = [](const Loop *Outer, const Loop *Inner) {
873 return !Outer || Outer->contains(Inner);
876 // To check that the movement of Inst to before NewLoc does not break LCSSA,
877 // we need to check two sets of uses for possible LCSSA violations at
878 // NewLoc: the users of NewInst, and the operands of NewInst.
880 // If we know we're hoisting Inst out of an inner loop to an outer loop,
881 // then the uses *of* Inst don't need to be checked.
883 if (!Contains(NewLoop, OldLoop)) {
884 for (Use &U : Inst->uses()) {
885 auto *UI = cast<Instruction>(U.getUser());
886 auto *UBB = isa<PHINode>(UI) ? cast<PHINode>(UI)->getIncomingBlock(U)
888 if (UBB != NewBB && getLoopFor(UBB) != NewLoop)
893 // If we know we're sinking Inst from an outer loop into an inner loop, then
894 // the *operands* of Inst don't need to be checked.
896 if (!Contains(OldLoop, NewLoop)) {
897 // See below on why we can't handle phi nodes here.
898 if (isa<PHINode>(Inst))
901 for (Use &U : Inst->operands()) {
902 auto *DefI = dyn_cast<Instruction>(U.get());
906 // This would need adjustment if we allow Inst to be a phi node -- the
907 // new use block won't simply be NewBB.
909 auto *DefBlock = DefI->getParent();
910 if (DefBlock != NewBB && getLoopFor(DefBlock) != NewLoop)
919 // Allow clients to walk the list of nested loops...
920 template <> struct GraphTraits<const Loop *> {
921 typedef const Loop *NodeRef;
922 typedef LoopInfo::iterator ChildIteratorType;
924 static NodeRef getEntryNode(const Loop *L) { return L; }
925 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
926 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
929 template <> struct GraphTraits<Loop *> {
930 typedef Loop *NodeRef;
931 typedef LoopInfo::iterator ChildIteratorType;
933 static NodeRef getEntryNode(Loop *L) { return L; }
934 static ChildIteratorType child_begin(NodeRef N) { return N->begin(); }
935 static ChildIteratorType child_end(NodeRef N) { return N->end(); }
938 /// Analysis pass that exposes the \c LoopInfo for a function.
939 class LoopAnalysis : public AnalysisInfoMixin<LoopAnalysis> {
940 friend AnalysisInfoMixin<LoopAnalysis>;
941 static AnalysisKey Key;
944 typedef LoopInfo Result;
946 LoopInfo run(Function &F, FunctionAnalysisManager &AM);
949 /// Printer pass for the \c LoopAnalysis results.
950 class LoopPrinterPass : public PassInfoMixin<LoopPrinterPass> {
954 explicit LoopPrinterPass(raw_ostream &OS) : OS(OS) {}
955 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
958 /// Verifier pass for the \c LoopAnalysis results.
959 struct LoopVerifierPass : public PassInfoMixin<LoopVerifierPass> {
960 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
963 /// The legacy pass manager's analysis pass to compute loop information.
964 class LoopInfoWrapperPass : public FunctionPass {
968 static char ID; // Pass identification, replacement for typeid
970 LoopInfoWrapperPass() : FunctionPass(ID) {
971 initializeLoopInfoWrapperPassPass(*PassRegistry::getPassRegistry());
974 LoopInfo &getLoopInfo() { return LI; }
975 const LoopInfo &getLoopInfo() const { return LI; }
977 /// Calculate the natural loop information for a given function.
978 bool runOnFunction(Function &F) override;
980 void verifyAnalysis() const override;
982 void releaseMemory() override { LI.releaseMemory(); }
984 void print(raw_ostream &O, const Module *M = nullptr) const override;
986 void getAnalysisUsage(AnalysisUsage &AU) const override;
989 /// Function to print a loop's contents as LLVM's text IR assembly.
990 void printLoop(Loop &L, raw_ostream &OS, const std::string &Banner = "");
992 } // End llvm namespace