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1 : //===- llvm/Analysis/LoopInfo.h - Natural Loop Calculator -------*- C++ -*-===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //===----------------------------------------------------------------------===//
9 : //
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.
14 : //
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.
18 : //
19 : // It can calculate on the fly various bits of information, for example:
20 : //
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
25 : // * the loop depth
26 : // * etc...
27 : //
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.
33 : //
34 : //===----------------------------------------------------------------------===//
35 :
36 : #ifndef LLVM_ANALYSIS_LOOPINFO_H
37 : #define LLVM_ANALYSIS_LOOPINFO_H
38 :
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"
50 : #include <algorithm>
51 : #include <utility>
52 :
53 : namespace llvm {
54 :
55 : class DominatorTree;
56 : class LoopInfo;
57 : class Loop;
58 : class MDNode;
59 : class PHINode;
60 : class raw_ostream;
61 : template <class N, bool IsPostDom> class DominatorTreeBase;
62 : template <class N, class M> class LoopInfoBase;
63 : template <class N, class M> class LoopBase;
64 :
65 : //===----------------------------------------------------------------------===//
66 : /// Instances of this class are used to represent loops that are detected in the
67 : /// flow graph.
68 : ///
69 : template <class BlockT, class LoopT> class LoopBase {
70 : LoopT *ParentLoop;
71 : // Loops contained entirely within this one.
72 : std::vector<LoopT *> SubLoops;
73 :
74 : // The list of blocks in this loop. First entry is the header node.
75 : std::vector<BlockT *> Blocks;
76 :
77 : SmallPtrSet<const BlockT *, 8> DenseBlockSet;
78 :
79 : #if LLVM_ENABLE_ABI_BREAKING_CHECKS
80 : /// Indicator that this loop is no longer a valid loop.
81 : bool IsInvalid = false;
82 : #endif
83 :
84 : LoopBase(const LoopBase<BlockT, LoopT> &) = delete;
85 : const LoopBase<BlockT, LoopT> &
86 : operator=(const LoopBase<BlockT, LoopT> &) = delete;
87 :
88 : public:
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 0 : unsigned getLoopDepth() const {
93 : assert(!isInvalid() && "Loop not in a valid state!");
94 : unsigned D = 1;
95 89127 : for (const LoopT *CurLoop = ParentLoop; CurLoop;
96 : CurLoop = CurLoop->ParentLoop)
97 16068 : ++D;
98 0 : return D;
99 : }
100 6502367 : BlockT *getHeader() const { return getBlocks().front(); }
101 1323201 : LoopT *getParentLoop() const { return ParentLoop; }
102 :
103 : /// This is a raw interface for bypassing addChildLoop.
104 0 : void setParentLoop(LoopT *L) {
105 : assert(!isInvalid() && "Loop not in a valid state!");
106 25212 : ParentLoop = L;
107 0 : }
108 :
109 : /// Return true if the specified loop is contained within in this loop.
110 0 : bool contains(const LoopT *L) const {
111 : assert(!isInvalid() && "Loop not in a valid state!");
112 1308099 : if (L == this)
113 : return true;
114 722442 : if (!L)
115 : return false;
116 419394 : return contains(L->getParentLoop());
117 : }
118 :
119 : /// Return true if the specified basic block is in this loop.
120 0 : bool contains(const BlockT *BB) const {
121 : assert(!isInvalid() && "Loop not in a valid state!");
122 14741609 : return DenseBlockSet.count(BB);
123 : }
124 :
125 : /// Return true if the specified instruction is in this loop.
126 : template <class InstT> bool contains(const InstT *Inst) const {
127 2226624 : return contains(Inst->getParent());
128 : }
129 :
130 : /// Return the loops contained entirely within this loop.
131 0 : const std::vector<LoopT *> &getSubLoops() const {
132 : assert(!isInvalid() && "Loop not in a valid state!");
133 47 : return SubLoops;
134 : }
135 0 : std::vector<LoopT *> &getSubLoopsVector() {
136 : assert(!isInvalid() && "Loop not in a valid state!");
137 172248 : return SubLoops;
138 : }
139 : typedef typename std::vector<LoopT *>::const_iterator iterator;
140 : typedef
141 : typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
142 185222 : iterator begin() const { return getSubLoops().begin(); }
143 199266 : iterator end() const { return getSubLoops().end(); }
144 0 : reverse_iterator rbegin() const { return getSubLoops().rbegin(); }
145 0 : reverse_iterator rend() const { return getSubLoops().rend(); }
146 0 : bool empty() const { return getSubLoops().empty(); }
147 :
148 : /// Get a list of the basic blocks which make up this loop.
149 0 : ArrayRef<BlockT *> getBlocks() const {
150 : assert(!isInvalid() && "Loop not in a valid state!");
151 0 : return Blocks;
152 : }
153 : typedef typename ArrayRef<BlockT *>::const_iterator block_iterator;
154 0 : block_iterator block_begin() const { return getBlocks().begin(); }
155 0 : block_iterator block_end() const { return getBlocks().end(); }
156 0 : inline iterator_range<block_iterator> blocks() const {
157 : assert(!isInvalid() && "Loop not in a valid state!");
158 0 : return make_range(block_begin(), block_end());
159 : }
160 :
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 0 : unsigned getNumBlocks() const {
164 : assert(!isInvalid() && "Loop not in a valid state!");
165 48814 : return Blocks.size();
166 : }
167 :
168 : /// Return a direct, mutable handle to the blocks vector so that we can
169 : /// mutate it efficiently with techniques like `std::remove`.
170 0 : std::vector<BlockT *> &getBlocksVector() {
171 : assert(!isInvalid() && "Loop not in a valid state!");
172 368 : return Blocks;
173 : }
174 : /// Return a direct, mutable handle to the blocks set so that we can
175 : /// mutate it efficiently.
176 0 : SmallPtrSetImpl<const BlockT *> &getBlocksSet() {
177 : assert(!isInvalid() && "Loop not in a valid state!");
178 0 : return DenseBlockSet;
179 : }
180 :
181 : /// Return a direct, immutable handle to the blocks set.
182 0 : const SmallPtrSetImpl<const BlockT *> &getBlocksSet() const {
183 : assert(!isInvalid() && "Loop not in a valid state!");
184 0 : return DenseBlockSet;
185 : }
186 :
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 0 : bool isInvalid() const {
194 : #if LLVM_ENABLE_ABI_BREAKING_CHECKS
195 : return IsInvalid;
196 : #else
197 0 : return false;
198 : #endif
199 : }
200 :
201 : /// True if terminator in the block can branch to another block that is
202 : /// outside of the current loop.
203 1419 : bool isLoopExiting(const BlockT *BB) const {
204 : assert(!isInvalid() && "Loop not in a valid state!");
205 476942 : for (const auto &Succ : children<const BlockT *>(BB)) {
206 362092 : if (!contains(Succ))
207 : return true;
208 : }
209 523 : return false;
210 : }
211 :
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 1419 : 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");
219 :
220 : BlockT *Header = getHeader();
221 0 : auto PredBegin = GraphTraits<Inverse<BlockT *>>::child_begin(Header);
222 : auto PredEnd = GraphTraits<Inverse<BlockT *>>::child_end(Header);
223 1419 : return std::find(PredBegin, PredEnd, BB) != PredEnd;
224 : }
225 :
226 : /// Calculate the number of back edges to the loop header.
227 0 : unsigned getNumBackEdges() const {
228 : assert(!isInvalid() && "Loop not in a valid state!");
229 : unsigned NumBackEdges = 0;
230 : BlockT *H = getHeader();
231 :
232 0 : for (const auto Pred : children<Inverse<BlockT *>>(H))
233 0 : if (contains(Pred))
234 0 : ++NumBackEdges;
235 :
236 0 : return NumBackEdges;
237 : }
238 :
239 : //===--------------------------------------------------------------------===//
240 : // APIs for simple analysis of the loop.
241 : //
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.
246 :
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;
251 :
252 : /// If getExitingBlocks would return exactly one block, return that block.
253 : /// Otherwise return null.
254 : BlockT *getExitingBlock() const;
255 :
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;
259 :
260 : /// If getExitBlocks would return exactly one block, return that block.
261 : /// Otherwise return null.
262 : BlockT *getExitBlock() const;
263 :
264 : /// Return true if no exit block for the loop has a predecessor that is
265 : /// outside the loop.
266 : bool hasDedicatedExits() const;
267 :
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
271 : /// dedicated exits.
272 : void getUniqueExitBlocks(SmallVectorImpl<BlockT *> &ExitBlocks) const;
273 :
274 : /// If getUniqueExitBlocks would return exactly one block, return that block.
275 : /// Otherwise return null.
276 : BlockT *getUniqueExitBlock() const;
277 :
278 : /// Edge type.
279 : typedef std::pair<const BlockT *, const BlockT *> Edge;
280 :
281 : /// Return all pairs of (_inside_block_,_outside_block_).
282 : void getExitEdges(SmallVectorImpl<Edge> &ExitEdges) const;
283 :
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.
288 : ///
289 : /// This method returns null if there is no preheader for the loop.
290 : BlockT *getLoopPreheader() const;
291 :
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;
297 :
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;
301 :
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 71750 : void getLoopLatches(SmallVectorImpl<BlockT *> &LoopLatches) const {
305 : assert(!isInvalid() && "Loop not in a valid state!");
306 : BlockT *H = getHeader();
307 215299 : for (const auto Pred : children<Inverse<BlockT *>>(H))
308 143549 : if (contains(Pred))
309 71794 : LoopLatches.push_back(Pred);
310 71750 : }
311 :
312 : //===--------------------------------------------------------------------===//
313 : // APIs for updating loop information after changing the CFG
314 : //
315 :
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);
322 :
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);
328 :
329 : /// Add the specified loop to be a child of this loop.
330 : /// This updates the loop depth of the new child.
331 0 : void addChildLoop(LoopT *NewChild) {
332 : assert(!isInvalid() && "Loop not in a valid state!");
333 : assert(!NewChild->ParentLoop && "NewChild already has a parent!");
334 579 : NewChild->ParentLoop = static_cast<LoopT *>(this);
335 579 : SubLoops.push_back(NewChild);
336 0 : }
337 :
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 0 : LoopT *removeChildLoop(iterator I) {
341 : assert(!isInvalid() && "Loop not in a valid state!");
342 : assert(I != SubLoops.end() && "Cannot remove end iterator!");
343 136 : LoopT *Child = *I;
344 : assert(Child->ParentLoop == this && "Child is not a child of this loop!");
345 252 : SubLoops.erase(SubLoops.begin() + (I - begin()));
346 129 : Child->ParentLoop = nullptr;
347 0 : return Child;
348 : }
349 :
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 18 : LoopT *removeChildLoop(LoopT *Child) {
353 18 : return removeChildLoop(llvm::find(*this, Child));
354 : }
355 :
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 800053 : void addBlockEntry(BlockT *BB) {
360 : assert(!isInvalid() && "Loop not in a valid state!");
361 800053 : Blocks.push_back(BB);
362 800053 : DenseBlockSet.insert(BB);
363 800053 : }
364 :
365 : /// interface to reverse Blocks[from, end of loop] in this loop
366 0 : void reverseBlock(unsigned from) {
367 : assert(!isInvalid() && "Loop not in a valid state!");
368 : std::reverse(Blocks.begin() + from, Blocks.end());
369 0 : }
370 :
371 : /// interface to do reserve() for Blocks
372 0 : void reserveBlocks(unsigned size) {
373 : assert(!isInvalid() && "Loop not in a valid state!");
374 146737 : Blocks.reserve(size);
375 0 : }
376 :
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 0 : void moveToHeader(BlockT *BB) {
380 : assert(!isInvalid() && "Loop not in a valid state!");
381 2614 : if (Blocks[0] == BB)
382 : return;
383 4866 : for (unsigned i = 0;; ++i) {
384 0 : assert(i != Blocks.size() && "Loop does not contain BB!");
385 14960 : if (Blocks[i] == BB) {
386 2614 : Blocks[i] = Blocks[0];
387 2614 : Blocks[0] = BB;
388 0 : return;
389 : }
390 : }
391 : }
392 :
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
395 : /// class.
396 41 : 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!");
400 41 : Blocks.erase(I);
401 :
402 41 : DenseBlockSet.erase(BB);
403 41 : }
404 :
405 : /// Verify loop structure
406 : void verifyLoop() const;
407 :
408 : /// Verify loop structure of this loop and all nested loops.
409 : void verifyLoopNest(DenseSet<const LoopT *> *Loops) const;
410 :
411 : /// Print loop with all the BBs inside it.
412 : void print(raw_ostream &OS, unsigned Depth = 0, bool Verbose = false) const;
413 :
414 : protected:
415 : friend class LoopInfoBase<BlockT, LoopT>;
416 :
417 : /// This creates an empty loop.
418 2374 : LoopBase() : ParentLoop(nullptr) {}
419 :
420 293260 : explicit LoopBase(BlockT *BB) : ParentLoop(nullptr) {
421 146630 : Blocks.push_back(BB);
422 146630 : DenseBlockSet.insert(BB);
423 146630 : }
424 :
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.
431 : //
432 : // To make it easier to follow this rule, we mark the destructor as
433 : // non-public.
434 147686 : ~LoopBase() {
435 172955 : for (auto *SubLoop : SubLoops)
436 25269 : SubLoop->~LoopT();
437 :
438 : #if LLVM_ENABLE_ABI_BREAKING_CHECKS
439 : IsInvalid = true;
440 : #endif
441 : SubLoops.clear();
442 : Blocks.clear();
443 147686 : DenseBlockSet.clear();
444 147686 : ParentLoop = nullptr;
445 147686 : }
446 : };
447 :
448 : template <class BlockT, class LoopT>
449 : raw_ostream &operator<<(raw_ostream &OS, const LoopBase<BlockT, LoopT> &Loop) {
450 431 : Loop.print(OS);
451 : return OS;
452 : }
453 :
454 : // Implementation in LoopInfoImpl.h
455 : extern template class LoopBase<BasicBlock, Loop>;
456 :
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> {
460 : public:
461 : /// A range representing the start and end location of a loop.
462 : class LocRange {
463 : DebugLoc Start;
464 : DebugLoc End;
465 :
466 : public:
467 : LocRange() {}
468 1929 : LocRange(DebugLoc Start) : Start(std::move(Start)), End(std::move(Start)) {}
469 4770 : LocRange(DebugLoc Start, DebugLoc End)
470 4770 : : Start(std::move(Start)), End(std::move(End)) {}
471 :
472 : const DebugLoc &getStart() const { return Start; }
473 : const DebugLoc &getEnd() const { return End; }
474 :
475 : /// Check for null.
476 : ///
477 : explicit operator bool() const { return Start && End; }
478 : };
479 :
480 : /// Return true if the specified value is loop invariant.
481 : bool isLoopInvariant(const Value *V) const;
482 :
483 : /// Return true if all the operands of the specified instruction are loop
484 : /// invariant.
485 : bool hasLoopInvariantOperands(const Instruction *I) const;
486 :
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
491 : /// isLoopInvariant.
492 : ///
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;
497 :
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
502 : /// isLoopInvariant.
503 : ///
504 : /// If InsertPt is specified, it is the point to hoist instructions to.
505 : /// If null, the terminator of the loop preheader is used.
506 : ///
507 : bool makeLoopInvariant(Instruction *I, bool &Changed,
508 : Instruction *InsertPt = nullptr) const;
509 :
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.
513 : ///
514 : /// The IndVarSimplify pass transforms loops to have a canonical induction
515 : /// variable.
516 : ///
517 : PHINode *getCanonicalInductionVariable() const;
518 :
519 : /// Return true if the Loop is in LCSSA form.
520 : bool isLCSSAForm(DominatorTree &DT) const;
521 :
522 : /// Return true if this Loop and all inner subloops are in LCSSA form.
523 : bool isRecursivelyLCSSAForm(DominatorTree &DT, const LoopInfo &LI) const;
524 :
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;
528 :
529 : /// Return true if the loop body is safe to clone in practice.
530 : bool isSafeToClone() const;
531 :
532 : /// Returns true if the loop is annotated parallel.
533 : ///
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
543 : /// iterations.
544 : bool isAnnotatedParallel() const;
545 :
546 : /// Return the llvm.loop loop id metadata node for this loop if it is present.
547 : ///
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
551 : /// 0 is returned.
552 : MDNode *getLoopID() const;
553 : /// Set the llvm.loop loop id metadata for this loop.
554 : ///
555 : /// The LoopID metadata node will be added to each terminator instruction in
556 : /// the loop that branches to the loop header.
557 : ///
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;
561 :
562 : /// Add llvm.loop.unroll.disable to this loop's loop id metadata.
563 : ///
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();
569 :
570 : void dump() const;
571 : void dumpVerbose() const;
572 :
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;
579 :
580 : /// Return the source code span of the loop.
581 : LocRange getLocRange() const;
582 :
583 26211 : StringRef getName() const {
584 26211 : if (BasicBlock *Header = getHeader())
585 26211 : if (Header->hasName())
586 7222 : return Header->getName();
587 18989 : return "<unnamed loop>";
588 : }
589 :
590 : private:
591 : Loop() = default;
592 :
593 : friend class LoopInfoBase<BasicBlock, Loop>;
594 : friend class LoopBase<BasicBlock, Loop>;
595 97350 : explicit Loop(BasicBlock *BB) : LoopBase<BasicBlock, Loop>(BB) {}
596 98429 : ~Loop() = default;
597 : };
598 :
599 : //===----------------------------------------------------------------------===//
600 : /// This class builds and contains all of the top-level loop
601 : /// structures in the specified function.
602 : ///
603 :
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;
609 :
610 : friend class LoopBase<BlockT, LoopT>;
611 : friend class LoopInfo;
612 :
613 : void operator=(const LoopInfoBase &) = delete;
614 : LoopInfoBase(const LoopInfoBase &) = delete;
615 :
616 : public:
617 221487 : LoopInfoBase() {}
618 404708 : ~LoopInfoBase() { releaseMemory(); }
619 :
620 0 : LoopInfoBase(LoopInfoBase &&Arg)
621 : : BBMap(std::move(Arg.BBMap)),
622 : TopLevelLoops(std::move(Arg.TopLevelLoops)),
623 0 : LoopAllocator(std::move(Arg.LoopAllocator)) {
624 : // We have to clear the arguments top level loops as we've taken ownership.
625 : Arg.TopLevelLoops.clear();
626 0 : }
627 0 : LoopInfoBase &operator=(LoopInfoBase &&RHS) {
628 0 : BBMap = std::move(RHS.BBMap);
629 :
630 0 : for (auto *L : TopLevelLoops)
631 : L->~LoopT();
632 :
633 0 : TopLevelLoops = std::move(RHS.TopLevelLoops);
634 0 : LoopAllocator = std::move(RHS.LoopAllocator);
635 : RHS.TopLevelLoops.clear();
636 0 : return *this;
637 : }
638 :
639 4937751 : void releaseMemory() {
640 4937751 : BBMap.clear();
641 :
642 5059223 : for (auto *L : TopLevelLoops)
643 : L->~LoopT();
644 : TopLevelLoops.clear();
645 4937752 : LoopAllocator.Reset();
646 4937752 : }
647 :
648 149004 : template <typename... ArgsTy> LoopT *AllocateLoop(ArgsTy &&... Args) {
649 149004 : LoopT *Storage = LoopAllocator.Allocate<LoopT>();
650 149004 : return new (Storage) LoopT(std::forward<ArgsTy>(Args)...);
651 : }
652 :
653 : /// iterator/begin/end - The interface to the top-level loops in the current
654 : /// function.
655 : ///
656 : typedef typename std::vector<LoopT *>::const_iterator iterator;
657 : typedef
658 : typename std::vector<LoopT *>::const_reverse_iterator reverse_iterator;
659 1705037 : iterator begin() const { return TopLevelLoops.begin(); }
660 1704955 : iterator end() const { return TopLevelLoops.end(); }
661 0 : reverse_iterator rbegin() const { return TopLevelLoops.rbegin(); }
662 0 : reverse_iterator rend() const { return TopLevelLoops.rend(); }
663 0 : bool empty() const { return TopLevelLoops.empty(); }
664 :
665 : /// Return all of the loops in the function in preorder across the loop
666 : /// nests, with siblings in forward program order.
667 : ///
668 : /// Note that because loops form a forest of trees, preorder is equivalent to
669 : /// reverse postorder.
670 : SmallVector<LoopT *, 4> getLoopsInPreorder();
671 :
672 : /// Return all of the loops in the function in preorder across the loop
673 : /// nests, with siblings in *reverse* program order.
674 : ///
675 : /// Note that because loops form a forest of trees, preorder is equivalent to
676 : /// reverse postorder.
677 : ///
678 : /// Also note that this is *not* a reverse preorder. Only the siblings are in
679 : /// reverse program order.
680 : SmallVector<LoopT *, 4> getLoopsInReverseSiblingPreorder();
681 :
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 33178981 : LoopT *getLoopFor(const BlockT *BB) const { return BBMap.lookup(BB); }
685 :
686 : /// Same as getLoopFor.
687 0 : const LoopT *operator[](const BlockT *BB) const { return getLoopFor(BB); }
688 :
689 : /// Return the loop nesting level of the specified block. A depth of 0 means
690 : /// the block is not inside any loop.
691 0 : unsigned getLoopDepth(const BlockT *BB) const {
692 : const LoopT *L = getLoopFor(BB);
693 0 : return L ? L->getLoopDepth() : 0;
694 : }
695 :
696 : // True if the block is a loop header node
697 0 : bool isLoopHeader(const BlockT *BB) const {
698 : const LoopT *L = getLoopFor(BB);
699 0 : return L && L->getHeader() == BB;
700 : }
701 :
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
704 : /// another loop.
705 0 : LoopT *removeLoop(iterator I) {
706 : assert(I != end() && "Cannot remove end iterator!");
707 0 : LoopT *L = *I;
708 : assert(!L->getParentLoop() && "Not a top-level loop!");
709 645 : TopLevelLoops.erase(TopLevelLoops.begin() + (I - begin()));
710 0 : return L;
711 : }
712 :
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
715 : /// tree.
716 749429 : void changeLoopFor(BlockT *BB, LoopT *L) {
717 749429 : if (!L) {
718 2851 : BBMap.erase(BB);
719 22 : return;
720 : }
721 749407 : BBMap[BB] = L;
722 : }
723 :
724 : /// Replace the specified loop in the top-level loops list with the indicated
725 : /// loop.
726 0 : void changeTopLevelLoop(LoopT *OldLoop, LoopT *NewLoop) {
727 : auto I = find(TopLevelLoops, OldLoop);
728 : assert(I != TopLevelLoops.end() && "Old loop not at top level!");
729 52 : *I = NewLoop;
730 : assert(!NewLoop->ParentLoop && !OldLoop->ParentLoop &&
731 : "Loops already embedded into a subloop!");
732 0 : }
733 :
734 : /// This adds the specified loop to the collection of top-level loops.
735 0 : void addTopLevelLoop(LoopT *New) {
736 : assert(!New->getParentLoop() && "Loop already in subloop!");
737 123376 : TopLevelLoops.push_back(New);
738 0 : }
739 :
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 0 : void removeBlock(BlockT *BB) {
744 0 : auto I = BBMap.find(BB);
745 0 : if (I != BBMap.end()) {
746 0 : for (LoopT *L = I->second; L; L = L->getParentLoop())
747 0 : L->removeBlockFromLoop(BB);
748 :
749 : BBMap.erase(I);
750 : }
751 0 : }
752 :
753 : // Internals
754 :
755 0 : static bool isNotAlreadyContainedIn(const LoopT *SubLoop,
756 : const LoopT *ParentLoop) {
757 0 : if (!SubLoop)
758 : return true;
759 0 : if (SubLoop == ParentLoop)
760 : return false;
761 0 : return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
762 : }
763 :
764 : /// Create the loop forest using a stable algorithm.
765 : void analyze(const DominatorTreeBase<BlockT, false> &DomTree);
766 :
767 : // Debugging
768 : void print(raw_ostream &OS) const;
769 :
770 : void verify(const DominatorTreeBase<BlockT, false> &DomTree) const;
771 :
772 : /// Destroy a loop that has been removed from the `LoopInfo` nest.
773 : ///
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.
777 : ///
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
781 : /// `erase' instead.
782 0 : void destroy(LoopT *L) {
783 : L->~LoopT();
784 :
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);
788 0 : }
789 : };
790 :
791 : // Implementation in LoopInfoImpl.h
792 : extern template class LoopInfoBase<BasicBlock, Loop>;
793 :
794 4382 : class LoopInfo : public LoopInfoBase<BasicBlock, Loop> {
795 : typedef LoopInfoBase<BasicBlock, Loop> BaseT;
796 :
797 : friend class LoopBase<BasicBlock, Loop>;
798 :
799 : void operator=(const LoopInfo &) = delete;
800 : LoopInfo(const LoopInfo &) = delete;
801 :
802 : public:
803 2129 : LoopInfo() {}
804 : explicit LoopInfo(const DominatorTreeBase<BasicBlock, false> &DomTree);
805 :
806 3732 : LoopInfo(LoopInfo &&Arg) : BaseT(std::move(static_cast<BaseT &>(Arg))) {}
807 : LoopInfo &operator=(LoopInfo &&RHS) {
808 : BaseT::operator=(std::move(static_cast<BaseT &>(RHS)));
809 : return *this;
810 : }
811 :
812 : /// Handle invalidation explicitly.
813 : bool invalidate(Function &F, const PreservedAnalyses &PA,
814 : FunctionAnalysisManager::Invalidator &);
815 :
816 : // Most of the public interface is provided via LoopInfoBase.
817 :
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.
822 : void erase(Loop *L);
823 :
824 : /// Returns true if replacing From with To everywhere is guaranteed to
825 : /// preserve LCSSA form.
826 32390 : bool replacementPreservesLCSSAForm(Instruction *From, Value *To) {
827 : // Preserving LCSSA form is only problematic if the replacing value is an
828 : // instruction.
829 : Instruction *I = dyn_cast<Instruction>(To);
830 : if (!I)
831 : return true;
832 : // If both instructions are defined in the same basic block then replacement
833 : // cannot break LCSSA form.
834 2238 : if (I->getParent() == From->getParent())
835 : return true;
836 : // If the instruction is not defined in a loop then it can safely replace
837 : // anything.
838 : Loop *ToLoop = getLoopFor(I->getParent());
839 1768 : if (!ToLoop)
840 338 : return true;
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 1768 : return ToLoop->contains(getLoopFor(From->getParent()));
845 : }
846 :
847 : /// Checks if moving a specific instruction can break LCSSA in any loop.
848 : ///
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
851 : /// in LCSSA form.
852 291 : bool movementPreservesLCSSAForm(Instruction *Inst, Instruction *NewLoc) {
853 : assert(Inst->getFunction() == NewLoc->getFunction() &&
854 : "Can't reason about IPO!");
855 :
856 291 : auto *OldBB = Inst->getParent();
857 291 : auto *NewBB = NewLoc->getParent();
858 :
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).
861 291 : if (OldBB == NewBB)
862 : return true;
863 :
864 : auto *OldLoop = getLoopFor(OldBB);
865 : auto *NewLoop = getLoopFor(NewBB);
866 :
867 26 : if (OldLoop == NewLoop)
868 : return true;
869 :
870 : // Check if Outer contains Inner; with the null loop counting as the
871 : // "outermost" loop.
872 : auto Contains = [](const Loop *Outer, const Loop *Inner) {
873 0 : return !Outer || Outer->contains(Inner);
874 : };
875 :
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.
879 :
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.
882 :
883 : if (!Contains(NewLoop, OldLoop)) {
884 0 : for (Use &U : Inst->uses()) {
885 0 : auto *UI = cast<Instruction>(U.getUser());
886 0 : auto *UBB = isa<PHINode>(UI) ? cast<PHINode>(UI)->getIncomingBlock(U)
887 0 : : UI->getParent();
888 0 : if (UBB != NewBB && getLoopFor(UBB) != NewLoop)
889 : return false;
890 : }
891 : }
892 :
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.
895 :
896 : if (!Contains(OldLoop, NewLoop)) {
897 : // See below on why we can't handle phi nodes here.
898 0 : if (isa<PHINode>(Inst))
899 : return false;
900 :
901 0 : for (Use &U : Inst->operands()) {
902 0 : auto *DefI = dyn_cast<Instruction>(U.get());
903 : if (!DefI)
904 : return false;
905 :
906 : // This would need adjustment if we allow Inst to be a phi node -- the
907 : // new use block won't simply be NewBB.
908 :
909 0 : auto *DefBlock = DefI->getParent();
910 0 : if (DefBlock != NewBB && getLoopFor(DefBlock) != NewLoop)
911 : return false;
912 : }
913 : }
914 :
915 : return true;
916 : }
917 : };
918 :
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;
923 :
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(); }
927 : };
928 :
929 : template <> struct GraphTraits<Loop *> {
930 : typedef Loop *NodeRef;
931 : typedef LoopInfo::iterator ChildIteratorType;
932 :
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(); }
936 : };
937 :
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;
942 :
943 : public:
944 : typedef LoopInfo Result;
945 :
946 : LoopInfo run(Function &F, FunctionAnalysisManager &AM);
947 : };
948 :
949 : /// Printer pass for the \c LoopAnalysis results.
950 : class LoopPrinterPass : public PassInfoMixin<LoopPrinterPass> {
951 : raw_ostream &OS;
952 :
953 : public:
954 1 : explicit LoopPrinterPass(raw_ostream &OS) : OS(OS) {}
955 : PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
956 : };
957 :
958 : /// Verifier pass for the \c LoopAnalysis results.
959 : struct LoopVerifierPass : public PassInfoMixin<LoopVerifierPass> {
960 : PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
961 : };
962 :
963 : /// The legacy pass manager's analysis pass to compute loop information.
964 : class LoopInfoWrapperPass : public FunctionPass {
965 : LoopInfo LI;
966 :
967 : public:
968 : static char ID; // Pass identification, replacement for typeid
969 :
970 237348 : LoopInfoWrapperPass() : FunctionPass(ID) {
971 118674 : initializeLoopInfoWrapperPassPass(*PassRegistry::getPassRegistry());
972 118674 : }
973 :
974 4659217 : LoopInfo &getLoopInfo() { return LI; }
975 : const LoopInfo &getLoopInfo() const { return LI; }
976 :
977 : /// Calculate the natural loop information for a given function.
978 : bool runOnFunction(Function &F) override;
979 :
980 : void verifyAnalysis() const override;
981 :
982 2682291 : void releaseMemory() override { LI.releaseMemory(); }
983 :
984 : void print(raw_ostream &O, const Module *M = nullptr) const override;
985 :
986 : void getAnalysisUsage(AnalysisUsage &AU) const override;
987 : };
988 :
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 = "");
991 :
992 : } // End llvm namespace
993 :
994 : #endif
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