1//===----------------- LoopRotationUtils.cpp -----------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file provides utilities to convert a loop into a loop with bottom test.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/Transforms/Utils/LoopRotationUtils.h"
14#include "llvm/ADT/Statistic.h"
15#include "llvm/Analysis/AssumptionCache.h"
16#include "llvm/Analysis/CodeMetrics.h"
17#include "llvm/Analysis/DomTreeUpdater.h"
18#include "llvm/Analysis/InstructionSimplify.h"
19#include "llvm/Analysis/LoopInfo.h"
20#include "llvm/Analysis/MemorySSA.h"
21#include "llvm/Analysis/MemorySSAUpdater.h"
22#include "llvm/Analysis/ScalarEvolution.h"
23#include "llvm/Analysis/ValueTracking.h"
24#include "llvm/IR/CFG.h"
25#include "llvm/IR/DebugInfo.h"
26#include "llvm/IR/Dominators.h"
27#include "llvm/IR/IntrinsicInst.h"
28#include "llvm/IR/MDBuilder.h"
29#include "llvm/IR/ProfDataUtils.h"
30#include "llvm/Support/CommandLine.h"
31#include "llvm/Support/Debug.h"
32#include "llvm/Support/raw_ostream.h"
33#include "llvm/Transforms/Utils/BasicBlockUtils.h"
34#include "llvm/Transforms/Utils/Cloning.h"
35#include "llvm/Transforms/Utils/Local.h"
36#include "llvm/Transforms/Utils/SSAUpdater.h"
37#include "llvm/Transforms/Utils/ValueMapper.h"
38using namespace llvm;
39
40#define DEBUG_TYPE "loop-rotate"
41
42STATISTIC(NumNotRotatedDueToHeaderSize,
43 "Number of loops not rotated due to the header size");
44STATISTIC(NumInstrsHoisted,
45 "Number of instructions hoisted into loop preheader");
46STATISTIC(NumInstrsDuplicated,
47 "Number of instructions cloned into loop preheader");
48STATISTIC(NumRotated, "Number of loops rotated");
49
50static cl::opt<bool>
51 MultiRotate("loop-rotate-multi", cl::init(Val: false), cl::Hidden,
52 cl::desc("Allow loop rotation multiple times in order to reach "
53 "a better latch exit"));
54
55// Probability that a rotated loop has zero trip count / is never entered.
56static constexpr uint32_t ZeroTripCountWeights[] = {1, 127};
57
58namespace {
59/// A simple loop rotation transformation.
60class LoopRotate {
61 const unsigned MaxHeaderSize;
62 LoopInfo *LI;
63 const TargetTransformInfo *TTI;
64 AssumptionCache *AC;
65 DominatorTree *DT;
66 ScalarEvolution *SE;
67 MemorySSAUpdater *MSSAU;
68 const SimplifyQuery &SQ;
69 bool RotationOnly;
70 bool IsUtilMode;
71 bool PrepareForLTO;
72
73public:
74 LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
75 const TargetTransformInfo *TTI, AssumptionCache *AC,
76 DominatorTree *DT, ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
77 const SimplifyQuery &SQ, bool RotationOnly, bool IsUtilMode,
78 bool PrepareForLTO)
79 : MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
80 MSSAU(MSSAU), SQ(SQ), RotationOnly(RotationOnly),
81 IsUtilMode(IsUtilMode), PrepareForLTO(PrepareForLTO) {}
82 bool processLoop(Loop *L);
83
84private:
85 bool rotateLoop(Loop *L, bool SimplifiedLatch);
86 bool simplifyLoopLatch(Loop *L);
87};
88} // end anonymous namespace
89
90/// Insert (K, V) pair into the ValueToValueMap, and verify the key did not
91/// previously exist in the map, and the value was inserted.
92static void InsertNewValueIntoMap(ValueToValueMapTy &VM, Value *K, Value *V) {
93 bool Inserted = VM.insert(KV: {K, V}).second;
94 assert(Inserted);
95 (void)Inserted;
96}
97/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
98/// old header into the preheader. If there were uses of the values produced by
99/// these instruction that were outside of the loop, we have to insert PHI nodes
100/// to merge the two values. Do this now.
101static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
102 BasicBlock *OrigPreheader,
103 ValueToValueMapTy &ValueMap,
104 ScalarEvolution *SE,
105 SmallVectorImpl<PHINode*> *InsertedPHIs) {
106 // Remove PHI node entries that are no longer live.
107 BasicBlock::iterator I, E = OrigHeader->end();
108 for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(Val&: I); ++I)
109 PN->removeIncomingValue(Idx: PN->getBasicBlockIndex(BB: OrigPreheader));
110
111 // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
112 // as necessary.
113 SSAUpdater SSA(InsertedPHIs);
114 for (I = OrigHeader->begin(); I != E; ++I) {
115 Value *OrigHeaderVal = &*I;
116
117 // If there are no uses of the value (e.g. because it returns void), there
118 // is nothing to rewrite.
119 if (OrigHeaderVal->use_empty())
120 continue;
121
122 Value *OrigPreHeaderVal = ValueMap.lookup(Val: OrigHeaderVal);
123
124 // The value now exits in two versions: the initial value in the preheader
125 // and the loop "next" value in the original header.
126 SSA.Initialize(Ty: OrigHeaderVal->getType(), Name: OrigHeaderVal->getName());
127 // Force re-computation of OrigHeaderVal, as some users now need to use the
128 // new PHI node.
129 if (SE)
130 SE->forgetValue(V: OrigHeaderVal);
131 SSA.AddAvailableValue(BB: OrigHeader, V: OrigHeaderVal);
132 SSA.AddAvailableValue(BB: OrigPreheader, V: OrigPreHeaderVal);
133
134 // Visit each use of the OrigHeader instruction.
135 for (Use &U : llvm::make_early_inc_range(Range: OrigHeaderVal->uses())) {
136 // SSAUpdater can't handle a non-PHI use in the same block as an
137 // earlier def. We can easily handle those cases manually.
138 Instruction *UserInst = cast<Instruction>(Val: U.getUser());
139 if (!isa<PHINode>(Val: UserInst)) {
140 BasicBlock *UserBB = UserInst->getParent();
141
142 // The original users in the OrigHeader are already using the
143 // original definitions.
144 if (UserBB == OrigHeader)
145 continue;
146
147 // Users in the OrigPreHeader need to use the value to which the
148 // original definitions are mapped.
149 if (UserBB == OrigPreheader) {
150 U = OrigPreHeaderVal;
151 continue;
152 }
153 }
154
155 // Anything else can be handled by SSAUpdater.
156 SSA.RewriteUse(U);
157 }
158
159 // Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
160 // intrinsics.
161 SmallVector<DbgValueInst *, 1> DbgValues;
162 SmallVector<DbgVariableRecord *, 1> DbgVariableRecords;
163 llvm::findDbgValues(DbgValues, V: OrigHeaderVal, DbgVariableRecords: &DbgVariableRecords);
164 for (auto &DbgValue : DbgValues) {
165 // The original users in the OrigHeader are already using the original
166 // definitions.
167 BasicBlock *UserBB = DbgValue->getParent();
168 if (UserBB == OrigHeader)
169 continue;
170
171 // Users in the OrigPreHeader need to use the value to which the
172 // original definitions are mapped and anything else can be handled by
173 // the SSAUpdater. To avoid adding PHINodes, check if the value is
174 // available in UserBB, if not substitute poison.
175 Value *NewVal;
176 if (UserBB == OrigPreheader)
177 NewVal = OrigPreHeaderVal;
178 else if (SSA.HasValueForBlock(BB: UserBB))
179 NewVal = SSA.GetValueInMiddleOfBlock(BB: UserBB);
180 else
181 NewVal = PoisonValue::get(T: OrigHeaderVal->getType());
182 DbgValue->replaceVariableLocationOp(OldValue: OrigHeaderVal, NewValue: NewVal);
183 }
184
185 // RemoveDIs: duplicate implementation for non-instruction debug-info
186 // storage in DbgVariableRecords.
187 for (DbgVariableRecord *DVR : DbgVariableRecords) {
188 // The original users in the OrigHeader are already using the original
189 // definitions.
190 BasicBlock *UserBB = DVR->getMarker()->getParent();
191 if (UserBB == OrigHeader)
192 continue;
193
194 // Users in the OrigPreHeader need to use the value to which the
195 // original definitions are mapped and anything else can be handled by
196 // the SSAUpdater. To avoid adding PHINodes, check if the value is
197 // available in UserBB, if not substitute poison.
198 Value *NewVal;
199 if (UserBB == OrigPreheader)
200 NewVal = OrigPreHeaderVal;
201 else if (SSA.HasValueForBlock(BB: UserBB))
202 NewVal = SSA.GetValueInMiddleOfBlock(BB: UserBB);
203 else
204 NewVal = PoisonValue::get(T: OrigHeaderVal->getType());
205 DVR->replaceVariableLocationOp(OldValue: OrigHeaderVal, NewValue: NewVal);
206 }
207 }
208}
209
210// Assuming both header and latch are exiting, look for a phi which is only
211// used outside the loop (via a LCSSA phi) in the exit from the header.
212// This means that rotating the loop can remove the phi.
213static bool profitableToRotateLoopExitingLatch(Loop *L) {
214 BasicBlock *Header = L->getHeader();
215 BranchInst *BI = dyn_cast<BranchInst>(Val: Header->getTerminator());
216 assert(BI && BI->isConditional() && "need header with conditional exit");
217 BasicBlock *HeaderExit = BI->getSuccessor(i: 0);
218 if (L->contains(BB: HeaderExit))
219 HeaderExit = BI->getSuccessor(i: 1);
220
221 for (auto &Phi : Header->phis()) {
222 // Look for uses of this phi in the loop/via exits other than the header.
223 if (llvm::any_of(Range: Phi.users(), P: [HeaderExit](const User *U) {
224 return cast<Instruction>(Val: U)->getParent() != HeaderExit;
225 }))
226 continue;
227 return true;
228 }
229 return false;
230}
231
232// Check that latch exit is deoptimizing (which means - very unlikely to happen)
233// and there is another exit from the loop which is non-deoptimizing.
234// If we rotate latch to that exit our loop has a better chance of being fully
235// canonical.
236//
237// It can give false positives in some rare cases.
238static bool canRotateDeoptimizingLatchExit(Loop *L) {
239 BasicBlock *Latch = L->getLoopLatch();
240 assert(Latch && "need latch");
241 BranchInst *BI = dyn_cast<BranchInst>(Val: Latch->getTerminator());
242 // Need normal exiting latch.
243 if (!BI || !BI->isConditional())
244 return false;
245
246 BasicBlock *Exit = BI->getSuccessor(i: 1);
247 if (L->contains(BB: Exit))
248 Exit = BI->getSuccessor(i: 0);
249
250 // Latch exit is non-deoptimizing, no need to rotate.
251 if (!Exit->getPostdominatingDeoptimizeCall())
252 return false;
253
254 SmallVector<BasicBlock *, 4> Exits;
255 L->getUniqueExitBlocks(ExitBlocks&: Exits);
256 if (!Exits.empty()) {
257 // There is at least one non-deoptimizing exit.
258 //
259 // Note, that BasicBlock::getPostdominatingDeoptimizeCall is not exact,
260 // as it can conservatively return false for deoptimizing exits with
261 // complex enough control flow down to deoptimize call.
262 //
263 // That means here we can report success for a case where
264 // all exits are deoptimizing but one of them has complex enough
265 // control flow (e.g. with loops).
266 //
267 // That should be a very rare case and false positives for this function
268 // have compile-time effect only.
269 return any_of(Range&: Exits, P: [](const BasicBlock *BB) {
270 return !BB->getPostdominatingDeoptimizeCall();
271 });
272 }
273 return false;
274}
275
276static void updateBranchWeights(BranchInst &PreHeaderBI, BranchInst &LoopBI,
277 bool HasConditionalPreHeader,
278 bool SuccsSwapped) {
279 MDNode *WeightMD = getBranchWeightMDNode(I: PreHeaderBI);
280 if (WeightMD == nullptr)
281 return;
282
283 // LoopBI should currently be a clone of PreHeaderBI with the same
284 // metadata. But we double check to make sure we don't have a degenerate case
285 // where instsimplify changed the instructions.
286 if (WeightMD != getBranchWeightMDNode(I: LoopBI))
287 return;
288
289 SmallVector<uint32_t, 2> Weights;
290 extractFromBranchWeightMD32(ProfileData: WeightMD, Weights);
291 if (Weights.size() != 2)
292 return;
293 uint32_t OrigLoopExitWeight = Weights[0];
294 uint32_t OrigLoopBackedgeWeight = Weights[1];
295
296 if (SuccsSwapped)
297 std::swap(a&: OrigLoopExitWeight, b&: OrigLoopBackedgeWeight);
298
299 // Update branch weights. Consider the following edge-counts:
300 //
301 // | |-------- |
302 // V V | V
303 // Br i1 ... | Br i1 ...
304 // | | | | |
305 // x| y| | becomes: | y0| |-----
306 // V V | | V V |
307 // Exit Loop | | Loop |
308 // | | | Br i1 ... |
309 // ----- | | | |
310 // x0| x1| y1 | |
311 // V V ----
312 // Exit
313 //
314 // The following must hold:
315 // - x == x0 + x1 # counts to "exit" must stay the same.
316 // - y0 == x - x0 == x1 # how often loop was entered at all.
317 // - y1 == y - y0 # How often loop was repeated (after first iter.).
318 //
319 // We cannot generally deduce how often we had a zero-trip count loop so we
320 // have to make a guess for how to distribute x among the new x0 and x1.
321
322 uint32_t ExitWeight0; // aka x0
323 uint32_t ExitWeight1; // aka x1
324 uint32_t EnterWeight; // aka y0
325 uint32_t LoopBackWeight; // aka y1
326 if (OrigLoopExitWeight > 0 && OrigLoopBackedgeWeight > 0) {
327 ExitWeight0 = 0;
328 if (HasConditionalPreHeader) {
329 // Here we cannot know how many 0-trip count loops we have, so we guess:
330 if (OrigLoopBackedgeWeight >= OrigLoopExitWeight) {
331 // If the loop count is bigger than the exit count then we set
332 // probabilities as if 0-trip count nearly never happens.
333 ExitWeight0 = ZeroTripCountWeights[0];
334 // Scale up counts if necessary so we can match `ZeroTripCountWeights`
335 // for the `ExitWeight0`:`ExitWeight1` (aka `x0`:`x1` ratio`) ratio.
336 while (OrigLoopExitWeight < ZeroTripCountWeights[1] + ExitWeight0) {
337 // ... but don't overflow.
338 uint32_t const HighBit = uint32_t{1} << (sizeof(uint32_t) * 8 - 1);
339 if ((OrigLoopBackedgeWeight & HighBit) != 0 ||
340 (OrigLoopExitWeight & HighBit) != 0)
341 break;
342 OrigLoopBackedgeWeight <<= 1;
343 OrigLoopExitWeight <<= 1;
344 }
345 } else {
346 // If there's a higher exit-count than backedge-count then we set
347 // probabilities as if there are only 0-trip and 1-trip cases.
348 ExitWeight0 = OrigLoopExitWeight - OrigLoopBackedgeWeight;
349 }
350 } else {
351 // Theoretically, if the loop body must be executed at least once, the
352 // backedge count must be not less than exit count. However the branch
353 // weight collected by sampling-based PGO may be not very accurate due to
354 // sampling. Therefore this workaround is required here to avoid underflow
355 // of unsigned in following update of branch weight.
356 if (OrigLoopExitWeight > OrigLoopBackedgeWeight)
357 OrigLoopBackedgeWeight = OrigLoopExitWeight;
358 }
359 assert(OrigLoopExitWeight >= ExitWeight0 && "Bad branch weight");
360 ExitWeight1 = OrigLoopExitWeight - ExitWeight0;
361 EnterWeight = ExitWeight1;
362 assert(OrigLoopBackedgeWeight >= EnterWeight && "Bad branch weight");
363 LoopBackWeight = OrigLoopBackedgeWeight - EnterWeight;
364 } else if (OrigLoopExitWeight == 0) {
365 if (OrigLoopBackedgeWeight == 0) {
366 // degenerate case... keep everything zero...
367 ExitWeight0 = 0;
368 ExitWeight1 = 0;
369 EnterWeight = 0;
370 LoopBackWeight = 0;
371 } else {
372 // Special case "LoopExitWeight == 0" weights which behaves like an
373 // endless where we don't want loop-enttry (y0) to be the same as
374 // loop-exit (x1).
375 ExitWeight0 = 0;
376 ExitWeight1 = 0;
377 EnterWeight = 1;
378 LoopBackWeight = OrigLoopBackedgeWeight;
379 }
380 } else {
381 // loop is never entered.
382 assert(OrigLoopBackedgeWeight == 0 && "remaining case is backedge zero");
383 ExitWeight0 = 1;
384 ExitWeight1 = 1;
385 EnterWeight = 0;
386 LoopBackWeight = 0;
387 }
388
389 const uint32_t LoopBIWeights[] = {
390 SuccsSwapped ? LoopBackWeight : ExitWeight1,
391 SuccsSwapped ? ExitWeight1 : LoopBackWeight,
392 };
393 setBranchWeights(I&: LoopBI, Weights: LoopBIWeights, /*IsExpected=*/false);
394 if (HasConditionalPreHeader) {
395 const uint32_t PreHeaderBIWeights[] = {
396 SuccsSwapped ? EnterWeight : ExitWeight0,
397 SuccsSwapped ? ExitWeight0 : EnterWeight,
398 };
399 setBranchWeights(I&: PreHeaderBI, Weights: PreHeaderBIWeights, /*IsExpected=*/false);
400 }
401}
402
403/// Rotate loop LP. Return true if the loop is rotated.
404///
405/// \param SimplifiedLatch is true if the latch was just folded into the final
406/// loop exit. In this case we may want to rotate even though the new latch is
407/// now an exiting branch. This rotation would have happened had the latch not
408/// been simplified. However, if SimplifiedLatch is false, then we avoid
409/// rotating loops in which the latch exits to avoid excessive or endless
410/// rotation. LoopRotate should be repeatable and converge to a canonical
411/// form. This property is satisfied because simplifying the loop latch can only
412/// happen once across multiple invocations of the LoopRotate pass.
413///
414/// If -loop-rotate-multi is enabled we can do multiple rotations in one go
415/// so to reach a suitable (non-deoptimizing) exit.
416bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
417 // If the loop has only one block then there is not much to rotate.
418 if (L->getBlocks().size() == 1)
419 return false;
420
421 bool Rotated = false;
422 do {
423 BasicBlock *OrigHeader = L->getHeader();
424 BasicBlock *OrigLatch = L->getLoopLatch();
425
426 BranchInst *BI = dyn_cast<BranchInst>(Val: OrigHeader->getTerminator());
427 if (!BI || BI->isUnconditional())
428 return Rotated;
429
430 // If the loop header is not one of the loop exiting blocks then
431 // either this loop is already rotated or it is not
432 // suitable for loop rotation transformations.
433 if (!L->isLoopExiting(BB: OrigHeader))
434 return Rotated;
435
436 // If the loop latch already contains a branch that leaves the loop then the
437 // loop is already rotated.
438 if (!OrigLatch)
439 return Rotated;
440
441 // Rotate if either the loop latch does *not* exit the loop, or if the loop
442 // latch was just simplified. Or if we think it will be profitable.
443 if (L->isLoopExiting(BB: OrigLatch) && !SimplifiedLatch && IsUtilMode == false &&
444 !profitableToRotateLoopExitingLatch(L) &&
445 !canRotateDeoptimizingLatchExit(L))
446 return Rotated;
447
448 // Check size of original header and reject loop if it is very big or we can't
449 // duplicate blocks inside it.
450 {
451 SmallPtrSet<const Value *, 32> EphValues;
452 CodeMetrics::collectEphemeralValues(L, AC, EphValues);
453
454 CodeMetrics Metrics;
455 Metrics.analyzeBasicBlock(BB: OrigHeader, TTI: *TTI, EphValues, PrepareForLTO);
456 if (Metrics.notDuplicatable) {
457 LLVM_DEBUG(
458 dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
459 << " instructions: ";
460 L->dump());
461 return Rotated;
462 }
463 if (Metrics.Convergence != ConvergenceKind::None) {
464 LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
465 "instructions: ";
466 L->dump());
467 return Rotated;
468 }
469 if (!Metrics.NumInsts.isValid()) {
470 LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains instructions"
471 " with invalid cost: ";
472 L->dump());
473 return Rotated;
474 }
475 if (Metrics.NumInsts > MaxHeaderSize) {
476 LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains "
477 << Metrics.NumInsts
478 << " instructions, which is more than the threshold ("
479 << MaxHeaderSize << " instructions): ";
480 L->dump());
481 ++NumNotRotatedDueToHeaderSize;
482 return Rotated;
483 }
484
485 // When preparing for LTO, avoid rotating loops with calls that could be
486 // inlined during the LTO stage.
487 if (PrepareForLTO && Metrics.NumInlineCandidates > 0)
488 return Rotated;
489 }
490
491 // Now, this loop is suitable for rotation.
492 BasicBlock *OrigPreheader = L->getLoopPreheader();
493
494 // If the loop could not be converted to canonical form, it must have an
495 // indirectbr in it, just give up.
496 if (!OrigPreheader || !L->hasDedicatedExits())
497 return Rotated;
498
499 // Anything ScalarEvolution may know about this loop or the PHI nodes
500 // in its header will soon be invalidated. We should also invalidate
501 // all outer loops because insertion and deletion of blocks that happens
502 // during the rotation may violate invariants related to backedge taken
503 // infos in them.
504 if (SE) {
505 SE->forgetTopmostLoop(L);
506 // We may hoist some instructions out of loop. In case if they were cached
507 // as "loop variant" or "loop computable", these caches must be dropped.
508 // We also may fold basic blocks, so cached block dispositions also need
509 // to be dropped.
510 SE->forgetBlockAndLoopDispositions();
511 }
512
513 LLVM_DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
514 if (MSSAU && VerifyMemorySSA)
515 MSSAU->getMemorySSA()->verifyMemorySSA();
516
517 // Find new Loop header. NewHeader is a Header's one and only successor
518 // that is inside loop. Header's other successor is outside the
519 // loop. Otherwise loop is not suitable for rotation.
520 BasicBlock *Exit = BI->getSuccessor(i: 0);
521 BasicBlock *NewHeader = BI->getSuccessor(i: 1);
522 bool BISuccsSwapped = L->contains(BB: Exit);
523 if (BISuccsSwapped)
524 std::swap(a&: Exit, b&: NewHeader);
525 assert(NewHeader && "Unable to determine new loop header");
526 assert(L->contains(NewHeader) && !L->contains(Exit) &&
527 "Unable to determine loop header and exit blocks");
528
529 // This code assumes that the new header has exactly one predecessor.
530 // Remove any single-entry PHI nodes in it.
531 assert(NewHeader->getSinglePredecessor() &&
532 "New header doesn't have one pred!");
533 FoldSingleEntryPHINodes(BB: NewHeader);
534
535 // Begin by walking OrigHeader and populating ValueMap with an entry for
536 // each Instruction.
537 BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
538 ValueToValueMapTy ValueMap, ValueMapMSSA;
539
540 // For PHI nodes, the value available in OldPreHeader is just the
541 // incoming value from OldPreHeader.
542 for (; PHINode *PN = dyn_cast<PHINode>(Val&: I); ++I)
543 InsertNewValueIntoMap(VM&: ValueMap, K: PN,
544 V: PN->getIncomingValueForBlock(BB: OrigPreheader));
545
546 // For the rest of the instructions, either hoist to the OrigPreheader if
547 // possible or create a clone in the OldPreHeader if not.
548 Instruction *LoopEntryBranch = OrigPreheader->getTerminator();
549
550 // Record all debug records preceding LoopEntryBranch to avoid
551 // duplication.
552 using DbgHash =
553 std::pair<std::pair<hash_code, DILocalVariable *>, DIExpression *>;
554 auto makeHash = [](const DbgVariableRecord *D) -> DbgHash {
555 auto VarLocOps = D->location_ops();
556 return {{hash_combine_range(R&: VarLocOps), D->getVariable()},
557 D->getExpression()};
558 };
559
560 SmallDenseSet<DbgHash, 8> DbgRecords;
561 // Build DbgVariableRecord hashes for DbgVariableRecords attached to the
562 // terminator.
563 for (const DbgVariableRecord &DVR :
564 filterDbgVars(R: OrigPreheader->getTerminator()->getDbgRecordRange()))
565 DbgRecords.insert(V: makeHash(&DVR));
566
567 // Remember the local noalias scope declarations in the header. After the
568 // rotation, they must be duplicated and the scope must be cloned. This
569 // avoids unwanted interaction across iterations.
570 SmallVector<NoAliasScopeDeclInst *, 6> NoAliasDeclInstructions;
571 for (Instruction &I : *OrigHeader)
572 if (auto *Decl = dyn_cast<NoAliasScopeDeclInst>(Val: &I))
573 NoAliasDeclInstructions.push_back(Elt: Decl);
574
575 Module *M = OrigHeader->getModule();
576
577 // Track the next DbgRecord to clone. If we have a sequence where an
578 // instruction is hoisted instead of being cloned:
579 // DbgRecord blah
580 // %foo = add i32 0, 0
581 // DbgRecord xyzzy
582 // %bar = call i32 @foobar()
583 // where %foo is hoisted, then the DbgRecord "blah" will be seen twice, once
584 // attached to %foo, then when %foo his hoisted it will "fall down" onto the
585 // function call:
586 // DbgRecord blah
587 // DbgRecord xyzzy
588 // %bar = call i32 @foobar()
589 // causing it to appear attached to the call too.
590 //
591 // To avoid this, cloneDebugInfoFrom takes an optional "start cloning from
592 // here" position to account for this behaviour. We point it at any
593 // DbgRecords on the next instruction, here labelled xyzzy, before we hoist
594 // %foo. Later, we only only clone DbgRecords from that position (xyzzy)
595 // onwards, which avoids cloning DbgRecord "blah" multiple times. (Stored as
596 // a range because it gives us a natural way of testing whether
597 // there were DbgRecords on the next instruction before we hoisted things).
598 iterator_range<DbgRecord::self_iterator> NextDbgInsts =
599 (I != E) ? I->getDbgRecordRange() : DbgMarker::getEmptyDbgRecordRange();
600
601 while (I != E) {
602 Instruction *Inst = &*I++;
603
604 // If the instruction's operands are invariant and it doesn't read or write
605 // memory, then it is safe to hoist. Doing this doesn't change the order of
606 // execution in the preheader, but does prevent the instruction from
607 // executing in each iteration of the loop. This means it is safe to hoist
608 // something that might trap, but isn't safe to hoist something that reads
609 // memory (without proving that the loop doesn't write).
610 if (L->hasLoopInvariantOperands(I: Inst) && !Inst->mayReadFromMemory() &&
611 !Inst->mayWriteToMemory() && !Inst->isTerminator() &&
612 !isa<AllocaInst>(Val: Inst) &&
613 // It is not safe to hoist the value of these instructions in
614 // coroutines, as the addresses of otherwise eligible variables (e.g.
615 // thread-local variables and errno) may change if the coroutine is
616 // resumed in a different thread.Therefore, we disable this
617 // optimization for correctness. However, this may block other correct
618 // optimizations.
619 // FIXME: This should be reverted once we have a better model for
620 // memory access in coroutines.
621 !Inst->getFunction()->isPresplitCoroutine()) {
622
623 if (!NextDbgInsts.empty()) {
624 auto DbgValueRange =
625 LoopEntryBranch->cloneDebugInfoFrom(From: Inst, FromHere: NextDbgInsts.begin());
626 RemapDbgRecordRange(M, Range: DbgValueRange, VM&: ValueMap,
627 Flags: RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
628 // Erase anything we've seen before.
629 for (DbgVariableRecord &DVR :
630 make_early_inc_range(Range: filterDbgVars(R: DbgValueRange)))
631 if (DbgRecords.count(V: makeHash(&DVR)))
632 DVR.eraseFromParent();
633 }
634
635 NextDbgInsts = I->getDbgRecordRange();
636
637 Inst->moveBefore(InsertPos: LoopEntryBranch->getIterator());
638
639 ++NumInstrsHoisted;
640 continue;
641 }
642
643 // Otherwise, create a duplicate of the instruction.
644 Instruction *C = Inst->clone();
645 if (const DebugLoc &DL = C->getDebugLoc())
646 mapAtomInstance(DL, VMap&: ValueMap);
647
648 C->insertBefore(InsertPos: LoopEntryBranch->getIterator());
649
650 ++NumInstrsDuplicated;
651
652 if (!NextDbgInsts.empty()) {
653 auto Range = C->cloneDebugInfoFrom(From: Inst, FromHere: NextDbgInsts.begin());
654 RemapDbgRecordRange(M, Range, VM&: ValueMap,
655 Flags: RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
656 NextDbgInsts = DbgMarker::getEmptyDbgRecordRange();
657 // Erase anything we've seen before.
658 for (DbgVariableRecord &DVR :
659 make_early_inc_range(Range: filterDbgVars(R: Range)))
660 if (DbgRecords.count(V: makeHash(&DVR)))
661 DVR.eraseFromParent();
662 }
663
664 // Eagerly remap the operands of the instruction.
665 RemapInstruction(I: C, VM&: ValueMap,
666 Flags: RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
667
668 // With the operands remapped, see if the instruction constant folds or is
669 // otherwise simplifyable. This commonly occurs because the entry from PHI
670 // nodes allows icmps and other instructions to fold.
671 Value *V = simplifyInstruction(I: C, Q: SQ);
672 if (V && LI->replacementPreservesLCSSAForm(From: C, To: V)) {
673 // If so, then delete the temporary instruction and stick the folded value
674 // in the map.
675 InsertNewValueIntoMap(VM&: ValueMap, K: Inst, V);
676 if (!C->mayHaveSideEffects()) {
677 C->eraseFromParent();
678 C = nullptr;
679 }
680 } else {
681 InsertNewValueIntoMap(VM&: ValueMap, K: Inst, V: C);
682 }
683 if (C) {
684 // Otherwise, stick the new instruction into the new block!
685 C->setName(Inst->getName());
686
687 if (auto *II = dyn_cast<AssumeInst>(Val: C))
688 AC->registerAssumption(CI: II);
689 // MemorySSA cares whether the cloned instruction was inserted or not, and
690 // not whether it can be remapped to a simplified value.
691 if (MSSAU)
692 InsertNewValueIntoMap(VM&: ValueMapMSSA, K: Inst, V: C);
693 }
694 }
695
696 if (!NoAliasDeclInstructions.empty()) {
697 // There are noalias scope declarations:
698 // (general):
699 // Original: OrigPre { OrigHeader NewHeader ... Latch }
700 // after: (OrigPre+OrigHeader') { NewHeader ... Latch OrigHeader }
701 //
702 // with D: llvm.experimental.noalias.scope.decl,
703 // U: !noalias or !alias.scope depending on D
704 // ... { D U1 U2 } can transform into:
705 // (0) : ... { D U1 U2 } // no relevant rotation for this part
706 // (1) : ... D' { U1 U2 D } // D is part of OrigHeader
707 // (2) : ... D' U1' { U2 D U1 } // D, U1 are part of OrigHeader
708 //
709 // We now want to transform:
710 // (1) -> : ... D' { D U1 U2 D'' }
711 // (2) -> : ... D' U1' { D U2 D'' U1'' }
712 // D: original llvm.experimental.noalias.scope.decl
713 // D', U1': duplicate with replaced scopes
714 // D'', U1'': different duplicate with replaced scopes
715 // This ensures a safe fallback to 'may_alias' introduced by the rotate,
716 // as U1'' and U1' scopes will not be compatible wrt to the local restrict
717
718 // Clone the llvm.experimental.noalias.decl again for the NewHeader.
719 BasicBlock::iterator NewHeaderInsertionPoint =
720 NewHeader->getFirstNonPHIIt();
721 for (NoAliasScopeDeclInst *NAD : NoAliasDeclInstructions) {
722 LLVM_DEBUG(dbgs() << " Cloning llvm.experimental.noalias.scope.decl:"
723 << *NAD << "\n");
724 Instruction *NewNAD = NAD->clone();
725 NewNAD->insertBefore(BB&: *NewHeader, InsertPos: NewHeaderInsertionPoint);
726 }
727
728 // Scopes must now be duplicated, once for OrigHeader and once for
729 // OrigPreHeader'.
730 {
731 auto &Context = NewHeader->getContext();
732
733 SmallVector<MDNode *, 8> NoAliasDeclScopes;
734 for (NoAliasScopeDeclInst *NAD : NoAliasDeclInstructions)
735 NoAliasDeclScopes.push_back(Elt: NAD->getScopeList());
736
737 LLVM_DEBUG(dbgs() << " Updating OrigHeader scopes\n");
738 cloneAndAdaptNoAliasScopes(NoAliasDeclScopes, NewBlocks: {OrigHeader}, Context,
739 Ext: "h.rot");
740 LLVM_DEBUG(OrigHeader->dump());
741
742 // Keep the compile time impact low by only adapting the inserted block
743 // of instructions in the OrigPreHeader. This might result in slightly
744 // more aliasing between these instructions and those that were already
745 // present, but it will be much faster when the original PreHeader is
746 // large.
747 LLVM_DEBUG(dbgs() << " Updating part of OrigPreheader scopes\n");
748 auto *FirstDecl =
749 cast<Instruction>(Val&: ValueMap[*NoAliasDeclInstructions.begin()]);
750 auto *LastInst = &OrigPreheader->back();
751 cloneAndAdaptNoAliasScopes(NoAliasDeclScopes, IStart: FirstDecl, IEnd: LastInst,
752 Context, Ext: "pre.rot");
753 LLVM_DEBUG(OrigPreheader->dump());
754
755 LLVM_DEBUG(dbgs() << " Updated NewHeader:\n");
756 LLVM_DEBUG(NewHeader->dump());
757 }
758 }
759
760 // Along with all the other instructions, we just cloned OrigHeader's
761 // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
762 // successors by duplicating their incoming values for OrigHeader.
763 for (BasicBlock *SuccBB : successors(BB: OrigHeader))
764 for (BasicBlock::iterator BI = SuccBB->begin();
765 PHINode *PN = dyn_cast<PHINode>(Val&: BI); ++BI)
766 PN->addIncoming(V: PN->getIncomingValueForBlock(BB: OrigHeader), BB: OrigPreheader);
767
768 // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
769 // OrigPreHeader's old terminator (the original branch into the loop), and
770 // remove the corresponding incoming values from the PHI nodes in OrigHeader.
771 LoopEntryBranch->eraseFromParent();
772 OrigPreheader->flushTerminatorDbgRecords();
773
774 // Update MemorySSA before the rewrite call below changes the 1:1
775 // instruction:cloned_instruction_or_value mapping.
776 if (MSSAU) {
777 InsertNewValueIntoMap(VM&: ValueMapMSSA, K: OrigHeader, V: OrigPreheader);
778 MSSAU->updateForClonedBlockIntoPred(BB: OrigHeader, P1: OrigPreheader,
779 VM: ValueMapMSSA);
780 }
781
782 SmallVector<PHINode*, 2> InsertedPHIs;
783 // If there were any uses of instructions in the duplicated block outside the
784 // loop, update them, inserting PHI nodes as required
785 RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap, SE,
786 InsertedPHIs: &InsertedPHIs);
787
788 // Attach debug records to the new phis if that phi uses a value that
789 // previously had debug metadata attached. This keeps the debug info
790 // up-to-date in the loop body.
791 if (!InsertedPHIs.empty())
792 insertDebugValuesForPHIs(BB: OrigHeader, InsertedPHIs);
793
794 // NewHeader is now the header of the loop.
795 L->moveToHeader(BB: NewHeader);
796 assert(L->getHeader() == NewHeader && "Latch block is our new header");
797
798 // Inform DT about changes to the CFG.
799 if (DT) {
800 // The OrigPreheader branches to the NewHeader and Exit now. Then, inform
801 // the DT about the removed edge to the OrigHeader (that got removed).
802 SmallVector<DominatorTree::UpdateType, 3> Updates = {
803 {DominatorTree::Insert, OrigPreheader, Exit},
804 {DominatorTree::Insert, OrigPreheader, NewHeader},
805 {DominatorTree::Delete, OrigPreheader, OrigHeader}};
806
807 if (MSSAU) {
808 MSSAU->applyUpdates(Updates, DT&: *DT, /*UpdateDT=*/UpdateDTFirst: true);
809 if (VerifyMemorySSA)
810 MSSAU->getMemorySSA()->verifyMemorySSA();
811 } else {
812 DT->applyUpdates(Updates);
813 }
814 }
815
816 // At this point, we've finished our major CFG changes. As part of cloning
817 // the loop into the preheader we've simplified instructions and the
818 // duplicated conditional branch may now be branching on a constant. If it is
819 // branching on a constant and if that constant means that we enter the loop,
820 // then we fold away the cond branch to an uncond branch. This simplifies the
821 // loop in cases important for nested loops, and it also means we don't have
822 // to split as many edges.
823 BranchInst *PHBI = cast<BranchInst>(Val: OrigPreheader->getTerminator());
824 assert(PHBI->isConditional() && "Should be clone of BI condbr!");
825 const Value *Cond = PHBI->getCondition();
826 const bool HasConditionalPreHeader =
827 !isa<ConstantInt>(Val: Cond) ||
828 PHBI->getSuccessor(i: cast<ConstantInt>(Val: Cond)->isZero()) != NewHeader;
829
830 updateBranchWeights(PreHeaderBI&: *PHBI, LoopBI&: *BI, HasConditionalPreHeader, SuccsSwapped: BISuccsSwapped);
831
832 if (HasConditionalPreHeader) {
833 // The conditional branch can't be folded, handle the general case.
834 // Split edges as necessary to preserve LoopSimplify form.
835
836 // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
837 // thus is not a preheader anymore.
838 // Split the edge to form a real preheader.
839 BasicBlock *NewPH = SplitCriticalEdge(
840 Src: OrigPreheader, Dst: NewHeader,
841 Options: CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
842 NewPH->setName(NewHeader->getName() + ".lr.ph");
843
844 // Preserve canonical loop form, which means that 'Exit' should have only
845 // one predecessor. Note that Exit could be an exit block for multiple
846 // nested loops, causing both of the edges to now be critical and need to
847 // be split.
848 SmallVector<BasicBlock *, 4> ExitPreds(predecessors(BB: Exit));
849 bool SplitLatchEdge = false;
850 for (BasicBlock *ExitPred : ExitPreds) {
851 // We only need to split loop exit edges.
852 Loop *PredLoop = LI->getLoopFor(BB: ExitPred);
853 if (!PredLoop || PredLoop->contains(BB: Exit) ||
854 isa<IndirectBrInst>(Val: ExitPred->getTerminator()))
855 continue;
856 SplitLatchEdge |= L->getLoopLatch() == ExitPred;
857 BasicBlock *ExitSplit = SplitCriticalEdge(
858 Src: ExitPred, Dst: Exit,
859 Options: CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
860 ExitSplit->moveBefore(MovePos: Exit);
861 }
862 assert(SplitLatchEdge &&
863 "Despite splitting all preds, failed to split latch exit?");
864 (void)SplitLatchEdge;
865 } else {
866 // We can fold the conditional branch in the preheader, this makes things
867 // simpler. The first step is to remove the extra edge to the Exit block.
868 Exit->removePredecessor(Pred: OrigPreheader, KeepOneInputPHIs: true /*preserve LCSSA*/);
869 BranchInst *NewBI = BranchInst::Create(IfTrue: NewHeader, InsertBefore: PHBI->getIterator());
870 NewBI->setDebugLoc(PHBI->getDebugLoc());
871 PHBI->eraseFromParent();
872
873 // With our CFG finalized, update DomTree if it is available.
874 if (DT) DT->deleteEdge(From: OrigPreheader, To: Exit);
875
876 // Update MSSA too, if available.
877 if (MSSAU)
878 MSSAU->removeEdge(From: OrigPreheader, To: Exit);
879 }
880
881 assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
882 assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
883
884 if (MSSAU && VerifyMemorySSA)
885 MSSAU->getMemorySSA()->verifyMemorySSA();
886
887 // Now that the CFG and DomTree are in a consistent state again, try to merge
888 // the OrigHeader block into OrigLatch. This will succeed if they are
889 // connected by an unconditional branch. This is just a cleanup so the
890 // emitted code isn't too gross in this common case.
891 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
892 BasicBlock *PredBB = OrigHeader->getUniquePredecessor();
893 bool DidMerge = MergeBlockIntoPredecessor(BB: OrigHeader, DTU: &DTU, LI, MSSAU);
894 if (DidMerge)
895 RemoveRedundantDbgInstrs(BB: PredBB);
896
897 if (MSSAU && VerifyMemorySSA)
898 MSSAU->getMemorySSA()->verifyMemorySSA();
899
900 LLVM_DEBUG(dbgs() << "LoopRotation: into "; L->dump());
901
902 ++NumRotated;
903
904 Rotated = true;
905 SimplifiedLatch = false;
906
907 // Check that new latch is a deoptimizing exit and then repeat rotation if possible.
908 // Deoptimizing latch exit is not a generally typical case, so we just loop over.
909 // TODO: if it becomes a performance bottleneck extend rotation algorithm
910 // to handle multiple rotations in one go.
911 } while (MultiRotate && canRotateDeoptimizingLatchExit(L));
912
913
914 return true;
915}
916
917/// Determine whether the instructions in this range may be safely and cheaply
918/// speculated. This is not an important enough situation to develop complex
919/// heuristics. We handle a single arithmetic instruction along with any type
920/// conversions.
921static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
922 BasicBlock::iterator End, Loop *L) {
923 bool seenIncrement = false;
924 bool MultiExitLoop = false;
925
926 if (!L->getExitingBlock())
927 MultiExitLoop = true;
928
929 for (BasicBlock::iterator I = Begin; I != End; ++I) {
930
931 if (!isSafeToSpeculativelyExecute(I: &*I))
932 return false;
933
934 switch (I->getOpcode()) {
935 default:
936 return false;
937 case Instruction::GetElementPtr:
938 // GEPs are cheap if all indices are constant.
939 if (!cast<GEPOperator>(Val&: I)->hasAllConstantIndices())
940 return false;
941 // fall-thru to increment case
942 [[fallthrough]];
943 case Instruction::Add:
944 case Instruction::Sub:
945 case Instruction::And:
946 case Instruction::Or:
947 case Instruction::Xor:
948 case Instruction::Shl:
949 case Instruction::LShr:
950 case Instruction::AShr: {
951 Value *IVOpnd =
952 !isa<Constant>(Val: I->getOperand(i: 0))
953 ? I->getOperand(i: 0)
954 : !isa<Constant>(Val: I->getOperand(i: 1)) ? I->getOperand(i: 1) : nullptr;
955 if (!IVOpnd)
956 return false;
957
958 // If increment operand is used outside of the loop, this speculation
959 // could cause extra live range interference.
960 if (MultiExitLoop) {
961 for (User *UseI : IVOpnd->users()) {
962 auto *UserInst = cast<Instruction>(Val: UseI);
963 if (!L->contains(Inst: UserInst))
964 return false;
965 }
966 }
967
968 if (seenIncrement)
969 return false;
970 seenIncrement = true;
971 break;
972 }
973 case Instruction::Trunc:
974 case Instruction::ZExt:
975 case Instruction::SExt:
976 // ignore type conversions
977 break;
978 }
979 }
980 return true;
981}
982
983/// Fold the loop tail into the loop exit by speculating the loop tail
984/// instructions. Typically, this is a single post-increment. In the case of a
985/// simple 2-block loop, hoisting the increment can be much better than
986/// duplicating the entire loop header. In the case of loops with early exits,
987/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
988/// canonical form so downstream passes can handle it.
989///
990/// I don't believe this invalidates SCEV.
991bool LoopRotate::simplifyLoopLatch(Loop *L) {
992 BasicBlock *Latch = L->getLoopLatch();
993 if (!Latch || Latch->hasAddressTaken())
994 return false;
995
996 BranchInst *Jmp = dyn_cast<BranchInst>(Val: Latch->getTerminator());
997 if (!Jmp || !Jmp->isUnconditional())
998 return false;
999
1000 BasicBlock *LastExit = Latch->getSinglePredecessor();
1001 if (!LastExit || !L->isLoopExiting(BB: LastExit))
1002 return false;
1003
1004 BranchInst *BI = dyn_cast<BranchInst>(Val: LastExit->getTerminator());
1005 if (!BI)
1006 return false;
1007
1008 if (!shouldSpeculateInstrs(Begin: Latch->begin(), End: Jmp->getIterator(), L))
1009 return false;
1010
1011 LLVM_DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
1012 << LastExit->getName() << "\n");
1013
1014 DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
1015 MergeBlockIntoPredecessor(BB: Latch, DTU: &DTU, LI, MSSAU, MemDep: nullptr,
1016 /*PredecessorWithTwoSuccessors=*/true);
1017
1018 if (SE) {
1019 // Merging blocks may remove blocks reference in the block disposition cache. Clear the cache.
1020 SE->forgetBlockAndLoopDispositions();
1021 }
1022
1023 if (MSSAU && VerifyMemorySSA)
1024 MSSAU->getMemorySSA()->verifyMemorySSA();
1025
1026 return true;
1027}
1028
1029/// Rotate \c L, and return true if any modification was made.
1030bool LoopRotate::processLoop(Loop *L) {
1031 // Save the loop metadata.
1032 MDNode *LoopMD = L->getLoopID();
1033
1034 bool SimplifiedLatch = false;
1035
1036 // Simplify the loop latch before attempting to rotate the header
1037 // upward. Rotation may not be needed if the loop tail can be folded into the
1038 // loop exit.
1039 if (!RotationOnly)
1040 SimplifiedLatch = simplifyLoopLatch(L);
1041
1042 bool MadeChange = rotateLoop(L, SimplifiedLatch);
1043 assert((!MadeChange || L->isLoopExiting(L->getLoopLatch())) &&
1044 "Loop latch should be exiting after loop-rotate.");
1045
1046 // Restore the loop metadata.
1047 // NB! We presume LoopRotation DOESN'T ADD its own metadata.
1048 if ((MadeChange || SimplifiedLatch) && LoopMD)
1049 L->setLoopID(LoopMD);
1050
1051 return MadeChange || SimplifiedLatch;
1052}
1053
1054
1055/// The utility to convert a loop into a loop with bottom test.
1056bool llvm::LoopRotation(Loop *L, LoopInfo *LI, const TargetTransformInfo *TTI,
1057 AssumptionCache *AC, DominatorTree *DT,
1058 ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
1059 const SimplifyQuery &SQ, bool RotationOnly = true,
1060 unsigned Threshold = unsigned(-1),
1061 bool IsUtilMode = true, bool PrepareForLTO) {
1062 LoopRotate LR(Threshold, LI, TTI, AC, DT, SE, MSSAU, SQ, RotationOnly,
1063 IsUtilMode, PrepareForLTO);
1064 return LR.processLoop(L);
1065}
1066