1//===-- LCSSA.cpp - Convert loops into loop-closed SSA form ---------------===//
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 pass transforms loops by placing phi nodes at the end of the loops for
10// all values that are live across the loop boundary. For example, it turns
11// the left into the right code:
12//
13// for (...) for (...)
14// if (c) if (c)
15// X1 = ... X1 = ...
16// else else
17// X2 = ... X2 = ...
18// X3 = phi(X1, X2) X3 = phi(X1, X2)
19// ... = X3 + 4 X4 = phi(X3)
20// ... = X4 + 4
21//
22// This is still valid LLVM; the extra phi nodes are purely redundant, and will
23// be trivially eliminated by InstCombine. The major benefit of this
24// transformation is that it makes many other loop optimizations, such as
25// LoopUnswitching, simpler.
26//
27//===----------------------------------------------------------------------===//
28
29#include "llvm/Transforms/Utils/LCSSA.h"
30#include "llvm/ADT/STLExtras.h"
31#include "llvm/ADT/Statistic.h"
32#include "llvm/Analysis/AliasAnalysis.h"
33#include "llvm/Analysis/BasicAliasAnalysis.h"
34#include "llvm/Analysis/BranchProbabilityInfo.h"
35#include "llvm/Analysis/GlobalsModRef.h"
36#include "llvm/Analysis/LoopInfo.h"
37#include "llvm/Analysis/LoopPass.h"
38#include "llvm/Analysis/MemorySSA.h"
39#include "llvm/Analysis/ScalarEvolution.h"
40#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
41#include "llvm/IR/DebugInfo.h"
42#include "llvm/IR/Dominators.h"
43#include "llvm/IR/Instructions.h"
44#include "llvm/IR/PredIteratorCache.h"
45#include "llvm/InitializePasses.h"
46#include "llvm/Pass.h"
47#include "llvm/Support/CommandLine.h"
48#include "llvm/Transforms/Utils.h"
49#include "llvm/Transforms/Utils/LoopUtils.h"
50#include "llvm/Transforms/Utils/SSAUpdater.h"
51using namespace llvm;
52
53#define DEBUG_TYPE "lcssa"
54
55STATISTIC(NumLCSSA, "Number of live out of a loop variables");
56
57#ifdef EXPENSIVE_CHECKS
58static bool VerifyLoopLCSSA = true;
59#else
60static bool VerifyLoopLCSSA = false;
61#endif
62static cl::opt<bool, true>
63 VerifyLoopLCSSAFlag("verify-loop-lcssa", cl::location(L&: VerifyLoopLCSSA),
64 cl::Hidden,
65 cl::desc("Verify loop lcssa form (time consuming)"));
66
67/// Return true if the specified block is in the list.
68static bool isExitBlock(BasicBlock *BB,
69 const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
70 return is_contained(Range: ExitBlocks, Element: BB);
71}
72
73// Cache the Loop ExitBlocks computed during the analysis. We expect to get a
74// lot of instructions within the same loops, computing the exit blocks is
75// expensive, and we're not mutating the loop structure.
76using LoopExitBlocksTy = SmallDenseMap<Loop *, SmallVector<BasicBlock *, 1>>;
77
78/// For every instruction from the worklist, check to see if it has any uses
79/// that are outside the current loop. If so, insert LCSSA PHI nodes and
80/// rewrite the uses.
81static bool
82formLCSSAForInstructionsImpl(SmallVectorImpl<Instruction *> &Worklist,
83 const DominatorTree &DT, const LoopInfo &LI,
84 ScalarEvolution *SE,
85 SmallVectorImpl<PHINode *> *PHIsToRemove,
86 SmallVectorImpl<PHINode *> *InsertedPHIs,
87 LoopExitBlocksTy &LoopExitBlocks) {
88 SmallVector<Use *, 16> UsesToRewrite;
89 SmallSetVector<PHINode *, 16> LocalPHIsToRemove;
90 PredIteratorCache PredCache;
91 bool Changed = false;
92
93 while (!Worklist.empty()) {
94 UsesToRewrite.clear();
95
96 Instruction *I = Worklist.pop_back_val();
97 assert(!I->getType()->isTokenTy() && "Tokens shouldn't be in the worklist");
98 BasicBlock *InstBB = I->getParent();
99 Loop *L = LI.getLoopFor(BB: InstBB);
100 assert(L && "Instruction belongs to a BB that's not part of a loop");
101 auto [It, Inserted] = LoopExitBlocks.try_emplace(Key: L);
102 if (Inserted)
103 L->getExitBlocks(ExitBlocks&: It->second);
104 const SmallVectorImpl<BasicBlock *> &ExitBlocks = It->second;
105
106 if (ExitBlocks.empty())
107 continue;
108
109 for (Use &U : make_early_inc_range(Range: I->uses())) {
110 Instruction *User = cast<Instruction>(Val: U.getUser());
111 BasicBlock *UserBB = User->getParent();
112
113 // Skip uses in unreachable blocks.
114 if (!DT.isReachableFromEntry(A: UserBB)) {
115 U.set(PoisonValue::get(T: I->getType()));
116 continue;
117 }
118
119 // For practical purposes, we consider that the use in a PHI
120 // occurs in the respective predecessor block. For more info,
121 // see the `phi` doc in LangRef and the LCSSA doc.
122 if (auto *PN = dyn_cast<PHINode>(Val: User))
123 UserBB = PN->getIncomingBlock(U);
124
125 if (InstBB != UserBB && !L->contains(BB: UserBB))
126 UsesToRewrite.push_back(Elt: &U);
127 }
128
129 // If there are no uses outside the loop, exit with no change.
130 if (UsesToRewrite.empty())
131 continue;
132
133 ++NumLCSSA; // We are applying the transformation
134
135 // Invoke instructions are special in that their result value is not
136 // available along their unwind edge. The code below tests to see whether
137 // DomBB dominates the value, so adjust DomBB to the normal destination
138 // block, which is effectively where the value is first usable.
139 BasicBlock *DomBB = InstBB;
140 if (auto *Inv = dyn_cast<InvokeInst>(Val: I))
141 DomBB = Inv->getNormalDest();
142
143 const DomTreeNode *DomNode = DT.getNode(BB: DomBB);
144
145 SmallVector<PHINode *, 16> AddedPHIs;
146 SmallVector<PHINode *, 8> PostProcessPHIs;
147
148 SmallVector<PHINode *, 4> LocalInsertedPHIs;
149 SSAUpdater SSAUpdate(&LocalInsertedPHIs);
150 SSAUpdate.Initialize(Ty: I->getType(), Name: I->getName());
151
152 // Insert the LCSSA phi's into all of the exit blocks dominated by the
153 // value, and add them to the Phi's map.
154 bool HasSCEV = SE && SE->isSCEVable(Ty: I->getType()) &&
155 SE->getExistingSCEV(V: I) != nullptr;
156 for (BasicBlock *ExitBB : ExitBlocks) {
157 if (!DT.dominates(A: DomNode, B: DT.getNode(BB: ExitBB)))
158 continue;
159
160 // If we already inserted something for this BB, don't reprocess it.
161 if (SSAUpdate.HasValueForBlock(BB: ExitBB))
162 continue;
163 PHINode *PN = PHINode::Create(Ty: I->getType(), NumReservedValues: PredCache.size(BB: ExitBB),
164 NameStr: I->getName() + ".lcssa");
165 PN->insertBefore(InsertPos: ExitBB->begin());
166 if (InsertedPHIs)
167 InsertedPHIs->push_back(Elt: PN);
168 // Get the debug location from the original instruction.
169 PN->setDebugLoc(I->getDebugLoc());
170
171 // Add inputs from inside the loop for this PHI. This is valid
172 // because `I` dominates `ExitBB` (checked above). This implies
173 // that every incoming block/edge is dominated by `I` as well,
174 // i.e. we can add uses of `I` to those incoming edges/append to the incoming
175 // blocks without violating the SSA dominance property.
176 for (BasicBlock *Pred : PredCache.get(BB: ExitBB)) {
177 PN->addIncoming(V: I, BB: Pred);
178
179 // If the exit block has a predecessor not within the loop, arrange for
180 // the incoming value use corresponding to that predecessor to be
181 // rewritten in terms of a different LCSSA PHI.
182 if (!L->contains(BB: Pred))
183 UsesToRewrite.push_back(
184 Elt: &PN->getOperandUse(i: PN->getOperandNumForIncomingValue(
185 i: PN->getNumIncomingValues() - 1)));
186 }
187
188 AddedPHIs.push_back(Elt: PN);
189
190 // Remember that this phi makes the value alive in this block.
191 SSAUpdate.AddAvailableValue(BB: ExitBB, V: PN);
192
193 // LoopSimplify might fail to simplify some loops (e.g. when indirect
194 // branches are involved). In such situations, it might happen that an
195 // exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we
196 // create PHIs in such an exit block, we are also inserting PHIs into L2's
197 // header. This could break LCSSA form for L2 because these inserted PHIs
198 // can also have uses outside of L2. Remember all PHIs in such situation
199 // as to revisit than later on. FIXME: Remove this if indirectbr support
200 // into LoopSimplify gets improved.
201 if (auto *OtherLoop = LI.getLoopFor(BB: ExitBB))
202 if (!L->contains(L: OtherLoop))
203 PostProcessPHIs.push_back(Elt: PN);
204
205 // If we have a cached SCEV for the original instruction, make sure the
206 // new LCSSA phi node is also cached. This makes sures that BECounts
207 // based on it will be invalidated when the LCSSA phi node is invalidated,
208 // which some passes rely on.
209 if (HasSCEV)
210 SE->getSCEV(V: PN);
211 }
212
213 // Rewrite all uses outside the loop in terms of the new PHIs we just
214 // inserted.
215 for (Use *UseToRewrite : UsesToRewrite) {
216 Instruction *User = cast<Instruction>(Val: UseToRewrite->getUser());
217 BasicBlock *UserBB = User->getParent();
218
219 // For practical purposes, we consider that the use in a PHI
220 // occurs in the respective predecessor block. For more info,
221 // see the `phi` doc in LangRef and the LCSSA doc.
222 if (auto *PN = dyn_cast<PHINode>(Val: User))
223 UserBB = PN->getIncomingBlock(U: *UseToRewrite);
224
225 // If this use is in an exit block, rewrite to use the newly inserted PHI.
226 // This is required for correctness because SSAUpdate doesn't handle uses
227 // in the same block. It assumes the PHI we inserted is at the end of the
228 // block.
229 if (isa<PHINode>(Val: UserBB->begin()) && isExitBlock(BB: UserBB, ExitBlocks)) {
230 UseToRewrite->set(&UserBB->front());
231 continue;
232 }
233
234 // If we added a single PHI, it must dominate all uses and we can directly
235 // rename it.
236 if (AddedPHIs.size() == 1) {
237 UseToRewrite->set(AddedPHIs[0]);
238 continue;
239 }
240
241 // Otherwise, do full PHI insertion.
242 SSAUpdate.RewriteUse(U&: *UseToRewrite);
243 }
244
245 SmallVector<DbgVariableRecord *, 4> DbgVariableRecords;
246 llvm::findDbgValues(V: I, DbgVariableRecords);
247
248 // Update pre-existing debug value uses that reside outside the loop.
249 for (DbgVariableRecord *DVR : DbgVariableRecords) {
250 BasicBlock *UserBB = DVR->getMarker()->getParent();
251 if (InstBB == UserBB || L->contains(BB: UserBB))
252 continue;
253 // We currently only handle debug values residing in blocks that were
254 // traversed while rewriting the uses. If we inserted just a single PHI,
255 // we will handle all relevant debug values.
256 Value *V = AddedPHIs.size() == 1 ? AddedPHIs[0]
257 : SSAUpdate.FindValueForBlock(BB: UserBB);
258 if (V)
259 DVR->replaceVariableLocationOp(OldValue: I, NewValue: V);
260 }
261
262 // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
263 // to post-process them to keep LCSSA form.
264 for (PHINode *InsertedPN : LocalInsertedPHIs) {
265 if (auto *OtherLoop = LI.getLoopFor(BB: InsertedPN->getParent()))
266 if (!L->contains(L: OtherLoop))
267 PostProcessPHIs.push_back(Elt: InsertedPN);
268 if (InsertedPHIs)
269 InsertedPHIs->push_back(Elt: InsertedPN);
270 }
271
272 // Post process PHI instructions that were inserted into another disjoint
273 // loop and update their exits properly.
274 for (auto *PostProcessPN : PostProcessPHIs)
275 if (!PostProcessPN->use_empty())
276 Worklist.push_back(Elt: PostProcessPN);
277
278 // Keep track of PHI nodes that we want to remove because they did not have
279 // any uses rewritten.
280 for (PHINode *PN : AddedPHIs)
281 if (PN->use_empty())
282 LocalPHIsToRemove.insert(X: PN);
283
284 Changed = true;
285 }
286
287 // Remove PHI nodes that did not have any uses rewritten or add them to
288 // PHIsToRemove, so the caller can remove them after some additional cleanup.
289 // We need to redo the use_empty() check here, because even if the PHI node
290 // wasn't used when added to LocalPHIsToRemove, later added PHI nodes can be
291 // using it. This cleanup is not guaranteed to handle trees/cycles of PHI
292 // nodes that only are used by each other. Such situations has only been
293 // noticed when the input IR contains unreachable code, and leaving some extra
294 // redundant PHI nodes in such situations is considered a minor problem.
295 if (PHIsToRemove) {
296 PHIsToRemove->append(in_start: LocalPHIsToRemove.begin(), in_end: LocalPHIsToRemove.end());
297 } else {
298 for (PHINode *PN : LocalPHIsToRemove)
299 if (PN->use_empty())
300 PN->eraseFromParent();
301 }
302 return Changed;
303}
304
305/// For every instruction from the worklist, check to see if it has any uses
306/// that are outside the current loop. If so, insert LCSSA PHI nodes and
307/// rewrite the uses.
308bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
309 const DominatorTree &DT, const LoopInfo &LI,
310 ScalarEvolution *SE,
311 SmallVectorImpl<PHINode *> *PHIsToRemove,
312 SmallVectorImpl<PHINode *> *InsertedPHIs) {
313 LoopExitBlocksTy LoopExitBlocks;
314
315 return formLCSSAForInstructionsImpl(Worklist, DT, LI, SE, PHIsToRemove,
316 InsertedPHIs, LoopExitBlocks);
317}
318
319// Compute the set of BasicBlocks in the loop `L` dominating at least one exit.
320static void computeBlocksDominatingExits(
321 Loop &L, const DominatorTree &DT, ArrayRef<BasicBlock *> ExitBlocks,
322 SmallSetVector<BasicBlock *, 8> &BlocksDominatingExits) {
323 // We start from the exit blocks, as every block trivially dominates itself
324 // (not strictly).
325 SmallVector<BasicBlock *, 8> BBWorklist(ExitBlocks);
326
327 while (!BBWorklist.empty()) {
328 BasicBlock *BB = BBWorklist.pop_back_val();
329
330 // Check if this is a loop header. If this is the case, we're done.
331 if (L.getHeader() == BB)
332 continue;
333
334 // Otherwise, add its immediate predecessor in the dominator tree to the
335 // worklist, unless we visited it already.
336 BasicBlock *IDomBB = DT.getNode(BB)->getIDom()->getBlock();
337
338 // Exit blocks can have an immediate dominator not belonging to the
339 // loop. For an exit block to be immediately dominated by another block
340 // outside the loop, it implies not all paths from that dominator, to the
341 // exit block, go through the loop.
342 // Example:
343 //
344 // |---- A
345 // | |
346 // | B<--
347 // | | |
348 // |---> C --
349 // |
350 // D
351 //
352 // C is the exit block of the loop and it's immediately dominated by A,
353 // which doesn't belong to the loop.
354 if (!L.contains(BB: IDomBB))
355 continue;
356
357 if (BlocksDominatingExits.insert(X: IDomBB))
358 BBWorklist.push_back(Elt: IDomBB);
359 }
360}
361
362static bool formLCSSAImpl(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
363 ScalarEvolution *SE,
364 LoopExitBlocksTy &LoopExitBlocks) {
365 bool Changed = false;
366
367#ifdef EXPENSIVE_CHECKS
368 // Verify all sub-loops are in LCSSA form already.
369 for (Loop *SubLoop: L) {
370 (void)SubLoop; // Silence unused variable warning.
371 assert(SubLoop->isRecursivelyLCSSAForm(DT, *LI) && "Subloop not in LCSSA!");
372 }
373#endif
374
375 auto [It, Inserted] = LoopExitBlocks.try_emplace(Key: &L);
376 if (Inserted)
377 L.getExitBlocks(ExitBlocks&: It->second);
378 const SmallVectorImpl<BasicBlock *> &ExitBlocks = It->second;
379 if (ExitBlocks.empty())
380 return false;
381
382 SmallSetVector<BasicBlock *, 8> BlocksDominatingExits;
383
384 // We want to avoid use-scanning leveraging dominance informations.
385 // If a block doesn't dominate any of the loop exits, the none of the values
386 // defined in the loop can be used outside.
387 // We compute the set of blocks fullfilling the conditions in advance
388 // walking the dominator tree upwards until we hit a loop header.
389 computeBlocksDominatingExits(L, DT, ExitBlocks, BlocksDominatingExits);
390
391 SmallVector<Instruction *, 8> Worklist;
392
393 // Look at all the instructions in the loop, checking to see if they have uses
394 // outside the loop. If so, put them into the worklist to rewrite those uses.
395 for (BasicBlock *BB : BlocksDominatingExits) {
396 // Skip blocks that are part of any sub-loops, they must be in LCSSA
397 // already.
398 if (LI->getLoopFor(BB) != &L)
399 continue;
400 for (Instruction &I : *BB) {
401 // Reject two common cases fast: instructions with no uses (like stores)
402 // and instructions with one use that is in the same block as this.
403 if (I.use_empty() ||
404 (I.hasOneUse() && I.user_back()->getParent() == BB &&
405 !isa<PHINode>(Val: I.user_back())))
406 continue;
407
408 // Tokens cannot be used in PHI nodes, so we skip over them.
409 // We can run into tokens which are live out of a loop with catchswitch
410 // instructions in Windows EH if the catchswitch has one catchpad which
411 // is inside the loop and another which is not.
412 if (I.getType()->isTokenTy())
413 continue;
414
415 Worklist.push_back(Elt: &I);
416 }
417 }
418
419 Changed = formLCSSAForInstructionsImpl(Worklist, DT, LI: *LI, SE, PHIsToRemove: nullptr,
420 InsertedPHIs: nullptr, LoopExitBlocks);
421
422 assert(L.isLCSSAForm(DT));
423
424 return Changed;
425}
426
427bool llvm::formLCSSA(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
428 ScalarEvolution *SE) {
429 LoopExitBlocksTy LoopExitBlocks;
430
431 return formLCSSAImpl(L, DT, LI, SE, LoopExitBlocks);
432}
433
434/// Process a loop nest depth first.
435static bool formLCSSARecursivelyImpl(Loop &L, const DominatorTree &DT,
436 const LoopInfo *LI, ScalarEvolution *SE,
437 LoopExitBlocksTy &LoopExitBlocks) {
438 bool Changed = false;
439
440 // Recurse depth-first through inner loops.
441 for (Loop *SubLoop : L.getSubLoops())
442 Changed |= formLCSSARecursivelyImpl(L&: *SubLoop, DT, LI, SE, LoopExitBlocks);
443
444 Changed |= formLCSSAImpl(L, DT, LI, SE, LoopExitBlocks);
445 return Changed;
446}
447
448/// Process a loop nest depth first.
449bool llvm::formLCSSARecursively(Loop &L, const DominatorTree &DT,
450 const LoopInfo *LI, ScalarEvolution *SE) {
451 LoopExitBlocksTy LoopExitBlocks;
452
453 return formLCSSARecursivelyImpl(L, DT, LI, SE, LoopExitBlocks);
454}
455
456/// Process all loops in the function, inner-most out.
457static bool formLCSSAOnAllLoops(const LoopInfo *LI, const DominatorTree &DT,
458 ScalarEvolution *SE) {
459 bool Changed = false;
460 for (const auto &L : *LI)
461 Changed |= formLCSSARecursively(L&: *L, DT, LI, SE);
462 return Changed;
463}
464
465namespace {
466struct LCSSAWrapperPass : public FunctionPass {
467 static char ID; // Pass identification, replacement for typeid
468 LCSSAWrapperPass() : FunctionPass(ID) {
469 initializeLCSSAWrapperPassPass(*PassRegistry::getPassRegistry());
470 }
471
472 // Cached analysis information for the current function.
473 DominatorTree *DT;
474 LoopInfo *LI;
475 ScalarEvolution *SE;
476
477 bool runOnFunction(Function &F) override;
478 void verifyAnalysis() const override {
479 // This check is very expensive. On the loop intensive compiles it may cause
480 // up to 10x slowdown. Currently it's disabled by default. LPPassManager
481 // always does limited form of the LCSSA verification. Similar reasoning
482 // was used for the LoopInfo verifier.
483 if (VerifyLoopLCSSA) {
484 assert(all_of(*LI,
485 [&](Loop *L) {
486 return L->isRecursivelyLCSSAForm(*DT, *LI);
487 }) &&
488 "LCSSA form is broken!");
489 }
490 };
491
492 /// This transformation requires natural loop information & requires that
493 /// loop preheaders be inserted into the CFG. It maintains both of these,
494 /// as well as the CFG. It also requires dominator information.
495 void getAnalysisUsage(AnalysisUsage &AU) const override {
496 AU.setPreservesCFG();
497
498 AU.addRequired<DominatorTreeWrapperPass>();
499 AU.addRequired<LoopInfoWrapperPass>();
500 AU.addPreservedID(ID&: LoopSimplifyID);
501 AU.addPreserved<AAResultsWrapperPass>();
502 AU.addPreserved<BasicAAWrapperPass>();
503 AU.addPreserved<GlobalsAAWrapperPass>();
504 AU.addPreserved<ScalarEvolutionWrapperPass>();
505 AU.addPreserved<SCEVAAWrapperPass>();
506 AU.addPreserved<BranchProbabilityInfoWrapperPass>();
507 AU.addPreserved<MemorySSAWrapperPass>();
508
509 // This is needed to perform LCSSA verification inside LPPassManager
510 AU.addRequired<LCSSAVerificationPass>();
511 AU.addPreserved<LCSSAVerificationPass>();
512 }
513};
514}
515
516char LCSSAWrapperPass::ID = 0;
517INITIALIZE_PASS_BEGIN(LCSSAWrapperPass, "lcssa", "Loop-Closed SSA Form Pass",
518 false, false)
519INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
520INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
521INITIALIZE_PASS_DEPENDENCY(LCSSAVerificationPass)
522INITIALIZE_PASS_END(LCSSAWrapperPass, "lcssa", "Loop-Closed SSA Form Pass",
523 false, false)
524
525Pass *llvm::createLCSSAPass() { return new LCSSAWrapperPass(); }
526char &llvm::LCSSAID = LCSSAWrapperPass::ID;
527
528/// Transform \p F into loop-closed SSA form.
529bool LCSSAWrapperPass::runOnFunction(Function &F) {
530 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
531 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
532 auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
533 SE = SEWP ? &SEWP->getSE() : nullptr;
534
535 return formLCSSAOnAllLoops(LI, DT: *DT, SE);
536}
537
538PreservedAnalyses LCSSAPass::run(Function &F, FunctionAnalysisManager &AM) {
539 auto &LI = AM.getResult<LoopAnalysis>(IR&: F);
540 auto &DT = AM.getResult<DominatorTreeAnalysis>(IR&: F);
541 auto *SE = AM.getCachedResult<ScalarEvolutionAnalysis>(IR&: F);
542 if (!formLCSSAOnAllLoops(LI: &LI, DT, SE))
543 return PreservedAnalyses::all();
544
545 PreservedAnalyses PA;
546 PA.preserveSet<CFGAnalyses>();
547 PA.preserve<ScalarEvolutionAnalysis>();
548 // BPI maps terminators to probabilities, since we don't modify the CFG, no
549 // updates are needed to preserve it.
550 PA.preserve<BranchProbabilityAnalysis>();
551 PA.preserve<MemorySSAAnalysis>();
552 return PA;
553}
554