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/IntrinsicInst.h"
45#include "llvm/IR/PredIteratorCache.h"
46#include "llvm/InitializePasses.h"
47#include "llvm/Pass.h"
48#include "llvm/Support/CommandLine.h"
49#include "llvm/Transforms/Utils.h"
50#include "llvm/Transforms/Utils/LoopUtils.h"
51#include "llvm/Transforms/Utils/SSAUpdater.h"
52using namespace llvm;
53
54#define DEBUG_TYPE "lcssa"
55
56STATISTIC(NumLCSSA, "Number of live out of a loop variables");
57
58#ifdef EXPENSIVE_CHECKS
59static bool VerifyLoopLCSSA = true;
60#else
61static bool VerifyLoopLCSSA = false;
62#endif
63static cl::opt<bool, true>
64 VerifyLoopLCSSAFlag("verify-loop-lcssa", cl::location(L&: VerifyLoopLCSSA),
65 cl::Hidden,
66 cl::desc("Verify loop lcssa form (time consuming)"));
67
68/// Return true if the specified block is in the list.
69static bool isExitBlock(BasicBlock *BB,
70 const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
71 return is_contained(Range: ExitBlocks, Element: BB);
72}
73
74// Cache the Loop ExitBlocks computed during the analysis. We expect to get a
75// lot of instructions within the same loops, computing the exit blocks is
76// expensive, and we're not mutating the loop structure.
77using LoopExitBlocksTy = SmallDenseMap<Loop *, SmallVector<BasicBlock *, 1>>;
78
79/// For every instruction from the worklist, check to see if it has any uses
80/// that are outside the current loop. If so, insert LCSSA PHI nodes and
81/// rewrite the uses.
82static bool
83formLCSSAForInstructionsImpl(SmallVectorImpl<Instruction *> &Worklist,
84 const DominatorTree &DT, const LoopInfo &LI,
85 ScalarEvolution *SE,
86 SmallVectorImpl<PHINode *> *PHIsToRemove,
87 SmallVectorImpl<PHINode *> *InsertedPHIs,
88 LoopExitBlocksTy &LoopExitBlocks) {
89 SmallVector<Use *, 16> UsesToRewrite;
90 SmallSetVector<PHINode *, 16> LocalPHIsToRemove;
91 PredIteratorCache PredCache;
92 bool Changed = false;
93
94 while (!Worklist.empty()) {
95 UsesToRewrite.clear();
96
97 Instruction *I = Worklist.pop_back_val();
98 assert(!I->getType()->isTokenTy() && "Tokens shouldn't be in the worklist");
99 BasicBlock *InstBB = I->getParent();
100 Loop *L = LI.getLoopFor(BB: InstBB);
101 assert(L && "Instruction belongs to a BB that's not part of a loop");
102 auto [It, Inserted] = LoopExitBlocks.try_emplace(Key: L);
103 if (Inserted)
104 L->getExitBlocks(ExitBlocks&: It->second);
105 const SmallVectorImpl<BasicBlock *> &ExitBlocks = It->second;
106
107 if (ExitBlocks.empty())
108 continue;
109
110 for (Use &U : make_early_inc_range(Range: I->uses())) {
111 Instruction *User = cast<Instruction>(Val: U.getUser());
112 BasicBlock *UserBB = User->getParent();
113
114 // Skip uses in unreachable blocks.
115 if (!DT.isReachableFromEntry(A: UserBB)) {
116 U.set(PoisonValue::get(T: I->getType()));
117 continue;
118 }
119
120 // For practical purposes, we consider that the use in a PHI
121 // occurs in the respective predecessor block. For more info,
122 // see the `phi` doc in LangRef and the LCSSA doc.
123 if (auto *PN = dyn_cast<PHINode>(Val: User))
124 UserBB = PN->getIncomingBlock(U);
125
126 if (InstBB != UserBB && !L->contains(BB: UserBB))
127 UsesToRewrite.push_back(Elt: &U);
128 }
129
130 // If there are no uses outside the loop, exit with no change.
131 if (UsesToRewrite.empty())
132 continue;
133
134 ++NumLCSSA; // We are applying the transformation
135
136 // Invoke instructions are special in that their result value is not
137 // available along their unwind edge. The code below tests to see whether
138 // DomBB dominates the value, so adjust DomBB to the normal destination
139 // block, which is effectively where the value is first usable.
140 BasicBlock *DomBB = InstBB;
141 if (auto *Inv = dyn_cast<InvokeInst>(Val: I))
142 DomBB = Inv->getNormalDest();
143
144 const DomTreeNode *DomNode = DT.getNode(BB: DomBB);
145
146 SmallVector<PHINode *, 16> AddedPHIs;
147 SmallVector<PHINode *, 8> PostProcessPHIs;
148
149 SmallVector<PHINode *, 4> LocalInsertedPHIs;
150 SSAUpdater SSAUpdate(&LocalInsertedPHIs);
151 SSAUpdate.Initialize(Ty: I->getType(), Name: I->getName());
152
153 // Insert the LCSSA phi's into all of the exit blocks dominated by the
154 // value, and add them to the Phi's map.
155 bool HasSCEV = SE && SE->isSCEVable(Ty: I->getType()) &&
156 SE->getExistingSCEV(V: I) != nullptr;
157 for (BasicBlock *ExitBB : ExitBlocks) {
158 if (!DT.dominates(A: DomNode, B: DT.getNode(BB: ExitBB)))
159 continue;
160
161 // If we already inserted something for this BB, don't reprocess it.
162 if (SSAUpdate.HasValueForBlock(BB: ExitBB))
163 continue;
164 PHINode *PN = PHINode::Create(Ty: I->getType(), NumReservedValues: PredCache.size(BB: ExitBB),
165 NameStr: I->getName() + ".lcssa");
166 PN->insertBefore(InsertPos: ExitBB->begin());
167 if (InsertedPHIs)
168 InsertedPHIs->push_back(Elt: PN);
169 // Get the debug location from the original instruction.
170 PN->setDebugLoc(I->getDebugLoc());
171
172 // Add inputs from inside the loop for this PHI. This is valid
173 // because `I` dominates `ExitBB` (checked above). This implies
174 // that every incoming block/edge is dominated by `I` as well,
175 // i.e. we can add uses of `I` to those incoming edges/append to the incoming
176 // blocks without violating the SSA dominance property.
177 for (BasicBlock *Pred : PredCache.get(BB: ExitBB)) {
178 PN->addIncoming(V: I, BB: Pred);
179
180 // If the exit block has a predecessor not within the loop, arrange for
181 // the incoming value use corresponding to that predecessor to be
182 // rewritten in terms of a different LCSSA PHI.
183 if (!L->contains(BB: Pred))
184 UsesToRewrite.push_back(
185 Elt: &PN->getOperandUse(i: PN->getOperandNumForIncomingValue(
186 i: PN->getNumIncomingValues() - 1)));
187 }
188
189 AddedPHIs.push_back(Elt: PN);
190
191 // Remember that this phi makes the value alive in this block.
192 SSAUpdate.AddAvailableValue(BB: ExitBB, V: PN);
193
194 // LoopSimplify might fail to simplify some loops (e.g. when indirect
195 // branches are involved). In such situations, it might happen that an
196 // exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we
197 // create PHIs in such an exit block, we are also inserting PHIs into L2's
198 // header. This could break LCSSA form for L2 because these inserted PHIs
199 // can also have uses outside of L2. Remember all PHIs in such situation
200 // as to revisit than later on. FIXME: Remove this if indirectbr support
201 // into LoopSimplify gets improved.
202 if (auto *OtherLoop = LI.getLoopFor(BB: ExitBB))
203 if (!L->contains(L: OtherLoop))
204 PostProcessPHIs.push_back(Elt: PN);
205
206 // If we have a cached SCEV for the original instruction, make sure the
207 // new LCSSA phi node is also cached. This makes sures that BECounts
208 // based on it will be invalidated when the LCSSA phi node is invalidated,
209 // which some passes rely on.
210 if (HasSCEV)
211 SE->getSCEV(V: PN);
212 }
213
214 // Rewrite all uses outside the loop in terms of the new PHIs we just
215 // inserted.
216 for (Use *UseToRewrite : UsesToRewrite) {
217 Instruction *User = cast<Instruction>(Val: UseToRewrite->getUser());
218 BasicBlock *UserBB = User->getParent();
219
220 // For practical purposes, we consider that the use in a PHI
221 // occurs in the respective predecessor block. For more info,
222 // see the `phi` doc in LangRef and the LCSSA doc.
223 if (auto *PN = dyn_cast<PHINode>(Val: User))
224 UserBB = PN->getIncomingBlock(U: *UseToRewrite);
225
226 // If this use is in an exit block, rewrite to use the newly inserted PHI.
227 // This is required for correctness because SSAUpdate doesn't handle uses
228 // in the same block. It assumes the PHI we inserted is at the end of the
229 // block.
230 if (isa<PHINode>(Val: UserBB->begin()) && isExitBlock(BB: UserBB, ExitBlocks)) {
231 UseToRewrite->set(&UserBB->front());
232 continue;
233 }
234
235 // If we added a single PHI, it must dominate all uses and we can directly
236 // rename it.
237 if (AddedPHIs.size() == 1) {
238 UseToRewrite->set(AddedPHIs[0]);
239 continue;
240 }
241
242 // Otherwise, do full PHI insertion.
243 SSAUpdate.RewriteUse(U&: *UseToRewrite);
244 }
245
246 SmallVector<DbgValueInst *, 4> DbgValues;
247 SmallVector<DbgVariableRecord *, 4> DbgVariableRecords;
248 llvm::findDbgValues(DbgValues, V: I, DbgVariableRecords: &DbgVariableRecords);
249
250 // Update pre-existing debug value uses that reside outside the loop.
251 for (auto *DVI : DbgValues) {
252 BasicBlock *UserBB = DVI->getParent();
253 if (InstBB == UserBB || L->contains(BB: UserBB))
254 continue;
255 // We currently only handle debug values residing in blocks that were
256 // traversed while rewriting the uses. If we inserted just a single PHI,
257 // we will handle all relevant debug values.
258 Value *V = AddedPHIs.size() == 1 ? AddedPHIs[0]
259 : SSAUpdate.FindValueForBlock(BB: UserBB);
260 if (V)
261 DVI->replaceVariableLocationOp(OldValue: I, NewValue: V);
262 }
263
264 // RemoveDIs: copy-paste of block above, using non-instruction debug-info
265 // records.
266 for (DbgVariableRecord *DVR : DbgVariableRecords) {
267 BasicBlock *UserBB = DVR->getMarker()->getParent();
268 if (InstBB == UserBB || L->contains(BB: UserBB))
269 continue;
270 // We currently only handle debug values residing in blocks that were
271 // traversed while rewriting the uses. If we inserted just a single PHI,
272 // we will handle all relevant debug values.
273 Value *V = AddedPHIs.size() == 1 ? AddedPHIs[0]
274 : SSAUpdate.FindValueForBlock(BB: UserBB);
275 if (V)
276 DVR->replaceVariableLocationOp(OldValue: I, NewValue: V);
277 }
278
279 // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
280 // to post-process them to keep LCSSA form.
281 for (PHINode *InsertedPN : LocalInsertedPHIs) {
282 if (auto *OtherLoop = LI.getLoopFor(BB: InsertedPN->getParent()))
283 if (!L->contains(L: OtherLoop))
284 PostProcessPHIs.push_back(Elt: InsertedPN);
285 if (InsertedPHIs)
286 InsertedPHIs->push_back(Elt: InsertedPN);
287 }
288
289 // Post process PHI instructions that were inserted into another disjoint
290 // loop and update their exits properly.
291 for (auto *PostProcessPN : PostProcessPHIs)
292 if (!PostProcessPN->use_empty())
293 Worklist.push_back(Elt: PostProcessPN);
294
295 // Keep track of PHI nodes that we want to remove because they did not have
296 // any uses rewritten.
297 for (PHINode *PN : AddedPHIs)
298 if (PN->use_empty())
299 LocalPHIsToRemove.insert(X: PN);
300
301 Changed = true;
302 }
303
304 // Remove PHI nodes that did not have any uses rewritten or add them to
305 // PHIsToRemove, so the caller can remove them after some additional cleanup.
306 // We need to redo the use_empty() check here, because even if the PHI node
307 // wasn't used when added to LocalPHIsToRemove, later added PHI nodes can be
308 // using it. This cleanup is not guaranteed to handle trees/cycles of PHI
309 // nodes that only are used by each other. Such situations has only been
310 // noticed when the input IR contains unreachable code, and leaving some extra
311 // redundant PHI nodes in such situations is considered a minor problem.
312 if (PHIsToRemove) {
313 PHIsToRemove->append(in_start: LocalPHIsToRemove.begin(), in_end: LocalPHIsToRemove.end());
314 } else {
315 for (PHINode *PN : LocalPHIsToRemove)
316 if (PN->use_empty())
317 PN->eraseFromParent();
318 }
319 return Changed;
320}
321
322/// For every instruction from the worklist, check to see if it has any uses
323/// that are outside the current loop. If so, insert LCSSA PHI nodes and
324/// rewrite the uses.
325bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
326 const DominatorTree &DT, const LoopInfo &LI,
327 ScalarEvolution *SE,
328 SmallVectorImpl<PHINode *> *PHIsToRemove,
329 SmallVectorImpl<PHINode *> *InsertedPHIs) {
330 LoopExitBlocksTy LoopExitBlocks;
331
332 return formLCSSAForInstructionsImpl(Worklist, DT, LI, SE, PHIsToRemove,
333 InsertedPHIs, LoopExitBlocks);
334}
335
336// Compute the set of BasicBlocks in the loop `L` dominating at least one exit.
337static void computeBlocksDominatingExits(
338 Loop &L, const DominatorTree &DT, ArrayRef<BasicBlock *> ExitBlocks,
339 SmallSetVector<BasicBlock *, 8> &BlocksDominatingExits) {
340 // We start from the exit blocks, as every block trivially dominates itself
341 // (not strictly).
342 SmallVector<BasicBlock *, 8> BBWorklist(ExitBlocks);
343
344 while (!BBWorklist.empty()) {
345 BasicBlock *BB = BBWorklist.pop_back_val();
346
347 // Check if this is a loop header. If this is the case, we're done.
348 if (L.getHeader() == BB)
349 continue;
350
351 // Otherwise, add its immediate predecessor in the dominator tree to the
352 // worklist, unless we visited it already.
353 BasicBlock *IDomBB = DT.getNode(BB)->getIDom()->getBlock();
354
355 // Exit blocks can have an immediate dominator not belonging to the
356 // loop. For an exit block to be immediately dominated by another block
357 // outside the loop, it implies not all paths from that dominator, to the
358 // exit block, go through the loop.
359 // Example:
360 //
361 // |---- A
362 // | |
363 // | B<--
364 // | | |
365 // |---> C --
366 // |
367 // D
368 //
369 // C is the exit block of the loop and it's immediately dominated by A,
370 // which doesn't belong to the loop.
371 if (!L.contains(BB: IDomBB))
372 continue;
373
374 if (BlocksDominatingExits.insert(X: IDomBB))
375 BBWorklist.push_back(Elt: IDomBB);
376 }
377}
378
379static bool formLCSSAImpl(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
380 ScalarEvolution *SE,
381 LoopExitBlocksTy &LoopExitBlocks) {
382 bool Changed = false;
383
384#ifdef EXPENSIVE_CHECKS
385 // Verify all sub-loops are in LCSSA form already.
386 for (Loop *SubLoop: L) {
387 (void)SubLoop; // Silence unused variable warning.
388 assert(SubLoop->isRecursivelyLCSSAForm(DT, *LI) && "Subloop not in LCSSA!");
389 }
390#endif
391
392 auto [It, Inserted] = LoopExitBlocks.try_emplace(Key: &L);
393 if (Inserted)
394 L.getExitBlocks(ExitBlocks&: It->second);
395 const SmallVectorImpl<BasicBlock *> &ExitBlocks = It->second;
396 if (ExitBlocks.empty())
397 return false;
398
399 SmallSetVector<BasicBlock *, 8> BlocksDominatingExits;
400
401 // We want to avoid use-scanning leveraging dominance informations.
402 // If a block doesn't dominate any of the loop exits, the none of the values
403 // defined in the loop can be used outside.
404 // We compute the set of blocks fullfilling the conditions in advance
405 // walking the dominator tree upwards until we hit a loop header.
406 computeBlocksDominatingExits(L, DT, ExitBlocks, BlocksDominatingExits);
407
408 SmallVector<Instruction *, 8> Worklist;
409
410 // Look at all the instructions in the loop, checking to see if they have uses
411 // outside the loop. If so, put them into the worklist to rewrite those uses.
412 for (BasicBlock *BB : BlocksDominatingExits) {
413 // Skip blocks that are part of any sub-loops, they must be in LCSSA
414 // already.
415 if (LI->getLoopFor(BB) != &L)
416 continue;
417 for (Instruction &I : *BB) {
418 // Reject two common cases fast: instructions with no uses (like stores)
419 // and instructions with one use that is in the same block as this.
420 if (I.use_empty() ||
421 (I.hasOneUse() && I.user_back()->getParent() == BB &&
422 !isa<PHINode>(Val: I.user_back())))
423 continue;
424
425 // Tokens cannot be used in PHI nodes, so we skip over them.
426 // We can run into tokens which are live out of a loop with catchswitch
427 // instructions in Windows EH if the catchswitch has one catchpad which
428 // is inside the loop and another which is not.
429 if (I.getType()->isTokenTy())
430 continue;
431
432 Worklist.push_back(Elt: &I);
433 }
434 }
435
436 Changed = formLCSSAForInstructionsImpl(Worklist, DT, LI: *LI, SE, PHIsToRemove: nullptr,
437 InsertedPHIs: nullptr, LoopExitBlocks);
438
439 assert(L.isLCSSAForm(DT));
440
441 return Changed;
442}
443
444bool llvm::formLCSSA(Loop &L, const DominatorTree &DT, const LoopInfo *LI,
445 ScalarEvolution *SE) {
446 LoopExitBlocksTy LoopExitBlocks;
447
448 return formLCSSAImpl(L, DT, LI, SE, LoopExitBlocks);
449}
450
451/// Process a loop nest depth first.
452static bool formLCSSARecursivelyImpl(Loop &L, const DominatorTree &DT,
453 const LoopInfo *LI, ScalarEvolution *SE,
454 LoopExitBlocksTy &LoopExitBlocks) {
455 bool Changed = false;
456
457 // Recurse depth-first through inner loops.
458 for (Loop *SubLoop : L.getSubLoops())
459 Changed |= formLCSSARecursivelyImpl(L&: *SubLoop, DT, LI, SE, LoopExitBlocks);
460
461 Changed |= formLCSSAImpl(L, DT, LI, SE, LoopExitBlocks);
462 return Changed;
463}
464
465/// Process a loop nest depth first.
466bool llvm::formLCSSARecursively(Loop &L, const DominatorTree &DT,
467 const LoopInfo *LI, ScalarEvolution *SE) {
468 LoopExitBlocksTy LoopExitBlocks;
469
470 return formLCSSARecursivelyImpl(L, DT, LI, SE, LoopExitBlocks);
471}
472
473/// Process all loops in the function, inner-most out.
474static bool formLCSSAOnAllLoops(const LoopInfo *LI, const DominatorTree &DT,
475 ScalarEvolution *SE) {
476 bool Changed = false;
477 for (const auto &L : *LI)
478 Changed |= formLCSSARecursively(L&: *L, DT, LI, SE);
479 return Changed;
480}
481
482namespace {
483struct LCSSAWrapperPass : public FunctionPass {
484 static char ID; // Pass identification, replacement for typeid
485 LCSSAWrapperPass() : FunctionPass(ID) {
486 initializeLCSSAWrapperPassPass(*PassRegistry::getPassRegistry());
487 }
488
489 // Cached analysis information for the current function.
490 DominatorTree *DT;
491 LoopInfo *LI;
492 ScalarEvolution *SE;
493
494 bool runOnFunction(Function &F) override;
495 void verifyAnalysis() const override {
496 // This check is very expensive. On the loop intensive compiles it may cause
497 // up to 10x slowdown. Currently it's disabled by default. LPPassManager
498 // always does limited form of the LCSSA verification. Similar reasoning
499 // was used for the LoopInfo verifier.
500 if (VerifyLoopLCSSA) {
501 assert(all_of(*LI,
502 [&](Loop *L) {
503 return L->isRecursivelyLCSSAForm(*DT, *LI);
504 }) &&
505 "LCSSA form is broken!");
506 }
507 };
508
509 /// This transformation requires natural loop information & requires that
510 /// loop preheaders be inserted into the CFG. It maintains both of these,
511 /// as well as the CFG. It also requires dominator information.
512 void getAnalysisUsage(AnalysisUsage &AU) const override {
513 AU.setPreservesCFG();
514
515 AU.addRequired<DominatorTreeWrapperPass>();
516 AU.addRequired<LoopInfoWrapperPass>();
517 AU.addPreservedID(ID&: LoopSimplifyID);
518 AU.addPreserved<AAResultsWrapperPass>();
519 AU.addPreserved<BasicAAWrapperPass>();
520 AU.addPreserved<GlobalsAAWrapperPass>();
521 AU.addPreserved<ScalarEvolutionWrapperPass>();
522 AU.addPreserved<SCEVAAWrapperPass>();
523 AU.addPreserved<BranchProbabilityInfoWrapperPass>();
524 AU.addPreserved<MemorySSAWrapperPass>();
525
526 // This is needed to perform LCSSA verification inside LPPassManager
527 AU.addRequired<LCSSAVerificationPass>();
528 AU.addPreserved<LCSSAVerificationPass>();
529 }
530};
531}
532
533char LCSSAWrapperPass::ID = 0;
534INITIALIZE_PASS_BEGIN(LCSSAWrapperPass, "lcssa", "Loop-Closed SSA Form Pass",
535 false, false)
536INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
537INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
538INITIALIZE_PASS_DEPENDENCY(LCSSAVerificationPass)
539INITIALIZE_PASS_END(LCSSAWrapperPass, "lcssa", "Loop-Closed SSA Form Pass",
540 false, false)
541
542Pass *llvm::createLCSSAPass() { return new LCSSAWrapperPass(); }
543char &llvm::LCSSAID = LCSSAWrapperPass::ID;
544
545/// Transform \p F into loop-closed SSA form.
546bool LCSSAWrapperPass::runOnFunction(Function &F) {
547 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
548 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
549 auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
550 SE = SEWP ? &SEWP->getSE() : nullptr;
551
552 return formLCSSAOnAllLoops(LI, DT: *DT, SE);
553}
554
555PreservedAnalyses LCSSAPass::run(Function &F, FunctionAnalysisManager &AM) {
556 auto &LI = AM.getResult<LoopAnalysis>(IR&: F);
557 auto &DT = AM.getResult<DominatorTreeAnalysis>(IR&: F);
558 auto *SE = AM.getCachedResult<ScalarEvolutionAnalysis>(IR&: F);
559 if (!formLCSSAOnAllLoops(LI: &LI, DT, SE))
560 return PreservedAnalyses::all();
561
562 PreservedAnalyses PA;
563 PA.preserveSet<CFGAnalyses>();
564 PA.preserve<ScalarEvolutionAnalysis>();
565 // BPI maps terminators to probabilities, since we don't modify the CFG, no
566 // updates are needed to preserve it.
567 PA.preserve<BranchProbabilityAnalysis>();
568 PA.preserve<MemorySSAAnalysis>();
569 return PA;
570}
571