1 //===- LoopUnrollAndJam.cpp - Loop unroll and jam pass --------------------===//
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 implements an unroll and jam pass. Most of the work is done by
10 // Utils/UnrollLoopAndJam.cpp.
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/Transforms/Scalar/LoopUnrollAndJamPass.h"
14 #include "llvm/ADT/None.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/StringRef.h"
18 #include "llvm/Analysis/AssumptionCache.h"
19 #include "llvm/Analysis/CodeMetrics.h"
20 #include "llvm/Analysis/DependenceAnalysis.h"
21 #include "llvm/Analysis/LoopAnalysisManager.h"
22 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/Analysis/LoopPass.h"
24 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
25 #include "llvm/Analysis/ScalarEvolution.h"
26 #include "llvm/Analysis/TargetTransformInfo.h"
27 #include "llvm/IR/BasicBlock.h"
28 #include "llvm/IR/CFG.h"
29 #include "llvm/IR/Constant.h"
30 #include "llvm/IR/Constants.h"
31 #include "llvm/IR/Dominators.h"
32 #include "llvm/IR/Function.h"
33 #include "llvm/IR/Instruction.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/Metadata.h"
37 #include "llvm/IR/PassManager.h"
38 #include "llvm/InitializePasses.h"
39 #include "llvm/Pass.h"
40 #include "llvm/Support/Casting.h"
41 #include "llvm/Support/CommandLine.h"
42 #include "llvm/Support/Debug.h"
43 #include "llvm/Support/ErrorHandling.h"
44 #include "llvm/Support/raw_ostream.h"
45 #include "llvm/Transforms/Scalar.h"
46 #include "llvm/Transforms/Scalar/LoopPassManager.h"
47 #include "llvm/Transforms/Utils.h"
48 #include "llvm/Transforms/Utils/LoopUtils.h"
49 #include "llvm/Transforms/Utils/UnrollLoop.h"
50 #include <algorithm>
51 #include <cassert>
52 #include <cstdint>
53 #include <string>
54 
55 using namespace llvm;
56 
57 #define DEBUG_TYPE "loop-unroll-and-jam"
58 
59 /// @{
60 /// Metadata attribute names
61 static const char *const LLVMLoopUnrollAndJamFollowupAll =
62     "llvm.loop.unroll_and_jam.followup_all";
63 static const char *const LLVMLoopUnrollAndJamFollowupInner =
64     "llvm.loop.unroll_and_jam.followup_inner";
65 static const char *const LLVMLoopUnrollAndJamFollowupOuter =
66     "llvm.loop.unroll_and_jam.followup_outer";
67 static const char *const LLVMLoopUnrollAndJamFollowupRemainderInner =
68     "llvm.loop.unroll_and_jam.followup_remainder_inner";
69 static const char *const LLVMLoopUnrollAndJamFollowupRemainderOuter =
70     "llvm.loop.unroll_and_jam.followup_remainder_outer";
71 /// @}
72 
73 static cl::opt<bool>
74     AllowUnrollAndJam("allow-unroll-and-jam", cl::Hidden,
75                       cl::desc("Allows loops to be unroll-and-jammed."));
76 
77 static cl::opt<unsigned> UnrollAndJamCount(
78     "unroll-and-jam-count", cl::Hidden,
79     cl::desc("Use this unroll count for all loops including those with "
80              "unroll_and_jam_count pragma values, for testing purposes"));
81 
82 static cl::opt<unsigned> UnrollAndJamThreshold(
83     "unroll-and-jam-threshold", cl::init(60), cl::Hidden,
84     cl::desc("Threshold to use for inner loop when doing unroll and jam."));
85 
86 static cl::opt<unsigned> PragmaUnrollAndJamThreshold(
87     "pragma-unroll-and-jam-threshold", cl::init(1024), cl::Hidden,
88     cl::desc("Unrolled size limit for loops with an unroll_and_jam(full) or "
89              "unroll_count pragma."));
90 
91 // Returns the loop hint metadata node with the given name (for example,
92 // "llvm.loop.unroll.count").  If no such metadata node exists, then nullptr is
93 // returned.
94 static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
95   if (MDNode *LoopID = L->getLoopID())
96     return GetUnrollMetadata(LoopID, Name);
97   return nullptr;
98 }
99 
100 // Returns true if the loop has any metadata starting with Prefix. For example a
101 // Prefix of "llvm.loop.unroll." returns true if we have any unroll metadata.
102 static bool HasAnyUnrollPragma(const Loop *L, StringRef Prefix) {
103   if (MDNode *LoopID = L->getLoopID()) {
104     // First operand should refer to the loop id itself.
105     assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
106     assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
107 
108     for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
109       MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
110       if (!MD)
111         continue;
112 
113       MDString *S = dyn_cast<MDString>(MD->getOperand(0));
114       if (!S)
115         continue;
116 
117       if (S->getString().startswith(Prefix))
118         return true;
119     }
120   }
121   return false;
122 }
123 
124 // Returns true if the loop has an unroll_and_jam(enable) pragma.
125 static bool HasUnrollAndJamEnablePragma(const Loop *L) {
126   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll_and_jam.enable");
127 }
128 
129 // If loop has an unroll_and_jam_count pragma return the (necessarily
130 // positive) value from the pragma.  Otherwise return 0.
131 static unsigned UnrollAndJamCountPragmaValue(const Loop *L) {
132   MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll_and_jam.count");
133   if (MD) {
134     assert(MD->getNumOperands() == 2 &&
135            "Unroll count hint metadata should have two operands.");
136     unsigned Count =
137         mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
138     assert(Count >= 1 && "Unroll count must be positive.");
139     return Count;
140   }
141   return 0;
142 }
143 
144 // Returns loop size estimation for unrolled loop.
145 static uint64_t
146 getUnrollAndJammedLoopSize(unsigned LoopSize,
147                            TargetTransformInfo::UnrollingPreferences &UP) {
148   assert(LoopSize >= UP.BEInsns && "LoopSize should not be less than BEInsns!");
149   return static_cast<uint64_t>(LoopSize - UP.BEInsns) * UP.Count + UP.BEInsns;
150 }
151 
152 // Calculates unroll and jam count and writes it to UP.Count. Returns true if
153 // unroll count was set explicitly.
154 static bool computeUnrollAndJamCount(
155     Loop *L, Loop *SubLoop, const TargetTransformInfo &TTI, DominatorTree &DT,
156     LoopInfo *LI, ScalarEvolution &SE,
157     const SmallPtrSetImpl<const Value *> &EphValues,
158     OptimizationRemarkEmitter *ORE, unsigned OuterTripCount,
159     unsigned OuterTripMultiple, unsigned OuterLoopSize, unsigned InnerTripCount,
160     unsigned InnerLoopSize, TargetTransformInfo::UnrollingPreferences &UP) {
161   // First up use computeUnrollCount from the loop unroller to get a count
162   // for unrolling the outer loop, plus any loops requiring explicit
163   // unrolling we leave to the unroller. This uses UP.Threshold /
164   // UP.PartialThreshold / UP.MaxCount to come up with sensible loop values.
165   // We have already checked that the loop has no unroll.* pragmas.
166   unsigned MaxTripCount = 0;
167   bool UseUpperBound = false;
168   bool ExplicitUnroll = computeUnrollCount(
169       L, TTI, DT, LI, SE, EphValues, ORE, OuterTripCount, MaxTripCount,
170       /*MaxOrZero*/ false, OuterTripMultiple, OuterLoopSize, UP, UseUpperBound);
171   if (ExplicitUnroll || UseUpperBound) {
172     // If the user explicitly set the loop as unrolled, dont UnJ it. Leave it
173     // for the unroller instead.
174     LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; explicit count set by "
175                          "computeUnrollCount\n");
176     UP.Count = 0;
177     return false;
178   }
179 
180   // Override with any explicit Count from the "unroll-and-jam-count" option.
181   bool UserUnrollCount = UnrollAndJamCount.getNumOccurrences() > 0;
182   if (UserUnrollCount) {
183     UP.Count = UnrollAndJamCount;
184     UP.Force = true;
185     if (UP.AllowRemainder &&
186         getUnrollAndJammedLoopSize(OuterLoopSize, UP) < UP.Threshold &&
187         getUnrollAndJammedLoopSize(InnerLoopSize, UP) <
188             UP.UnrollAndJamInnerLoopThreshold)
189       return true;
190   }
191 
192   // Check for unroll_and_jam pragmas
193   unsigned PragmaCount = UnrollAndJamCountPragmaValue(L);
194   if (PragmaCount > 0) {
195     UP.Count = PragmaCount;
196     UP.Runtime = true;
197     UP.Force = true;
198     if ((UP.AllowRemainder || (OuterTripMultiple % PragmaCount == 0)) &&
199         getUnrollAndJammedLoopSize(OuterLoopSize, UP) < UP.Threshold &&
200         getUnrollAndJammedLoopSize(InnerLoopSize, UP) <
201             UP.UnrollAndJamInnerLoopThreshold)
202       return true;
203   }
204 
205   bool PragmaEnableUnroll = HasUnrollAndJamEnablePragma(L);
206   bool ExplicitUnrollAndJamCount = PragmaCount > 0 || UserUnrollCount;
207   bool ExplicitUnrollAndJam = PragmaEnableUnroll || ExplicitUnrollAndJamCount;
208 
209   // If the loop has an unrolling pragma, we want to be more aggressive with
210   // unrolling limits.
211   if (ExplicitUnrollAndJam)
212     UP.UnrollAndJamInnerLoopThreshold = PragmaUnrollAndJamThreshold;
213 
214   if (!UP.AllowRemainder && getUnrollAndJammedLoopSize(InnerLoopSize, UP) >=
215                                 UP.UnrollAndJamInnerLoopThreshold) {
216     LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; can't create remainder and "
217                          "inner loop too large\n");
218     UP.Count = 0;
219     return false;
220   }
221 
222   // We have a sensible limit for the outer loop, now adjust it for the inner
223   // loop and UP.UnrollAndJamInnerLoopThreshold. If the outer limit was set
224   // explicitly, we want to stick to it.
225   if (!ExplicitUnrollAndJamCount && UP.AllowRemainder) {
226     while (UP.Count != 0 && getUnrollAndJammedLoopSize(InnerLoopSize, UP) >=
227                                 UP.UnrollAndJamInnerLoopThreshold)
228       UP.Count--;
229   }
230 
231   // If we are explicitly unroll and jamming, we are done. Otherwise there are a
232   // number of extra performance heuristics to check.
233   if (ExplicitUnrollAndJam)
234     return true;
235 
236   // If the inner loop count is known and small, leave the entire loop nest to
237   // be the unroller
238   if (InnerTripCount && InnerLoopSize * InnerTripCount < UP.Threshold) {
239     LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; small inner loop count is "
240                          "being left for the unroller\n");
241     UP.Count = 0;
242     return false;
243   }
244 
245   // Check for situations where UnJ is likely to be unprofitable. Including
246   // subloops with more than 1 block.
247   if (SubLoop->getBlocks().size() != 1) {
248     LLVM_DEBUG(
249         dbgs() << "Won't unroll-and-jam; More than one inner loop block\n");
250     UP.Count = 0;
251     return false;
252   }
253 
254   // Limit to loops where there is something to gain from unrolling and
255   // jamming the loop. In this case, look for loads that are invariant in the
256   // outer loop and can become shared.
257   unsigned NumInvariant = 0;
258   for (BasicBlock *BB : SubLoop->getBlocks()) {
259     for (Instruction &I : *BB) {
260       if (auto *Ld = dyn_cast<LoadInst>(&I)) {
261         Value *V = Ld->getPointerOperand();
262         const SCEV *LSCEV = SE.getSCEVAtScope(V, L);
263         if (SE.isLoopInvariant(LSCEV, L))
264           NumInvariant++;
265       }
266     }
267   }
268   if (NumInvariant == 0) {
269     LLVM_DEBUG(dbgs() << "Won't unroll-and-jam; No loop invariant loads\n");
270     UP.Count = 0;
271     return false;
272   }
273 
274   return false;
275 }
276 
277 static LoopUnrollResult
278 tryToUnrollAndJamLoop(Loop *L, DominatorTree &DT, LoopInfo *LI,
279                       ScalarEvolution &SE, const TargetTransformInfo &TTI,
280                       AssumptionCache &AC, DependenceInfo &DI,
281                       OptimizationRemarkEmitter &ORE, int OptLevel) {
282   // Quick checks of the correct loop form
283   if (!L->isLoopSimplifyForm() || L->getSubLoops().size() != 1)
284     return LoopUnrollResult::Unmodified;
285   Loop *SubLoop = L->getSubLoops()[0];
286   if (!SubLoop->isLoopSimplifyForm())
287     return LoopUnrollResult::Unmodified;
288 
289   BasicBlock *Latch = L->getLoopLatch();
290   BasicBlock *Exit = L->getExitingBlock();
291   BasicBlock *SubLoopLatch = SubLoop->getLoopLatch();
292   BasicBlock *SubLoopExit = SubLoop->getExitingBlock();
293 
294   if (Latch != Exit || SubLoopLatch != SubLoopExit)
295     return LoopUnrollResult::Unmodified;
296 
297   TargetTransformInfo::UnrollingPreferences UP =
298       gatherUnrollingPreferences(L, SE, TTI, nullptr, nullptr, OptLevel, None,
299                                  None, None, None, None, None, None, None);
300   if (AllowUnrollAndJam.getNumOccurrences() > 0)
301     UP.UnrollAndJam = AllowUnrollAndJam;
302   if (UnrollAndJamThreshold.getNumOccurrences() > 0)
303     UP.UnrollAndJamInnerLoopThreshold = UnrollAndJamThreshold;
304   // Exit early if unrolling is disabled.
305   if (!UP.UnrollAndJam || UP.UnrollAndJamInnerLoopThreshold == 0)
306     return LoopUnrollResult::Unmodified;
307 
308   LLVM_DEBUG(dbgs() << "Loop Unroll and Jam: F["
309                     << L->getHeader()->getParent()->getName() << "] Loop %"
310                     << L->getHeader()->getName() << "\n");
311 
312   TransformationMode EnableMode = hasUnrollAndJamTransformation(L);
313   if (EnableMode & TM_Disable)
314     return LoopUnrollResult::Unmodified;
315 
316   // A loop with any unroll pragma (enabling/disabling/count/etc) is left for
317   // the unroller, so long as it does not explicitly have unroll_and_jam
318   // metadata. This means #pragma nounroll will disable unroll and jam as well
319   // as unrolling
320   if (HasAnyUnrollPragma(L, "llvm.loop.unroll.") &&
321       !HasAnyUnrollPragma(L, "llvm.loop.unroll_and_jam.")) {
322     LLVM_DEBUG(dbgs() << "  Disabled due to pragma.\n");
323     return LoopUnrollResult::Unmodified;
324   }
325 
326   if (!isSafeToUnrollAndJam(L, SE, DT, DI)) {
327     LLVM_DEBUG(dbgs() << "  Disabled due to not being safe.\n");
328     return LoopUnrollResult::Unmodified;
329   }
330 
331   // Approximate the loop size and collect useful info
332   unsigned NumInlineCandidates;
333   bool NotDuplicatable;
334   bool Convergent;
335   SmallPtrSet<const Value *, 32> EphValues;
336   CodeMetrics::collectEphemeralValues(L, &AC, EphValues);
337   unsigned InnerLoopSize =
338       ApproximateLoopSize(SubLoop, NumInlineCandidates, NotDuplicatable,
339                           Convergent, TTI, EphValues, UP.BEInsns);
340   unsigned OuterLoopSize =
341       ApproximateLoopSize(L, NumInlineCandidates, NotDuplicatable, Convergent,
342                           TTI, EphValues, UP.BEInsns);
343   LLVM_DEBUG(dbgs() << "  Outer Loop Size: " << OuterLoopSize << "\n");
344   LLVM_DEBUG(dbgs() << "  Inner Loop Size: " << InnerLoopSize << "\n");
345   if (NotDuplicatable) {
346     LLVM_DEBUG(dbgs() << "  Not unrolling loop which contains non-duplicatable "
347                          "instructions.\n");
348     return LoopUnrollResult::Unmodified;
349   }
350   if (NumInlineCandidates != 0) {
351     LLVM_DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");
352     return LoopUnrollResult::Unmodified;
353   }
354   if (Convergent) {
355     LLVM_DEBUG(
356         dbgs() << "  Not unrolling loop with convergent instructions.\n");
357     return LoopUnrollResult::Unmodified;
358   }
359 
360   // Save original loop IDs for after the transformation.
361   MDNode *OrigOuterLoopID = L->getLoopID();
362   MDNode *OrigSubLoopID = SubLoop->getLoopID();
363 
364   // To assign the loop id of the epilogue, assign it before unrolling it so it
365   // is applied to every inner loop of the epilogue. We later apply the loop ID
366   // for the jammed inner loop.
367   Optional<MDNode *> NewInnerEpilogueLoopID = makeFollowupLoopID(
368       OrigOuterLoopID, {LLVMLoopUnrollAndJamFollowupAll,
369                         LLVMLoopUnrollAndJamFollowupRemainderInner});
370   if (NewInnerEpilogueLoopID.hasValue())
371     SubLoop->setLoopID(NewInnerEpilogueLoopID.getValue());
372 
373   // Find trip count and trip multiple
374   unsigned OuterTripCount = SE.getSmallConstantTripCount(L, Latch);
375   unsigned OuterTripMultiple = SE.getSmallConstantTripMultiple(L, Latch);
376   unsigned InnerTripCount = SE.getSmallConstantTripCount(SubLoop, SubLoopLatch);
377 
378   // Decide if, and by how much, to unroll
379   bool IsCountSetExplicitly = computeUnrollAndJamCount(
380       L, SubLoop, TTI, DT, LI, SE, EphValues, &ORE, OuterTripCount,
381       OuterTripMultiple, OuterLoopSize, InnerTripCount, InnerLoopSize, UP);
382   if (UP.Count <= 1)
383     return LoopUnrollResult::Unmodified;
384   // Unroll factor (Count) must be less or equal to TripCount.
385   if (OuterTripCount && UP.Count > OuterTripCount)
386     UP.Count = OuterTripCount;
387 
388   Loop *EpilogueOuterLoop = nullptr;
389   LoopUnrollResult UnrollResult = UnrollAndJamLoop(
390       L, UP.Count, OuterTripCount, OuterTripMultiple, UP.UnrollRemainder, LI,
391       &SE, &DT, &AC, &ORE, &EpilogueOuterLoop);
392 
393   // Assign new loop attributes.
394   if (EpilogueOuterLoop) {
395     Optional<MDNode *> NewOuterEpilogueLoopID = makeFollowupLoopID(
396         OrigOuterLoopID, {LLVMLoopUnrollAndJamFollowupAll,
397                           LLVMLoopUnrollAndJamFollowupRemainderOuter});
398     if (NewOuterEpilogueLoopID.hasValue())
399       EpilogueOuterLoop->setLoopID(NewOuterEpilogueLoopID.getValue());
400   }
401 
402   Optional<MDNode *> NewInnerLoopID =
403       makeFollowupLoopID(OrigOuterLoopID, {LLVMLoopUnrollAndJamFollowupAll,
404                                            LLVMLoopUnrollAndJamFollowupInner});
405   if (NewInnerLoopID.hasValue())
406     SubLoop->setLoopID(NewInnerLoopID.getValue());
407   else
408     SubLoop->setLoopID(OrigSubLoopID);
409 
410   if (UnrollResult == LoopUnrollResult::PartiallyUnrolled) {
411     Optional<MDNode *> NewOuterLoopID = makeFollowupLoopID(
412         OrigOuterLoopID,
413         {LLVMLoopUnrollAndJamFollowupAll, LLVMLoopUnrollAndJamFollowupOuter});
414     if (NewOuterLoopID.hasValue()) {
415       L->setLoopID(NewOuterLoopID.getValue());
416 
417       // Do not setLoopAlreadyUnrolled if a followup was given.
418       return UnrollResult;
419     }
420   }
421 
422   // If loop has an unroll count pragma or unrolled by explicitly set count
423   // mark loop as unrolled to prevent unrolling beyond that requested.
424   if (UnrollResult != LoopUnrollResult::FullyUnrolled && IsCountSetExplicitly)
425     L->setLoopAlreadyUnrolled();
426 
427   return UnrollResult;
428 }
429 
430 static bool tryToUnrollAndJamLoop(Function &F, DominatorTree &DT, LoopInfo &LI,
431                                   ScalarEvolution &SE,
432                                   const TargetTransformInfo &TTI,
433                                   AssumptionCache &AC, DependenceInfo &DI,
434                                   OptimizationRemarkEmitter &ORE,
435                                   int OptLevel) {
436   bool DidSomething = false;
437 
438   // The loop unroll and jam pass requires loops to be in simplified form, and also needs LCSSA.
439   // Since simplification may add new inner loops, it has to run before the
440   // legality and profitability checks. This means running the loop unroll and jam pass
441   // will simplify all loops, regardless of whether anything end up being
442   // unroll and jammed.
443   for (auto &L : LI) {
444     DidSomething |=
445         simplifyLoop(L, &DT, &LI, &SE, &AC, nullptr, false /* PreserveLCSSA */);
446     DidSomething |= formLCSSARecursively(*L, DT, &LI, &SE);
447   }
448 
449   SmallPriorityWorklist<Loop *, 4> Worklist;
450   internal::appendLoopsToWorklist(reverse(LI), Worklist);
451   while (!Worklist.empty()) {
452     Loop *L = Worklist.pop_back_val();
453     formLCSSA(*L, DT, &LI, &SE);
454     LoopUnrollResult Result =
455         tryToUnrollAndJamLoop(L, DT, &LI, SE, TTI, AC, DI, ORE, OptLevel);
456     if (Result != LoopUnrollResult::Unmodified)
457       DidSomething = true;
458   }
459 
460   return DidSomething;
461 }
462 
463 namespace {
464 
465 class LoopUnrollAndJam : public FunctionPass {
466 public:
467   static char ID; // Pass ID, replacement for typeid
468   unsigned OptLevel;
469 
470   LoopUnrollAndJam(int OptLevel = 2) : FunctionPass(ID), OptLevel(OptLevel) {
471     initializeLoopUnrollAndJamPass(*PassRegistry::getPassRegistry());
472   }
473 
474   bool runOnFunction(Function &F) override {
475     if (skipFunction(F))
476       return false;
477 
478     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
479     LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
480     ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
481     const TargetTransformInfo &TTI =
482         getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
483     auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
484     auto &DI = getAnalysis<DependenceAnalysisWrapperPass>().getDI();
485     auto &ORE = getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
486 
487     return tryToUnrollAndJamLoop(F, DT, LI, SE, TTI, AC, DI, ORE, OptLevel);
488   }
489 
490   /// This transformation requires natural loop information & requires that
491   /// loop preheaders be inserted into the CFG...
492   void getAnalysisUsage(AnalysisUsage &AU) const override {
493     AU.addRequired<DominatorTreeWrapperPass>();
494     AU.addRequired<LoopInfoWrapperPass>();
495     AU.addRequired<ScalarEvolutionWrapperPass>();
496     AU.addRequired<TargetTransformInfoWrapperPass>();
497     AU.addRequired<AssumptionCacheTracker>();
498     AU.addRequired<DependenceAnalysisWrapperPass>();
499     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
500   }
501 };
502 
503 } // end anonymous namespace
504 
505 char LoopUnrollAndJam::ID = 0;
506 
507 INITIALIZE_PASS_BEGIN(LoopUnrollAndJam, "loop-unroll-and-jam",
508                       "Unroll and Jam loops", false, false)
509 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
510 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
511 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
512 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
513 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
514 INITIALIZE_PASS_DEPENDENCY(DependenceAnalysisWrapperPass)
515 INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
516 INITIALIZE_PASS_END(LoopUnrollAndJam, "loop-unroll-and-jam",
517                     "Unroll and Jam loops", false, false)
518 
519 Pass *llvm::createLoopUnrollAndJamPass(int OptLevel) {
520   return new LoopUnrollAndJam(OptLevel);
521 }
522 
523 PreservedAnalyses LoopUnrollAndJamPass::run(Function &F,
524                                             FunctionAnalysisManager &AM) {
525   ScalarEvolution &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
526   LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
527   TargetTransformInfo &TTI = AM.getResult<TargetIRAnalysis>(F);
528   AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
529   DominatorTree &DT = AM.getResult<DominatorTreeAnalysis>(F);
530   DependenceInfo &DI = AM.getResult<DependenceAnalysis>(F);
531   OptimizationRemarkEmitter &ORE =
532       AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
533 
534   if (!tryToUnrollAndJamLoop(F, DT, LI, SE, TTI, AC, DI, ORE, OptLevel))
535     return PreservedAnalyses::all();
536 
537   return getLoopPassPreservedAnalyses();
538 }
539