xref: /freebsd/contrib/llvm-project/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp (revision 2f513db72b034fd5ef7f080b11be5c711c15186a)
1 //===- LoopUnroll.cpp - Loop unroller 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 a simple loop unroller.  It works best when loops have
10 // been canonicalized by the -indvars pass, allowing it to determine the trip
11 // counts of loops easily.
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Transforms/Scalar/LoopUnrollPass.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/DenseMapInfo.h"
17 #include "llvm/ADT/DenseSet.h"
18 #include "llvm/ADT/None.h"
19 #include "llvm/ADT/Optional.h"
20 #include "llvm/ADT/STLExtras.h"
21 #include "llvm/ADT/SetVector.h"
22 #include "llvm/ADT/SmallPtrSet.h"
23 #include "llvm/ADT/SmallVector.h"
24 #include "llvm/ADT/StringRef.h"
25 #include "llvm/Analysis/AssumptionCache.h"
26 #include "llvm/Analysis/BlockFrequencyInfo.h"
27 #include "llvm/Analysis/CodeMetrics.h"
28 #include "llvm/Analysis/LazyBlockFrequencyInfo.h"
29 #include "llvm/Analysis/LoopAnalysisManager.h"
30 #include "llvm/Analysis/LoopInfo.h"
31 #include "llvm/Analysis/LoopPass.h"
32 #include "llvm/Analysis/LoopUnrollAnalyzer.h"
33 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
34 #include "llvm/Analysis/ProfileSummaryInfo.h"
35 #include "llvm/Analysis/ScalarEvolution.h"
36 #include "llvm/Analysis/TargetTransformInfo.h"
37 #include "llvm/IR/BasicBlock.h"
38 #include "llvm/IR/CFG.h"
39 #include "llvm/IR/Constant.h"
40 #include "llvm/IR/Constants.h"
41 #include "llvm/IR/DiagnosticInfo.h"
42 #include "llvm/IR/Dominators.h"
43 #include "llvm/IR/Function.h"
44 #include "llvm/IR/Instruction.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/IR/IntrinsicInst.h"
47 #include "llvm/IR/Metadata.h"
48 #include "llvm/IR/PassManager.h"
49 #include "llvm/Pass.h"
50 #include "llvm/Support/Casting.h"
51 #include "llvm/Support/CommandLine.h"
52 #include "llvm/Support/Debug.h"
53 #include "llvm/Support/ErrorHandling.h"
54 #include "llvm/Support/raw_ostream.h"
55 #include "llvm/Transforms/Scalar.h"
56 #include "llvm/Transforms/Scalar/LoopPassManager.h"
57 #include "llvm/Transforms/Utils.h"
58 #include "llvm/Transforms/Utils/LoopSimplify.h"
59 #include "llvm/Transforms/Utils/LoopUtils.h"
60 #include "llvm/Transforms/Utils/SizeOpts.h"
61 #include "llvm/Transforms/Utils/UnrollLoop.h"
62 #include <algorithm>
63 #include <cassert>
64 #include <cstdint>
65 #include <limits>
66 #include <string>
67 #include <tuple>
68 #include <utility>
69 
70 using namespace llvm;
71 
72 #define DEBUG_TYPE "loop-unroll"
73 
74 cl::opt<bool> llvm::ForgetSCEVInLoopUnroll(
75     "forget-scev-loop-unroll", cl::init(false), cl::Hidden,
76     cl::desc("Forget everything in SCEV when doing LoopUnroll, instead of just"
77              " the current top-most loop. This is somtimes preferred to reduce"
78              " compile time."));
79 
80 static cl::opt<unsigned>
81     UnrollThreshold("unroll-threshold", cl::Hidden,
82                     cl::desc("The cost threshold for loop unrolling"));
83 
84 static cl::opt<unsigned> UnrollPartialThreshold(
85     "unroll-partial-threshold", cl::Hidden,
86     cl::desc("The cost threshold for partial loop unrolling"));
87 
88 static cl::opt<unsigned> UnrollMaxPercentThresholdBoost(
89     "unroll-max-percent-threshold-boost", cl::init(400), cl::Hidden,
90     cl::desc("The maximum 'boost' (represented as a percentage >= 100) applied "
91              "to the threshold when aggressively unrolling a loop due to the "
92              "dynamic cost savings. If completely unrolling a loop will reduce "
93              "the total runtime from X to Y, we boost the loop unroll "
94              "threshold to DefaultThreshold*std::min(MaxPercentThresholdBoost, "
95              "X/Y). This limit avoids excessive code bloat."));
96 
97 static cl::opt<unsigned> UnrollMaxIterationsCountToAnalyze(
98     "unroll-max-iteration-count-to-analyze", cl::init(10), cl::Hidden,
99     cl::desc("Don't allow loop unrolling to simulate more than this number of"
100              "iterations when checking full unroll profitability"));
101 
102 static cl::opt<unsigned> UnrollCount(
103     "unroll-count", cl::Hidden,
104     cl::desc("Use this unroll count for all loops including those with "
105              "unroll_count pragma values, for testing purposes"));
106 
107 static cl::opt<unsigned> UnrollMaxCount(
108     "unroll-max-count", cl::Hidden,
109     cl::desc("Set the max unroll count for partial and runtime unrolling, for"
110              "testing purposes"));
111 
112 static cl::opt<unsigned> UnrollFullMaxCount(
113     "unroll-full-max-count", cl::Hidden,
114     cl::desc(
115         "Set the max unroll count for full unrolling, for testing purposes"));
116 
117 static cl::opt<unsigned> UnrollPeelCount(
118     "unroll-peel-count", cl::Hidden,
119     cl::desc("Set the unroll peeling count, for testing purposes"));
120 
121 static cl::opt<bool>
122     UnrollAllowPartial("unroll-allow-partial", cl::Hidden,
123                        cl::desc("Allows loops to be partially unrolled until "
124                                 "-unroll-threshold loop size is reached."));
125 
126 static cl::opt<bool> UnrollAllowRemainder(
127     "unroll-allow-remainder", cl::Hidden,
128     cl::desc("Allow generation of a loop remainder (extra iterations) "
129              "when unrolling a loop."));
130 
131 static cl::opt<bool>
132     UnrollRuntime("unroll-runtime", cl::ZeroOrMore, cl::Hidden,
133                   cl::desc("Unroll loops with run-time trip counts"));
134 
135 static cl::opt<unsigned> UnrollMaxUpperBound(
136     "unroll-max-upperbound", cl::init(8), cl::Hidden,
137     cl::desc(
138         "The max of trip count upper bound that is considered in unrolling"));
139 
140 static cl::opt<unsigned> PragmaUnrollThreshold(
141     "pragma-unroll-threshold", cl::init(16 * 1024), cl::Hidden,
142     cl::desc("Unrolled size limit for loops with an unroll(full) or "
143              "unroll_count pragma."));
144 
145 static cl::opt<unsigned> FlatLoopTripCountThreshold(
146     "flat-loop-tripcount-threshold", cl::init(5), cl::Hidden,
147     cl::desc("If the runtime tripcount for the loop is lower than the "
148              "threshold, the loop is considered as flat and will be less "
149              "aggressively unrolled."));
150 
151 static cl::opt<bool>
152     UnrollAllowPeeling("unroll-allow-peeling", cl::init(true), cl::Hidden,
153                        cl::desc("Allows loops to be peeled when the dynamic "
154                                 "trip count is known to be low."));
155 
156 static cl::opt<bool> UnrollUnrollRemainder(
157   "unroll-remainder", cl::Hidden,
158   cl::desc("Allow the loop remainder to be unrolled."));
159 
160 // This option isn't ever intended to be enabled, it serves to allow
161 // experiments to check the assumptions about when this kind of revisit is
162 // necessary.
163 static cl::opt<bool> UnrollRevisitChildLoops(
164     "unroll-revisit-child-loops", cl::Hidden,
165     cl::desc("Enqueue and re-visit child loops in the loop PM after unrolling. "
166              "This shouldn't typically be needed as child loops (or their "
167              "clones) were already visited."));
168 
169 /// A magic value for use with the Threshold parameter to indicate
170 /// that the loop unroll should be performed regardless of how much
171 /// code expansion would result.
172 static const unsigned NoThreshold = std::numeric_limits<unsigned>::max();
173 
174 /// Gather the various unrolling parameters based on the defaults, compiler
175 /// flags, TTI overrides and user specified parameters.
176 TargetTransformInfo::UnrollingPreferences llvm::gatherUnrollingPreferences(
177     Loop *L, ScalarEvolution &SE, const TargetTransformInfo &TTI,
178     BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI, int OptLevel,
179     Optional<unsigned> UserThreshold, Optional<unsigned> UserCount,
180     Optional<bool> UserAllowPartial, Optional<bool> UserRuntime,
181     Optional<bool> UserUpperBound, Optional<bool> UserAllowPeeling) {
182   TargetTransformInfo::UnrollingPreferences UP;
183 
184   // Set up the defaults
185   UP.Threshold = OptLevel > 2 ? 300 : 150;
186   UP.MaxPercentThresholdBoost = 400;
187   UP.OptSizeThreshold = 0;
188   UP.PartialThreshold = 150;
189   UP.PartialOptSizeThreshold = 0;
190   UP.Count = 0;
191   UP.PeelCount = 0;
192   UP.DefaultUnrollRuntimeCount = 8;
193   UP.MaxCount = std::numeric_limits<unsigned>::max();
194   UP.FullUnrollMaxCount = std::numeric_limits<unsigned>::max();
195   UP.BEInsns = 2;
196   UP.Partial = false;
197   UP.Runtime = false;
198   UP.AllowRemainder = true;
199   UP.UnrollRemainder = false;
200   UP.AllowExpensiveTripCount = false;
201   UP.Force = false;
202   UP.UpperBound = false;
203   UP.AllowPeeling = true;
204   UP.UnrollAndJam = false;
205   UP.UnrollAndJamInnerLoopThreshold = 60;
206 
207   // Override with any target specific settings
208   TTI.getUnrollingPreferences(L, SE, UP);
209 
210   // Apply size attributes
211   bool OptForSize = L->getHeader()->getParent()->hasOptSize() ||
212                     llvm::shouldOptimizeForSize(L->getHeader(), PSI, BFI);
213   if (OptForSize) {
214     UP.Threshold = UP.OptSizeThreshold;
215     UP.PartialThreshold = UP.PartialOptSizeThreshold;
216     UP.MaxPercentThresholdBoost = 100;
217   }
218 
219   // Apply any user values specified by cl::opt
220   if (UnrollThreshold.getNumOccurrences() > 0)
221     UP.Threshold = UnrollThreshold;
222   if (UnrollPartialThreshold.getNumOccurrences() > 0)
223     UP.PartialThreshold = UnrollPartialThreshold;
224   if (UnrollMaxPercentThresholdBoost.getNumOccurrences() > 0)
225     UP.MaxPercentThresholdBoost = UnrollMaxPercentThresholdBoost;
226   if (UnrollMaxCount.getNumOccurrences() > 0)
227     UP.MaxCount = UnrollMaxCount;
228   if (UnrollFullMaxCount.getNumOccurrences() > 0)
229     UP.FullUnrollMaxCount = UnrollFullMaxCount;
230   if (UnrollPeelCount.getNumOccurrences() > 0)
231     UP.PeelCount = UnrollPeelCount;
232   if (UnrollAllowPartial.getNumOccurrences() > 0)
233     UP.Partial = UnrollAllowPartial;
234   if (UnrollAllowRemainder.getNumOccurrences() > 0)
235     UP.AllowRemainder = UnrollAllowRemainder;
236   if (UnrollRuntime.getNumOccurrences() > 0)
237     UP.Runtime = UnrollRuntime;
238   if (UnrollMaxUpperBound == 0)
239     UP.UpperBound = false;
240   if (UnrollAllowPeeling.getNumOccurrences() > 0)
241     UP.AllowPeeling = UnrollAllowPeeling;
242   if (UnrollUnrollRemainder.getNumOccurrences() > 0)
243     UP.UnrollRemainder = UnrollUnrollRemainder;
244 
245   // Apply user values provided by argument
246   if (UserThreshold.hasValue()) {
247     UP.Threshold = *UserThreshold;
248     UP.PartialThreshold = *UserThreshold;
249   }
250   if (UserCount.hasValue())
251     UP.Count = *UserCount;
252   if (UserAllowPartial.hasValue())
253     UP.Partial = *UserAllowPartial;
254   if (UserRuntime.hasValue())
255     UP.Runtime = *UserRuntime;
256   if (UserUpperBound.hasValue())
257     UP.UpperBound = *UserUpperBound;
258   if (UserAllowPeeling.hasValue())
259     UP.AllowPeeling = *UserAllowPeeling;
260 
261   return UP;
262 }
263 
264 namespace {
265 
266 /// A struct to densely store the state of an instruction after unrolling at
267 /// each iteration.
268 ///
269 /// This is designed to work like a tuple of <Instruction *, int> for the
270 /// purposes of hashing and lookup, but to be able to associate two boolean
271 /// states with each key.
272 struct UnrolledInstState {
273   Instruction *I;
274   int Iteration : 30;
275   unsigned IsFree : 1;
276   unsigned IsCounted : 1;
277 };
278 
279 /// Hashing and equality testing for a set of the instruction states.
280 struct UnrolledInstStateKeyInfo {
281   using PtrInfo = DenseMapInfo<Instruction *>;
282   using PairInfo = DenseMapInfo<std::pair<Instruction *, int>>;
283 
284   static inline UnrolledInstState getEmptyKey() {
285     return {PtrInfo::getEmptyKey(), 0, 0, 0};
286   }
287 
288   static inline UnrolledInstState getTombstoneKey() {
289     return {PtrInfo::getTombstoneKey(), 0, 0, 0};
290   }
291 
292   static inline unsigned getHashValue(const UnrolledInstState &S) {
293     return PairInfo::getHashValue({S.I, S.Iteration});
294   }
295 
296   static inline bool isEqual(const UnrolledInstState &LHS,
297                              const UnrolledInstState &RHS) {
298     return PairInfo::isEqual({LHS.I, LHS.Iteration}, {RHS.I, RHS.Iteration});
299   }
300 };
301 
302 struct EstimatedUnrollCost {
303   /// The estimated cost after unrolling.
304   unsigned UnrolledCost;
305 
306   /// The estimated dynamic cost of executing the instructions in the
307   /// rolled form.
308   unsigned RolledDynamicCost;
309 };
310 
311 } // end anonymous namespace
312 
313 /// Figure out if the loop is worth full unrolling.
314 ///
315 /// Complete loop unrolling can make some loads constant, and we need to know
316 /// if that would expose any further optimization opportunities.  This routine
317 /// estimates this optimization.  It computes cost of unrolled loop
318 /// (UnrolledCost) and dynamic cost of the original loop (RolledDynamicCost). By
319 /// dynamic cost we mean that we won't count costs of blocks that are known not
320 /// to be executed (i.e. if we have a branch in the loop and we know that at the
321 /// given iteration its condition would be resolved to true, we won't add up the
322 /// cost of the 'false'-block).
323 /// \returns Optional value, holding the RolledDynamicCost and UnrolledCost. If
324 /// the analysis failed (no benefits expected from the unrolling, or the loop is
325 /// too big to analyze), the returned value is None.
326 static Optional<EstimatedUnrollCost> analyzeLoopUnrollCost(
327     const Loop *L, unsigned TripCount, DominatorTree &DT, ScalarEvolution &SE,
328     const SmallPtrSetImpl<const Value *> &EphValues,
329     const TargetTransformInfo &TTI, unsigned MaxUnrolledLoopSize) {
330   // We want to be able to scale offsets by the trip count and add more offsets
331   // to them without checking for overflows, and we already don't want to
332   // analyze *massive* trip counts, so we force the max to be reasonably small.
333   assert(UnrollMaxIterationsCountToAnalyze <
334              (unsigned)(std::numeric_limits<int>::max() / 2) &&
335          "The unroll iterations max is too large!");
336 
337   // Only analyze inner loops. We can't properly estimate cost of nested loops
338   // and we won't visit inner loops again anyway.
339   if (!L->empty())
340     return None;
341 
342   // Don't simulate loops with a big or unknown tripcount
343   if (!UnrollMaxIterationsCountToAnalyze || !TripCount ||
344       TripCount > UnrollMaxIterationsCountToAnalyze)
345     return None;
346 
347   SmallSetVector<BasicBlock *, 16> BBWorklist;
348   SmallSetVector<std::pair<BasicBlock *, BasicBlock *>, 4> ExitWorklist;
349   DenseMap<Value *, Constant *> SimplifiedValues;
350   SmallVector<std::pair<Value *, Constant *>, 4> SimplifiedInputValues;
351 
352   // The estimated cost of the unrolled form of the loop. We try to estimate
353   // this by simplifying as much as we can while computing the estimate.
354   unsigned UnrolledCost = 0;
355 
356   // We also track the estimated dynamic (that is, actually executed) cost in
357   // the rolled form. This helps identify cases when the savings from unrolling
358   // aren't just exposing dead control flows, but actual reduced dynamic
359   // instructions due to the simplifications which we expect to occur after
360   // unrolling.
361   unsigned RolledDynamicCost = 0;
362 
363   // We track the simplification of each instruction in each iteration. We use
364   // this to recursively merge costs into the unrolled cost on-demand so that
365   // we don't count the cost of any dead code. This is essentially a map from
366   // <instruction, int> to <bool, bool>, but stored as a densely packed struct.
367   DenseSet<UnrolledInstState, UnrolledInstStateKeyInfo> InstCostMap;
368 
369   // A small worklist used to accumulate cost of instructions from each
370   // observable and reached root in the loop.
371   SmallVector<Instruction *, 16> CostWorklist;
372 
373   // PHI-used worklist used between iterations while accumulating cost.
374   SmallVector<Instruction *, 4> PHIUsedList;
375 
376   // Helper function to accumulate cost for instructions in the loop.
377   auto AddCostRecursively = [&](Instruction &RootI, int Iteration) {
378     assert(Iteration >= 0 && "Cannot have a negative iteration!");
379     assert(CostWorklist.empty() && "Must start with an empty cost list");
380     assert(PHIUsedList.empty() && "Must start with an empty phi used list");
381     CostWorklist.push_back(&RootI);
382     for (;; --Iteration) {
383       do {
384         Instruction *I = CostWorklist.pop_back_val();
385 
386         // InstCostMap only uses I and Iteration as a key, the other two values
387         // don't matter here.
388         auto CostIter = InstCostMap.find({I, Iteration, 0, 0});
389         if (CostIter == InstCostMap.end())
390           // If an input to a PHI node comes from a dead path through the loop
391           // we may have no cost data for it here. What that actually means is
392           // that it is free.
393           continue;
394         auto &Cost = *CostIter;
395         if (Cost.IsCounted)
396           // Already counted this instruction.
397           continue;
398 
399         // Mark that we are counting the cost of this instruction now.
400         Cost.IsCounted = true;
401 
402         // If this is a PHI node in the loop header, just add it to the PHI set.
403         if (auto *PhiI = dyn_cast<PHINode>(I))
404           if (PhiI->getParent() == L->getHeader()) {
405             assert(Cost.IsFree && "Loop PHIs shouldn't be evaluated as they "
406                                   "inherently simplify during unrolling.");
407             if (Iteration == 0)
408               continue;
409 
410             // Push the incoming value from the backedge into the PHI used list
411             // if it is an in-loop instruction. We'll use this to populate the
412             // cost worklist for the next iteration (as we count backwards).
413             if (auto *OpI = dyn_cast<Instruction>(
414                     PhiI->getIncomingValueForBlock(L->getLoopLatch())))
415               if (L->contains(OpI))
416                 PHIUsedList.push_back(OpI);
417             continue;
418           }
419 
420         // First accumulate the cost of this instruction.
421         if (!Cost.IsFree) {
422           UnrolledCost += TTI.getUserCost(I);
423           LLVM_DEBUG(dbgs() << "Adding cost of instruction (iteration "
424                             << Iteration << "): ");
425           LLVM_DEBUG(I->dump());
426         }
427 
428         // We must count the cost of every operand which is not free,
429         // recursively. If we reach a loop PHI node, simply add it to the set
430         // to be considered on the next iteration (backwards!).
431         for (Value *Op : I->operands()) {
432           // Check whether this operand is free due to being a constant or
433           // outside the loop.
434           auto *OpI = dyn_cast<Instruction>(Op);
435           if (!OpI || !L->contains(OpI))
436             continue;
437 
438           // Otherwise accumulate its cost.
439           CostWorklist.push_back(OpI);
440         }
441       } while (!CostWorklist.empty());
442 
443       if (PHIUsedList.empty())
444         // We've exhausted the search.
445         break;
446 
447       assert(Iteration > 0 &&
448              "Cannot track PHI-used values past the first iteration!");
449       CostWorklist.append(PHIUsedList.begin(), PHIUsedList.end());
450       PHIUsedList.clear();
451     }
452   };
453 
454   // Ensure that we don't violate the loop structure invariants relied on by
455   // this analysis.
456   assert(L->isLoopSimplifyForm() && "Must put loop into normal form first.");
457   assert(L->isLCSSAForm(DT) &&
458          "Must have loops in LCSSA form to track live-out values.");
459 
460   LLVM_DEBUG(dbgs() << "Starting LoopUnroll profitability analysis...\n");
461 
462   // Simulate execution of each iteration of the loop counting instructions,
463   // which would be simplified.
464   // Since the same load will take different values on different iterations,
465   // we literally have to go through all loop's iterations.
466   for (unsigned Iteration = 0; Iteration < TripCount; ++Iteration) {
467     LLVM_DEBUG(dbgs() << " Analyzing iteration " << Iteration << "\n");
468 
469     // Prepare for the iteration by collecting any simplified entry or backedge
470     // inputs.
471     for (Instruction &I : *L->getHeader()) {
472       auto *PHI = dyn_cast<PHINode>(&I);
473       if (!PHI)
474         break;
475 
476       // The loop header PHI nodes must have exactly two input: one from the
477       // loop preheader and one from the loop latch.
478       assert(
479           PHI->getNumIncomingValues() == 2 &&
480           "Must have an incoming value only for the preheader and the latch.");
481 
482       Value *V = PHI->getIncomingValueForBlock(
483           Iteration == 0 ? L->getLoopPreheader() : L->getLoopLatch());
484       Constant *C = dyn_cast<Constant>(V);
485       if (Iteration != 0 && !C)
486         C = SimplifiedValues.lookup(V);
487       if (C)
488         SimplifiedInputValues.push_back({PHI, C});
489     }
490 
491     // Now clear and re-populate the map for the next iteration.
492     SimplifiedValues.clear();
493     while (!SimplifiedInputValues.empty())
494       SimplifiedValues.insert(SimplifiedInputValues.pop_back_val());
495 
496     UnrolledInstAnalyzer Analyzer(Iteration, SimplifiedValues, SE, L);
497 
498     BBWorklist.clear();
499     BBWorklist.insert(L->getHeader());
500     // Note that we *must not* cache the size, this loop grows the worklist.
501     for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
502       BasicBlock *BB = BBWorklist[Idx];
503 
504       // Visit all instructions in the given basic block and try to simplify
505       // it.  We don't change the actual IR, just count optimization
506       // opportunities.
507       for (Instruction &I : *BB) {
508         // These won't get into the final code - don't even try calculating the
509         // cost for them.
510         if (isa<DbgInfoIntrinsic>(I) || EphValues.count(&I))
511           continue;
512 
513         // Track this instruction's expected baseline cost when executing the
514         // rolled loop form.
515         RolledDynamicCost += TTI.getUserCost(&I);
516 
517         // Visit the instruction to analyze its loop cost after unrolling,
518         // and if the visitor returns true, mark the instruction as free after
519         // unrolling and continue.
520         bool IsFree = Analyzer.visit(I);
521         bool Inserted = InstCostMap.insert({&I, (int)Iteration,
522                                            (unsigned)IsFree,
523                                            /*IsCounted*/ false}).second;
524         (void)Inserted;
525         assert(Inserted && "Cannot have a state for an unvisited instruction!");
526 
527         if (IsFree)
528           continue;
529 
530         // Can't properly model a cost of a call.
531         // FIXME: With a proper cost model we should be able to do it.
532         if (auto *CI = dyn_cast<CallInst>(&I)) {
533           const Function *Callee = CI->getCalledFunction();
534           if (!Callee || TTI.isLoweredToCall(Callee)) {
535             LLVM_DEBUG(dbgs() << "Can't analyze cost of loop with call\n");
536             return None;
537           }
538         }
539 
540         // If the instruction might have a side-effect recursively account for
541         // the cost of it and all the instructions leading up to it.
542         if (I.mayHaveSideEffects())
543           AddCostRecursively(I, Iteration);
544 
545         // If unrolled body turns out to be too big, bail out.
546         if (UnrolledCost > MaxUnrolledLoopSize) {
547           LLVM_DEBUG(dbgs() << "  Exceeded threshold.. exiting.\n"
548                             << "  UnrolledCost: " << UnrolledCost
549                             << ", MaxUnrolledLoopSize: " << MaxUnrolledLoopSize
550                             << "\n");
551           return None;
552         }
553       }
554 
555       Instruction *TI = BB->getTerminator();
556 
557       // Add in the live successors by first checking whether we have terminator
558       // that may be simplified based on the values simplified by this call.
559       BasicBlock *KnownSucc = nullptr;
560       if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
561         if (BI->isConditional()) {
562           if (Constant *SimpleCond =
563                   SimplifiedValues.lookup(BI->getCondition())) {
564             // Just take the first successor if condition is undef
565             if (isa<UndefValue>(SimpleCond))
566               KnownSucc = BI->getSuccessor(0);
567             else if (ConstantInt *SimpleCondVal =
568                          dyn_cast<ConstantInt>(SimpleCond))
569               KnownSucc = BI->getSuccessor(SimpleCondVal->isZero() ? 1 : 0);
570           }
571         }
572       } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
573         if (Constant *SimpleCond =
574                 SimplifiedValues.lookup(SI->getCondition())) {
575           // Just take the first successor if condition is undef
576           if (isa<UndefValue>(SimpleCond))
577             KnownSucc = SI->getSuccessor(0);
578           else if (ConstantInt *SimpleCondVal =
579                        dyn_cast<ConstantInt>(SimpleCond))
580             KnownSucc = SI->findCaseValue(SimpleCondVal)->getCaseSuccessor();
581         }
582       }
583       if (KnownSucc) {
584         if (L->contains(KnownSucc))
585           BBWorklist.insert(KnownSucc);
586         else
587           ExitWorklist.insert({BB, KnownSucc});
588         continue;
589       }
590 
591       // Add BB's successors to the worklist.
592       for (BasicBlock *Succ : successors(BB))
593         if (L->contains(Succ))
594           BBWorklist.insert(Succ);
595         else
596           ExitWorklist.insert({BB, Succ});
597       AddCostRecursively(*TI, Iteration);
598     }
599 
600     // If we found no optimization opportunities on the first iteration, we
601     // won't find them on later ones too.
602     if (UnrolledCost == RolledDynamicCost) {
603       LLVM_DEBUG(dbgs() << "  No opportunities found.. exiting.\n"
604                         << "  UnrolledCost: " << UnrolledCost << "\n");
605       return None;
606     }
607   }
608 
609   while (!ExitWorklist.empty()) {
610     BasicBlock *ExitingBB, *ExitBB;
611     std::tie(ExitingBB, ExitBB) = ExitWorklist.pop_back_val();
612 
613     for (Instruction &I : *ExitBB) {
614       auto *PN = dyn_cast<PHINode>(&I);
615       if (!PN)
616         break;
617 
618       Value *Op = PN->getIncomingValueForBlock(ExitingBB);
619       if (auto *OpI = dyn_cast<Instruction>(Op))
620         if (L->contains(OpI))
621           AddCostRecursively(*OpI, TripCount - 1);
622     }
623   }
624 
625   LLVM_DEBUG(dbgs() << "Analysis finished:\n"
626                     << "UnrolledCost: " << UnrolledCost << ", "
627                     << "RolledDynamicCost: " << RolledDynamicCost << "\n");
628   return {{UnrolledCost, RolledDynamicCost}};
629 }
630 
631 /// ApproximateLoopSize - Approximate the size of the loop.
632 unsigned llvm::ApproximateLoopSize(
633     const Loop *L, unsigned &NumCalls, bool &NotDuplicatable, bool &Convergent,
634     const TargetTransformInfo &TTI,
635     const SmallPtrSetImpl<const Value *> &EphValues, unsigned BEInsns) {
636   CodeMetrics Metrics;
637   for (BasicBlock *BB : L->blocks())
638     Metrics.analyzeBasicBlock(BB, TTI, EphValues);
639   NumCalls = Metrics.NumInlineCandidates;
640   NotDuplicatable = Metrics.notDuplicatable;
641   Convergent = Metrics.convergent;
642 
643   unsigned LoopSize = Metrics.NumInsts;
644 
645   // Don't allow an estimate of size zero.  This would allows unrolling of loops
646   // with huge iteration counts, which is a compile time problem even if it's
647   // not a problem for code quality. Also, the code using this size may assume
648   // that each loop has at least three instructions (likely a conditional
649   // branch, a comparison feeding that branch, and some kind of loop increment
650   // feeding that comparison instruction).
651   LoopSize = std::max(LoopSize, BEInsns + 1);
652 
653   return LoopSize;
654 }
655 
656 // Returns the loop hint metadata node with the given name (for example,
657 // "llvm.loop.unroll.count").  If no such metadata node exists, then nullptr is
658 // returned.
659 static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
660   if (MDNode *LoopID = L->getLoopID())
661     return GetUnrollMetadata(LoopID, Name);
662   return nullptr;
663 }
664 
665 // Returns true if the loop has an unroll(full) pragma.
666 static bool HasUnrollFullPragma(const Loop *L) {
667   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full");
668 }
669 
670 // Returns true if the loop has an unroll(enable) pragma. This metadata is used
671 // for both "#pragma unroll" and "#pragma clang loop unroll(enable)" directives.
672 static bool HasUnrollEnablePragma(const Loop *L) {
673   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.enable");
674 }
675 
676 // Returns true if the loop has an runtime unroll(disable) pragma.
677 static bool HasRuntimeUnrollDisablePragma(const Loop *L) {
678   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.runtime.disable");
679 }
680 
681 // If loop has an unroll_count pragma return the (necessarily
682 // positive) value from the pragma.  Otherwise return 0.
683 static unsigned UnrollCountPragmaValue(const Loop *L) {
684   MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
685   if (MD) {
686     assert(MD->getNumOperands() == 2 &&
687            "Unroll count hint metadata should have two operands.");
688     unsigned Count =
689         mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
690     assert(Count >= 1 && "Unroll count must be positive.");
691     return Count;
692   }
693   return 0;
694 }
695 
696 // Computes the boosting factor for complete unrolling.
697 // If fully unrolling the loop would save a lot of RolledDynamicCost, it would
698 // be beneficial to fully unroll the loop even if unrolledcost is large. We
699 // use (RolledDynamicCost / UnrolledCost) to model the unroll benefits to adjust
700 // the unroll threshold.
701 static unsigned getFullUnrollBoostingFactor(const EstimatedUnrollCost &Cost,
702                                             unsigned MaxPercentThresholdBoost) {
703   if (Cost.RolledDynamicCost >= std::numeric_limits<unsigned>::max() / 100)
704     return 100;
705   else if (Cost.UnrolledCost != 0)
706     // The boosting factor is RolledDynamicCost / UnrolledCost
707     return std::min(100 * Cost.RolledDynamicCost / Cost.UnrolledCost,
708                     MaxPercentThresholdBoost);
709   else
710     return MaxPercentThresholdBoost;
711 }
712 
713 // Returns loop size estimation for unrolled loop.
714 static uint64_t getUnrolledLoopSize(
715     unsigned LoopSize,
716     TargetTransformInfo::UnrollingPreferences &UP) {
717   assert(LoopSize >= UP.BEInsns && "LoopSize should not be less than BEInsns!");
718   return (uint64_t)(LoopSize - UP.BEInsns) * UP.Count + UP.BEInsns;
719 }
720 
721 // Returns true if unroll count was set explicitly.
722 // Calculates unroll count and writes it to UP.Count.
723 // Unless IgnoreUser is true, will also use metadata and command-line options
724 // that are specific to to the LoopUnroll pass (which, for instance, are
725 // irrelevant for the LoopUnrollAndJam pass).
726 // FIXME: This function is used by LoopUnroll and LoopUnrollAndJam, but consumes
727 // many LoopUnroll-specific options. The shared functionality should be
728 // refactored into it own function.
729 bool llvm::computeUnrollCount(
730     Loop *L, const TargetTransformInfo &TTI, DominatorTree &DT, LoopInfo *LI,
731     ScalarEvolution &SE, const SmallPtrSetImpl<const Value *> &EphValues,
732     OptimizationRemarkEmitter *ORE, unsigned &TripCount, unsigned MaxTripCount,
733     unsigned &TripMultiple, unsigned LoopSize,
734     TargetTransformInfo::UnrollingPreferences &UP, bool &UseUpperBound) {
735 
736   // Check for explicit Count.
737   // 1st priority is unroll count set by "unroll-count" option.
738   bool UserUnrollCount = UnrollCount.getNumOccurrences() > 0;
739   if (UserUnrollCount) {
740     UP.Count = UnrollCount;
741     UP.AllowExpensiveTripCount = true;
742     UP.Force = true;
743     if (UP.AllowRemainder && getUnrolledLoopSize(LoopSize, UP) < UP.Threshold)
744       return true;
745   }
746 
747   // 2nd priority is unroll count set by pragma.
748   unsigned PragmaCount = UnrollCountPragmaValue(L);
749   if (PragmaCount > 0) {
750     UP.Count = PragmaCount;
751     UP.Runtime = true;
752     UP.AllowExpensiveTripCount = true;
753     UP.Force = true;
754     if ((UP.AllowRemainder || (TripMultiple % PragmaCount == 0)) &&
755         getUnrolledLoopSize(LoopSize, UP) < PragmaUnrollThreshold)
756       return true;
757   }
758   bool PragmaFullUnroll = HasUnrollFullPragma(L);
759   if (PragmaFullUnroll && TripCount != 0) {
760     UP.Count = TripCount;
761     if (getUnrolledLoopSize(LoopSize, UP) < PragmaUnrollThreshold)
762       return false;
763   }
764 
765   bool PragmaEnableUnroll = HasUnrollEnablePragma(L);
766   bool ExplicitUnroll = PragmaCount > 0 || PragmaFullUnroll ||
767                         PragmaEnableUnroll || UserUnrollCount;
768 
769   if (ExplicitUnroll && TripCount != 0) {
770     // If the loop has an unrolling pragma, we want to be more aggressive with
771     // unrolling limits. Set thresholds to at least the PragmaUnrollThreshold
772     // value which is larger than the default limits.
773     UP.Threshold = std::max<unsigned>(UP.Threshold, PragmaUnrollThreshold);
774     UP.PartialThreshold =
775         std::max<unsigned>(UP.PartialThreshold, PragmaUnrollThreshold);
776   }
777 
778   // 3rd priority is full unroll count.
779   // Full unroll makes sense only when TripCount or its upper bound could be
780   // statically calculated.
781   // Also we need to check if we exceed FullUnrollMaxCount.
782   // If using the upper bound to unroll, TripMultiple should be set to 1 because
783   // we do not know when loop may exit.
784   // MaxTripCount and ExactTripCount cannot both be non zero since we only
785   // compute the former when the latter is zero.
786   unsigned ExactTripCount = TripCount;
787   assert((ExactTripCount == 0 || MaxTripCount == 0) &&
788          "ExtractTripCount and MaxTripCount cannot both be non zero.");
789   unsigned FullUnrollTripCount = ExactTripCount ? ExactTripCount : MaxTripCount;
790   UP.Count = FullUnrollTripCount;
791   if (FullUnrollTripCount && FullUnrollTripCount <= UP.FullUnrollMaxCount) {
792     // When computing the unrolled size, note that BEInsns are not replicated
793     // like the rest of the loop body.
794     if (getUnrolledLoopSize(LoopSize, UP) < UP.Threshold) {
795       UseUpperBound = (MaxTripCount == FullUnrollTripCount);
796       TripCount = FullUnrollTripCount;
797       TripMultiple = UP.UpperBound ? 1 : TripMultiple;
798       return ExplicitUnroll;
799     } else {
800       // The loop isn't that small, but we still can fully unroll it if that
801       // helps to remove a significant number of instructions.
802       // To check that, run additional analysis on the loop.
803       if (Optional<EstimatedUnrollCost> Cost = analyzeLoopUnrollCost(
804               L, FullUnrollTripCount, DT, SE, EphValues, TTI,
805               UP.Threshold * UP.MaxPercentThresholdBoost / 100)) {
806         unsigned Boost =
807             getFullUnrollBoostingFactor(*Cost, UP.MaxPercentThresholdBoost);
808         if (Cost->UnrolledCost < UP.Threshold * Boost / 100) {
809           UseUpperBound = (MaxTripCount == FullUnrollTripCount);
810           TripCount = FullUnrollTripCount;
811           TripMultiple = UP.UpperBound ? 1 : TripMultiple;
812           return ExplicitUnroll;
813         }
814       }
815     }
816   }
817 
818   // 4th priority is loop peeling.
819   computePeelCount(L, LoopSize, UP, TripCount, SE);
820   if (UP.PeelCount) {
821     UP.Runtime = false;
822     UP.Count = 1;
823     return ExplicitUnroll;
824   }
825 
826   // 5th priority is partial unrolling.
827   // Try partial unroll only when TripCount could be statically calculated.
828   if (TripCount) {
829     UP.Partial |= ExplicitUnroll;
830     if (!UP.Partial) {
831       LLVM_DEBUG(dbgs() << "  will not try to unroll partially because "
832                         << "-unroll-allow-partial not given\n");
833       UP.Count = 0;
834       return false;
835     }
836     if (UP.Count == 0)
837       UP.Count = TripCount;
838     if (UP.PartialThreshold != NoThreshold) {
839       // Reduce unroll count to be modulo of TripCount for partial unrolling.
840       if (getUnrolledLoopSize(LoopSize, UP) > UP.PartialThreshold)
841         UP.Count =
842             (std::max(UP.PartialThreshold, UP.BEInsns + 1) - UP.BEInsns) /
843             (LoopSize - UP.BEInsns);
844       if (UP.Count > UP.MaxCount)
845         UP.Count = UP.MaxCount;
846       while (UP.Count != 0 && TripCount % UP.Count != 0)
847         UP.Count--;
848       if (UP.AllowRemainder && UP.Count <= 1) {
849         // If there is no Count that is modulo of TripCount, set Count to
850         // largest power-of-two factor that satisfies the threshold limit.
851         // As we'll create fixup loop, do the type of unrolling only if
852         // remainder loop is allowed.
853         UP.Count = UP.DefaultUnrollRuntimeCount;
854         while (UP.Count != 0 &&
855                getUnrolledLoopSize(LoopSize, UP) > UP.PartialThreshold)
856           UP.Count >>= 1;
857       }
858       if (UP.Count < 2) {
859         if (PragmaEnableUnroll)
860           ORE->emit([&]() {
861             return OptimizationRemarkMissed(DEBUG_TYPE,
862                                             "UnrollAsDirectedTooLarge",
863                                             L->getStartLoc(), L->getHeader())
864                    << "Unable to unroll loop as directed by unroll(enable) "
865                       "pragma "
866                       "because unrolled size is too large.";
867           });
868         UP.Count = 0;
869       }
870     } else {
871       UP.Count = TripCount;
872     }
873     if (UP.Count > UP.MaxCount)
874       UP.Count = UP.MaxCount;
875     if ((PragmaFullUnroll || PragmaEnableUnroll) && TripCount &&
876         UP.Count != TripCount)
877       ORE->emit([&]() {
878         return OptimizationRemarkMissed(DEBUG_TYPE,
879                                         "FullUnrollAsDirectedTooLarge",
880                                         L->getStartLoc(), L->getHeader())
881                << "Unable to fully unroll loop as directed by unroll pragma "
882                   "because "
883                   "unrolled size is too large.";
884       });
885     return ExplicitUnroll;
886   }
887   assert(TripCount == 0 &&
888          "All cases when TripCount is constant should be covered here.");
889   if (PragmaFullUnroll)
890     ORE->emit([&]() {
891       return OptimizationRemarkMissed(
892                  DEBUG_TYPE, "CantFullUnrollAsDirectedRuntimeTripCount",
893                  L->getStartLoc(), L->getHeader())
894              << "Unable to fully unroll loop as directed by unroll(full) "
895                 "pragma "
896                 "because loop has a runtime trip count.";
897     });
898 
899   // 6th priority is runtime unrolling.
900   // Don't unroll a runtime trip count loop when it is disabled.
901   if (HasRuntimeUnrollDisablePragma(L)) {
902     UP.Count = 0;
903     return false;
904   }
905 
906   // Check if the runtime trip count is too small when profile is available.
907   if (L->getHeader()->getParent()->hasProfileData()) {
908     if (auto ProfileTripCount = getLoopEstimatedTripCount(L)) {
909       if (*ProfileTripCount < FlatLoopTripCountThreshold)
910         return false;
911       else
912         UP.AllowExpensiveTripCount = true;
913     }
914   }
915 
916   // Reduce count based on the type of unrolling and the threshold values.
917   UP.Runtime |= PragmaEnableUnroll || PragmaCount > 0 || UserUnrollCount;
918   if (!UP.Runtime) {
919     LLVM_DEBUG(
920         dbgs() << "  will not try to unroll loop with runtime trip count "
921                << "-unroll-runtime not given\n");
922     UP.Count = 0;
923     return false;
924   }
925   if (UP.Count == 0)
926     UP.Count = UP.DefaultUnrollRuntimeCount;
927 
928   // Reduce unroll count to be the largest power-of-two factor of
929   // the original count which satisfies the threshold limit.
930   while (UP.Count != 0 &&
931          getUnrolledLoopSize(LoopSize, UP) > UP.PartialThreshold)
932     UP.Count >>= 1;
933 
934 #ifndef NDEBUG
935   unsigned OrigCount = UP.Count;
936 #endif
937 
938   if (!UP.AllowRemainder && UP.Count != 0 && (TripMultiple % UP.Count) != 0) {
939     while (UP.Count != 0 && TripMultiple % UP.Count != 0)
940       UP.Count >>= 1;
941     LLVM_DEBUG(
942         dbgs() << "Remainder loop is restricted (that could architecture "
943                   "specific or because the loop contains a convergent "
944                   "instruction), so unroll count must divide the trip "
945                   "multiple, "
946                << TripMultiple << ".  Reducing unroll count from " << OrigCount
947                << " to " << UP.Count << ".\n");
948 
949     using namespace ore;
950 
951     if (PragmaCount > 0 && !UP.AllowRemainder)
952       ORE->emit([&]() {
953         return OptimizationRemarkMissed(DEBUG_TYPE,
954                                         "DifferentUnrollCountFromDirected",
955                                         L->getStartLoc(), L->getHeader())
956                << "Unable to unroll loop the number of times directed by "
957                   "unroll_count pragma because remainder loop is restricted "
958                   "(that could architecture specific or because the loop "
959                   "contains a convergent instruction) and so must have an "
960                   "unroll "
961                   "count that divides the loop trip multiple of "
962                << NV("TripMultiple", TripMultiple) << ".  Unrolling instead "
963                << NV("UnrollCount", UP.Count) << " time(s).";
964       });
965   }
966 
967   if (UP.Count > UP.MaxCount)
968     UP.Count = UP.MaxCount;
969   LLVM_DEBUG(dbgs() << "  partially unrolling with count: " << UP.Count
970                     << "\n");
971   if (UP.Count < 2)
972     UP.Count = 0;
973   return ExplicitUnroll;
974 }
975 
976 static LoopUnrollResult tryToUnrollLoop(
977     Loop *L, DominatorTree &DT, LoopInfo *LI, ScalarEvolution &SE,
978     const TargetTransformInfo &TTI, AssumptionCache &AC,
979     OptimizationRemarkEmitter &ORE,
980     BlockFrequencyInfo *BFI, ProfileSummaryInfo *PSI,
981     bool PreserveLCSSA, int OptLevel,
982     bool OnlyWhenForced, bool ForgetAllSCEV, Optional<unsigned> ProvidedCount,
983     Optional<unsigned> ProvidedThreshold, Optional<bool> ProvidedAllowPartial,
984     Optional<bool> ProvidedRuntime, Optional<bool> ProvidedUpperBound,
985     Optional<bool> ProvidedAllowPeeling) {
986   LLVM_DEBUG(dbgs() << "Loop Unroll: F["
987                     << L->getHeader()->getParent()->getName() << "] Loop %"
988                     << L->getHeader()->getName() << "\n");
989   TransformationMode TM = hasUnrollTransformation(L);
990   if (TM & TM_Disable)
991     return LoopUnrollResult::Unmodified;
992   if (!L->isLoopSimplifyForm()) {
993     LLVM_DEBUG(
994         dbgs() << "  Not unrolling loop which is not in loop-simplify form.\n");
995     return LoopUnrollResult::Unmodified;
996   }
997 
998   // When automtatic unrolling is disabled, do not unroll unless overridden for
999   // this loop.
1000   if (OnlyWhenForced && !(TM & TM_Enable))
1001     return LoopUnrollResult::Unmodified;
1002 
1003   bool OptForSize = L->getHeader()->getParent()->hasOptSize();
1004   unsigned NumInlineCandidates;
1005   bool NotDuplicatable;
1006   bool Convergent;
1007   TargetTransformInfo::UnrollingPreferences UP = gatherUnrollingPreferences(
1008       L, SE, TTI, BFI, PSI, OptLevel, ProvidedThreshold, ProvidedCount,
1009       ProvidedAllowPartial, ProvidedRuntime, ProvidedUpperBound,
1010       ProvidedAllowPeeling);
1011 
1012   // Exit early if unrolling is disabled. For OptForSize, we pick the loop size
1013   // as threshold later on.
1014   if (UP.Threshold == 0 && (!UP.Partial || UP.PartialThreshold == 0) &&
1015       !OptForSize)
1016     return LoopUnrollResult::Unmodified;
1017 
1018   SmallPtrSet<const Value *, 32> EphValues;
1019   CodeMetrics::collectEphemeralValues(L, &AC, EphValues);
1020 
1021   unsigned LoopSize =
1022       ApproximateLoopSize(L, NumInlineCandidates, NotDuplicatable, Convergent,
1023                           TTI, EphValues, UP.BEInsns);
1024   LLVM_DEBUG(dbgs() << "  Loop Size = " << LoopSize << "\n");
1025   if (NotDuplicatable) {
1026     LLVM_DEBUG(dbgs() << "  Not unrolling loop which contains non-duplicatable"
1027                       << " instructions.\n");
1028     return LoopUnrollResult::Unmodified;
1029   }
1030 
1031   // When optimizing for size, use LoopSize as threshold, to (fully) unroll
1032   // loops, if it does not increase code size.
1033   if (OptForSize)
1034     UP.Threshold = std::max(UP.Threshold, LoopSize);
1035 
1036   if (NumInlineCandidates != 0) {
1037     LLVM_DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");
1038     return LoopUnrollResult::Unmodified;
1039   }
1040 
1041   // Find trip count and trip multiple if count is not available
1042   unsigned TripCount = 0;
1043   unsigned MaxTripCount = 0;
1044   unsigned TripMultiple = 1;
1045   // If there are multiple exiting blocks but one of them is the latch, use the
1046   // latch for the trip count estimation. Otherwise insist on a single exiting
1047   // block for the trip count estimation.
1048   BasicBlock *ExitingBlock = L->getLoopLatch();
1049   if (!ExitingBlock || !L->isLoopExiting(ExitingBlock))
1050     ExitingBlock = L->getExitingBlock();
1051   if (ExitingBlock) {
1052     TripCount = SE.getSmallConstantTripCount(L, ExitingBlock);
1053     TripMultiple = SE.getSmallConstantTripMultiple(L, ExitingBlock);
1054   }
1055 
1056   // If the loop contains a convergent operation, the prelude we'd add
1057   // to do the first few instructions before we hit the unrolled loop
1058   // is unsafe -- it adds a control-flow dependency to the convergent
1059   // operation.  Therefore restrict remainder loop (try unrollig without).
1060   //
1061   // TODO: This is quite conservative.  In practice, convergent_op()
1062   // is likely to be called unconditionally in the loop.  In this
1063   // case, the program would be ill-formed (on most architectures)
1064   // unless n were the same on all threads in a thread group.
1065   // Assuming n is the same on all threads, any kind of unrolling is
1066   // safe.  But currently llvm's notion of convergence isn't powerful
1067   // enough to express this.
1068   if (Convergent)
1069     UP.AllowRemainder = false;
1070 
1071   // Try to find the trip count upper bound if we cannot find the exact trip
1072   // count.
1073   bool MaxOrZero = false;
1074   if (!TripCount) {
1075     MaxTripCount = SE.getSmallConstantMaxTripCount(L);
1076     MaxOrZero = SE.isBackedgeTakenCountMaxOrZero(L);
1077     // We can unroll by the upper bound amount if it's generally allowed or if
1078     // we know that the loop is executed either the upper bound or zero times.
1079     // (MaxOrZero unrolling keeps only the first loop test, so the number of
1080     // loop tests remains the same compared to the non-unrolled version, whereas
1081     // the generic upper bound unrolling keeps all but the last loop test so the
1082     // number of loop tests goes up which may end up being worse on targets with
1083     // constrained branch predictor resources so is controlled by an option.)
1084     // In addition we only unroll small upper bounds.
1085     if (!(UP.UpperBound || MaxOrZero) || MaxTripCount > UnrollMaxUpperBound) {
1086       MaxTripCount = 0;
1087     }
1088   }
1089 
1090   // computeUnrollCount() decides whether it is beneficial to use upper bound to
1091   // fully unroll the loop.
1092   bool UseUpperBound = false;
1093   bool IsCountSetExplicitly = computeUnrollCount(
1094       L, TTI, DT, LI, SE, EphValues, &ORE, TripCount, MaxTripCount,
1095       TripMultiple, LoopSize, UP, UseUpperBound);
1096   if (!UP.Count)
1097     return LoopUnrollResult::Unmodified;
1098   // Unroll factor (Count) must be less or equal to TripCount.
1099   if (TripCount && UP.Count > TripCount)
1100     UP.Count = TripCount;
1101 
1102   // Save loop properties before it is transformed.
1103   MDNode *OrigLoopID = L->getLoopID();
1104 
1105   // Unroll the loop.
1106   Loop *RemainderLoop = nullptr;
1107   LoopUnrollResult UnrollResult = UnrollLoop(
1108       L,
1109       {UP.Count, TripCount, UP.Force, UP.Runtime, UP.AllowExpensiveTripCount,
1110        UseUpperBound, MaxOrZero, TripMultiple, UP.PeelCount, UP.UnrollRemainder,
1111        ForgetAllSCEV},
1112       LI, &SE, &DT, &AC, &ORE, PreserveLCSSA, &RemainderLoop);
1113   if (UnrollResult == LoopUnrollResult::Unmodified)
1114     return LoopUnrollResult::Unmodified;
1115 
1116   if (RemainderLoop) {
1117     Optional<MDNode *> RemainderLoopID =
1118         makeFollowupLoopID(OrigLoopID, {LLVMLoopUnrollFollowupAll,
1119                                         LLVMLoopUnrollFollowupRemainder});
1120     if (RemainderLoopID.hasValue())
1121       RemainderLoop->setLoopID(RemainderLoopID.getValue());
1122   }
1123 
1124   if (UnrollResult != LoopUnrollResult::FullyUnrolled) {
1125     Optional<MDNode *> NewLoopID =
1126         makeFollowupLoopID(OrigLoopID, {LLVMLoopUnrollFollowupAll,
1127                                         LLVMLoopUnrollFollowupUnrolled});
1128     if (NewLoopID.hasValue()) {
1129       L->setLoopID(NewLoopID.getValue());
1130 
1131       // Do not setLoopAlreadyUnrolled if loop attributes have been specified
1132       // explicitly.
1133       return UnrollResult;
1134     }
1135   }
1136 
1137   // If loop has an unroll count pragma or unrolled by explicitly set count
1138   // mark loop as unrolled to prevent unrolling beyond that requested.
1139   // If the loop was peeled, we already "used up" the profile information
1140   // we had, so we don't want to unroll or peel again.
1141   if (UnrollResult != LoopUnrollResult::FullyUnrolled &&
1142       (IsCountSetExplicitly || UP.PeelCount))
1143     L->setLoopAlreadyUnrolled();
1144 
1145   return UnrollResult;
1146 }
1147 
1148 namespace {
1149 
1150 class LoopUnroll : public LoopPass {
1151 public:
1152   static char ID; // Pass ID, replacement for typeid
1153 
1154   int OptLevel;
1155 
1156   /// If false, use a cost model to determine whether unrolling of a loop is
1157   /// profitable. If true, only loops that explicitly request unrolling via
1158   /// metadata are considered. All other loops are skipped.
1159   bool OnlyWhenForced;
1160 
1161   /// If false, when SCEV is invalidated, only forget everything in the
1162   /// top-most loop (call forgetTopMostLoop), of the loop being processed.
1163   /// Otherwise, forgetAllLoops and rebuild when needed next.
1164   bool ForgetAllSCEV;
1165 
1166   Optional<unsigned> ProvidedCount;
1167   Optional<unsigned> ProvidedThreshold;
1168   Optional<bool> ProvidedAllowPartial;
1169   Optional<bool> ProvidedRuntime;
1170   Optional<bool> ProvidedUpperBound;
1171   Optional<bool> ProvidedAllowPeeling;
1172 
1173   LoopUnroll(int OptLevel = 2, bool OnlyWhenForced = false,
1174              bool ForgetAllSCEV = false, Optional<unsigned> Threshold = None,
1175              Optional<unsigned> Count = None,
1176              Optional<bool> AllowPartial = None, Optional<bool> Runtime = None,
1177              Optional<bool> UpperBound = None,
1178              Optional<bool> AllowPeeling = None)
1179       : LoopPass(ID), OptLevel(OptLevel), OnlyWhenForced(OnlyWhenForced),
1180         ForgetAllSCEV(ForgetAllSCEV), ProvidedCount(std::move(Count)),
1181         ProvidedThreshold(Threshold), ProvidedAllowPartial(AllowPartial),
1182         ProvidedRuntime(Runtime), ProvidedUpperBound(UpperBound),
1183         ProvidedAllowPeeling(AllowPeeling) {
1184     initializeLoopUnrollPass(*PassRegistry::getPassRegistry());
1185   }
1186 
1187   bool runOnLoop(Loop *L, LPPassManager &LPM) override {
1188     if (skipLoop(L))
1189       return false;
1190 
1191     Function &F = *L->getHeader()->getParent();
1192 
1193     auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
1194     LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
1195     ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
1196     const TargetTransformInfo &TTI =
1197         getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
1198     auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
1199     // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
1200     // pass.  Function analyses need to be preserved across loop transformations
1201     // but ORE cannot be preserved (see comment before the pass definition).
1202     OptimizationRemarkEmitter ORE(&F);
1203     bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
1204 
1205     LoopUnrollResult Result = tryToUnrollLoop(
1206         L, DT, LI, SE, TTI, AC, ORE, nullptr, nullptr,
1207         PreserveLCSSA, OptLevel, OnlyWhenForced,
1208         ForgetAllSCEV, ProvidedCount, ProvidedThreshold, ProvidedAllowPartial,
1209         ProvidedRuntime, ProvidedUpperBound, ProvidedAllowPeeling);
1210 
1211     if (Result == LoopUnrollResult::FullyUnrolled)
1212       LPM.markLoopAsDeleted(*L);
1213 
1214     return Result != LoopUnrollResult::Unmodified;
1215   }
1216 
1217   /// This transformation requires natural loop information & requires that
1218   /// loop preheaders be inserted into the CFG...
1219   void getAnalysisUsage(AnalysisUsage &AU) const override {
1220     AU.addRequired<AssumptionCacheTracker>();
1221     AU.addRequired<TargetTransformInfoWrapperPass>();
1222     // FIXME: Loop passes are required to preserve domtree, and for now we just
1223     // recreate dom info if anything gets unrolled.
1224     getLoopAnalysisUsage(AU);
1225   }
1226 };
1227 
1228 } // end anonymous namespace
1229 
1230 char LoopUnroll::ID = 0;
1231 
1232 INITIALIZE_PASS_BEGIN(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
1233 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
1234 INITIALIZE_PASS_DEPENDENCY(LoopPass)
1235 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
1236 INITIALIZE_PASS_END(LoopUnroll, "loop-unroll", "Unroll loops", false, false)
1237 
1238 Pass *llvm::createLoopUnrollPass(int OptLevel, bool OnlyWhenForced,
1239                                  bool ForgetAllSCEV, int Threshold, int Count,
1240                                  int AllowPartial, int Runtime, int UpperBound,
1241                                  int AllowPeeling) {
1242   // TODO: It would make more sense for this function to take the optionals
1243   // directly, but that's dangerous since it would silently break out of tree
1244   // callers.
1245   return new LoopUnroll(
1246       OptLevel, OnlyWhenForced, ForgetAllSCEV,
1247       Threshold == -1 ? None : Optional<unsigned>(Threshold),
1248       Count == -1 ? None : Optional<unsigned>(Count),
1249       AllowPartial == -1 ? None : Optional<bool>(AllowPartial),
1250       Runtime == -1 ? None : Optional<bool>(Runtime),
1251       UpperBound == -1 ? None : Optional<bool>(UpperBound),
1252       AllowPeeling == -1 ? None : Optional<bool>(AllowPeeling));
1253 }
1254 
1255 Pass *llvm::createSimpleLoopUnrollPass(int OptLevel, bool OnlyWhenForced,
1256                                        bool ForgetAllSCEV) {
1257   return createLoopUnrollPass(OptLevel, OnlyWhenForced, ForgetAllSCEV, -1, -1,
1258                               0, 0, 0, 0);
1259 }
1260 
1261 PreservedAnalyses LoopFullUnrollPass::run(Loop &L, LoopAnalysisManager &AM,
1262                                           LoopStandardAnalysisResults &AR,
1263                                           LPMUpdater &Updater) {
1264   const auto &FAM =
1265       AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
1266   Function *F = L.getHeader()->getParent();
1267 
1268   auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F);
1269   // FIXME: This should probably be optional rather than required.
1270   if (!ORE)
1271     report_fatal_error(
1272         "LoopFullUnrollPass: OptimizationRemarkEmitterAnalysis not "
1273         "cached at a higher level");
1274 
1275   // Keep track of the previous loop structure so we can identify new loops
1276   // created by unrolling.
1277   Loop *ParentL = L.getParentLoop();
1278   SmallPtrSet<Loop *, 4> OldLoops;
1279   if (ParentL)
1280     OldLoops.insert(ParentL->begin(), ParentL->end());
1281   else
1282     OldLoops.insert(AR.LI.begin(), AR.LI.end());
1283 
1284   std::string LoopName = L.getName();
1285 
1286   bool Changed =
1287       tryToUnrollLoop(&L, AR.DT, &AR.LI, AR.SE, AR.TTI, AR.AC, *ORE,
1288                       /*BFI*/ nullptr, /*PSI*/ nullptr,
1289                       /*PreserveLCSSA*/ true, OptLevel, OnlyWhenForced,
1290                       ForgetSCEV, /*Count*/ None,
1291                       /*Threshold*/ None, /*AllowPartial*/ false,
1292                       /*Runtime*/ false, /*UpperBound*/ false,
1293                       /*AllowPeeling*/ false) != LoopUnrollResult::Unmodified;
1294   if (!Changed)
1295     return PreservedAnalyses::all();
1296 
1297   // The parent must not be damaged by unrolling!
1298 #ifndef NDEBUG
1299   if (ParentL)
1300     ParentL->verifyLoop();
1301 #endif
1302 
1303   // Unrolling can do several things to introduce new loops into a loop nest:
1304   // - Full unrolling clones child loops within the current loop but then
1305   //   removes the current loop making all of the children appear to be new
1306   //   sibling loops.
1307   //
1308   // When a new loop appears as a sibling loop after fully unrolling,
1309   // its nesting structure has fundamentally changed and we want to revisit
1310   // it to reflect that.
1311   //
1312   // When unrolling has removed the current loop, we need to tell the
1313   // infrastructure that it is gone.
1314   //
1315   // Finally, we support a debugging/testing mode where we revisit child loops
1316   // as well. These are not expected to require further optimizations as either
1317   // they or the loop they were cloned from have been directly visited already.
1318   // But the debugging mode allows us to check this assumption.
1319   bool IsCurrentLoopValid = false;
1320   SmallVector<Loop *, 4> SibLoops;
1321   if (ParentL)
1322     SibLoops.append(ParentL->begin(), ParentL->end());
1323   else
1324     SibLoops.append(AR.LI.begin(), AR.LI.end());
1325   erase_if(SibLoops, [&](Loop *SibLoop) {
1326     if (SibLoop == &L) {
1327       IsCurrentLoopValid = true;
1328       return true;
1329     }
1330 
1331     // Otherwise erase the loop from the list if it was in the old loops.
1332     return OldLoops.count(SibLoop) != 0;
1333   });
1334   Updater.addSiblingLoops(SibLoops);
1335 
1336   if (!IsCurrentLoopValid) {
1337     Updater.markLoopAsDeleted(L, LoopName);
1338   } else {
1339     // We can only walk child loops if the current loop remained valid.
1340     if (UnrollRevisitChildLoops) {
1341       // Walk *all* of the child loops.
1342       SmallVector<Loop *, 4> ChildLoops(L.begin(), L.end());
1343       Updater.addChildLoops(ChildLoops);
1344     }
1345   }
1346 
1347   return getLoopPassPreservedAnalyses();
1348 }
1349 
1350 template <typename RangeT>
1351 static SmallVector<Loop *, 8> appendLoopsToWorklist(RangeT &&Loops) {
1352   SmallVector<Loop *, 8> Worklist;
1353   // We use an internal worklist to build up the preorder traversal without
1354   // recursion.
1355   SmallVector<Loop *, 4> PreOrderLoops, PreOrderWorklist;
1356 
1357   for (Loop *RootL : Loops) {
1358     assert(PreOrderLoops.empty() && "Must start with an empty preorder walk.");
1359     assert(PreOrderWorklist.empty() &&
1360            "Must start with an empty preorder walk worklist.");
1361     PreOrderWorklist.push_back(RootL);
1362     do {
1363       Loop *L = PreOrderWorklist.pop_back_val();
1364       PreOrderWorklist.append(L->begin(), L->end());
1365       PreOrderLoops.push_back(L);
1366     } while (!PreOrderWorklist.empty());
1367 
1368     Worklist.append(PreOrderLoops.begin(), PreOrderLoops.end());
1369     PreOrderLoops.clear();
1370   }
1371   return Worklist;
1372 }
1373 
1374 PreservedAnalyses LoopUnrollPass::run(Function &F,
1375                                       FunctionAnalysisManager &AM) {
1376   auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
1377   auto &LI = AM.getResult<LoopAnalysis>(F);
1378   auto &TTI = AM.getResult<TargetIRAnalysis>(F);
1379   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
1380   auto &AC = AM.getResult<AssumptionAnalysis>(F);
1381   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
1382 
1383   LoopAnalysisManager *LAM = nullptr;
1384   if (auto *LAMProxy = AM.getCachedResult<LoopAnalysisManagerFunctionProxy>(F))
1385     LAM = &LAMProxy->getManager();
1386 
1387   const ModuleAnalysisManager &MAM =
1388       AM.getResult<ModuleAnalysisManagerFunctionProxy>(F).getManager();
1389   ProfileSummaryInfo *PSI =
1390       MAM.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
1391   auto *BFI = (PSI && PSI->hasProfileSummary()) ?
1392       &AM.getResult<BlockFrequencyAnalysis>(F) : nullptr;
1393 
1394   bool Changed = false;
1395 
1396   // The unroller requires loops to be in simplified form, and also needs LCSSA.
1397   // Since simplification may add new inner loops, it has to run before the
1398   // legality and profitability checks. This means running the loop unroller
1399   // will simplify all loops, regardless of whether anything end up being
1400   // unrolled.
1401   for (auto &L : LI) {
1402     Changed |=
1403         simplifyLoop(L, &DT, &LI, &SE, &AC, nullptr, false /* PreserveLCSSA */);
1404     Changed |= formLCSSARecursively(*L, DT, &LI, &SE);
1405   }
1406 
1407   SmallVector<Loop *, 8> Worklist = appendLoopsToWorklist(LI);
1408 
1409   while (!Worklist.empty()) {
1410     // Because the LoopInfo stores the loops in RPO, we walk the worklist
1411     // from back to front so that we work forward across the CFG, which
1412     // for unrolling is only needed to get optimization remarks emitted in
1413     // a forward order.
1414     Loop &L = *Worklist.pop_back_val();
1415 #ifndef NDEBUG
1416     Loop *ParentL = L.getParentLoop();
1417 #endif
1418 
1419     // Check if the profile summary indicates that the profiled application
1420     // has a huge working set size, in which case we disable peeling to avoid
1421     // bloating it further.
1422     Optional<bool> LocalAllowPeeling = UnrollOpts.AllowPeeling;
1423     if (PSI && PSI->hasHugeWorkingSetSize())
1424       LocalAllowPeeling = false;
1425     std::string LoopName = L.getName();
1426     // The API here is quite complex to call and we allow to select some
1427     // flavors of unrolling during construction time (by setting UnrollOpts).
1428     LoopUnrollResult Result = tryToUnrollLoop(
1429         &L, DT, &LI, SE, TTI, AC, ORE, BFI, PSI,
1430         /*PreserveLCSSA*/ true, UnrollOpts.OptLevel, UnrollOpts.OnlyWhenForced,
1431         UnrollOpts.ForgetSCEV, /*Count*/ None,
1432         /*Threshold*/ None, UnrollOpts.AllowPartial, UnrollOpts.AllowRuntime,
1433         UnrollOpts.AllowUpperBound, LocalAllowPeeling);
1434     Changed |= Result != LoopUnrollResult::Unmodified;
1435 
1436     // The parent must not be damaged by unrolling!
1437 #ifndef NDEBUG
1438     if (Result != LoopUnrollResult::Unmodified && ParentL)
1439       ParentL->verifyLoop();
1440 #endif
1441 
1442     // Clear any cached analysis results for L if we removed it completely.
1443     if (LAM && Result == LoopUnrollResult::FullyUnrolled)
1444       LAM->clear(L, LoopName);
1445   }
1446 
1447   if (!Changed)
1448     return PreservedAnalyses::all();
1449 
1450   return getLoopPassPreservedAnalyses();
1451 }
1452