1//===- LoopPass.cpp - Loop Pass and Loop Pass Manager ---------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements LoopPass and LPPassManager. All loop optimization
10// and transformation passes are derived from LoopPass. LPPassManager is
11// responsible for managing LoopPasses.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Analysis/LoopPass.h"
16#include "llvm/Analysis/LoopInfo.h"
17#include "llvm/IR/Dominators.h"
18#include "llvm/IR/LLVMContext.h"
19#include "llvm/IR/OptBisect.h"
20#include "llvm/IR/PassTimingInfo.h"
21#include "llvm/IR/PrintPasses.h"
22#include "llvm/InitializePasses.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/TimeProfiler.h"
25#include "llvm/Support/Timer.h"
26#include "llvm/Support/raw_ostream.h"
27using namespace llvm;
28
29#define DEBUG_TYPE "loop-pass-manager"
30
31namespace {
32
33/// PrintLoopPass - Print a Function corresponding to a Loop.
34///
35class PrintLoopPassWrapper : public LoopPass {
36  raw_ostream &OS;
37  std::string Banner;
38
39public:
40  static char ID;
41  PrintLoopPassWrapper() : LoopPass(ID), OS(dbgs()) {}
42  PrintLoopPassWrapper(raw_ostream &OS, const std::string &Banner)
43      : LoopPass(ID), OS(OS), Banner(Banner) {}
44
45  void getAnalysisUsage(AnalysisUsage &AU) const override {
46    AU.setPreservesAll();
47  }
48
49  bool runOnLoop(Loop *L, LPPassManager &) override {
50    auto BBI = llvm::find_if(L->blocks(), [](BasicBlock *BB) { return BB; });
51    if (BBI != L->blocks().end() &&
52        isFunctionInPrintList((*BBI)->getParent()->getName())) {
53      printLoop(*L, OS, Banner);
54    }
55    return false;
56  }
57
58  StringRef getPassName() const override { return "Print Loop IR"; }
59};
60
61char PrintLoopPassWrapper::ID = 0;
62}
63
64//===----------------------------------------------------------------------===//
65// LPPassManager
66//
67
68char LPPassManager::ID = 0;
69
70LPPassManager::LPPassManager() : FunctionPass(ID) {
71  LI = nullptr;
72  CurrentLoop = nullptr;
73}
74
75// Insert loop into loop nest (LoopInfo) and loop queue (LQ).
76void LPPassManager::addLoop(Loop &L) {
77  if (L.isOutermost()) {
78    // This is the top level loop.
79    LQ.push_front(&L);
80    return;
81  }
82
83  // Insert L into the loop queue after the parent loop.
84  for (auto I = LQ.begin(), E = LQ.end(); I != E; ++I) {
85    if (*I == L.getParentLoop()) {
86      // deque does not support insert after.
87      ++I;
88      LQ.insert(I, 1, &L);
89      return;
90    }
91  }
92}
93
94// Recurse through all subloops and all loops  into LQ.
95static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
96  LQ.push_back(L);
97  for (Loop *I : reverse(*L))
98    addLoopIntoQueue(I, LQ);
99}
100
101/// Pass Manager itself does not invalidate any analysis info.
102void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
103  // LPPassManager needs LoopInfo. In the long term LoopInfo class will
104  // become part of LPPassManager.
105  Info.addRequired<LoopInfoWrapperPass>();
106  Info.addRequired<DominatorTreeWrapperPass>();
107  Info.setPreservesAll();
108}
109
110void LPPassManager::markLoopAsDeleted(Loop &L) {
111  assert((&L == CurrentLoop || CurrentLoop->contains(&L)) &&
112         "Must not delete loop outside the current loop tree!");
113  // If this loop appears elsewhere within the queue, we also need to remove it
114  // there. However, we have to be careful to not remove the back of the queue
115  // as that is assumed to match the current loop.
116  assert(LQ.back() == CurrentLoop && "Loop queue back isn't the current loop!");
117  llvm::erase(LQ, &L);
118
119  if (&L == CurrentLoop) {
120    CurrentLoopDeleted = true;
121    // Add this loop back onto the back of the queue to preserve our invariants.
122    LQ.push_back(&L);
123  }
124}
125
126/// run - Execute all of the passes scheduled for execution.  Keep track of
127/// whether any of the passes modifies the function, and if so, return true.
128bool LPPassManager::runOnFunction(Function &F) {
129  auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
130  LI = &LIWP.getLoopInfo();
131  Module &M = *F.getParent();
132#if 0
133  DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
134#endif
135  bool Changed = false;
136
137  // Collect inherited analysis from Module level pass manager.
138  populateInheritedAnalysis(TPM->activeStack);
139
140  // Populate the loop queue in reverse program order. There is no clear need to
141  // process sibling loops in either forward or reverse order. There may be some
142  // advantage in deleting uses in a later loop before optimizing the
143  // definitions in an earlier loop. If we find a clear reason to process in
144  // forward order, then a forward variant of LoopPassManager should be created.
145  //
146  // Note that LoopInfo::iterator visits loops in reverse program
147  // order. Here, reverse_iterator gives us a forward order, and the LoopQueue
148  // reverses the order a third time by popping from the back.
149  for (Loop *L : reverse(*LI))
150    addLoopIntoQueue(L, LQ);
151
152  if (LQ.empty()) // No loops, skip calling finalizers
153    return false;
154
155  // Initialization
156  for (Loop *L : LQ) {
157    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
158      LoopPass *P = getContainedPass(Index);
159      Changed |= P->doInitialization(L, *this);
160    }
161  }
162
163  // Walk Loops
164  unsigned InstrCount, FunctionSize = 0;
165  StringMap<std::pair<unsigned, unsigned>> FunctionToInstrCount;
166  bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
167  // Collect the initial size of the module and the function we're looking at.
168  if (EmitICRemark) {
169    InstrCount = initSizeRemarkInfo(M, FunctionToInstrCount);
170    FunctionSize = F.getInstructionCount();
171  }
172  while (!LQ.empty()) {
173    CurrentLoopDeleted = false;
174    CurrentLoop = LQ.back();
175
176    // Run all passes on the current Loop.
177    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
178      LoopPass *P = getContainedPass(Index);
179
180      llvm::TimeTraceScope LoopPassScope("RunLoopPass", P->getPassName());
181
182      dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
183                   CurrentLoop->getHeader()->getName());
184      dumpRequiredSet(P);
185
186      initializeAnalysisImpl(P);
187
188      bool LocalChanged = false;
189      {
190        PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
191        TimeRegion PassTimer(getPassTimer(P));
192#ifdef EXPENSIVE_CHECKS
193        uint64_t RefHash = P->structuralHash(F);
194#endif
195        LocalChanged = P->runOnLoop(CurrentLoop, *this);
196
197#ifdef EXPENSIVE_CHECKS
198        if (!LocalChanged && (RefHash != P->structuralHash(F))) {
199          llvm::errs() << "Pass modifies its input and doesn't report it: "
200                       << P->getPassName() << "\n";
201          llvm_unreachable("Pass modifies its input and doesn't report it");
202        }
203#endif
204
205        Changed |= LocalChanged;
206        if (EmitICRemark) {
207          unsigned NewSize = F.getInstructionCount();
208          // Update the size of the function, emit a remark, and update the
209          // size of the module.
210          if (NewSize != FunctionSize) {
211            int64_t Delta = static_cast<int64_t>(NewSize) -
212                            static_cast<int64_t>(FunctionSize);
213            emitInstrCountChangedRemark(P, M, Delta, InstrCount,
214                                        FunctionToInstrCount, &F);
215            InstrCount = static_cast<int64_t>(InstrCount) + Delta;
216            FunctionSize = NewSize;
217          }
218        }
219      }
220
221      if (LocalChanged)
222        dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
223                     CurrentLoopDeleted ? "<deleted loop>"
224                                        : CurrentLoop->getName());
225      dumpPreservedSet(P);
226
227      if (!CurrentLoopDeleted) {
228        // Manually check that this loop is still healthy. This is done
229        // instead of relying on LoopInfo::verifyLoop since LoopInfo
230        // is a function pass and it's really expensive to verify every
231        // loop in the function every time. That level of checking can be
232        // enabled with the -verify-loop-info option.
233        {
234          TimeRegion PassTimer(getPassTimer(&LIWP));
235          CurrentLoop->verifyLoop();
236        }
237        // Here we apply same reasoning as in the above case. Only difference
238        // is that LPPassManager might run passes which do not require LCSSA
239        // form (LoopPassPrinter for example). We should skip verification for
240        // such passes.
241        // FIXME: Loop-sink currently break LCSSA. Fix it and reenable the
242        // verification!
243#if 0
244        if (mustPreserveAnalysisID(LCSSAVerificationPass::ID))
245          assert(CurrentLoop->isRecursivelyLCSSAForm(*DT, *LI));
246#endif
247
248        // Then call the regular verifyAnalysis functions.
249        verifyPreservedAnalysis(P);
250
251        F.getContext().yield();
252      }
253
254      if (LocalChanged)
255        removeNotPreservedAnalysis(P);
256      recordAvailableAnalysis(P);
257      removeDeadPasses(P,
258                       CurrentLoopDeleted ? "<deleted>"
259                                          : CurrentLoop->getHeader()->getName(),
260                       ON_LOOP_MSG);
261
262      if (CurrentLoopDeleted)
263        // Do not run other passes on this loop.
264        break;
265    }
266
267    // If the loop was deleted, release all the loop passes. This frees up
268    // some memory, and avoids trouble with the pass manager trying to call
269    // verifyAnalysis on them.
270    if (CurrentLoopDeleted) {
271      for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
272        Pass *P = getContainedPass(Index);
273        freePass(P, "<deleted>", ON_LOOP_MSG);
274      }
275    }
276
277    // Pop the loop from queue after running all passes.
278    LQ.pop_back();
279  }
280
281  // Finalization
282  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
283    LoopPass *P = getContainedPass(Index);
284    Changed |= P->doFinalization();
285  }
286
287  return Changed;
288}
289
290/// Print passes managed by this manager
291void LPPassManager::dumpPassStructure(unsigned Offset) {
292  errs().indent(Offset*2) << "Loop Pass Manager\n";
293  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
294    Pass *P = getContainedPass(Index);
295    P->dumpPassStructure(Offset + 1);
296    dumpLastUses(P, Offset+1);
297  }
298}
299
300
301//===----------------------------------------------------------------------===//
302// LoopPass
303
304Pass *LoopPass::createPrinterPass(raw_ostream &O,
305                                  const std::string &Banner) const {
306  return new PrintLoopPassWrapper(O, Banner);
307}
308
309// Check if this pass is suitable for the current LPPassManager, if
310// available. This pass P is not suitable for a LPPassManager if P
311// is not preserving higher level analysis info used by other
312// LPPassManager passes. In such case, pop LPPassManager from the
313// stack. This will force assignPassManager() to create new
314// LPPassManger as expected.
315void LoopPass::preparePassManager(PMStack &PMS) {
316
317  // Find LPPassManager
318  while (!PMS.empty() &&
319         PMS.top()->getPassManagerType() > PMT_LoopPassManager)
320    PMS.pop();
321
322  // If this pass is destroying high level information that is used
323  // by other passes that are managed by LPM then do not insert
324  // this pass in current LPM. Use new LPPassManager.
325  if (PMS.top()->getPassManagerType() == PMT_LoopPassManager &&
326      !PMS.top()->preserveHigherLevelAnalysis(this))
327    PMS.pop();
328}
329
330/// Assign pass manager to manage this pass.
331void LoopPass::assignPassManager(PMStack &PMS,
332                                 PassManagerType PreferredType) {
333  // Find LPPassManager
334  while (!PMS.empty() &&
335         PMS.top()->getPassManagerType() > PMT_LoopPassManager)
336    PMS.pop();
337
338  LPPassManager *LPPM;
339  if (PMS.top()->getPassManagerType() == PMT_LoopPassManager)
340    LPPM = (LPPassManager*)PMS.top();
341  else {
342    // Create new Loop Pass Manager if it does not exist.
343    assert (!PMS.empty() && "Unable to create Loop Pass Manager");
344    PMDataManager *PMD = PMS.top();
345
346    // [1] Create new Loop Pass Manager
347    LPPM = new LPPassManager();
348    LPPM->populateInheritedAnalysis(PMS);
349
350    // [2] Set up new manager's top level manager
351    PMTopLevelManager *TPM = PMD->getTopLevelManager();
352    TPM->addIndirectPassManager(LPPM);
353
354    // [3] Assign manager to manage this new manager. This may create
355    // and push new managers into PMS
356    Pass *P = LPPM->getAsPass();
357    TPM->schedulePass(P);
358
359    // [4] Push new manager into PMS
360    PMS.push(LPPM);
361  }
362
363  LPPM->add(this);
364}
365
366static std::string getDescription(const Loop &L) {
367  return "loop";
368}
369
370bool LoopPass::skipLoop(const Loop *L) const {
371  const Function *F = L->getHeader()->getParent();
372  if (!F)
373    return false;
374  // Check the opt bisect limit.
375  OptPassGate &Gate = F->getContext().getOptPassGate();
376  if (Gate.isEnabled() &&
377      !Gate.shouldRunPass(this->getPassName(), getDescription(*L)))
378    return true;
379  // Check for the OptimizeNone attribute.
380  if (F->hasOptNone()) {
381    // FIXME: Report this to dbgs() only once per function.
382    LLVM_DEBUG(dbgs() << "Skipping pass '" << getPassName() << "' in function "
383                      << F->getName() << "\n");
384    // FIXME: Delete loop from pass manager's queue?
385    return true;
386  }
387  return false;
388}
389
390LCSSAVerificationPass::LCSSAVerificationPass() : FunctionPass(ID) {
391  initializeLCSSAVerificationPassPass(*PassRegistry::getPassRegistry());
392}
393
394char LCSSAVerificationPass::ID = 0;
395INITIALIZE_PASS(LCSSAVerificationPass, "lcssa-verification", "LCSSA Verifier",
396                false, false)
397