llvm/lib/Analysis/LoopPass.cpp

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