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/LoopAnalysisManager.h"
  17 #include "llvm/IR/Dominators.h"
  18 #include "llvm/IR/IRPrintingPasses.h"
  19 #include "llvm/IR/LLVMContext.h"
  20 #include "llvm/IR/OptBisect.h"
  21 #include "llvm/IR/PassManager.h"
  22 #include "llvm/IR/PassTimingInfo.h"
  23 #include "llvm/Support/Debug.h"
  24 #include "llvm/Support/Timer.h"
  25 #include "llvm/Support/TimeProfiler.h"
  26 #include "llvm/Support/raw_ostream.h"
  27 using namespace llvm;
  28
  29 #define DEBUG_TYPE "loop-pass-manager"
  30
  31 namespace {
  32
  33 /// PrintLoopPass - Print a Function corresponding to a Loop.
  34 ///
  35 class PrintLoopPassWrapper : public LoopPass {
  36   raw_ostream &OS;
  37   std::string Banner;
  38
  39 public:
  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
  61 char PrintLoopPassWrapper::ID = 0;
  62 }
  63
  64 //===----------------------------------------------------------------------===//
  65 // LPPassManager
  66 //
  67
  68 char LPPassManager::ID = 0;
  69
  70 LPPassManager::LPPassManager()
  71   : FunctionPass(ID), PMDataManager() {
  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.getParentLoop()) {
  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 /// cloneBasicBlockSimpleAnalysis - Invoke cloneBasicBlockAnalysis hook for
  96 /// all loop passes.
  97 void LPPassManager::cloneBasicBlockSimpleAnalysis(BasicBlock *From,
  98                                                   BasicBlock *To, Loop *L) {
  99   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 100     LoopPass *LP = getContainedPass(Index);
 101     LP->cloneBasicBlockAnalysis(From, To, L);
 102   }
 103 }
 104
 105 /// deleteSimpleAnalysisValue - Invoke deleteAnalysisValue hook for all passes.
 106 void LPPassManager::deleteSimpleAnalysisValue(Value *V, Loop *L) {
 107   if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
 108     for (Instruction &I : *BB) {
 109       deleteSimpleAnalysisValue(&I, L);
 110     }
 111   }
 112   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 113     LoopPass *LP = getContainedPass(Index);
 114     LP->deleteAnalysisValue(V, L);
 115   }
 116 }
 117
 118 /// Invoke deleteAnalysisLoop hook for all passes.
 119 void LPPassManager::deleteSimpleAnalysisLoop(Loop *L) {
 120   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 121     LoopPass *LP = getContainedPass(Index);
 122     LP->deleteAnalysisLoop(L);
 123   }
 124 }
 125
 126
 127 // Recurse through all subloops and all loops  into LQ.
 128 static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
 129   LQ.push_back(L);
 130   for (Loop *I : reverse(*L))
 131     addLoopIntoQueue(I, LQ);
 132 }
 133
 134 /// Pass Manager itself does not invalidate any analysis info.
 135 void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
 136   // LPPassManager needs LoopInfo. In the long term LoopInfo class will
 137   // become part of LPPassManager.
 138   Info.addRequired<LoopInfoWrapperPass>();
 139   Info.addRequired<DominatorTreeWrapperPass>();
 140   Info.setPreservesAll();
 141 }
 142
 143 void LPPassManager::markLoopAsDeleted(Loop &L) {
 144   assert((&L == CurrentLoop || CurrentLoop->contains(&L)) &&
 145          "Must not delete loop outside the current loop tree!");
 146   // If this loop appears elsewhere within the queue, we also need to remove it
 147   // there. However, we have to be careful to not remove the back of the queue
 148   // as that is assumed to match the current loop.
 149   assert(LQ.back() == CurrentLoop && "Loop queue back isn't the current loop!");
 150   LQ.erase(std::remove(LQ.begin(), LQ.end(), &L), LQ.end());
 151
 152   if (&L == CurrentLoop) {
 153     CurrentLoopDeleted = true;
 154     // Add this loop back onto the back of the queue to preserve our invariants.
 155     LQ.push_back(&L);
 156   }
 157 }
 158
 159 /// run - Execute all of the passes scheduled for execution.  Keep track of
 160 /// whether any of the passes modifies the function, and if so, return true.
 161 bool LPPassManager::runOnFunction(Function &F) {
 162   auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
 163   LI = &LIWP.getLoopInfo();
 164   Module &M = *F.getParent();
 165 #if 0
 166   DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
 167 #endif
 168   bool Changed = false;
 169
 170   // Collect inherited analysis from Module level pass manager.
 171   populateInheritedAnalysis(TPM->activeStack);
 172
 173   // Populate the loop queue in reverse program order. There is no clear need to
 174   // process sibling loops in either forward or reverse order. There may be some
 175   // advantage in deleting uses in a later loop before optimizing the
 176   // definitions in an earlier loop. If we find a clear reason to process in
 177   // forward order, then a forward variant of LoopPassManager should be created.
 178   //
 179   // Note that LoopInfo::iterator visits loops in reverse program
 180   // order. Here, reverse_iterator gives us a forward order, and the LoopQueue
 181   // reverses the order a third time by popping from the back.
 182   for (Loop *L : reverse(*LI))
 183     addLoopIntoQueue(L, LQ);
 184
 185   if (LQ.empty()) // No loops, skip calling finalizers
 186     return false;
 187
 188   // Initialization
 189   for (Loop *L : LQ) {
 190     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 191       LoopPass *P = getContainedPass(Index);
 192       Changed |= P->doInitialization(L, *this);
 193     }
 194   }
 195
 196   // Walk Loops
 197   unsigned InstrCount, FunctionSize = 0;
 198   StringMap<std::pair<unsigned, unsigned>> FunctionToInstrCount;
 199   bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
 200   // Collect the initial size of the module and the function we're looking at.
 201   if (EmitICRemark) {
 202     InstrCount = initSizeRemarkInfo(M, FunctionToInstrCount);
 203     FunctionSize = F.getInstructionCount();
 204   }
 205   while (!LQ.empty()) {
 206     CurrentLoopDeleted = false;
 207     CurrentLoop = LQ.back();
 208
 209     // Run all passes on the current Loop.
 210     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 211       LoopPass *P = getContainedPass(Index);
 212
 213       llvm::TimeTraceScope LoopPassScope("RunLoopPass", P->getPassName());
 214
 215       dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
 216                    CurrentLoop->getHeader()->getName());
 217       dumpRequiredSet(P);
 218
 219       initializeAnalysisImpl(P);
 220
 221       bool LocalChanged = false;
 222       {
 223         PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
 224         TimeRegion PassTimer(getPassTimer(P));
 225         LocalChanged = P->runOnLoop(CurrentLoop, *this);
 226         Changed |= LocalChanged;
 227         if (EmitICRemark) {
 228           unsigned NewSize = F.getInstructionCount();
 229           // Update the size of the function, emit a remark, and update the
 230           // size of the module.
 231           if (NewSize != FunctionSize) {
 232             int64_t Delta = static_cast<int64_t>(NewSize) -
 233                             static_cast<int64_t>(FunctionSize);
 234             emitInstrCountChangedRemark(P, M, Delta, InstrCount,
 235                                         FunctionToInstrCount, &F);
 236             InstrCount = static_cast<int64_t>(InstrCount) + Delta;
 237             FunctionSize = NewSize;
 238           }
 239         }
 240       }
 241
 242       if (LocalChanged)
 243         dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
 244                      CurrentLoopDeleted ? "<deleted loop>"
 245                                         : CurrentLoop->getName());
 246       dumpPreservedSet(P);
 247
 248       if (CurrentLoopDeleted) {
 249         // Notify passes that the loop is being deleted.
 250         deleteSimpleAnalysisLoop(CurrentLoop);
 251       } else {
 252         // Manually check that this loop is still healthy. This is done
 253         // instead of relying on LoopInfo::verifyLoop since LoopInfo
 254         // is a function pass and it's really expensive to verify every
 255         // loop in the function every time. That level of checking can be
 256         // enabled with the -verify-loop-info option.
 257         {
 258           TimeRegion PassTimer(getPassTimer(&LIWP));
 259           CurrentLoop->verifyLoop();
 260         }
 261         // Here we apply same reasoning as in the above case. Only difference
 262         // is that LPPassManager might run passes which do not require LCSSA
 263         // form (LoopPassPrinter for example). We should skip verification for
 264         // such passes.
 265         // FIXME: Loop-sink currently break LCSSA. Fix it and reenable the
 266         // verification!
 267 #if 0
 268         if (mustPreserveAnalysisID(LCSSAVerificationPass::ID))
 269           assert(CurrentLoop->isRecursivelyLCSSAForm(*DT, *LI));
 270 #endif
 271
 272         // Then call the regular verifyAnalysis functions.
 273         verifyPreservedAnalysis(P);
 274
 275         F.getContext().yield();
 276       }
 277
 278       removeNotPreservedAnalysis(P);
 279       recordAvailableAnalysis(P);
 280       removeDeadPasses(P,
 281                        CurrentLoopDeleted ? "<deleted>"
 282                                           : CurrentLoop->getHeader()->getName(),
 283                        ON_LOOP_MSG);
 284
 285       if (CurrentLoopDeleted)
 286         // Do not run other passes on this loop.
 287         break;
 288     }
 289
 290     // If the loop was deleted, release all the loop passes. This frees up
 291     // some memory, and avoids trouble with the pass manager trying to call
 292     // verifyAnalysis on them.
 293     if (CurrentLoopDeleted) {
 294       for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 295         Pass *P = getContainedPass(Index);
 296         freePass(P, "<deleted>", ON_LOOP_MSG);
 297       }
 298     }
 299
 300     // Pop the loop from queue after running all passes.
 301     LQ.pop_back();
 302   }
 303
 304   // Finalization
 305   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 306     LoopPass *P = getContainedPass(Index);
 307     Changed |= P->doFinalization();
 308   }
 309
 310   return Changed;
 311 }
 312
 313 /// Print passes managed by this manager
 314 void LPPassManager::dumpPassStructure(unsigned Offset) {
 315   errs().indent(Offset*2) << "Loop Pass Manager\n";
 316   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
 317     Pass *P = getContainedPass(Index);
 318     P->dumpPassStructure(Offset + 1);
 319     dumpLastUses(P, Offset+1);
 320   }
 321 }
 322
 323
 324 //===----------------------------------------------------------------------===//
 325 // LoopPass
 326
 327 Pass *LoopPass::createPrinterPass(raw_ostream &O,
 328                                   const std::string &Banner) const {
 329   return new PrintLoopPassWrapper(O, Banner);
 330 }
 331
 332 // Check if this pass is suitable for the current LPPassManager, if
 333 // available. This pass P is not suitable for a LPPassManager if P
 334 // is not preserving higher level analysis info used by other
 335 // LPPassManager passes. In such case, pop LPPassManager from the
 336 // stack. This will force assignPassManager() to create new
 337 // LPPassManger as expected.
 338 void LoopPass::preparePassManager(PMStack &PMS) {
 339
 340   // Find LPPassManager
 341   while (!PMS.empty() &&
 342          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
 343     PMS.pop();
 344
 345   // If this pass is destroying high level information that is used
 346   // by other passes that are managed by LPM then do not insert
 347   // this pass in current LPM. Use new LPPassManager.
 348   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager &&
 349       !PMS.top()->preserveHigherLevelAnalysis(this))
 350     PMS.pop();
 351 }
 352
 353 /// Assign pass manager to manage this pass.
 354 void LoopPass::assignPassManager(PMStack &PMS,
 355                                  PassManagerType PreferredType) {
 356   // Find LPPassManager
 357   while (!PMS.empty() &&
 358          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
 359     PMS.pop();
 360
 361   LPPassManager *LPPM;
 362   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager)
 363     LPPM = (LPPassManager*)PMS.top();
 364   else {
 365     // Create new Loop Pass Manager if it does not exist.
 366     assert (!PMS.empty() && "Unable to create Loop Pass Manager");
 367     PMDataManager *PMD = PMS.top();
 368
 369     // [1] Create new Loop Pass Manager
 370     LPPM = new LPPassManager();
 371     LPPM->populateInheritedAnalysis(PMS);
 372
 373     // [2] Set up new manager's top level manager
 374     PMTopLevelManager *TPM = PMD->getTopLevelManager();
 375     TPM->addIndirectPassManager(LPPM);
 376
 377     // [3] Assign manager to manage this new manager. This may create
 378     // and push new managers into PMS
 379     Pass *P = LPPM->getAsPass();
 380     TPM->schedulePass(P);
 381
 382     // [4] Push new manager into PMS
 383     PMS.push(LPPM);
 384   }
 385
 386   LPPM->add(this);
 387 }
 388
 389 static std::string getDescription(const Loop &L) {
 390   return "loop";
 391 }
 392
 393 bool LoopPass::skipLoop(const Loop *L) const {
 394   const Function *F = L->getHeader()->getParent();
 395   if (!F)
 396     return false;
 397   // Check the opt bisect limit.
 398   OptPassGate &Gate = F->getContext().getOptPassGate();
 399   if (Gate.isEnabled() && !Gate.shouldRunPass(this, getDescription(*L)))
 400     return true;
 401   // Check for the OptimizeNone attribute.
 402   if (F->hasOptNone()) {
 403     // FIXME: Report this to dbgs() only once per function.
 404     LLVM_DEBUG(dbgs() << "Skipping pass '" << getPassName() << "' in function "
 405                       << F->getName() << "\n");
 406     // FIXME: Delete loop from pass manager's queue?
 407     return true;
 408   }
 409   return false;
 410 }
 411
 412 char LCSSAVerificationPass::ID = 0;
 413 INITIALIZE_PASS(LCSSAVerificationPass, "lcssa-verification", "LCSSA Verifier",
 414                 false, false)