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      1 //===- LoopPass.cpp - Loop Pass and Loop Pass Manager ---------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements LoopPass and LPPassManager. All loop optimization
     11 // and transformation passes are derived from LoopPass. LPPassManager is
     12 // responsible for managing LoopPasses.
     13 //
     14 //===----------------------------------------------------------------------===//
     15 
     16 #include "llvm/Analysis/LoopPass.h"
     17 #include "llvm/DebugInfoProbe.h"
     18 #include "llvm/Assembly/PrintModulePass.h"
     19 #include "llvm/Support/Debug.h"
     20 #include "llvm/Support/ManagedStatic.h"
     21 #include "llvm/Support/Timer.h"
     22 using namespace llvm;
     23 
     24 namespace {
     25 
     26 /// PrintLoopPass - Print a Function corresponding to a Loop.
     27 ///
     28 class PrintLoopPass : public LoopPass {
     29 private:
     30   std::string Banner;
     31   raw_ostream &Out;       // raw_ostream to print on.
     32 
     33 public:
     34   static char ID;
     35   PrintLoopPass(const std::string &B, raw_ostream &o)
     36       : LoopPass(ID), Banner(B), Out(o) {}
     37 
     38   virtual void getAnalysisUsage(AnalysisUsage &AU) const {
     39     AU.setPreservesAll();
     40   }
     41 
     42   bool runOnLoop(Loop *L, LPPassManager &) {
     43     Out << Banner;
     44     for (Loop::block_iterator b = L->block_begin(), be = L->block_end();
     45          b != be;
     46          ++b) {
     47       (*b)->print(Out);
     48     }
     49     return false;
     50   }
     51 };
     52 
     53 char PrintLoopPass::ID = 0;
     54 }
     55 
     56 //===----------------------------------------------------------------------===//
     57 // DebugInfoProbe
     58 
     59 static DebugInfoProbeInfo *TheDebugProbe;
     60 static void createDebugInfoProbe() {
     61   if (TheDebugProbe) return;
     62 
     63   // Constructed the first time this is called. This guarantees that the
     64   // object will be constructed, if -enable-debug-info-probe is set,
     65   // before static globals, thus it will be destroyed before them.
     66   static ManagedStatic<DebugInfoProbeInfo> DIP;
     67   TheDebugProbe = &*DIP;
     68 }
     69 
     70 //===----------------------------------------------------------------------===//
     71 // LPPassManager
     72 //
     73 
     74 char LPPassManager::ID = 0;
     75 
     76 LPPassManager::LPPassManager(int Depth)
     77   : FunctionPass(ID), PMDataManager(Depth) {
     78   skipThisLoop = false;
     79   redoThisLoop = false;
     80   LI = NULL;
     81   CurrentLoop = NULL;
     82 }
     83 
     84 /// Delete loop from the loop queue and loop hierarchy (LoopInfo).
     85 void LPPassManager::deleteLoopFromQueue(Loop *L) {
     86 
     87   if (Loop *ParentLoop = L->getParentLoop()) { // Not a top-level loop.
     88     // Reparent all of the blocks in this loop.  Since BBLoop had a parent,
     89     // they are now all in it.
     90     for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
     91          I != E; ++I)
     92       if (LI->getLoopFor(*I) == L)    // Don't change blocks in subloops.
     93         LI->changeLoopFor(*I, ParentLoop);
     94 
     95     // Remove the loop from its parent loop.
     96     for (Loop::iterator I = ParentLoop->begin(), E = ParentLoop->end();;
     97          ++I) {
     98       assert(I != E && "Couldn't find loop");
     99       if (*I == L) {
    100         ParentLoop->removeChildLoop(I);
    101         break;
    102       }
    103     }
    104 
    105     // Move all subloops into the parent loop.
    106     while (!L->empty())
    107       ParentLoop->addChildLoop(L->removeChildLoop(L->end()-1));
    108   } else {
    109     // Reparent all of the blocks in this loop.  Since BBLoop had no parent,
    110     // they no longer in a loop at all.
    111 
    112     for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
    113       // Don't change blocks in subloops.
    114       if (LI->getLoopFor(L->getBlocks()[i]) == L) {
    115         LI->removeBlock(L->getBlocks()[i]);
    116         --i;
    117       }
    118     }
    119 
    120     // Remove the loop from the top-level LoopInfo object.
    121     for (LoopInfo::iterator I = LI->begin(), E = LI->end();; ++I) {
    122       assert(I != E && "Couldn't find loop");
    123       if (*I == L) {
    124         LI->removeLoop(I);
    125         break;
    126       }
    127     }
    128 
    129     // Move all of the subloops to the top-level.
    130     while (!L->empty())
    131       LI->addTopLevelLoop(L->removeChildLoop(L->end()-1));
    132   }
    133 
    134   delete L;
    135 
    136   // If L is current loop then skip rest of the passes and let
    137   // runOnFunction remove L from LQ. Otherwise, remove L from LQ now
    138   // and continue applying other passes on CurrentLoop.
    139   if (CurrentLoop == L) {
    140     skipThisLoop = true;
    141     return;
    142   }
    143 
    144   for (std::deque<Loop *>::iterator I = LQ.begin(),
    145          E = LQ.end(); I != E; ++I) {
    146     if (*I == L) {
    147       LQ.erase(I);
    148       break;
    149     }
    150   }
    151 }
    152 
    153 // Inset loop into loop nest (LoopInfo) and loop queue (LQ).
    154 void LPPassManager::insertLoop(Loop *L, Loop *ParentLoop) {
    155 
    156   assert (CurrentLoop != L && "Cannot insert CurrentLoop");
    157 
    158   // Insert into loop nest
    159   if (ParentLoop)
    160     ParentLoop->addChildLoop(L);
    161   else
    162     LI->addTopLevelLoop(L);
    163 
    164   insertLoopIntoQueue(L);
    165 }
    166 
    167 void LPPassManager::insertLoopIntoQueue(Loop *L) {
    168   // Insert L into loop queue
    169   if (L == CurrentLoop)
    170     redoLoop(L);
    171   else if (!L->getParentLoop())
    172     // This is top level loop.
    173     LQ.push_front(L);
    174   else {
    175     // Insert L after the parent loop.
    176     for (std::deque<Loop *>::iterator I = LQ.begin(),
    177            E = LQ.end(); I != E; ++I) {
    178       if (*I == L->getParentLoop()) {
    179         // deque does not support insert after.
    180         ++I;
    181         LQ.insert(I, 1, L);
    182         break;
    183       }
    184     }
    185   }
    186 }
    187 
    188 // Reoptimize this loop. LPPassManager will re-insert this loop into the
    189 // queue. This allows LoopPass to change loop nest for the loop. This
    190 // utility may send LPPassManager into infinite loops so use caution.
    191 void LPPassManager::redoLoop(Loop *L) {
    192   assert (CurrentLoop == L && "Can redo only CurrentLoop");
    193   redoThisLoop = true;
    194 }
    195 
    196 /// cloneBasicBlockSimpleAnalysis - Invoke cloneBasicBlockAnalysis hook for
    197 /// all loop passes.
    198 void LPPassManager::cloneBasicBlockSimpleAnalysis(BasicBlock *From,
    199                                                   BasicBlock *To, Loop *L) {
    200   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    201     LoopPass *LP = getContainedPass(Index);
    202     LP->cloneBasicBlockAnalysis(From, To, L);
    203   }
    204 }
    205 
    206 /// deleteSimpleAnalysisValue - Invoke deleteAnalysisValue hook for all passes.
    207 void LPPassManager::deleteSimpleAnalysisValue(Value *V, Loop *L) {
    208   if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
    209     for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;
    210          ++BI) {
    211       Instruction &I = *BI;
    212       deleteSimpleAnalysisValue(&I, L);
    213     }
    214   }
    215   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    216     LoopPass *LP = getContainedPass(Index);
    217     LP->deleteAnalysisValue(V, L);
    218   }
    219 }
    220 
    221 
    222 // Recurse through all subloops and all loops  into LQ.
    223 static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
    224   LQ.push_back(L);
    225   for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
    226     addLoopIntoQueue(*I, LQ);
    227 }
    228 
    229 /// Pass Manager itself does not invalidate any analysis info.
    230 void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
    231   // LPPassManager needs LoopInfo. In the long term LoopInfo class will
    232   // become part of LPPassManager.
    233   Info.addRequired<LoopInfo>();
    234   Info.setPreservesAll();
    235 }
    236 
    237 /// run - Execute all of the passes scheduled for execution.  Keep track of
    238 /// whether any of the passes modifies the function, and if so, return true.
    239 bool LPPassManager::runOnFunction(Function &F) {
    240   LI = &getAnalysis<LoopInfo>();
    241   bool Changed = false;
    242   createDebugInfoProbe();
    243 
    244   // Collect inherited analysis from Module level pass manager.
    245   populateInheritedAnalysis(TPM->activeStack);
    246 
    247   // Populate Loop Queue
    248   for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
    249     addLoopIntoQueue(*I, LQ);
    250 
    251   if (LQ.empty()) // No loops, skip calling finalizers
    252     return false;
    253 
    254   // Initialization
    255   for (std::deque<Loop *>::const_iterator I = LQ.begin(), E = LQ.end();
    256        I != E; ++I) {
    257     Loop *L = *I;
    258     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    259       LoopPass *P = getContainedPass(Index);
    260       Changed |= P->doInitialization(L, *this);
    261     }
    262   }
    263 
    264   // Walk Loops
    265   while (!LQ.empty()) {
    266 
    267     CurrentLoop  = LQ.back();
    268     skipThisLoop = false;
    269     redoThisLoop = false;
    270 
    271     // Run all passes on the current Loop.
    272     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    273       LoopPass *P = getContainedPass(Index);
    274       dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
    275                    CurrentLoop->getHeader()->getName());
    276       dumpRequiredSet(P);
    277 
    278       initializeAnalysisImpl(P);
    279       if (TheDebugProbe)
    280         TheDebugProbe->initialize(P, F);
    281       {
    282         PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
    283         TimeRegion PassTimer(getPassTimer(P));
    284 
    285         Changed |= P->runOnLoop(CurrentLoop, *this);
    286       }
    287       if (TheDebugProbe)
    288         TheDebugProbe->finalize(P, F);
    289 
    290       if (Changed)
    291         dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
    292                      skipThisLoop ? "<deleted>" :
    293                                     CurrentLoop->getHeader()->getName());
    294       dumpPreservedSet(P);
    295 
    296       if (!skipThisLoop) {
    297         // Manually check that this loop is still healthy. This is done
    298         // instead of relying on LoopInfo::verifyLoop since LoopInfo
    299         // is a function pass and it's really expensive to verify every
    300         // loop in the function every time. That level of checking can be
    301         // enabled with the -verify-loop-info option.
    302         {
    303           TimeRegion PassTimer(getPassTimer(LI));
    304           CurrentLoop->verifyLoop();
    305         }
    306 
    307         // Then call the regular verifyAnalysis functions.
    308         verifyPreservedAnalysis(P);
    309       }
    310 
    311       removeNotPreservedAnalysis(P);
    312       recordAvailableAnalysis(P);
    313       removeDeadPasses(P,
    314                        skipThisLoop ? "<deleted>" :
    315                                       CurrentLoop->getHeader()->getName(),
    316                        ON_LOOP_MSG);
    317 
    318       if (skipThisLoop)
    319         // Do not run other passes on this loop.
    320         break;
    321     }
    322 
    323     // If the loop was deleted, release all the loop passes. This frees up
    324     // some memory, and avoids trouble with the pass manager trying to call
    325     // verifyAnalysis on them.
    326     if (skipThisLoop)
    327       for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    328         Pass *P = getContainedPass(Index);
    329         freePass(P, "<deleted>", ON_LOOP_MSG);
    330       }
    331 
    332     // Pop the loop from queue after running all passes.
    333     LQ.pop_back();
    334 
    335     if (redoThisLoop)
    336       LQ.push_back(CurrentLoop);
    337   }
    338 
    339   // Finalization
    340   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    341     LoopPass *P = getContainedPass(Index);
    342     Changed |= P->doFinalization();
    343   }
    344 
    345   return Changed;
    346 }
    347 
    348 /// Print passes managed by this manager
    349 void LPPassManager::dumpPassStructure(unsigned Offset) {
    350   errs().indent(Offset*2) << "Loop Pass Manager\n";
    351   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
    352     Pass *P = getContainedPass(Index);
    353     P->dumpPassStructure(Offset + 1);
    354     dumpLastUses(P, Offset+1);
    355   }
    356 }
    357 
    358 
    359 //===----------------------------------------------------------------------===//
    360 // LoopPass
    361 
    362 Pass *LoopPass::createPrinterPass(raw_ostream &O,
    363                                   const std::string &Banner) const {
    364   return new PrintLoopPass(Banner, O);
    365 }
    366 
    367 // Check if this pass is suitable for the current LPPassManager, if
    368 // available. This pass P is not suitable for a LPPassManager if P
    369 // is not preserving higher level analysis info used by other
    370 // LPPassManager passes. In such case, pop LPPassManager from the
    371 // stack. This will force assignPassManager() to create new
    372 // LPPassManger as expected.
    373 void LoopPass::preparePassManager(PMStack &PMS) {
    374 
    375   // Find LPPassManager
    376   while (!PMS.empty() &&
    377          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
    378     PMS.pop();
    379 
    380   // If this pass is destroying high level information that is used
    381   // by other passes that are managed by LPM then do not insert
    382   // this pass in current LPM. Use new LPPassManager.
    383   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager &&
    384       !PMS.top()->preserveHigherLevelAnalysis(this))
    385     PMS.pop();
    386 }
    387 
    388 /// Assign pass manager to manage this pass.
    389 void LoopPass::assignPassManager(PMStack &PMS,
    390                                  PassManagerType PreferredType) {
    391   // Find LPPassManager
    392   while (!PMS.empty() &&
    393          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
    394     PMS.pop();
    395 
    396   LPPassManager *LPPM;
    397   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager)
    398     LPPM = (LPPassManager*)PMS.top();
    399   else {
    400     // Create new Loop Pass Manager if it does not exist.
    401     assert (!PMS.empty() && "Unable to create Loop Pass Manager");
    402     PMDataManager *PMD = PMS.top();
    403 
    404     // [1] Create new Call Graph Pass Manager
    405     LPPM = new LPPassManager(PMD->getDepth() + 1);
    406     LPPM->populateInheritedAnalysis(PMS);
    407 
    408     // [2] Set up new manager's top level manager
    409     PMTopLevelManager *TPM = PMD->getTopLevelManager();
    410     TPM->addIndirectPassManager(LPPM);
    411 
    412     // [3] Assign manager to manage this new manager. This may create
    413     // and push new managers into PMS
    414     Pass *P = LPPM->getAsPass();
    415     TPM->schedulePass(P);
    416 
    417     // [4] Push new manager into PMS
    418     PMS.push(LPPM);
    419   }
    420 
    421   LPPM->add(this);
    422 }
    423