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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/IR/IRPrintingPasses.h"
18 #include "llvm/IR/LLVMContext.h"
19 #include "llvm/Support/Debug.h"
20 #include "llvm/Support/Timer.h"
21 using namespace llvm;
22 
23 #define DEBUG_TYPE "loop-pass-manager"
24 
25 namespace {
26 
27 /// PrintLoopPass - Print a Function corresponding to a Loop.
28 ///
29 class PrintLoopPass : public LoopPass {
30 private:
31   std::string Banner;
32   raw_ostream &Out;       // raw_ostream to print on.
33 
34 public:
35   static char ID;
PrintLoopPass(const std::string & B,raw_ostream & o)36   PrintLoopPass(const std::string &B, raw_ostream &o)
37       : LoopPass(ID), Banner(B), Out(o) {}
38 
getAnalysisUsage(AnalysisUsage & AU) const39   void getAnalysisUsage(AnalysisUsage &AU) const override {
40     AU.setPreservesAll();
41   }
42 
runOnLoop(Loop * L,LPPassManager &)43   bool runOnLoop(Loop *L, LPPassManager &) override {
44     Out << Banner;
45     for (Loop::block_iterator b = L->block_begin(), be = L->block_end();
46          b != be;
47          ++b) {
48       if (*b)
49         (*b)->print(Out);
50       else
51         Out << "Printing <null> block";
52     }
53     return false;
54   }
55 };
56 
57 char PrintLoopPass::ID = 0;
58 }
59 
60 //===----------------------------------------------------------------------===//
61 // LPPassManager
62 //
63 
64 char LPPassManager::ID = 0;
65 
LPPassManager()66 LPPassManager::LPPassManager()
67   : FunctionPass(ID), PMDataManager() {
68   skipThisLoop = false;
69   redoThisLoop = false;
70   LI = nullptr;
71   CurrentLoop = nullptr;
72 }
73 
74 /// Delete loop from the loop queue and loop hierarchy (LoopInfo).
deleteLoopFromQueue(Loop * L)75 void LPPassManager::deleteLoopFromQueue(Loop *L) {
76 
77   LI->updateUnloop(L);
78 
79   // If L is current loop then skip rest of the passes and let
80   // runOnFunction remove L from LQ. Otherwise, remove L from LQ now
81   // and continue applying other passes on CurrentLoop.
82   if (CurrentLoop == L)
83     skipThisLoop = true;
84 
85   delete L;
86 
87   if (skipThisLoop)
88     return;
89 
90   for (std::deque<Loop *>::iterator I = LQ.begin(),
91          E = LQ.end(); I != E; ++I) {
92     if (*I == L) {
93       LQ.erase(I);
94       break;
95     }
96   }
97 }
98 
99 // Inset loop into loop nest (LoopInfo) and loop queue (LQ).
insertLoop(Loop * L,Loop * ParentLoop)100 void LPPassManager::insertLoop(Loop *L, Loop *ParentLoop) {
101 
102   assert (CurrentLoop != L && "Cannot insert CurrentLoop");
103 
104   // Insert into loop nest
105   if (ParentLoop)
106     ParentLoop->addChildLoop(L);
107   else
108     LI->addTopLevelLoop(L);
109 
110   insertLoopIntoQueue(L);
111 }
112 
insertLoopIntoQueue(Loop * L)113 void LPPassManager::insertLoopIntoQueue(Loop *L) {
114   // Insert L into loop queue
115   if (L == CurrentLoop)
116     redoLoop(L);
117   else if (!L->getParentLoop())
118     // This is top level loop.
119     LQ.push_front(L);
120   else {
121     // Insert L after the parent loop.
122     for (std::deque<Loop *>::iterator I = LQ.begin(),
123            E = LQ.end(); I != E; ++I) {
124       if (*I == L->getParentLoop()) {
125         // deque does not support insert after.
126         ++I;
127         LQ.insert(I, 1, L);
128         break;
129       }
130     }
131   }
132 }
133 
134 // Reoptimize this loop. LPPassManager will re-insert this loop into the
135 // queue. This allows LoopPass to change loop nest for the loop. This
136 // utility may send LPPassManager into infinite loops so use caution.
redoLoop(Loop * L)137 void LPPassManager::redoLoop(Loop *L) {
138   assert (CurrentLoop == L && "Can redo only CurrentLoop");
139   redoThisLoop = true;
140 }
141 
142 /// cloneBasicBlockSimpleAnalysis - Invoke cloneBasicBlockAnalysis hook for
143 /// all loop passes.
cloneBasicBlockSimpleAnalysis(BasicBlock * From,BasicBlock * To,Loop * L)144 void LPPassManager::cloneBasicBlockSimpleAnalysis(BasicBlock *From,
145                                                   BasicBlock *To, Loop *L) {
146   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
147     LoopPass *LP = getContainedPass(Index);
148     LP->cloneBasicBlockAnalysis(From, To, L);
149   }
150 }
151 
152 /// deleteSimpleAnalysisValue - Invoke deleteAnalysisValue hook for all passes.
deleteSimpleAnalysisValue(Value * V,Loop * L)153 void LPPassManager::deleteSimpleAnalysisValue(Value *V, Loop *L) {
154   if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
155     for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;
156          ++BI) {
157       Instruction &I = *BI;
158       deleteSimpleAnalysisValue(&I, L);
159     }
160   }
161   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
162     LoopPass *LP = getContainedPass(Index);
163     LP->deleteAnalysisValue(V, L);
164   }
165 }
166 
167 
168 // Recurse through all subloops and all loops  into LQ.
addLoopIntoQueue(Loop * L,std::deque<Loop * > & LQ)169 static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
170   LQ.push_back(L);
171   for (Loop::reverse_iterator I = L->rbegin(), E = L->rend(); I != E; ++I)
172     addLoopIntoQueue(*I, LQ);
173 }
174 
175 /// Pass Manager itself does not invalidate any analysis info.
getAnalysisUsage(AnalysisUsage & Info) const176 void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
177   // LPPassManager needs LoopInfo. In the long term LoopInfo class will
178   // become part of LPPassManager.
179   Info.addRequired<LoopInfo>();
180   Info.setPreservesAll();
181 }
182 
183 /// run - Execute all of the passes scheduled for execution.  Keep track of
184 /// whether any of the passes modifies the function, and if so, return true.
runOnFunction(Function & F)185 bool LPPassManager::runOnFunction(Function &F) {
186   LI = &getAnalysis<LoopInfo>();
187   bool Changed = false;
188 
189   // Collect inherited analysis from Module level pass manager.
190   populateInheritedAnalysis(TPM->activeStack);
191 
192   // Populate the loop queue in reverse program order. There is no clear need to
193   // process sibling loops in either forward or reverse order. There may be some
194   // advantage in deleting uses in a later loop before optimizing the
195   // definitions in an earlier loop. If we find a clear reason to process in
196   // forward order, then a forward variant of LoopPassManager should be created.
197   //
198   // Note that LoopInfo::iterator visits loops in reverse program
199   // order. Here, reverse_iterator gives us a forward order, and the LoopQueue
200   // reverses the order a third time by popping from the back.
201   for (LoopInfo::reverse_iterator I = LI->rbegin(), E = LI->rend(); I != E; ++I)
202     addLoopIntoQueue(*I, LQ);
203 
204   if (LQ.empty()) // No loops, skip calling finalizers
205     return false;
206 
207   // Initialization
208   for (std::deque<Loop *>::const_iterator I = LQ.begin(), E = LQ.end();
209        I != E; ++I) {
210     Loop *L = *I;
211     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
212       LoopPass *P = getContainedPass(Index);
213       Changed |= P->doInitialization(L, *this);
214     }
215   }
216 
217   // Walk Loops
218   while (!LQ.empty()) {
219 
220     CurrentLoop  = LQ.back();
221     skipThisLoop = false;
222     redoThisLoop = false;
223 
224     // Run all passes on the current Loop.
225     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
226       LoopPass *P = getContainedPass(Index);
227 
228       dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
229                    CurrentLoop->getHeader()->getName());
230       dumpRequiredSet(P);
231 
232       initializeAnalysisImpl(P);
233 
234       {
235         PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
236         TimeRegion PassTimer(getPassTimer(P));
237 
238         Changed |= P->runOnLoop(CurrentLoop, *this);
239       }
240 
241       if (Changed)
242         dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
243                      skipThisLoop ? "<deleted>" :
244                                     CurrentLoop->getHeader()->getName());
245       dumpPreservedSet(P);
246 
247       if (!skipThisLoop) {
248         // Manually check that this loop is still healthy. This is done
249         // instead of relying on LoopInfo::verifyLoop since LoopInfo
250         // is a function pass and it's really expensive to verify every
251         // loop in the function every time. That level of checking can be
252         // enabled with the -verify-loop-info option.
253         {
254           TimeRegion PassTimer(getPassTimer(LI));
255           CurrentLoop->verifyLoop();
256         }
257 
258         // Then call the regular verifyAnalysis functions.
259         verifyPreservedAnalysis(P);
260 
261         F.getContext().yield();
262       }
263 
264       removeNotPreservedAnalysis(P);
265       recordAvailableAnalysis(P);
266       removeDeadPasses(P,
267                        skipThisLoop ? "<deleted>" :
268                                       CurrentLoop->getHeader()->getName(),
269                        ON_LOOP_MSG);
270 
271       if (skipThisLoop)
272         // Do not run other passes on this loop.
273         break;
274     }
275 
276     // If the loop was deleted, release all the loop passes. This frees up
277     // some memory, and avoids trouble with the pass manager trying to call
278     // verifyAnalysis on them.
279     if (skipThisLoop)
280       for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
281         Pass *P = getContainedPass(Index);
282         freePass(P, "<deleted>", ON_LOOP_MSG);
283       }
284 
285     // Pop the loop from queue after running all passes.
286     LQ.pop_back();
287 
288     if (redoThisLoop)
289       LQ.push_back(CurrentLoop);
290   }
291 
292   // Finalization
293   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
294     LoopPass *P = getContainedPass(Index);
295     Changed |= P->doFinalization();
296   }
297 
298   return Changed;
299 }
300 
301 /// Print passes managed by this manager
dumpPassStructure(unsigned Offset)302 void LPPassManager::dumpPassStructure(unsigned Offset) {
303   errs().indent(Offset*2) << "Loop Pass Manager\n";
304   for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
305     Pass *P = getContainedPass(Index);
306     P->dumpPassStructure(Offset + 1);
307     dumpLastUses(P, Offset+1);
308   }
309 }
310 
311 
312 //===----------------------------------------------------------------------===//
313 // LoopPass
314 
createPrinterPass(raw_ostream & O,const std::string & Banner) const315 Pass *LoopPass::createPrinterPass(raw_ostream &O,
316                                   const std::string &Banner) const {
317   return new PrintLoopPass(Banner, O);
318 }
319 
320 // Check if this pass is suitable for the current LPPassManager, if
321 // available. This pass P is not suitable for a LPPassManager if P
322 // is not preserving higher level analysis info used by other
323 // LPPassManager passes. In such case, pop LPPassManager from the
324 // stack. This will force assignPassManager() to create new
325 // LPPassManger as expected.
preparePassManager(PMStack & PMS)326 void LoopPass::preparePassManager(PMStack &PMS) {
327 
328   // Find LPPassManager
329   while (!PMS.empty() &&
330          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
331     PMS.pop();
332 
333   // If this pass is destroying high level information that is used
334   // by other passes that are managed by LPM then do not insert
335   // this pass in current LPM. Use new LPPassManager.
336   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager &&
337       !PMS.top()->preserveHigherLevelAnalysis(this))
338     PMS.pop();
339 }
340 
341 /// Assign pass manager to manage this pass.
assignPassManager(PMStack & PMS,PassManagerType PreferredType)342 void LoopPass::assignPassManager(PMStack &PMS,
343                                  PassManagerType PreferredType) {
344   // Find LPPassManager
345   while (!PMS.empty() &&
346          PMS.top()->getPassManagerType() > PMT_LoopPassManager)
347     PMS.pop();
348 
349   LPPassManager *LPPM;
350   if (PMS.top()->getPassManagerType() == PMT_LoopPassManager)
351     LPPM = (LPPassManager*)PMS.top();
352   else {
353     // Create new Loop Pass Manager if it does not exist.
354     assert (!PMS.empty() && "Unable to create Loop Pass Manager");
355     PMDataManager *PMD = PMS.top();
356 
357     // [1] Create new Loop Pass Manager
358     LPPM = new LPPassManager();
359     LPPM->populateInheritedAnalysis(PMS);
360 
361     // [2] Set up new manager's top level manager
362     PMTopLevelManager *TPM = PMD->getTopLevelManager();
363     TPM->addIndirectPassManager(LPPM);
364 
365     // [3] Assign manager to manage this new manager. This may create
366     // and push new managers into PMS
367     Pass *P = LPPM->getAsPass();
368     TPM->schedulePass(P);
369 
370     // [4] Push new manager into PMS
371     PMS.push(LPPM);
372   }
373 
374   LPPM->add(this);
375 }
376 
377 // Containing function has Attribute::OptimizeNone and transformation
378 // passes should skip it.
skipOptnoneFunction(const Loop * L) const379 bool LoopPass::skipOptnoneFunction(const Loop *L) const {
380   const Function *F = L->getHeader()->getParent();
381   if (F && F->hasFnAttribute(Attribute::OptimizeNone)) {
382     // FIXME: Report this to dbgs() only once per function.
383     DEBUG(dbgs() << "Skipping pass '" << getPassName()
384           << "' in function " << F->getName() << "\n");
385     // FIXME: Delete loop from pass manager's queue?
386     return true;
387   }
388   return false;
389 }
390