LoopPass.cpp revision 1d8f83d0a00e912c55ec0974eba6122666cc6fa1 
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/Support/Timer.h"
18using namespace llvm;
19
20//===----------------------------------------------------------------------===//
21// LPPassManager
22//
23
24char LPPassManager::ID = 0;
25
26LPPassManager::LPPassManager(int Depth)
27  : FunctionPass(&ID), PMDataManager(Depth) {
28  skipThisLoop = false;
29  redoThisLoop = false;
30  LI = NULL;
31  CurrentLoop = NULL;
32}
33
34/// Delete loop from the loop queue and loop hierarchy (LoopInfo).
35void LPPassManager::deleteLoopFromQueue(Loop *L) {
36
37  if (Loop *ParentLoop = L->getParentLoop()) { // Not a top-level loop.
38    // Reparent all of the blocks in this loop.  Since BBLoop had a parent,
39    // they are now all in it.
40    for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
41         I != E; ++I)
42      if (LI->getLoopFor(*I) == L)    // Don't change blocks in subloops.
43        LI->changeLoopFor(*I, ParentLoop);
44
45    // Remove the loop from its parent loop.
46    for (Loop::iterator I = ParentLoop->begin(), E = ParentLoop->end();;
47         ++I) {
48      assert(I != E && "Couldn't find loop");
49      if (*I == L) {
50        ParentLoop->removeChildLoop(I);
51        break;
52      }
53    }
54
55    // Move all subloops into the parent loop.
56    while (!L->empty())
57      ParentLoop->addChildLoop(L->removeChildLoop(L->end()-1));
58  } else {
59    // Reparent all of the blocks in this loop.  Since BBLoop had no parent,
60    // they no longer in a loop at all.
61
62    for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
63      // Don't change blocks in subloops.
64      if (LI->getLoopFor(L->getBlocks()[i]) == L) {
65        LI->removeBlock(L->getBlocks()[i]);
66        --i;
67      }
68    }
69
70    // Remove the loop from the top-level LoopInfo object.
71    for (LoopInfo::iterator I = LI->begin(), E = LI->end();; ++I) {
72      assert(I != E && "Couldn't find loop");
73      if (*I == L) {
74        LI->removeLoop(I);
75        break;
76      }
77    }
78
79    // Move all of the subloops to the top-level.
80    while (!L->empty())
81      LI->addTopLevelLoop(L->removeChildLoop(L->end()-1));
82  }
83
84  delete L;
85
86  // If L is current loop then skip rest of the passes and let
87  // runOnFunction remove L from LQ. Otherwise, remove L from LQ now
88  // and continue applying other passes on CurrentLoop.
89  if (CurrentLoop == L) {
90    skipThisLoop = true;
91    return;
92  }
93
94  for (std::deque<Loop *>::iterator I = LQ.begin(),
95         E = LQ.end(); I != E; ++I) {
96    if (*I == L) {
97      LQ.erase(I);
98      break;
99    }
100  }
101}
102
103// Inset loop into loop nest (LoopInfo) and loop queue (LQ).
104void LPPassManager::insertLoop(Loop *L, Loop *ParentLoop) {
105
106  assert (CurrentLoop != L && "Cannot insert CurrentLoop");
107
108  // Insert into loop nest
109  if (ParentLoop)
110    ParentLoop->addChildLoop(L);
111  else
112    LI->addTopLevelLoop(L);
113
114  insertLoopIntoQueue(L);
115}
116
117void LPPassManager::insertLoopIntoQueue(Loop *L) {
118  // Insert L into loop queue
119  if (L == CurrentLoop)
120    redoLoop(L);
121  else if (!L->getParentLoop())
122    // This is top level loop.
123    LQ.push_front(L);
124  else {
125    // Insert L after the parent loop.
126    for (std::deque<Loop *>::iterator I = LQ.begin(),
127           E = LQ.end(); I != E; ++I) {
128      if (*I == L->getParentLoop()) {
129        // deque does not support insert after.
130        ++I;
131        LQ.insert(I, 1, L);
132        break;
133      }
134    }
135  }
136}
137
138// Reoptimize this loop. LPPassManager will re-insert this loop into the
139// queue. This allows LoopPass to change loop nest for the loop. This
140// utility may send LPPassManager into infinite loops so use caution.
141void LPPassManager::redoLoop(Loop *L) {
142  assert (CurrentLoop == L && "Can redo only CurrentLoop");
143  redoThisLoop = true;
144}
145
146/// cloneBasicBlockSimpleAnalysis - Invoke cloneBasicBlockAnalysis hook for
147/// all loop passes.
148void LPPassManager::cloneBasicBlockSimpleAnalysis(BasicBlock *From,
149                                                  BasicBlock *To, Loop *L) {
150  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
151    LoopPass *LP = (LoopPass *)getContainedPass(Index);
152    LP->cloneBasicBlockAnalysis(From, To, L);
153  }
154}
155
156/// deleteSimpleAnalysisValue - Invoke deleteAnalysisValue hook for all passes.
157void LPPassManager::deleteSimpleAnalysisValue(Value *V, Loop *L) {
158  if (BasicBlock *BB = dyn_cast<BasicBlock>(V)) {
159    for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;
160         ++BI) {
161      Instruction &I = *BI;
162      deleteSimpleAnalysisValue(&I, L);
163    }
164  }
165  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
166    LoopPass *LP = (LoopPass *)getContainedPass(Index);
167    LP->deleteAnalysisValue(V, L);
168  }
169}
170
171
172// Recurse through all subloops and all loops  into LQ.
173static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
174  LQ.push_back(L);
175  for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
176    addLoopIntoQueue(*I, LQ);
177}
178
179/// Pass Manager itself does not invalidate any analysis info.
180void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
181  // LPPassManager needs LoopInfo. In the long term LoopInfo class will
182  // become part of LPPassManager.
183  Info.addRequired<LoopInfo>();
184  Info.setPreservesAll();
185}
186
187/// run - Execute all of the passes scheduled for execution.  Keep track of
188/// whether any of the passes modifies the function, and if so, return true.
189bool LPPassManager::runOnFunction(Function &F) {
190  LI = &getAnalysis<LoopInfo>();
191  bool Changed = false;
192
193  // Collect inherited analysis from Module level pass manager.
194  populateInheritedAnalysis(TPM->activeStack);
195
196  // Populate Loop Queue
197  for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
198    addLoopIntoQueue(*I, LQ);
199
200  if (LQ.empty()) // No loops, skip calling finalizers
201    return false;
202
203  // Initialization
204  for (std::deque<Loop *>::const_iterator I = LQ.begin(), E = LQ.end();
205       I != E; ++I) {
206    Loop *L = *I;
207    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
208      LoopPass *P = (LoopPass*)getContainedPass(Index);
209      Changed |= P->doInitialization(L, *this);
210    }
211  }
212
213  // Walk Loops
214  while (!LQ.empty()) {
215
216    CurrentLoop  = LQ.back();
217    skipThisLoop = false;
218    redoThisLoop = false;
219
220    // Run all passes on the current Loop.
221    for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
222      LoopPass *P = (LoopPass*)getContainedPass(Index);
223
224      dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
225                   CurrentLoop->getHeader()->getName());
226      dumpRequiredSet(P);
227
228      initializeAnalysisImpl(P);
229
230      {
231        PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
232        TimeRegion PassTimer(getPassTimer(P));
233
234        Changed |= P->runOnLoop(CurrentLoop, *this);
235      }
236
237      if (Changed)
238        dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,
239                     skipThisLoop ? "<deleted>" :
240                                    CurrentLoop->getHeader()->getName());
241      dumpPreservedSet(P);
242
243      if (!skipThisLoop) {
244        // Manually check that this loop is still healthy. This is done
245        // instead of relying on LoopInfo::verifyLoop since LoopInfo
246        // is a function pass and it's really expensive to verify every
247        // loop in the function every time. That level of checking can be
248        // enabled with the -verify-loop-info option.
249        {
250          TimeRegion PassTimer(getPassTimer(LI));
251          CurrentLoop->verifyLoop();
252        }
253
254        // Then call the regular verifyAnalysis functions.
255        verifyPreservedAnalysis(P);
256      }
257
258      removeNotPreservedAnalysis(P);
259      recordAvailableAnalysis(P);
260      removeDeadPasses(P,
261                       skipThisLoop ? "<deleted>" :
262                                      CurrentLoop->getHeader()->getName(),
263                       ON_LOOP_MSG);
264
265      if (skipThisLoop)
266        // Do not run other passes on this loop.
267        break;
268    }
269
270    // If the loop was deleted, release all the loop passes. This frees up
271    // some memory, and avoids trouble with the pass manager trying to call
272    // verifyAnalysis on them.
273    if (skipThisLoop)
274      for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
275        Pass *P = getContainedPass(Index);
276        freePass(P, "<deleted>", ON_LOOP_MSG);
277      }
278
279    // Pop the loop from queue after running all passes.
280    LQ.pop_back();
281
282    if (redoThisLoop)
283      LQ.push_back(CurrentLoop);
284  }
285
286  // Finalization
287  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
288    LoopPass *P = (LoopPass *)getContainedPass(Index);
289    Changed |= P->doFinalization();
290  }
291
292  return Changed;
293}
294
295/// Print passes managed by this manager
296void LPPassManager::dumpPassStructure(unsigned Offset) {
297  errs().indent(Offset*2) << "Loop Pass Manager\n";
298  for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
299    Pass *P = getContainedPass(Index);
300    P->dumpPassStructure(Offset + 1);
301    dumpLastUses(P, Offset+1);
302  }
303}
304
305
306//===----------------------------------------------------------------------===//
307// LoopPass
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 Call Graph Pass Manager
347    LPPM = new LPPassManager(PMD->getDepth() + 1);
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