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/OptBisect.h"
20#include "llvm/IR/PassTimingInfo.h"
21#include "llvm/IR/PrintPasses.h"
22#include "llvm/InitializePasses.h"
23#include "llvm/Support/Debug.h"
24#include "llvm/Support/TimeProfiler.h"
25#include "llvm/Support/Timer.h"
26#include "llvm/Support/raw_ostream.h"
27using namespace llvm;
28
29#define DEBUG_TYPE "loop-pass-manager"
30
31namespace {
32
33/// PrintLoopPass - Print a Function corresponding to a Loop.
34///
35class PrintLoopPassWrapper : public LoopPass {
36 raw_ostream &OS;
37 std::string Banner;
38
39public:
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(Range: L->blocks(), P: [](BasicBlock *BB) { return BB; });
51 if (BBI != L->blocks().end() &&
52 isFunctionInPrintList(FunctionName: (*BBI)->getParent()->getName())) {
53 printLoop(L&: *L, OS, Banner);
54 }
55 return false;
56 }
57
58 StringRef getPassName() const override { return "Print Loop IR"; }
59};
60
61char PrintLoopPassWrapper::ID = 0;
62}
63
64//===----------------------------------------------------------------------===//
65// LPPassManager
66//
67
68char LPPassManager::ID = 0;
69
70LPPassManager::LPPassManager() : FunctionPass(ID) {
71 LI = nullptr;
72 CurrentLoop = nullptr;
73}
74
75// Insert loop into loop nest (LoopInfo) and loop queue (LQ).
76void LPPassManager::addLoop(Loop &L) {
77 if (L.isOutermost()) {
78 // This is the top level loop.
79 LQ.push_front(x: &L);
80 return;
81 }
82
83 // Insert L into the loop queue after the parent loop.
84 for (auto I = LQ.begin(), E = LQ.end(); I != E; ++I) {
85 if (*I == L.getParentLoop()) {
86 // deque does not support insert after.
87 ++I;
88 LQ.insert(position: I, n: 1, x: &L);
89 return;
90 }
91 }
92}
93
94// Recurse through all subloops and all loops into LQ.
95static void addLoopIntoQueue(Loop *L, std::deque<Loop *> &LQ) {
96 LQ.push_back(x: L);
97 for (Loop *I : reverse(C&: *L))
98 addLoopIntoQueue(L: I, LQ);
99}
100
101/// Pass Manager itself does not invalidate any analysis info.
102void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
103 // LPPassManager needs LoopInfo. In the long term LoopInfo class will
104 // become part of LPPassManager.
105 Info.addRequired<LoopInfoWrapperPass>();
106 Info.addRequired<DominatorTreeWrapperPass>();
107 Info.setPreservesAll();
108}
109
110void LPPassManager::markLoopAsDeleted(Loop &L) {
111 assert((&L == CurrentLoop || CurrentLoop->contains(&L)) &&
112 "Must not delete loop outside the current loop tree!");
113 // If this loop appears elsewhere within the queue, we also need to remove it
114 // there. However, we have to be careful to not remove the back of the queue
115 // as that is assumed to match the current loop.
116 assert(LQ.back() == CurrentLoop && "Loop queue back isn't the current loop!");
117 llvm::erase(C&: LQ, V: &L);
118
119 if (&L == CurrentLoop) {
120 CurrentLoopDeleted = true;
121 // Add this loop back onto the back of the queue to preserve our invariants.
122 LQ.push_back(x: &L);
123 }
124}
125
126/// run - Execute all of the passes scheduled for execution. Keep track of
127/// whether any of the passes modifies the function, and if so, return true.
128bool LPPassManager::runOnFunction(Function &F) {
129 auto &LIWP = getAnalysis<LoopInfoWrapperPass>();
130 LI = &LIWP.getLoopInfo();
131 Module &M = *F.getParent();
132#if 0
133 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
134#endif
135 bool Changed = false;
136
137 // Collect inherited analysis from Module level pass manager.
138 populateInheritedAnalysis(PMS&: TPM->activeStack);
139
140 // Populate the loop queue in reverse program order. There is no clear need to
141 // process sibling loops in either forward or reverse order. There may be some
142 // advantage in deleting uses in a later loop before optimizing the
143 // definitions in an earlier loop. If we find a clear reason to process in
144 // forward order, then a forward variant of LoopPassManager should be created.
145 //
146 // Note that LoopInfo::iterator visits loops in reverse program
147 // order. Here, reverse_iterator gives us a forward order, and the LoopQueue
148 // reverses the order a third time by popping from the back.
149 for (Loop *L : reverse(C&: *LI))
150 addLoopIntoQueue(L, LQ);
151
152 if (LQ.empty()) // No loops, skip calling finalizers
153 return false;
154
155 // Initialization
156 for (Loop *L : LQ) {
157 for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
158 LoopPass *P = getContainedPass(N: Index);
159 Changed |= P->doInitialization(L, LPM&: *this);
160 }
161 }
162
163 // Walk Loops
164 unsigned InstrCount, FunctionSize = 0;
165 StringMap<std::pair<unsigned, unsigned>> FunctionToInstrCount;
166 bool EmitICRemark = M.shouldEmitInstrCountChangedRemark();
167 // Collect the initial size of the module and the function we're looking at.
168 if (EmitICRemark) {
169 InstrCount = initSizeRemarkInfo(M, FunctionToInstrCount);
170 FunctionSize = F.getInstructionCount();
171 }
172 while (!LQ.empty()) {
173 CurrentLoopDeleted = false;
174 CurrentLoop = LQ.back();
175
176 // Run all passes on the current Loop.
177 for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
178 LoopPass *P = getContainedPass(N: Index);
179
180 llvm::TimeTraceScope LoopPassScope("RunLoopPass", P->getPassName());
181
182 dumpPassInfo(P, S1: EXECUTION_MSG, S2: ON_LOOP_MSG,
183 Msg: CurrentLoop->getHeader()->getName());
184 dumpRequiredSet(P);
185
186 initializeAnalysisImpl(P);
187
188 bool LocalChanged = false;
189 {
190 PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
191 TimeRegion PassTimer(getPassTimer(P));
192#ifdef EXPENSIVE_CHECKS
193 uint64_t RefHash = P->structuralHash(F);
194#endif
195 LocalChanged = P->runOnLoop(L: CurrentLoop, LPM&: *this);
196
197#ifdef EXPENSIVE_CHECKS
198 if (!LocalChanged && (RefHash != P->structuralHash(F))) {
199 llvm::errs() << "Pass modifies its input and doesn't report it: "
200 << P->getPassName() << "\n";
201 llvm_unreachable("Pass modifies its input and doesn't report it");
202 }
203#endif
204
205 Changed |= LocalChanged;
206 if (EmitICRemark) {
207 unsigned NewSize = F.getInstructionCount();
208 // Update the size of the function, emit a remark, and update the
209 // size of the module.
210 if (NewSize != FunctionSize) {
211 int64_t Delta = static_cast<int64_t>(NewSize) -
212 static_cast<int64_t>(FunctionSize);
213 emitInstrCountChangedRemark(P, M, Delta, CountBefore: InstrCount,
214 FunctionToInstrCount, F: &F);
215 InstrCount = static_cast<int64_t>(InstrCount) + Delta;
216 FunctionSize = NewSize;
217 }
218 }
219 }
220
221 if (LocalChanged)
222 dumpPassInfo(P, S1: MODIFICATION_MSG, S2: ON_LOOP_MSG,
223 Msg: CurrentLoopDeleted ? "<deleted loop>"
224 : CurrentLoop->getName());
225 dumpPreservedSet(P);
226
227 if (!CurrentLoopDeleted) {
228 // Manually check that this loop is still healthy. This is done
229 // instead of relying on LoopInfo::verifyLoop since LoopInfo
230 // is a function pass and it's really expensive to verify every
231 // loop in the function every time. That level of checking can be
232 // enabled with the -verify-loop-info option.
233 {
234 TimeRegion PassTimer(getPassTimer(&LIWP));
235 CurrentLoop->verifyLoop();
236 }
237 // Here we apply same reasoning as in the above case. Only difference
238 // is that LPPassManager might run passes which do not require LCSSA
239 // form (LoopPassPrinter for example). We should skip verification for
240 // such passes.
241 // FIXME: Loop-sink currently break LCSSA. Fix it and reenable the
242 // verification!
243#if 0
244 if (mustPreserveAnalysisID(LCSSAVerificationPass::ID))
245 assert(CurrentLoop->isRecursivelyLCSSAForm(*DT, *LI));
246#endif
247
248 // Then call the regular verifyAnalysis functions.
249 verifyPreservedAnalysis(P);
250
251 F.getContext().yield();
252 }
253
254 if (LocalChanged)
255 removeNotPreservedAnalysis(P);
256 recordAvailableAnalysis(P);
257 removeDeadPasses(P,
258 Msg: CurrentLoopDeleted ? "<deleted>"
259 : CurrentLoop->getHeader()->getName(),
260 ON_LOOP_MSG);
261
262 if (CurrentLoopDeleted)
263 // Do not run other passes on this loop.
264 break;
265 }
266
267 // If the loop was deleted, release all the loop passes. This frees up
268 // some memory, and avoids trouble with the pass manager trying to call
269 // verifyAnalysis on them.
270 if (CurrentLoopDeleted) {
271 for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
272 Pass *P = getContainedPass(N: Index);
273 freePass(P, Msg: "<deleted>", ON_LOOP_MSG);
274 }
275 }
276
277 // Pop the loop from queue after running all passes.
278 LQ.pop_back();
279 }
280
281 // Finalization
282 for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
283 LoopPass *P = getContainedPass(N: Index);
284 Changed |= P->doFinalization();
285 }
286
287 return Changed;
288}
289
290/// Print passes managed by this manager
291void LPPassManager::dumpPassStructure(unsigned Offset) {
292 errs().indent(NumSpaces: Offset*2) << "Loop Pass Manager\n";
293 for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
294 Pass *P = getContainedPass(N: Index);
295 P->dumpPassStructure(Offset: Offset + 1);
296 dumpLastUses(P, Offset: Offset+1);
297 }
298}
299
300
301//===----------------------------------------------------------------------===//
302// LoopPass
303
304Pass *LoopPass::createPrinterPass(raw_ostream &O,
305 const std::string &Banner) const {
306 return new PrintLoopPassWrapper(O, Banner);
307}
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(P: 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 Loop Pass Manager
347 LPPM = new LPPassManager();
348 LPPM->populateInheritedAnalysis(PMS);
349
350 // [2] Set up new manager's top level manager
351 PMTopLevelManager *TPM = PMD->getTopLevelManager();
352 TPM->addIndirectPassManager(Manager: 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(PM: LPPM);
361 }
362
363 LPPM->add(P: this);
364}
365
366static std::string getDescription(const Loop &L) {
367 return "loop";
368}
369
370bool LoopPass::skipLoop(const Loop *L) const {
371 const Function *F = L->getHeader()->getParent();
372 if (!F)
373 return false;
374 // Check the opt bisect limit.
375 OptPassGate &Gate = F->getContext().getOptPassGate();
376 if (Gate.isEnabled() &&
377 !Gate.shouldRunPass(PassName: this->getPassName(), IRDescription: getDescription(L: *L)))
378 return true;
379 // Check for the OptimizeNone attribute.
380 if (F->hasOptNone()) {
381 // FIXME: Report this to dbgs() only once per function.
382 LLVM_DEBUG(dbgs() << "Skipping pass '" << getPassName() << "' in function "
383 << F->getName() << "\n");
384 // FIXME: Delete loop from pass manager's queue?
385 return true;
386 }
387 return false;
388}
389
390LCSSAVerificationPass::LCSSAVerificationPass() : FunctionPass(ID) {
391 initializeLCSSAVerificationPassPass(*PassRegistry::getPassRegistry());
392}
393
394char LCSSAVerificationPass::ID = 0;
395INITIALIZE_PASS(LCSSAVerificationPass, "lcssa-verification", "LCSSA Verifier",
396 false, false)
397

source code of llvm/lib/Analysis/LoopPass.cpp