1 //===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements bookkeeping for "interesting" users of expressions
11 // computed from induction variables.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Analysis/IVUsers.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/Analysis/AssumptionCache.h"
18 #include "llvm/Analysis/CodeMetrics.h"
19 #include "llvm/Analysis/LoopPass.h"
20 #include "llvm/Analysis/LoopPassManager.h"
21 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
22 #include "llvm/Analysis/ValueTracking.h"
23 #include "llvm/IR/Constants.h"
24 #include "llvm/IR/DataLayout.h"
25 #include "llvm/IR/DerivedTypes.h"
26 #include "llvm/IR/Dominators.h"
27 #include "llvm/IR/Instructions.h"
28 #include "llvm/IR/Module.h"
29 #include "llvm/IR/Type.h"
30 #include "llvm/Support/Debug.h"
31 #include "llvm/Support/raw_ostream.h"
35 #define DEBUG_TYPE "iv-users"
37 AnalysisKey IVUsersAnalysis::Key;
39 IVUsers IVUsersAnalysis::run(Loop &L, LoopAnalysisManager &AM) {
41 AM.getResult<FunctionAnalysisManagerLoopProxy>(L).getManager();
42 Function *F = L.getHeader()->getParent();
44 return IVUsers(&L, FAM.getCachedResult<AssumptionAnalysis>(*F),
45 FAM.getCachedResult<LoopAnalysis>(*F),
46 FAM.getCachedResult<DominatorTreeAnalysis>(*F),
47 FAM.getCachedResult<ScalarEvolutionAnalysis>(*F));
50 PreservedAnalyses IVUsersPrinterPass::run(Loop &L, LoopAnalysisManager &AM) {
51 AM.getResult<IVUsersAnalysis>(L).print(OS);
52 return PreservedAnalyses::all();
55 char IVUsersWrapperPass::ID = 0;
56 INITIALIZE_PASS_BEGIN(IVUsersWrapperPass, "iv-users",
57 "Induction Variable Users", false, true)
58 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
59 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
60 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
61 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
62 INITIALIZE_PASS_END(IVUsersWrapperPass, "iv-users", "Induction Variable Users",
65 Pass *llvm::createIVUsersPass() { return new IVUsersWrapperPass(); }
67 /// isInteresting - Test whether the given expression is "interesting" when
68 /// used by the given expression, within the context of analyzing the
70 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
71 ScalarEvolution *SE, LoopInfo *LI) {
72 // An addrec is interesting if it's affine or if it has an interesting start.
73 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
74 // Keep things simple. Don't touch loop-variant strides unless they're
75 // only used outside the loop and we can simplify them.
76 if (AR->getLoop() == L)
77 return AR->isAffine() ||
79 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
80 // Otherwise recurse to see if the start value is interesting, and that
81 // the step value is not interesting, since we don't yet know how to
82 // do effective SCEV expansions for addrecs with interesting steps.
83 return isInteresting(AR->getStart(), I, L, SE, LI) &&
84 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
87 // An add is interesting if exactly one of its operands is interesting.
88 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
89 bool AnyInterestingYet = false;
90 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
92 if (isInteresting(*OI, I, L, SE, LI)) {
93 if (AnyInterestingYet)
95 AnyInterestingYet = true;
97 return AnyInterestingYet;
100 // Nothing else is interesting here.
104 /// Return true if all loop headers that dominate this block are in simplified
106 static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
108 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
109 Loop *NearestLoop = nullptr;
110 for (DomTreeNode *Rung = DT->getNode(BB);
111 Rung; Rung = Rung->getIDom()) {
112 BasicBlock *DomBB = Rung->getBlock();
113 Loop *DomLoop = LI->getLoopFor(DomBB);
114 if (DomLoop && DomLoop->getHeader() == DomBB) {
115 // If the domtree walk reaches a loop with no preheader, return false.
116 if (!DomLoop->isLoopSimplifyForm())
118 // If we have already checked this loop nest, stop checking.
119 if (SimpleLoopNests.count(DomLoop))
121 // If we have not already checked this loop nest, remember the loop
122 // header nearest to BB. The nearest loop may not contain BB.
124 NearestLoop = DomLoop;
128 SimpleLoopNests.insert(NearestLoop);
132 /// AddUsersImpl - Inspect the specified instruction. If it is a
133 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
134 /// return true. Otherwise, return false.
135 bool IVUsers::AddUsersImpl(Instruction *I,
136 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
137 const DataLayout &DL = I->getModule()->getDataLayout();
139 // Add this IV user to the Processed set before returning false to ensure that
140 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
141 if (!Processed.insert(I).second)
142 return true; // Instruction already handled.
144 if (!SE->isSCEVable(I->getType()))
145 return false; // Void and FP expressions cannot be reduced.
147 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
148 // pass to SCEVExpander. Expressions are not safe to expand if they represent
149 // operations that are not safe to speculate, namely integer division.
150 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I))
153 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
154 // Also avoid creating IVs of non-native types. For example, we don't want a
155 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
156 uint64_t Width = SE->getTypeSizeInBits(I->getType());
157 if (Width > 64 || !DL.isLegalInteger(Width))
160 // Don't attempt to promote ephemeral values to indvars. They will be removed
162 if (EphValues.count(I))
165 // Get the symbolic expression for this instruction.
166 const SCEV *ISE = SE->getSCEV(I);
168 // If we've come to an uninteresting expression, stop the traversal and
170 if (!isInteresting(ISE, I, L, SE, LI))
173 SmallPtrSet<Instruction *, 4> UniqueUsers;
174 for (Use &U : I->uses()) {
175 Instruction *User = cast<Instruction>(U.getUser());
176 if (!UniqueUsers.insert(User).second)
179 // Do not infinitely recurse on PHI nodes.
180 if (isa<PHINode>(User) && Processed.count(User))
183 // Only consider IVUsers that are dominated by simplified loop
184 // headers. Otherwise, SCEVExpander will crash.
185 BasicBlock *UseBB = User->getParent();
186 // A phi's use is live out of its predecessor block.
187 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
188 unsigned OperandNo = U.getOperandNo();
189 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
190 UseBB = PHI->getIncomingBlock(ValNo);
192 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
195 // Descend recursively, but not into PHI nodes outside the current loop.
196 // It's important to see the entire expression outside the loop to get
197 // choices that depend on addressing mode use right, although we won't
198 // consider references outside the loop in all cases.
199 // If User is already in Processed, we don't want to recurse into it again,
200 // but do want to record a second reference in the same instruction.
201 bool AddUserToIVUsers = false;
202 if (LI->getLoopFor(User->getParent()) != L) {
203 if (isa<PHINode>(User) || Processed.count(User) ||
204 !AddUsersImpl(User, SimpleLoopNests)) {
205 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
206 << " OF SCEV: " << *ISE << '\n');
207 AddUserToIVUsers = true;
209 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
210 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
211 << " OF SCEV: " << *ISE << '\n');
212 AddUserToIVUsers = true;
215 if (AddUserToIVUsers) {
216 // Okay, we found a user that we cannot reduce.
217 IVStrideUse &NewUse = AddUser(User, I);
218 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
219 // The regular return value here is discarded; instead of recording
220 // it, we just recompute it when we need it.
221 const SCEV *OriginalISE = ISE;
222 ISE = TransformForPostIncUse(NormalizeAutodetect,
227 // PostIncNormalization effectively simplifies the expression under
228 // pre-increment assumptions. Those assumptions (no wrapping) might not
229 // hold for the post-inc value. Catch such cases by making sure the
230 // transformation is invertible.
231 if (OriginalISE != ISE) {
232 const SCEV *DenormalizedISE =
233 TransformForPostIncUse(Denormalize, ISE, User, I,
234 NewUse.PostIncLoops, *SE, *DT);
236 // If we normalized the expression, but denormalization doesn't give the
237 // original one, discard this user.
238 if (OriginalISE != DenormalizedISE) {
239 DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
245 DEBUG(if (SE->getSCEV(I) != ISE)
246 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
252 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
253 // SCEVExpander can only handle users that are dominated by simplified loop
254 // entries. Keep track of all loops that are only dominated by other simple
255 // loops so we don't traverse the domtree for each user.
256 SmallPtrSet<Loop*,16> SimpleLoopNests;
258 return AddUsersImpl(I, SimpleLoopNests);
261 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
262 IVUses.push_back(new IVStrideUse(this, User, Operand));
263 return IVUses.back();
266 IVUsers::IVUsers(Loop *L, AssumptionCache *AC, LoopInfo *LI, DominatorTree *DT,
268 : L(L), AC(AC), LI(LI), DT(DT), SE(SE), IVUses() {
269 // Collect ephemeral values so that AddUsersIfInteresting skips them.
271 CodeMetrics::collectEphemeralValues(L, AC, EphValues);
273 // Find all uses of induction variables in this loop, and categorize
274 // them by stride. Start by finding all of the PHI nodes in the header for
275 // this loop. If they are induction variables, inspect their uses.
276 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
277 (void)AddUsersIfInteresting(&*I);
280 void IVUsers::print(raw_ostream &OS, const Module *M) const {
281 OS << "IV Users for loop ";
282 L->getHeader()->printAsOperand(OS, false);
283 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
284 OS << " with backedge-taken count " << *SE->getBackedgeTakenCount(L);
288 for (const IVStrideUse &IVUse : IVUses) {
290 IVUse.getOperandValToReplace()->printAsOperand(OS, false);
291 OS << " = " << *getReplacementExpr(IVUse);
292 for (auto PostIncLoop : IVUse.PostIncLoops) {
293 OS << " (post-inc with loop ";
294 PostIncLoop->getHeader()->printAsOperand(OS, false);
299 IVUse.getUser()->print(OS);
301 OS << "Printing <null> User";
306 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
307 LLVM_DUMP_METHOD void IVUsers::dump() const { print(dbgs()); }
310 void IVUsers::releaseMemory() {
315 IVUsersWrapperPass::IVUsersWrapperPass() : LoopPass(ID) {
316 initializeIVUsersWrapperPassPass(*PassRegistry::getPassRegistry());
319 void IVUsersWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
320 AU.addRequired<AssumptionCacheTracker>();
321 AU.addRequired<LoopInfoWrapperPass>();
322 AU.addRequired<DominatorTreeWrapperPass>();
323 AU.addRequired<ScalarEvolutionWrapperPass>();
324 AU.setPreservesAll();
327 bool IVUsersWrapperPass::runOnLoop(Loop *L, LPPassManager &LPM) {
328 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
329 *L->getHeader()->getParent());
330 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
331 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
332 auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
334 IU.reset(new IVUsers(L, AC, LI, DT, SE));
338 void IVUsersWrapperPass::print(raw_ostream &OS, const Module *M) const {
342 void IVUsersWrapperPass::releaseMemory() { IU->releaseMemory(); }
344 /// getReplacementExpr - Return a SCEV expression which computes the
345 /// value of the OperandValToReplace.
346 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
347 return SE->getSCEV(IU.getOperandValToReplace());
350 /// getExpr - Return the expression for the use.
351 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
353 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
354 IU.getUser(), IU.getOperandValToReplace(),
355 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
359 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
360 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
361 if (AR->getLoop() == L)
363 return findAddRecForLoop(AR->getStart(), L);
366 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
367 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
369 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
377 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
378 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
379 return AR->getStepRecurrence(*SE);
383 void IVStrideUse::transformToPostInc(const Loop *L) {
384 PostIncLoops.insert(L);
387 void IVStrideUse::deleted() {
388 // Remove this user from the list.
389 Parent->Processed.erase(this->getUser());
390 Parent->IVUses.erase(this);