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/LoopAnalysisManager.h"
20 #include "llvm/Analysis/LoopPass.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,
40 LoopStandardAnalysisResults &AR) {
41 return IVUsers(&L, &AR.AC, &AR.LI, &AR.DT, &AR.SE);
44 char IVUsersWrapperPass::ID = 0;
45 INITIALIZE_PASS_BEGIN(IVUsersWrapperPass, "iv-users",
46 "Induction Variable Users", false, true)
47 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
48 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
49 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
50 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
51 INITIALIZE_PASS_END(IVUsersWrapperPass, "iv-users", "Induction Variable Users",
54 Pass *llvm::createIVUsersPass() { return new IVUsersWrapperPass(); }
56 /// isInteresting - Test whether the given expression is "interesting" when
57 /// used by the given expression, within the context of analyzing the
59 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
60 ScalarEvolution *SE, LoopInfo *LI) {
61 // An addrec is interesting if it's affine or if it has an interesting start.
62 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
63 // Keep things simple. Don't touch loop-variant strides unless they're
64 // only used outside the loop and we can simplify them.
65 if (AR->getLoop() == L)
66 return AR->isAffine() ||
68 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
69 // Otherwise recurse to see if the start value is interesting, and that
70 // the step value is not interesting, since we don't yet know how to
71 // do effective SCEV expansions for addrecs with interesting steps.
72 return isInteresting(AR->getStart(), I, L, SE, LI) &&
73 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
76 // An add is interesting if exactly one of its operands is interesting.
77 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
78 bool AnyInterestingYet = false;
79 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
81 if (isInteresting(*OI, I, L, SE, LI)) {
82 if (AnyInterestingYet)
84 AnyInterestingYet = true;
86 return AnyInterestingYet;
89 // Nothing else is interesting here.
93 /// Return true if all loop headers that dominate this block are in simplified
95 static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
97 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
98 Loop *NearestLoop = nullptr;
99 for (DomTreeNode *Rung = DT->getNode(BB);
100 Rung; Rung = Rung->getIDom()) {
101 BasicBlock *DomBB = Rung->getBlock();
102 Loop *DomLoop = LI->getLoopFor(DomBB);
103 if (DomLoop && DomLoop->getHeader() == DomBB) {
104 // If the domtree walk reaches a loop with no preheader, return false.
105 if (!DomLoop->isLoopSimplifyForm())
107 // If we have already checked this loop nest, stop checking.
108 if (SimpleLoopNests.count(DomLoop))
110 // If we have not already checked this loop nest, remember the loop
111 // header nearest to BB. The nearest loop may not contain BB.
113 NearestLoop = DomLoop;
117 SimpleLoopNests.insert(NearestLoop);
121 /// AddUsersImpl - Inspect the specified instruction. If it is a
122 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
123 /// return true. Otherwise, return false.
124 bool IVUsers::AddUsersImpl(Instruction *I,
125 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
126 const DataLayout &DL = I->getModule()->getDataLayout();
128 // Add this IV user to the Processed set before returning false to ensure that
129 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
130 if (!Processed.insert(I).second)
131 return true; // Instruction already handled.
133 if (!SE->isSCEVable(I->getType()))
134 return false; // Void and FP expressions cannot be reduced.
136 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
137 // pass to SCEVExpander. Expressions are not safe to expand if they represent
138 // operations that are not safe to speculate, namely integer division.
139 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I))
142 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
143 // Also avoid creating IVs of non-native types. For example, we don't want a
144 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
145 uint64_t Width = SE->getTypeSizeInBits(I->getType());
146 if (Width > 64 || !DL.isLegalInteger(Width))
149 // Don't attempt to promote ephemeral values to indvars. They will be removed
151 if (EphValues.count(I))
154 // Get the symbolic expression for this instruction.
155 const SCEV *ISE = SE->getSCEV(I);
157 // If we've come to an uninteresting expression, stop the traversal and
159 if (!isInteresting(ISE, I, L, SE, LI))
162 SmallPtrSet<Instruction *, 4> UniqueUsers;
163 for (Use &U : I->uses()) {
164 Instruction *User = cast<Instruction>(U.getUser());
165 if (!UniqueUsers.insert(User).second)
168 // Do not infinitely recurse on PHI nodes.
169 if (isa<PHINode>(User) && Processed.count(User))
172 // Only consider IVUsers that are dominated by simplified loop
173 // headers. Otherwise, SCEVExpander will crash.
174 BasicBlock *UseBB = User->getParent();
175 // A phi's use is live out of its predecessor block.
176 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
177 unsigned OperandNo = U.getOperandNo();
178 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
179 UseBB = PHI->getIncomingBlock(ValNo);
181 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
184 // Descend recursively, but not into PHI nodes outside the current loop.
185 // It's important to see the entire expression outside the loop to get
186 // choices that depend on addressing mode use right, although we won't
187 // consider references outside the loop in all cases.
188 // If User is already in Processed, we don't want to recurse into it again,
189 // but do want to record a second reference in the same instruction.
190 bool AddUserToIVUsers = false;
191 if (LI->getLoopFor(User->getParent()) != L) {
192 if (isa<PHINode>(User) || Processed.count(User) ||
193 !AddUsersImpl(User, SimpleLoopNests)) {
194 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
195 << " OF SCEV: " << *ISE << '\n');
196 AddUserToIVUsers = true;
198 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
199 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
200 << " OF SCEV: " << *ISE << '\n');
201 AddUserToIVUsers = true;
204 if (AddUserToIVUsers) {
205 // Okay, we found a user that we cannot reduce.
206 IVStrideUse &NewUse = AddUser(User, I);
207 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
208 // The regular return value here is discarded; instead of recording
209 // it, we just recompute it when we need it.
210 const SCEV *OriginalISE = ISE;
211 ISE = TransformForPostIncUse(NormalizeAutodetect,
216 // PostIncNormalization effectively simplifies the expression under
217 // pre-increment assumptions. Those assumptions (no wrapping) might not
218 // hold for the post-inc value. Catch such cases by making sure the
219 // transformation is invertible.
220 if (OriginalISE != ISE) {
221 const SCEV *DenormalizedISE =
222 TransformForPostIncUse(Denormalize, ISE, User, I,
223 NewUse.PostIncLoops, *SE, *DT);
225 // If we normalized the expression, but denormalization doesn't give the
226 // original one, discard this user.
227 if (OriginalISE != DenormalizedISE) {
228 DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
234 DEBUG(if (SE->getSCEV(I) != ISE)
235 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
241 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
242 // SCEVExpander can only handle users that are dominated by simplified loop
243 // entries. Keep track of all loops that are only dominated by other simple
244 // loops so we don't traverse the domtree for each user.
245 SmallPtrSet<Loop*,16> SimpleLoopNests;
247 return AddUsersImpl(I, SimpleLoopNests);
250 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
251 IVUses.push_back(new IVStrideUse(this, User, Operand));
252 return IVUses.back();
255 IVUsers::IVUsers(Loop *L, AssumptionCache *AC, LoopInfo *LI, DominatorTree *DT,
257 : L(L), AC(AC), LI(LI), DT(DT), SE(SE), IVUses() {
258 // Collect ephemeral values so that AddUsersIfInteresting skips them.
260 CodeMetrics::collectEphemeralValues(L, AC, EphValues);
262 // Find all uses of induction variables in this loop, and categorize
263 // them by stride. Start by finding all of the PHI nodes in the header for
264 // this loop. If they are induction variables, inspect their uses.
265 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
266 (void)AddUsersIfInteresting(&*I);
269 void IVUsers::print(raw_ostream &OS, const Module *M) const {
270 OS << "IV Users for loop ";
271 L->getHeader()->printAsOperand(OS, false);
272 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
273 OS << " with backedge-taken count " << *SE->getBackedgeTakenCount(L);
277 for (const IVStrideUse &IVUse : IVUses) {
279 IVUse.getOperandValToReplace()->printAsOperand(OS, false);
280 OS << " = " << *getReplacementExpr(IVUse);
281 for (auto PostIncLoop : IVUse.PostIncLoops) {
282 OS << " (post-inc with loop ";
283 PostIncLoop->getHeader()->printAsOperand(OS, false);
288 IVUse.getUser()->print(OS);
290 OS << "Printing <null> User";
295 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
296 LLVM_DUMP_METHOD void IVUsers::dump() const { print(dbgs()); }
299 void IVUsers::releaseMemory() {
304 IVUsersWrapperPass::IVUsersWrapperPass() : LoopPass(ID) {
305 initializeIVUsersWrapperPassPass(*PassRegistry::getPassRegistry());
308 void IVUsersWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
309 AU.addRequired<AssumptionCacheTracker>();
310 AU.addRequired<LoopInfoWrapperPass>();
311 AU.addRequired<DominatorTreeWrapperPass>();
312 AU.addRequired<ScalarEvolutionWrapperPass>();
313 AU.setPreservesAll();
316 bool IVUsersWrapperPass::runOnLoop(Loop *L, LPPassManager &LPM) {
317 auto *AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
318 *L->getHeader()->getParent());
319 auto *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
320 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
321 auto *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
323 IU.reset(new IVUsers(L, AC, LI, DT, SE));
327 void IVUsersWrapperPass::print(raw_ostream &OS, const Module *M) const {
331 void IVUsersWrapperPass::releaseMemory() { IU->releaseMemory(); }
333 /// getReplacementExpr - Return a SCEV expression which computes the
334 /// value of the OperandValToReplace.
335 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
336 return SE->getSCEV(IU.getOperandValToReplace());
339 /// getExpr - Return the expression for the use.
340 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
342 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
343 IU.getUser(), IU.getOperandValToReplace(),
344 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
348 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
349 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
350 if (AR->getLoop() == L)
352 return findAddRecForLoop(AR->getStart(), L);
355 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
356 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
358 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
366 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
367 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
368 return AR->getStepRecurrence(*SE);
372 void IVStrideUse::transformToPostInc(const Loop *L) {
373 PostIncLoops.insert(L);
376 void IVStrideUse::deleted() {
377 // Remove this user from the list.
378 Parent->Processed.erase(this->getUser());
379 Parent->IVUses.erase(this);