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 #define DEBUG_TYPE "iv-users"
16 #include "llvm/Analysis/IVUsers.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/Analysis/LoopPass.h"
19 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
20 #include "llvm/Analysis/ValueTracking.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/DerivedTypes.h"
24 #include "llvm/IR/Dominators.h"
25 #include "llvm/IR/Instructions.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/raw_ostream.h"
33 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
34 "Induction Variable Users", false, true)
35 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
36 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
37 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
38 INITIALIZE_PASS_END(IVUsers, "iv-users",
39 "Induction Variable Users", false, true)
41 Pass *llvm::createIVUsersPass() {
45 /// isInteresting - Test whether the given expression is "interesting" when
46 /// used by the given expression, within the context of analyzing the
48 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
49 ScalarEvolution *SE, LoopInfo *LI) {
50 // An addrec is interesting if it's affine or if it has an interesting start.
51 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
52 // Keep things simple. Don't touch loop-variant strides unless they're
53 // only used outside the loop and we can simplify them.
54 if (AR->getLoop() == L)
55 return AR->isAffine() ||
57 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
58 // Otherwise recurse to see if the start value is interesting, and that
59 // the step value is not interesting, since we don't yet know how to
60 // do effective SCEV expansions for addrecs with interesting steps.
61 return isInteresting(AR->getStart(), I, L, SE, LI) &&
62 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
65 // An add is interesting if exactly one of its operands is interesting.
66 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
67 bool AnyInterestingYet = false;
68 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
70 if (isInteresting(*OI, I, L, SE, LI)) {
71 if (AnyInterestingYet)
73 AnyInterestingYet = true;
75 return AnyInterestingYet;
78 // Nothing else is interesting here.
82 /// Return true if all loop headers that dominate this block are in simplified
84 static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
86 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
87 Loop *NearestLoop = 0;
88 for (DomTreeNode *Rung = DT->getNode(BB);
89 Rung; Rung = Rung->getIDom()) {
90 BasicBlock *DomBB = Rung->getBlock();
91 Loop *DomLoop = LI->getLoopFor(DomBB);
92 if (DomLoop && DomLoop->getHeader() == DomBB) {
93 // If the domtree walk reaches a loop with no preheader, return false.
94 if (!DomLoop->isLoopSimplifyForm())
96 // If we have already checked this loop nest, stop checking.
97 if (SimpleLoopNests.count(DomLoop))
99 // If we have not already checked this loop nest, remember the loop
100 // header nearest to BB. The nearest loop may not contain BB.
102 NearestLoop = DomLoop;
106 SimpleLoopNests.insert(NearestLoop);
110 /// AddUsersImpl - Inspect the specified instruction. If it is a
111 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
112 /// return true. Otherwise, return false.
113 bool IVUsers::AddUsersImpl(Instruction *I,
114 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
115 // Add this IV user to the Processed set before returning false to ensure that
116 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
117 if (!Processed.insert(I))
118 return true; // Instruction already handled.
120 if (!SE->isSCEVable(I->getType()))
121 return false; // Void and FP expressions cannot be reduced.
123 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
124 // pass to SCEVExpander. Expressions are not safe to expand if they represent
125 // operations that are not safe to speculate, namely integer division.
126 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I, DL))
129 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
130 // Also avoid creating IVs of non-native types. For example, we don't want a
131 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
132 uint64_t Width = SE->getTypeSizeInBits(I->getType());
133 if (Width > 64 || (DL && !DL->isLegalInteger(Width)))
136 // Get the symbolic expression for this instruction.
137 const SCEV *ISE = SE->getSCEV(I);
139 // If we've come to an uninteresting expression, stop the traversal and
141 if (!isInteresting(ISE, I, L, SE, LI))
144 SmallPtrSet<Instruction *, 4> UniqueUsers;
145 for (Use &U : I->uses()) {
146 Instruction *User = cast<Instruction>(U.getUser());
147 if (!UniqueUsers.insert(User))
150 // Do not infinitely recurse on PHI nodes.
151 if (isa<PHINode>(User) && Processed.count(User))
154 // Only consider IVUsers that are dominated by simplified loop
155 // headers. Otherwise, SCEVExpander will crash.
156 BasicBlock *UseBB = User->getParent();
157 // A phi's use is live out of its predecessor block.
158 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
159 unsigned OperandNo = U.getOperandNo();
160 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
161 UseBB = PHI->getIncomingBlock(ValNo);
163 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
166 // Descend recursively, but not into PHI nodes outside the current loop.
167 // It's important to see the entire expression outside the loop to get
168 // choices that depend on addressing mode use right, although we won't
169 // consider references outside the loop in all cases.
170 // If User is already in Processed, we don't want to recurse into it again,
171 // but do want to record a second reference in the same instruction.
172 bool AddUserToIVUsers = false;
173 if (LI->getLoopFor(User->getParent()) != L) {
174 if (isa<PHINode>(User) || Processed.count(User) ||
175 !AddUsersImpl(User, SimpleLoopNests)) {
176 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
177 << " OF SCEV: " << *ISE << '\n');
178 AddUserToIVUsers = true;
180 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
181 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
182 << " OF SCEV: " << *ISE << '\n');
183 AddUserToIVUsers = true;
186 if (AddUserToIVUsers) {
187 // Okay, we found a user that we cannot reduce.
188 IVStrideUse &NewUse = AddUser(User, I);
189 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
190 // The regular return value here is discarded; instead of recording
191 // it, we just recompute it when we need it.
192 const SCEV *OriginalISE = ISE;
193 ISE = TransformForPostIncUse(NormalizeAutodetect,
198 // PostIncNormalization effectively simplifies the expression under
199 // pre-increment assumptions. Those assumptions (no wrapping) might not
200 // hold for the post-inc value. Catch such cases by making sure the
201 // transformation is invertible.
202 if (OriginalISE != ISE) {
203 const SCEV *DenormalizedISE =
204 TransformForPostIncUse(Denormalize, ISE, User, I,
205 NewUse.PostIncLoops, *SE, *DT);
207 // If we normalized the expression, but denormalization doesn't give the
208 // original one, discard this user.
209 if (OriginalISE != DenormalizedISE) {
210 DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
216 DEBUG(if (SE->getSCEV(I) != ISE)
217 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
223 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
224 // SCEVExpander can only handle users that are dominated by simplified loop
225 // entries. Keep track of all loops that are only dominated by other simple
226 // loops so we don't traverse the domtree for each user.
227 SmallPtrSet<Loop*,16> SimpleLoopNests;
229 return AddUsersImpl(I, SimpleLoopNests);
232 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
233 IVUses.push_back(new IVStrideUse(this, User, Operand));
234 return IVUses.back();
239 initializeIVUsersPass(*PassRegistry::getPassRegistry());
242 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
243 AU.addRequired<LoopInfo>();
244 AU.addRequired<DominatorTreeWrapperPass>();
245 AU.addRequired<ScalarEvolution>();
246 AU.setPreservesAll();
249 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
252 LI = &getAnalysis<LoopInfo>();
253 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
254 SE = &getAnalysis<ScalarEvolution>();
255 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
256 DL = DLP ? &DLP->getDataLayout() : 0;
258 // Find all uses of induction variables in this loop, and categorize
259 // them by stride. Start by finding all of the PHI nodes in the header for
260 // this loop. If they are induction variables, inspect their uses.
261 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
262 (void)AddUsersIfInteresting(I);
267 void IVUsers::print(raw_ostream &OS, const Module *M) const {
268 OS << "IV Users for loop ";
269 L->getHeader()->printAsOperand(OS, false);
270 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
271 OS << " with backedge-taken count "
272 << *SE->getBackedgeTakenCount(L);
276 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
277 E = IVUses.end(); UI != E; ++UI) {
279 UI->getOperandValToReplace()->printAsOperand(OS, false);
280 OS << " = " << *getReplacementExpr(*UI);
281 for (PostIncLoopSet::const_iterator
282 I = UI->PostIncLoops.begin(),
283 E = UI->PostIncLoops.end(); I != E; ++I) {
284 OS << " (post-inc with loop ";
285 (*I)->getHeader()->printAsOperand(OS, false);
289 UI->getUser()->print(OS);
294 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
295 void IVUsers::dump() const {
300 void IVUsers::releaseMemory() {
305 /// getReplacementExpr - Return a SCEV expression which computes the
306 /// value of the OperandValToReplace.
307 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
308 return SE->getSCEV(IU.getOperandValToReplace());
311 /// getExpr - Return the expression for the use.
312 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
314 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
315 IU.getUser(), IU.getOperandValToReplace(),
316 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
320 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
321 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
322 if (AR->getLoop() == L)
324 return findAddRecForLoop(AR->getStart(), L);
327 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
328 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
330 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
338 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
339 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
340 return AR->getStepRecurrence(*SE);
344 void IVStrideUse::transformToPostInc(const Loop *L) {
345 PostIncLoops.insert(L);
348 void IVStrideUse::deleted() {
349 // Remove this user from the list.
350 Parent->Processed.erase(this->getUser());
351 Parent->IVUses.erase(this);