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/LoopPass.h"
18 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
19 #include "llvm/Analysis/ValueTracking.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/DerivedTypes.h"
23 #include "llvm/IR/Dominators.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/raw_ostream.h"
32 #define DEBUG_TYPE "iv-users"
35 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
36 "Induction Variable Users", false, true)
37 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
38 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
39 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
40 INITIALIZE_PASS_END(IVUsers, "iv-users",
41 "Induction Variable Users", false, true)
43 Pass *llvm::createIVUsersPass() {
47 /// isInteresting - Test whether the given expression is "interesting" when
48 /// used by the given expression, within the context of analyzing the
50 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
51 ScalarEvolution *SE, LoopInfo *LI) {
52 // An addrec is interesting if it's affine or if it has an interesting start.
53 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
54 // Keep things simple. Don't touch loop-variant strides unless they're
55 // only used outside the loop and we can simplify them.
56 if (AR->getLoop() == L)
57 return AR->isAffine() ||
59 SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
60 // Otherwise recurse to see if the start value is interesting, and that
61 // the step value is not interesting, since we don't yet know how to
62 // do effective SCEV expansions for addrecs with interesting steps.
63 return isInteresting(AR->getStart(), I, L, SE, LI) &&
64 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
67 // An add is interesting if exactly one of its operands is interesting.
68 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
69 bool AnyInterestingYet = false;
70 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
72 if (isInteresting(*OI, I, L, SE, LI)) {
73 if (AnyInterestingYet)
75 AnyInterestingYet = true;
77 return AnyInterestingYet;
80 // Nothing else is interesting here.
84 /// Return true if all loop headers that dominate this block are in simplified
86 static bool isSimplifiedLoopNest(BasicBlock *BB, const DominatorTree *DT,
88 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
89 Loop *NearestLoop = nullptr;
90 for (DomTreeNode *Rung = DT->getNode(BB);
91 Rung; Rung = Rung->getIDom()) {
92 BasicBlock *DomBB = Rung->getBlock();
93 Loop *DomLoop = LI->getLoopFor(DomBB);
94 if (DomLoop && DomLoop->getHeader() == DomBB) {
95 // If the domtree walk reaches a loop with no preheader, return false.
96 if (!DomLoop->isLoopSimplifyForm())
98 // If we have already checked this loop nest, stop checking.
99 if (SimpleLoopNests.count(DomLoop))
101 // If we have not already checked this loop nest, remember the loop
102 // header nearest to BB. The nearest loop may not contain BB.
104 NearestLoop = DomLoop;
108 SimpleLoopNests.insert(NearestLoop);
112 /// AddUsersImpl - Inspect the specified instruction. If it is a
113 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
114 /// return true. Otherwise, return false.
115 bool IVUsers::AddUsersImpl(Instruction *I,
116 SmallPtrSetImpl<Loop*> &SimpleLoopNests) {
117 // Add this IV user to the Processed set before returning false to ensure that
118 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
119 if (!Processed.insert(I).second)
120 return true; // Instruction already handled.
122 if (!SE->isSCEVable(I->getType()))
123 return false; // Void and FP expressions cannot be reduced.
125 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
126 // pass to SCEVExpander. Expressions are not safe to expand if they represent
127 // operations that are not safe to speculate, namely integer division.
128 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I, DL))
131 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
132 // Also avoid creating IVs of non-native types. For example, we don't want a
133 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
134 uint64_t Width = SE->getTypeSizeInBits(I->getType());
135 if (Width > 64 || (DL && !DL->isLegalInteger(Width)))
138 // Get the symbolic expression for this instruction.
139 const SCEV *ISE = SE->getSCEV(I);
141 // If we've come to an uninteresting expression, stop the traversal and
143 if (!isInteresting(ISE, I, L, SE, LI))
146 SmallPtrSet<Instruction *, 4> UniqueUsers;
147 for (Use &U : I->uses()) {
148 Instruction *User = cast<Instruction>(U.getUser());
149 if (!UniqueUsers.insert(User).second)
152 // Do not infinitely recurse on PHI nodes.
153 if (isa<PHINode>(User) && Processed.count(User))
156 // Only consider IVUsers that are dominated by simplified loop
157 // headers. Otherwise, SCEVExpander will crash.
158 BasicBlock *UseBB = User->getParent();
159 // A phi's use is live out of its predecessor block.
160 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
161 unsigned OperandNo = U.getOperandNo();
162 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
163 UseBB = PHI->getIncomingBlock(ValNo);
165 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
168 // Descend recursively, but not into PHI nodes outside the current loop.
169 // It's important to see the entire expression outside the loop to get
170 // choices that depend on addressing mode use right, although we won't
171 // consider references outside the loop in all cases.
172 // If User is already in Processed, we don't want to recurse into it again,
173 // but do want to record a second reference in the same instruction.
174 bool AddUserToIVUsers = false;
175 if (LI->getLoopFor(User->getParent()) != L) {
176 if (isa<PHINode>(User) || Processed.count(User) ||
177 !AddUsersImpl(User, SimpleLoopNests)) {
178 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
179 << " OF SCEV: " << *ISE << '\n');
180 AddUserToIVUsers = true;
182 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
183 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
184 << " OF SCEV: " << *ISE << '\n');
185 AddUserToIVUsers = true;
188 if (AddUserToIVUsers) {
189 // Okay, we found a user that we cannot reduce.
190 IVStrideUse &NewUse = AddUser(User, I);
191 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
192 // The regular return value here is discarded; instead of recording
193 // it, we just recompute it when we need it.
194 const SCEV *OriginalISE = ISE;
195 ISE = TransformForPostIncUse(NormalizeAutodetect,
200 // PostIncNormalization effectively simplifies the expression under
201 // pre-increment assumptions. Those assumptions (no wrapping) might not
202 // hold for the post-inc value. Catch such cases by making sure the
203 // transformation is invertible.
204 if (OriginalISE != ISE) {
205 const SCEV *DenormalizedISE =
206 TransformForPostIncUse(Denormalize, ISE, User, I,
207 NewUse.PostIncLoops, *SE, *DT);
209 // If we normalized the expression, but denormalization doesn't give the
210 // original one, discard this user.
211 if (OriginalISE != DenormalizedISE) {
212 DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
218 DEBUG(if (SE->getSCEV(I) != ISE)
219 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
225 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
226 // SCEVExpander can only handle users that are dominated by simplified loop
227 // entries. Keep track of all loops that are only dominated by other simple
228 // loops so we don't traverse the domtree for each user.
229 SmallPtrSet<Loop*,16> SimpleLoopNests;
231 return AddUsersImpl(I, SimpleLoopNests);
234 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
235 IVUses.push_back(new IVStrideUse(this, User, Operand));
236 return IVUses.back();
241 initializeIVUsersPass(*PassRegistry::getPassRegistry());
244 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
245 AU.addRequired<LoopInfoWrapperPass>();
246 AU.addRequired<DominatorTreeWrapperPass>();
247 AU.addRequired<ScalarEvolution>();
248 AU.setPreservesAll();
251 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
254 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
255 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
256 SE = &getAnalysis<ScalarEvolution>();
257 DL = &L->getHeader()->getModule()->getDataLayout();
259 // Find all uses of induction variables in this loop, and categorize
260 // them by stride. Start by finding all of the PHI nodes in the header for
261 // this loop. If they are induction variables, inspect their uses.
262 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
263 (void)AddUsersIfInteresting(I);
268 void IVUsers::print(raw_ostream &OS, const Module *M) const {
269 OS << "IV Users for loop ";
270 L->getHeader()->printAsOperand(OS, false);
271 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
272 OS << " with backedge-taken count "
273 << *SE->getBackedgeTakenCount(L);
277 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
278 E = IVUses.end(); UI != E; ++UI) {
280 UI->getOperandValToReplace()->printAsOperand(OS, false);
281 OS << " = " << *getReplacementExpr(*UI);
282 for (PostIncLoopSet::const_iterator
283 I = UI->PostIncLoops.begin(),
284 E = UI->PostIncLoops.end(); I != E; ++I) {
285 OS << " (post-inc with loop ";
286 (*I)->getHeader()->printAsOperand(OS, false);
291 UI->getUser()->print(OS);
293 OS << "Printing <null> User";
298 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
299 void IVUsers::dump() const {
304 void IVUsers::releaseMemory() {
309 /// getReplacementExpr - Return a SCEV expression which computes the
310 /// value of the OperandValToReplace.
311 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
312 return SE->getSCEV(IU.getOperandValToReplace());
315 /// getExpr - Return the expression for the use.
316 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
318 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
319 IU.getUser(), IU.getOperandValToReplace(),
320 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
324 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
325 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
326 if (AR->getLoop() == L)
328 return findAddRecForLoop(AR->getStart(), L);
331 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
332 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
334 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
342 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
343 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
344 return AR->getStepRecurrence(*SE);
348 void IVStrideUse::transformToPostInc(const Loop *L) {
349 PostIncLoops.insert(L);
352 void IVStrideUse::deleted() {
353 // Remove this user from the list.
354 Parent->Processed.erase(this->getUser());
355 Parent->IVUses.erase(this);