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 const DataLayout &DL = I->getModule()->getDataLayout();
119 // Add this IV user to the Processed set before returning false to ensure that
120 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
121 if (!Processed.insert(I).second)
122 return true; // Instruction already handled.
124 if (!SE->isSCEVable(I->getType()))
125 return false; // Void and FP expressions cannot be reduced.
127 // IVUsers is used by LSR which assumes that all SCEV expressions are safe to
128 // pass to SCEVExpander. Expressions are not safe to expand if they represent
129 // operations that are not safe to speculate, namely integer division.
130 if (!isa<PHINode>(I) && !isSafeToSpeculativelyExecute(I))
133 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
134 // Also avoid creating IVs of non-native types. For example, we don't want a
135 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
136 uint64_t Width = SE->getTypeSizeInBits(I->getType());
137 if (Width > 64 || !DL.isLegalInteger(Width))
140 // Get the symbolic expression for this instruction.
141 const SCEV *ISE = SE->getSCEV(I);
143 // If we've come to an uninteresting expression, stop the traversal and
145 if (!isInteresting(ISE, I, L, SE, LI))
148 SmallPtrSet<Instruction *, 4> UniqueUsers;
149 for (Use &U : I->uses()) {
150 Instruction *User = cast<Instruction>(U.getUser());
151 if (!UniqueUsers.insert(User).second)
154 // Do not infinitely recurse on PHI nodes.
155 if (isa<PHINode>(User) && Processed.count(User))
158 // Only consider IVUsers that are dominated by simplified loop
159 // headers. Otherwise, SCEVExpander will crash.
160 BasicBlock *UseBB = User->getParent();
161 // A phi's use is live out of its predecessor block.
162 if (PHINode *PHI = dyn_cast<PHINode>(User)) {
163 unsigned OperandNo = U.getOperandNo();
164 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
165 UseBB = PHI->getIncomingBlock(ValNo);
167 if (!isSimplifiedLoopNest(UseBB, DT, LI, SimpleLoopNests))
170 // Descend recursively, but not into PHI nodes outside the current loop.
171 // It's important to see the entire expression outside the loop to get
172 // choices that depend on addressing mode use right, although we won't
173 // consider references outside the loop in all cases.
174 // If User is already in Processed, we don't want to recurse into it again,
175 // but do want to record a second reference in the same instruction.
176 bool AddUserToIVUsers = false;
177 if (LI->getLoopFor(User->getParent()) != L) {
178 if (isa<PHINode>(User) || Processed.count(User) ||
179 !AddUsersImpl(User, SimpleLoopNests)) {
180 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
181 << " OF SCEV: " << *ISE << '\n');
182 AddUserToIVUsers = true;
184 } else if (Processed.count(User) || !AddUsersImpl(User, SimpleLoopNests)) {
185 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
186 << " OF SCEV: " << *ISE << '\n');
187 AddUserToIVUsers = true;
190 if (AddUserToIVUsers) {
191 // Okay, we found a user that we cannot reduce.
192 IVStrideUse &NewUse = AddUser(User, I);
193 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
194 // The regular return value here is discarded; instead of recording
195 // it, we just recompute it when we need it.
196 const SCEV *OriginalISE = ISE;
197 ISE = TransformForPostIncUse(NormalizeAutodetect,
202 // PostIncNormalization effectively simplifies the expression under
203 // pre-increment assumptions. Those assumptions (no wrapping) might not
204 // hold for the post-inc value. Catch such cases by making sure the
205 // transformation is invertible.
206 if (OriginalISE != ISE) {
207 const SCEV *DenormalizedISE =
208 TransformForPostIncUse(Denormalize, ISE, User, I,
209 NewUse.PostIncLoops, *SE, *DT);
211 // If we normalized the expression, but denormalization doesn't give the
212 // original one, discard this user.
213 if (OriginalISE != DenormalizedISE) {
214 DEBUG(dbgs() << " DISCARDING (NORMALIZATION ISN'T INVERTIBLE): "
220 DEBUG(if (SE->getSCEV(I) != ISE)
221 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
227 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
228 // SCEVExpander can only handle users that are dominated by simplified loop
229 // entries. Keep track of all loops that are only dominated by other simple
230 // loops so we don't traverse the domtree for each user.
231 SmallPtrSet<Loop*,16> SimpleLoopNests;
233 return AddUsersImpl(I, SimpleLoopNests);
236 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
237 IVUses.push_back(new IVStrideUse(this, User, Operand));
238 return IVUses.back();
243 initializeIVUsersPass(*PassRegistry::getPassRegistry());
246 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
247 AU.addRequired<LoopInfoWrapperPass>();
248 AU.addRequired<DominatorTreeWrapperPass>();
249 AU.addRequired<ScalarEvolution>();
250 AU.setPreservesAll();
253 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
256 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
257 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
258 SE = &getAnalysis<ScalarEvolution>();
260 // Find all uses of induction variables in this loop, and categorize
261 // them by stride. Start by finding all of the PHI nodes in the header for
262 // this loop. If they are induction variables, inspect their uses.
263 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
264 (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 "
274 << *SE->getBackedgeTakenCount(L);
278 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
279 E = IVUses.end(); UI != E; ++UI) {
281 UI->getOperandValToReplace()->printAsOperand(OS, false);
282 OS << " = " << *getReplacementExpr(*UI);
283 for (PostIncLoopSet::const_iterator
284 I = UI->PostIncLoops.begin(),
285 E = UI->PostIncLoops.end(); I != E; ++I) {
286 OS << " (post-inc with loop ";
287 (*I)->getHeader()->printAsOperand(OS, false);
292 UI->getUser()->print(OS);
294 OS << "Printing <null> User";
299 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
300 void IVUsers::dump() const {
305 void IVUsers::releaseMemory() {
310 /// getReplacementExpr - Return a SCEV expression which computes the
311 /// value of the OperandValToReplace.
312 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
313 return SE->getSCEV(IU.getOperandValToReplace());
316 /// getExpr - Return the expression for the use.
317 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
319 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
320 IU.getUser(), IU.getOperandValToReplace(),
321 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
325 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
326 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
327 if (AR->getLoop() == L)
329 return findAddRecForLoop(AR->getStart(), L);
332 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
333 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
335 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
343 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
344 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
345 return AR->getStepRecurrence(*SE);
349 void IVStrideUse::transformToPostInc(const Loop *L) {
350 PostIncLoops.insert(L);
353 void IVStrideUse::deleted() {
354 // Remove this user from the list.
355 Parent->Processed.erase(this->getUser());
356 Parent->IVUses.erase(this);