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/Constants.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Type.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Analysis/Dominators.h"
22 #include "llvm/Analysis/LoopPass.h"
23 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Assembly/Writer.h"
26 #include "llvm/ADT/STLExtras.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(DominatorTree)
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 this loop and all loop headers that dominate it are in
84 static bool isSimplifiedLoopNest(Loop *L, const DominatorTree *DT,
86 if (!L->isLoopSimplifyForm())
89 for (DomTreeNode *Rung = DT->getNode(L->getLoopPreheader());
90 Rung; Rung = Rung->getIDom()) {
91 BasicBlock *BB = Rung->getBlock();
92 const Loop *DomLoop = LI->getLoopFor(BB);
93 if (DomLoop && DomLoop->getHeader() == BB) {
94 if (!DomLoop->isLoopSimplifyForm())
101 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
102 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
103 /// return true. Otherwise, return false.
104 bool IVUsers::AddUsersIfInteresting(Instruction *I,
105 SmallPtrSet<Loop*,16> &SimpleLoopNests) {
106 // Add this IV user to the Processed set before returning false to ensure that
107 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
108 if (!Processed.insert(I))
109 return true; // Instruction already handled.
111 if (!SE->isSCEVable(I->getType()))
112 return false; // Void and FP expressions cannot be reduced.
114 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
115 // Also avoid creating IVs of non-native types. For example, we don't want a
116 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
117 uint64_t Width = SE->getTypeSizeInBits(I->getType());
118 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
121 // Get the symbolic expression for this instruction.
122 const SCEV *ISE = SE->getSCEV(I);
124 // If we've come to an uninteresting expression, stop the traversal and
126 if (!isInteresting(ISE, I, L, SE, LI))
129 SmallPtrSet<Instruction *, 4> UniqueUsers;
130 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
132 Instruction *User = cast<Instruction>(*UI);
133 if (!UniqueUsers.insert(User))
136 // Do not infinitely recurse on PHI nodes.
137 if (isa<PHINode>(User) && Processed.count(User))
140 Loop *UserLoop = LI->getLoopFor(User->getParent());
142 // Only consider IVUsers that are dominated by simplified loop
143 // headers. Otherwise, SCEVExpander will crash.
144 if (UserLoop && !SimpleLoopNests.count(UserLoop)) {
145 if (!isSimplifiedLoopNest(UserLoop, DT, LI))
147 SimpleLoopNests.insert(UserLoop);
150 // Descend recursively, but not into PHI nodes outside the current loop.
151 // It's important to see the entire expression outside the loop to get
152 // choices that depend on addressing mode use right, although we won't
153 // consider references outside the loop in all cases.
154 // If User is already in Processed, we don't want to recurse into it again,
155 // but do want to record a second reference in the same instruction.
156 bool AddUserToIVUsers = false;
158 if (isa<PHINode>(User) || Processed.count(User) ||
159 !AddUsersIfInteresting(User, SimpleLoopNests)) {
160 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
161 << " OF SCEV: " << *ISE << '\n');
162 AddUserToIVUsers = true;
164 } else if (Processed.count(User)
165 || !AddUsersIfInteresting(User, SimpleLoopNests)) {
166 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
167 << " OF SCEV: " << *ISE << '\n');
168 AddUserToIVUsers = true;
171 if (AddUserToIVUsers) {
172 // Okay, we found a user that we cannot reduce.
173 IVUses.push_back(new IVStrideUse(this, User, I));
174 IVStrideUse &NewUse = IVUses.back();
175 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
176 // The regular return value here is discarded; instead of recording
177 // it, we just recompute it when we need it.
178 ISE = TransformForPostIncUse(NormalizeAutodetect,
182 DEBUG(if (SE->getSCEV(I) != ISE)
183 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
189 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
190 IVUses.push_back(new IVStrideUse(this, User, Operand));
191 return IVUses.back();
196 initializeIVUsersPass(*PassRegistry::getPassRegistry());
199 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
200 AU.addRequired<LoopInfo>();
201 AU.addRequired<DominatorTree>();
202 AU.addRequired<ScalarEvolution>();
203 AU.setPreservesAll();
206 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
209 LI = &getAnalysis<LoopInfo>();
210 DT = &getAnalysis<DominatorTree>();
211 SE = &getAnalysis<ScalarEvolution>();
212 TD = getAnalysisIfAvailable<TargetData>();
214 // SCEVExpander can only handle users that are dominated by simplified loop
215 // entries. Keep track of all loops that are only dominated by other simple
216 // loops so we don't traverse the domtree for each user.
217 SmallPtrSet<Loop*,16> SimpleLoopNests;
219 // Find all uses of induction variables in this loop, and categorize
220 // them by stride. Start by finding all of the PHI nodes in the header for
221 // this loop. If they are induction variables, inspect their uses.
222 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
223 (void)AddUsersIfInteresting(I, SimpleLoopNests);
228 void IVUsers::print(raw_ostream &OS, const Module *M) const {
229 OS << "IV Users for loop ";
230 WriteAsOperand(OS, L->getHeader(), false);
231 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
232 OS << " with backedge-taken count "
233 << *SE->getBackedgeTakenCount(L);
237 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
238 E = IVUses.end(); UI != E; ++UI) {
240 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
241 OS << " = " << *getReplacementExpr(*UI);
242 for (PostIncLoopSet::const_iterator
243 I = UI->PostIncLoops.begin(),
244 E = UI->PostIncLoops.end(); I != E; ++I) {
245 OS << " (post-inc with loop ";
246 WriteAsOperand(OS, (*I)->getHeader(), false);
250 UI->getUser()->print(OS);
255 void IVUsers::dump() const {
259 void IVUsers::releaseMemory() {
264 /// getReplacementExpr - Return a SCEV expression which computes the
265 /// value of the OperandValToReplace.
266 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
267 return SE->getSCEV(IU.getOperandValToReplace());
270 /// getExpr - Return the expression for the use.
271 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
273 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
274 IU.getUser(), IU.getOperandValToReplace(),
275 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
279 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
280 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
281 if (AR->getLoop() == L)
283 return findAddRecForLoop(AR->getStart(), L);
286 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
287 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
289 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
297 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
298 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
299 return AR->getStepRecurrence(*SE);
303 void IVStrideUse::transformToPostInc(const Loop *L) {
304 PostIncLoops.insert(L);
307 void IVStrideUse::deleted() {
308 // Remove this user from the list.
309 Parent->Processed.erase(this->getUser());
310 Parent->IVUses.erase(this);