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 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
83 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
84 /// return true. Otherwise, return false.
85 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
86 // Add this IV user to the Processed set before returning false to ensure that
87 // all IV users are members of the set. See IVUsers::isIVUserOrOperand.
88 if (!Processed.insert(I))
89 return true; // Instruction already handled.
91 if (!SE->isSCEVable(I->getType()))
92 return false; // Void and FP expressions cannot be reduced.
94 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
95 // Also avoid creating IVs of non-native types. For example, we don't want a
96 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
97 uint64_t Width = SE->getTypeSizeInBits(I->getType());
98 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
101 // Get the symbolic expression for this instruction.
102 const SCEV *ISE = SE->getSCEV(I);
104 // If we've come to an uninteresting expression, stop the traversal and
106 if (!isInteresting(ISE, I, L, SE, LI))
109 SmallPtrSet<Instruction *, 4> UniqueUsers;
110 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
112 Instruction *User = cast<Instruction>(*UI);
113 if (!UniqueUsers.insert(User))
116 // Do not infinitely recurse on PHI nodes.
117 if (isa<PHINode>(User) && Processed.count(User))
120 // Descend recursively, but not into PHI nodes outside the current loop.
121 // It's important to see the entire expression outside the loop to get
122 // choices that depend on addressing mode use right, although we won't
123 // consider references outside the loop in all cases.
124 // If User is already in Processed, we don't want to recurse into it again,
125 // but do want to record a second reference in the same instruction.
126 bool AddUserToIVUsers = false;
127 if (LI->getLoopFor(User->getParent()) != L) {
128 if (isa<PHINode>(User) || Processed.count(User) ||
129 !AddUsersIfInteresting(User)) {
130 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
131 << " OF SCEV: " << *ISE << '\n');
132 AddUserToIVUsers = true;
134 } else if (Processed.count(User) || !AddUsersIfInteresting(User)) {
135 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
136 << " OF SCEV: " << *ISE << '\n');
137 AddUserToIVUsers = true;
140 if (AddUserToIVUsers) {
141 // Okay, we found a user that we cannot reduce.
142 IVUses.push_back(new IVStrideUse(this, User, I));
143 IVStrideUse &NewUse = IVUses.back();
144 // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
145 // The regular return value here is discarded; instead of recording
146 // it, we just recompute it when we need it.
147 ISE = TransformForPostIncUse(NormalizeAutodetect,
151 DEBUG(if (SE->getSCEV(I) != ISE)
152 dbgs() << " NORMALIZED TO: " << *ISE << '\n');
158 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
159 IVUses.push_back(new IVStrideUse(this, User, Operand));
160 return IVUses.back();
165 initializeIVUsersPass(*PassRegistry::getPassRegistry());
168 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
169 AU.addRequired<LoopInfo>();
170 AU.addRequired<DominatorTree>();
171 AU.addRequired<ScalarEvolution>();
172 AU.setPreservesAll();
175 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
178 LI = &getAnalysis<LoopInfo>();
179 DT = &getAnalysis<DominatorTree>();
180 SE = &getAnalysis<ScalarEvolution>();
181 TD = getAnalysisIfAvailable<TargetData>();
183 // Find all uses of induction variables in this loop, and categorize
184 // them by stride. Start by finding all of the PHI nodes in the header for
185 // this loop. If they are induction variables, inspect their uses.
186 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
187 (void)AddUsersIfInteresting(I);
192 void IVUsers::print(raw_ostream &OS, const Module *M) const {
193 OS << "IV Users for loop ";
194 WriteAsOperand(OS, L->getHeader(), false);
195 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
196 OS << " with backedge-taken count "
197 << *SE->getBackedgeTakenCount(L);
201 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
202 E = IVUses.end(); UI != E; ++UI) {
204 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
205 OS << " = " << *getReplacementExpr(*UI);
206 for (PostIncLoopSet::const_iterator
207 I = UI->PostIncLoops.begin(),
208 E = UI->PostIncLoops.end(); I != E; ++I) {
209 OS << " (post-inc with loop ";
210 WriteAsOperand(OS, (*I)->getHeader(), false);
214 UI->getUser()->print(OS);
219 void IVUsers::dump() const {
223 void IVUsers::releaseMemory() {
228 /// getReplacementExpr - Return a SCEV expression which computes the
229 /// value of the OperandValToReplace.
230 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
231 return SE->getSCEV(IU.getOperandValToReplace());
234 /// getExpr - Return the expression for the use.
235 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
237 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
238 IU.getUser(), IU.getOperandValToReplace(),
239 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
243 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
244 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
245 if (AR->getLoop() == L)
247 return findAddRecForLoop(AR->getStart(), L);
250 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
251 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
253 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
261 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
262 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
263 return AR->getStepRecurrence(*SE);
267 void IVStrideUse::transformToPostInc(const Loop *L) {
268 PostIncLoops.insert(L);
271 void IVStrideUse::deleted() {
272 // Remove this user from the list.
273 Parent->Processed.erase(this->getUser());
274 Parent->IVUses.erase(this);