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/Assembly/Writer.h"
25 #include "llvm/ADT/STLExtras.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/raw_ostream.h"
32 INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
33 "Induction Variable Users", false, true)
34 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
35 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
36 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
37 INITIALIZE_PASS_END(IVUsers, "iv-users",
38 "Induction Variable Users", false, true)
40 Pass *llvm::createIVUsersPass() {
44 /// isInteresting - Test whether the given expression is "interesting" when
45 /// used by the given expression, within the context of analyzing the
47 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
48 ScalarEvolution *SE) {
49 // An addrec is interesting if it's affine or if it has an interesting start.
50 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
51 // Keep things simple. Don't touch loop-variant strides.
52 if (AR->getLoop() == L)
53 return AR->isAffine() || !L->contains(I);
54 // Otherwise recurse to see if the start value is interesting, and that
55 // the step value is not interesting, since we don't yet know how to
56 // do effective SCEV expansions for addrecs with interesting steps.
57 return isInteresting(AR->getStart(), I, L, SE) &&
58 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
61 // An add is interesting if exactly one of its operands is interesting.
62 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
63 bool AnyInterestingYet = false;
64 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
66 if (isInteresting(*OI, I, L, SE)) {
67 if (AnyInterestingYet)
69 AnyInterestingYet = true;
71 return AnyInterestingYet;
74 // Nothing else is interesting here.
78 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
79 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
80 /// return true. Otherwise, return false.
81 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
82 if (!SE->isSCEVable(I->getType()))
83 return false; // Void and FP expressions cannot be reduced.
85 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
86 if (SE->getTypeSizeInBits(I->getType()) > 64)
89 if (!Processed.insert(I))
90 return true; // Instruction already handled.
92 // Get the symbolic expression for this instruction.
93 const SCEV *ISE = SE->getSCEV(I);
95 // If we've come to an uninteresting expression, stop the traversal and
97 if (!isInteresting(ISE, I, L, SE))
100 SmallPtrSet<Instruction *, 4> UniqueUsers;
101 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
103 Instruction *User = cast<Instruction>(*UI);
104 if (!UniqueUsers.insert(User))
107 // Do not infinitely recurse on PHI nodes.
108 if (isa<PHINode>(User) && Processed.count(User))
111 // Descend recursively, but not into PHI nodes outside the current loop.
112 // It's important to see the entire expression outside the loop to get
113 // choices that depend on addressing mode use right, although we won't
114 // consider references outside the loop in all cases.
115 // If User is already in Processed, we don't want to recurse into it again,
116 // but do want to record a second reference in the same instruction.
117 bool AddUserToIVUsers = false;
118 if (LI->getLoopFor(User->getParent()) != L) {
119 if (isa<PHINode>(User) || Processed.count(User) ||
120 !AddUsersIfInteresting(User)) {
121 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
122 << " OF SCEV: " << *ISE << '\n');
123 AddUserToIVUsers = true;
125 } else if (Processed.count(User) ||
126 !AddUsersIfInteresting(User)) {
127 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
128 << " OF SCEV: " << *ISE << '\n');
129 AddUserToIVUsers = true;
132 if (AddUserToIVUsers) {
133 // Okay, we found a user that we cannot reduce.
134 IVUses.push_back(new IVStrideUse(this, User, I));
135 IVStrideUse &NewUse = IVUses.back();
136 // Transform the expression into a normalized form.
137 ISE = TransformForPostIncUse(NormalizeAutodetect,
141 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
147 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
148 IVUses.push_back(new IVStrideUse(this, User, Operand));
149 return IVUses.back();
154 initializeIVUsersPass(*PassRegistry::getPassRegistry());
157 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
158 AU.addRequired<LoopInfo>();
159 AU.addRequired<DominatorTree>();
160 AU.addRequired<ScalarEvolution>();
161 AU.setPreservesAll();
164 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
167 LI = &getAnalysis<LoopInfo>();
168 DT = &getAnalysis<DominatorTree>();
169 SE = &getAnalysis<ScalarEvolution>();
171 // Find all uses of induction variables in this loop, and categorize
172 // them by stride. Start by finding all of the PHI nodes in the header for
173 // this loop. If they are induction variables, inspect their uses.
174 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
175 (void)AddUsersIfInteresting(I);
180 void IVUsers::print(raw_ostream &OS, const Module *M) const {
181 OS << "IV Users for loop ";
182 WriteAsOperand(OS, L->getHeader(), false);
183 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
184 OS << " with backedge-taken count "
185 << *SE->getBackedgeTakenCount(L);
189 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
190 E = IVUses.end(); UI != E; ++UI) {
192 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
193 OS << " = " << *getReplacementExpr(*UI);
194 for (PostIncLoopSet::const_iterator
195 I = UI->PostIncLoops.begin(),
196 E = UI->PostIncLoops.end(); I != E; ++I) {
197 OS << " (post-inc with loop ";
198 WriteAsOperand(OS, (*I)->getHeader(), false);
202 UI->getUser()->print(OS);
207 void IVUsers::dump() const {
211 void IVUsers::releaseMemory() {
216 /// getReplacementExpr - Return a SCEV expression which computes the
217 /// value of the OperandValToReplace.
218 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
219 return SE->getSCEV(IU.getOperandValToReplace());
222 /// getExpr - Return the expression for the use.
223 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
225 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
226 IU.getUser(), IU.getOperandValToReplace(),
227 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
231 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
232 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
233 if (AR->getLoop() == L)
235 return findAddRecForLoop(AR->getStart(), L);
238 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
239 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
241 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
249 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
250 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
251 return AR->getStepRecurrence(*SE);
255 void IVStrideUse::transformToPostInc(const Loop *L) {
256 PostIncLoops.insert(L);
259 void IVStrideUse::deleted() {
260 // Remove this user from the list.
261 Parent->IVUses.erase(this);