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/ADT/STLExtras.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/raw_ostream.h"
31 INITIALIZE_PASS(IVUsers, "iv-users", "Induction Variable Users", false, true)
33 Pass *llvm::createIVUsersPass() {
37 /// isInteresting - Test whether the given expression is "interesting" when
38 /// used by the given expression, within the context of analyzing the
40 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
41 ScalarEvolution *SE) {
42 // An addrec is interesting if it's affine or if it has an interesting start.
43 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
44 // Keep things simple. Don't touch loop-variant strides.
45 if (AR->getLoop() == L)
46 return AR->isAffine() || !L->contains(I);
47 // Otherwise recurse to see if the start value is interesting, and that
48 // the step value is not interesting, since we don't yet know how to
49 // do effective SCEV expansions for addrecs with interesting steps.
50 return isInteresting(AR->getStart(), I, L, SE) &&
51 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
54 // An add is interesting if exactly one of its operands is interesting.
55 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
56 bool AnyInterestingYet = false;
57 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
59 if (isInteresting(*OI, I, L, SE)) {
60 if (AnyInterestingYet)
62 AnyInterestingYet = true;
64 return AnyInterestingYet;
67 // Nothing else is interesting here.
71 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
72 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
73 /// return true. Otherwise, return false.
74 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
75 if (!SE->isSCEVable(I->getType()))
76 return false; // Void and FP expressions cannot be reduced.
78 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
79 if (SE->getTypeSizeInBits(I->getType()) > 64)
82 if (!Processed.insert(I))
83 return true; // Instruction already handled.
85 // Get the symbolic expression for this instruction.
86 const SCEV *ISE = SE->getSCEV(I);
88 // If we've come to an uninteresting expression, stop the traversal and
90 if (!isInteresting(ISE, I, L, SE))
93 SmallPtrSet<Instruction *, 4> UniqueUsers;
94 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
96 Instruction *User = cast<Instruction>(*UI);
97 if (!UniqueUsers.insert(User))
100 // Do not infinitely recurse on PHI nodes.
101 if (isa<PHINode>(User) && Processed.count(User))
104 // Descend recursively, but not into PHI nodes outside the current loop.
105 // It's important to see the entire expression outside the loop to get
106 // choices that depend on addressing mode use right, although we won't
107 // consider references outside the loop in all cases.
108 // If User is already in Processed, we don't want to recurse into it again,
109 // but do want to record a second reference in the same instruction.
110 bool AddUserToIVUsers = false;
111 if (LI->getLoopFor(User->getParent()) != L) {
112 if (isa<PHINode>(User) || Processed.count(User) ||
113 !AddUsersIfInteresting(User)) {
114 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
115 << " OF SCEV: " << *ISE << '\n');
116 AddUserToIVUsers = true;
118 } else if (Processed.count(User) ||
119 !AddUsersIfInteresting(User)) {
120 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
121 << " OF SCEV: " << *ISE << '\n');
122 AddUserToIVUsers = true;
125 if (AddUserToIVUsers) {
126 // Okay, we found a user that we cannot reduce.
127 IVUses.push_back(new IVStrideUse(this, User, I));
128 IVStrideUse &NewUse = IVUses.back();
129 // Transform the expression into a normalized form.
130 ISE = TransformForPostIncUse(NormalizeAutodetect,
134 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
140 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
141 IVUses.push_back(new IVStrideUse(this, User, Operand));
142 return IVUses.back();
149 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
150 AU.addRequired<LoopInfo>();
151 AU.addRequired<DominatorTree>();
152 AU.addRequired<ScalarEvolution>();
153 AU.setPreservesAll();
156 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
159 LI = &getAnalysis<LoopInfo>();
160 DT = &getAnalysis<DominatorTree>();
161 SE = &getAnalysis<ScalarEvolution>();
163 // Find all uses of induction variables in this loop, and categorize
164 // them by stride. Start by finding all of the PHI nodes in the header for
165 // this loop. If they are induction variables, inspect their uses.
166 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
167 (void)AddUsersIfInteresting(I);
172 void IVUsers::print(raw_ostream &OS, const Module *M) const {
173 OS << "IV Users for loop ";
174 WriteAsOperand(OS, L->getHeader(), false);
175 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
176 OS << " with backedge-taken count "
177 << *SE->getBackedgeTakenCount(L);
181 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
182 E = IVUses.end(); UI != E; ++UI) {
184 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
185 OS << " = " << *getReplacementExpr(*UI);
186 for (PostIncLoopSet::const_iterator
187 I = UI->PostIncLoops.begin(),
188 E = UI->PostIncLoops.end(); I != E; ++I) {
189 OS << " (post-inc with loop ";
190 WriteAsOperand(OS, (*I)->getHeader(), false);
194 UI->getUser()->print(OS);
199 void IVUsers::dump() const {
203 void IVUsers::releaseMemory() {
208 /// getReplacementExpr - Return a SCEV expression which computes the
209 /// value of the OperandValToReplace.
210 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
211 return SE->getSCEV(IU.getOperandValToReplace());
214 /// getExpr - Return the expression for the use.
215 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
217 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
218 IU.getUser(), IU.getOperandValToReplace(),
219 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
223 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
224 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
225 if (AR->getLoop() == L)
227 return findAddRecForLoop(AR->getStart(), L);
230 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
231 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
233 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
241 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
242 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
243 return AR->getStepRecurrence(*SE);
247 void IVStrideUse::transformToPostInc(const Loop *L) {
248 PostIncLoops.insert(L);
251 void IVStrideUse::deleted() {
252 // Remove this user from the list.
253 Parent->IVUses.erase(this);