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) {
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.
53 if (AR->getLoop() == L)
54 return AR->isAffine() || !L->contains(I);
55 // Otherwise recurse to see if the start value is interesting, and that
56 // the step value is not interesting, since we don't yet know how to
57 // do effective SCEV expansions for addrecs with interesting steps.
58 return isInteresting(AR->getStart(), I, L, SE) &&
59 !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
62 // An add is interesting if exactly one of its operands is interesting.
63 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
64 bool AnyInterestingYet = false;
65 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
67 if (isInteresting(*OI, I, L, SE)) {
68 if (AnyInterestingYet)
70 AnyInterestingYet = true;
72 return AnyInterestingYet;
75 // Nothing else is interesting here.
79 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
80 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
81 /// return true. Otherwise, return false.
82 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
83 if (!SE->isSCEVable(I->getType()))
84 return false; // Void and FP expressions cannot be reduced.
86 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
87 // Also avoid creating IVs of non-native types. For example, we don't want a
88 // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
89 uint64_t Width = SE->getTypeSizeInBits(I->getType());
90 if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
93 if (!Processed.insert(I))
94 return true; // Instruction already handled.
96 // Get the symbolic expression for this instruction.
97 const SCEV *ISE = SE->getSCEV(I);
99 // If we've come to an uninteresting expression, stop the traversal and
101 if (!isInteresting(ISE, I, L, SE))
104 SmallPtrSet<Instruction *, 4> UniqueUsers;
105 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
107 Instruction *User = cast<Instruction>(*UI);
108 if (!UniqueUsers.insert(User))
111 // Do not infinitely recurse on PHI nodes.
112 if (isa<PHINode>(User) && Processed.count(User))
115 // Descend recursively, but not into PHI nodes outside the current loop.
116 // It's important to see the entire expression outside the loop to get
117 // choices that depend on addressing mode use right, although we won't
118 // consider references outside the loop in all cases.
119 // If User is already in Processed, we don't want to recurse into it again,
120 // but do want to record a second reference in the same instruction.
121 bool AddUserToIVUsers = false;
122 if (LI->getLoopFor(User->getParent()) != L) {
123 if (isa<PHINode>(User) || Processed.count(User) ||
124 !AddUsersIfInteresting(User)) {
125 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
126 << " OF SCEV: " << *ISE << '\n');
127 AddUserToIVUsers = true;
129 } else if (Processed.count(User) ||
130 !AddUsersIfInteresting(User)) {
131 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
132 << " OF SCEV: " << *ISE << '\n');
133 AddUserToIVUsers = true;
136 if (AddUserToIVUsers) {
137 // Okay, we found a user that we cannot reduce.
138 IVUses.push_back(new IVStrideUse(this, User, I));
139 IVStrideUse &NewUse = IVUses.back();
140 // Transform the expression into a normalized form.
141 ISE = TransformForPostIncUse(NormalizeAutodetect,
145 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
151 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
152 IVUses.push_back(new IVStrideUse(this, User, Operand));
153 return IVUses.back();
158 initializeIVUsersPass(*PassRegistry::getPassRegistry());
161 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
162 AU.addRequired<LoopInfo>();
163 AU.addRequired<DominatorTree>();
164 AU.addRequired<ScalarEvolution>();
165 AU.setPreservesAll();
168 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
171 LI = &getAnalysis<LoopInfo>();
172 DT = &getAnalysis<DominatorTree>();
173 SE = &getAnalysis<ScalarEvolution>();
174 TD = getAnalysisIfAvailable<TargetData>();
176 // Find all uses of induction variables in this loop, and categorize
177 // them by stride. Start by finding all of the PHI nodes in the header for
178 // this loop. If they are induction variables, inspect their uses.
179 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
180 (void)AddUsersIfInteresting(I);
185 void IVUsers::print(raw_ostream &OS, const Module *M) const {
186 OS << "IV Users for loop ";
187 WriteAsOperand(OS, L->getHeader(), false);
188 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
189 OS << " with backedge-taken count "
190 << *SE->getBackedgeTakenCount(L);
194 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
195 E = IVUses.end(); UI != E; ++UI) {
197 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
198 OS << " = " << *getReplacementExpr(*UI);
199 for (PostIncLoopSet::const_iterator
200 I = UI->PostIncLoops.begin(),
201 E = UI->PostIncLoops.end(); I != E; ++I) {
202 OS << " (post-inc with loop ";
203 WriteAsOperand(OS, (*I)->getHeader(), false);
207 UI->getUser()->print(OS);
212 void IVUsers::dump() const {
216 void IVUsers::releaseMemory() {
221 /// getReplacementExpr - Return a SCEV expression which computes the
222 /// value of the OperandValToReplace.
223 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
224 return SE->getSCEV(IU.getOperandValToReplace());
227 /// getExpr - Return the expression for the use.
228 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
230 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
231 IU.getUser(), IU.getOperandValToReplace(),
232 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
236 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
237 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
238 if (AR->getLoop() == L)
240 return findAddRecForLoop(AR->getStart(), L);
243 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
244 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
246 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
254 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
255 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
256 return AR->getStepRecurrence(*SE);
260 void IVStrideUse::transformToPostInc(const Loop *L) {
261 PostIncLoops.insert(L);
264 void IVStrideUse::deleted() {
265 // Remove this user from the list.
266 Parent->IVUses.erase(this);