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/AsmAnnotationWriter.h"
25 #include "llvm/ADT/STLExtras.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/raw_ostream.h"
32 INITIALIZE_PASS(IVUsers, "iv-users", "Induction Variable Users", false, true);
34 Pass *llvm::createIVUsersPass() {
38 /// isInteresting - Test whether the given expression is "interesting" when
39 /// used by the given expression, within the context of analyzing the
41 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
42 // Anything loop-invariant is interesting.
43 if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
46 // An addrec is interesting if it's affine or if it has an interesting start.
47 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
48 // Keep things simple. Don't touch loop-variant strides.
49 if (AR->getLoop() == L)
50 return AR->isAffine() || !L->contains(I);
51 // Otherwise recurse to see if the start value is interesting.
52 return isInteresting(AR->getStart(), I, L);
55 // An add is interesting if any of its operands is.
56 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
57 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
59 if (isInteresting(*OI, I, L))
64 // Nothing else is interesting here.
68 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
69 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
70 /// return true. Otherwise, return false.
71 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
72 if (!SE->isSCEVable(I->getType()))
73 return false; // Void and FP expressions cannot be reduced.
75 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
76 if (SE->getTypeSizeInBits(I->getType()) > 64)
79 if (!Processed.insert(I))
80 return true; // Instruction already handled.
82 // Get the symbolic expression for this instruction.
83 const SCEV *ISE = SE->getSCEV(I);
85 // If we've come to an uninteresting expression, stop the traversal and
87 if (!isInteresting(ISE, I, L))
90 SmallPtrSet<Instruction *, 4> UniqueUsers;
91 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
93 Instruction *User = cast<Instruction>(*UI);
94 if (!UniqueUsers.insert(User))
97 // Do not infinitely recurse on PHI nodes.
98 if (isa<PHINode>(User) && Processed.count(User))
101 // Descend recursively, but not into PHI nodes outside the current loop.
102 // It's important to see the entire expression outside the loop to get
103 // choices that depend on addressing mode use right, although we won't
104 // consider references outside the loop in all cases.
105 // If User is already in Processed, we don't want to recurse into it again,
106 // but do want to record a second reference in the same instruction.
107 bool AddUserToIVUsers = false;
108 if (LI->getLoopFor(User->getParent()) != L) {
109 if (isa<PHINode>(User) || Processed.count(User) ||
110 !AddUsersIfInteresting(User)) {
111 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
112 << " OF SCEV: " << *ISE << '\n');
113 AddUserToIVUsers = true;
115 } else if (Processed.count(User) ||
116 !AddUsersIfInteresting(User)) {
117 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
118 << " OF SCEV: " << *ISE << '\n');
119 AddUserToIVUsers = true;
122 if (AddUserToIVUsers) {
123 // Okay, we found a user that we cannot reduce.
124 IVUses.push_back(new IVStrideUse(this, User, I));
125 IVStrideUse &NewUse = IVUses.back();
126 // Transform the expression into a normalized form.
127 ISE = TransformForPostIncUse(NormalizeAutodetect,
131 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
137 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
138 IVUses.push_back(new IVStrideUse(this, User, Operand));
139 return IVUses.back();
146 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
147 AU.addRequired<LoopInfo>();
148 AU.addRequired<DominatorTree>();
149 AU.addRequired<ScalarEvolution>();
150 AU.setPreservesAll();
153 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
156 LI = &getAnalysis<LoopInfo>();
157 DT = &getAnalysis<DominatorTree>();
158 SE = &getAnalysis<ScalarEvolution>();
160 // Find all uses of induction variables in this loop, and categorize
161 // them by stride. Start by finding all of the PHI nodes in the header for
162 // this loop. If they are induction variables, inspect their uses.
163 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
164 (void)AddUsersIfInteresting(I);
169 void IVUsers::print(raw_ostream &OS, const Module *M) const {
170 OS << "IV Users for loop ";
171 WriteAsOperand(OS, L->getHeader(), false);
172 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
173 OS << " with backedge-taken count "
174 << *SE->getBackedgeTakenCount(L);
178 // Use a default AssemblyAnnotationWriter to suppress the default info
179 // comments, which aren't relevant here.
180 AssemblyAnnotationWriter Annotator;
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, &Annotator);
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);