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 static RegisterPass<IVUsers>
33 X("iv-users", "Induction Variable Users", false, true);
35 Pass *llvm::createIVUsersPass() {
39 /// isInteresting - Test whether the given expression is "interesting" when
40 /// used by the given expression, within the context of analyzing the
42 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
43 // Anything loop-invariant is interesting.
44 if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
47 // An addrec is interesting if it's affine or if it has an interesting start.
48 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
49 // Keep things simple. Don't touch loop-variant strides.
50 if (AR->getLoop() == L)
51 return AR->isAffine() || !L->contains(I);
52 // Otherwise recurse to see if the start value is interesting.
53 return isInteresting(AR->getStart(), I, L);
56 // An add is interesting if any of its operands is.
57 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
58 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
60 if (isInteresting(*OI, I, L))
65 // Nothing else is interesting here.
69 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
70 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
71 /// return true. Otherwise, return false.
72 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
73 if (!SE->isSCEVable(I->getType()))
74 return false; // Void and FP expressions cannot be reduced.
76 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
77 if (SE->getTypeSizeInBits(I->getType()) > 64)
80 if (!Processed.insert(I))
81 return true; // Instruction already handled.
83 // Get the symbolic expression for this instruction.
84 const SCEV *ISE = SE->getSCEV(I);
86 // If we've come to an uninteresting expression, stop the traversal and
88 if (!isInteresting(ISE, I, L))
91 SmallPtrSet<Instruction *, 4> UniqueUsers;
92 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
94 Instruction *User = cast<Instruction>(*UI);
95 if (!UniqueUsers.insert(User))
98 // Do not infinitely recurse on PHI nodes.
99 if (isa<PHINode>(User) && Processed.count(User))
102 // Descend recursively, but not into PHI nodes outside the current loop.
103 // It's important to see the entire expression outside the loop to get
104 // choices that depend on addressing mode use right, although we won't
105 // consider references outside the loop in all cases.
106 // If User is already in Processed, we don't want to recurse into it again,
107 // but do want to record a second reference in the same instruction.
108 bool AddUserToIVUsers = false;
109 if (LI->getLoopFor(User->getParent()) != L) {
110 if (isa<PHINode>(User) || Processed.count(User) ||
111 !AddUsersIfInteresting(User)) {
112 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
113 << " OF SCEV: " << *ISE << '\n');
114 AddUserToIVUsers = true;
116 } else if (Processed.count(User) ||
117 !AddUsersIfInteresting(User)) {
118 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
119 << " OF SCEV: " << *ISE << '\n');
120 AddUserToIVUsers = true;
123 if (AddUserToIVUsers) {
124 // Okay, we found a user that we cannot reduce.
125 IVUses.push_back(new IVStrideUse(this, User, I));
126 IVStrideUse &NewUse = IVUses.back();
127 // Transform the expression into a normalized form.
128 ISE = TransformForPostIncUse(NormalizeAutodetect,
132 DEBUG(dbgs() << " NORMALIZED TO: " << *ISE << '\n');
138 IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
139 IVUses.push_back(new IVStrideUse(this, User, Operand));
140 return IVUses.back();
147 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
148 AU.addRequired<LoopInfo>();
149 AU.addRequired<DominatorTree>();
150 AU.addRequired<ScalarEvolution>();
151 AU.setPreservesAll();
154 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
157 LI = &getAnalysis<LoopInfo>();
158 DT = &getAnalysis<DominatorTree>();
159 SE = &getAnalysis<ScalarEvolution>();
161 // Find all uses of induction variables in this loop, and categorize
162 // them by stride. Start by finding all of the PHI nodes in the header for
163 // this loop. If they are induction variables, inspect their uses.
164 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
165 (void)AddUsersIfInteresting(I);
170 void IVUsers::print(raw_ostream &OS, const Module *M) const {
171 OS << "IV Users for loop ";
172 WriteAsOperand(OS, L->getHeader(), false);
173 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
174 OS << " with backedge-taken count "
175 << *SE->getBackedgeTakenCount(L);
179 // Use a default AssemblyAnnotationWriter to suppress the default info
180 // comments, which aren't relevant here.
181 AssemblyAnnotationWriter Annotator;
182 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
183 E = IVUses.end(); UI != E; ++UI) {
185 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
186 OS << " = " << *getReplacementExpr(*UI);
187 for (PostIncLoopSet::const_iterator
188 I = UI->PostIncLoops.begin(),
189 E = UI->PostIncLoops.end(); I != E; ++I) {
190 OS << " (post-inc with loop ";
191 WriteAsOperand(OS, (*I)->getHeader(), false);
195 UI->getUser()->print(OS, &Annotator);
200 void IVUsers::dump() const {
204 void IVUsers::releaseMemory() {
209 /// getReplacementExpr - Return a SCEV expression which computes the
210 /// value of the OperandValToReplace.
211 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
212 return SE->getSCEV(IU.getOperandValToReplace());
215 /// getExpr - Return the expression for the use.
216 const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
218 TransformForPostIncUse(Normalize, getReplacementExpr(IU),
219 IU.getUser(), IU.getOperandValToReplace(),
220 const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
224 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
225 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
226 if (AR->getLoop() == L)
228 return findAddRecForLoop(AR->getStart(), L);
231 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
232 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
234 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
242 const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
243 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
244 return AR->getStepRecurrence(*SE);
248 void IVStrideUse::transformToPostInc(const Loop *L) {
249 PostIncLoops.insert(L);
252 void IVStrideUse::deleted() {
253 // Remove this user from the list.
254 Parent->IVUses.erase(this);