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 /// CollectSubexprs - Split S into subexpressions which can be pulled out into
40 /// separate registers.
41 static void CollectSubexprs(const SCEV *S,
42 SmallVectorImpl<const SCEV *> &Ops,
43 ScalarEvolution &SE) {
44 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
45 // Break out add operands.
46 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
48 CollectSubexprs(*I, Ops, SE);
50 } else if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
51 // Split a non-zero base out of an addrec.
52 if (!AR->getStart()->isZero()) {
53 CollectSubexprs(AR->getStart(), Ops, SE);
54 CollectSubexprs(SE.getAddRecExpr(SE.getIntegerSCEV(0, AR->getType()),
55 AR->getStepRecurrence(SE),
56 AR->getLoop()), Ops, SE);
61 // Otherwise use the value itself.
65 /// isInteresting - Test whether the given expression is "interesting" when
66 /// used by the given expression, within the context of analyzing the
68 static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L) {
69 // Anything loop-invariant is interesting.
70 if (!isa<SCEVUnknown>(S) && S->isLoopInvariant(L))
73 // An addrec is interesting if it's affine or if it has an interesting start.
74 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
75 // Keep things simple. Don't touch loop-variant strides.
76 if (AR->getLoop() == L && (AR->isAffine() || !L->contains(I)))
78 // Otherwise recurse to see if the start value is interesting.
79 return isInteresting(AR->getStart(), I, L);
82 // An add is interesting if any of its operands is.
83 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
84 for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
86 if (isInteresting(*OI, I, L))
91 // Nothing else is interesting here.
95 /// AddUsersIfInteresting - Inspect the specified instruction. If it is a
96 /// reducible SCEV, recursively add its users to the IVUsesByStride set and
97 /// return true. Otherwise, return false.
98 bool IVUsers::AddUsersIfInteresting(Instruction *I) {
99 if (!SE->isSCEVable(I->getType()))
100 return false; // Void and FP expressions cannot be reduced.
102 // LSR is not APInt clean, do not touch integers bigger than 64-bits.
103 if (SE->getTypeSizeInBits(I->getType()) > 64)
106 if (!Processed.insert(I))
107 return true; // Instruction already handled.
109 // Get the symbolic expression for this instruction.
110 const SCEV *ISE = SE->getSCEV(I);
111 if (isa<SCEVCouldNotCompute>(ISE)) return false;
113 // If we've come to an uninteresting expression, stop the traversal and
115 if (!isInteresting(ISE, I, L))
118 SmallPtrSet<Instruction *, 4> UniqueUsers;
119 for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
121 Instruction *User = cast<Instruction>(*UI);
122 if (!UniqueUsers.insert(User))
125 // Do not infinitely recurse on PHI nodes.
126 if (isa<PHINode>(User) && Processed.count(User))
129 // Descend recursively, but not into PHI nodes outside the current loop.
130 // It's important to see the entire expression outside the loop to get
131 // choices that depend on addressing mode use right, although we won't
132 // consider references outside the loop in all cases.
133 // If User is already in Processed, we don't want to recurse into it again,
134 // but do want to record a second reference in the same instruction.
135 bool AddUserToIVUsers = false;
136 if (LI->getLoopFor(User->getParent()) != L) {
137 if (isa<PHINode>(User) || Processed.count(User) ||
138 !AddUsersIfInteresting(User)) {
139 DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
140 << " OF SCEV: " << *ISE << '\n');
141 AddUserToIVUsers = true;
143 } else if (Processed.count(User) ||
144 !AddUsersIfInteresting(User)) {
145 DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
146 << " OF SCEV: " << *ISE << '\n');
147 AddUserToIVUsers = true;
150 if (AddUserToIVUsers) {
151 // Okay, we found a user that we cannot reduce.
152 IVUses.push_back(new IVStrideUse(this, ISE, User, I));
153 IVStrideUse &NewUse = IVUses.back();
154 // Transform the expression into a normalized form.
156 TransformForPostIncUse(NormalizeAutodetect, NewUse.Expr,
160 DEBUG(dbgs() << " NORMALIZED TO: " << *NewUse.Expr << '\n');
166 IVStrideUse &IVUsers::AddUser(const SCEV *Expr,
167 Instruction *User, Value *Operand) {
168 IVUses.push_back(new IVStrideUse(this, Expr, User, Operand));
169 return IVUses.back();
176 void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
177 AU.addRequired<LoopInfo>();
178 AU.addRequired<DominatorTree>();
179 AU.addRequired<ScalarEvolution>();
180 AU.setPreservesAll();
183 bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
186 LI = &getAnalysis<LoopInfo>();
187 DT = &getAnalysis<DominatorTree>();
188 SE = &getAnalysis<ScalarEvolution>();
190 // Find all uses of induction variables in this loop, and categorize
191 // them by stride. Start by finding all of the PHI nodes in the header for
192 // this loop. If they are induction variables, inspect their uses.
193 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
194 AddUsersIfInteresting(I);
199 /// getReplacementExpr - Return a SCEV expression which computes the
200 /// value of the OperandValToReplace of the given IVStrideUse.
201 const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const {
202 PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(U.PostIncLoops);
203 return TransformForPostIncUse(Denormalize, U.getExpr(),
204 U.getUser(), U.getOperandValToReplace(),
208 void IVUsers::print(raw_ostream &OS, const Module *M) const {
209 OS << "IV Users for loop ";
210 WriteAsOperand(OS, L->getHeader(), false);
211 if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
212 OS << " with backedge-taken count "
213 << *SE->getBackedgeTakenCount(L);
217 // Use a default AssemblyAnnotationWriter to suppress the default info
218 // comments, which aren't relevant here.
219 AssemblyAnnotationWriter Annotator;
220 for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
221 E = IVUses.end(); UI != E; ++UI) {
223 WriteAsOperand(OS, UI->getOperandValToReplace(), false);
225 << *getReplacementExpr(*UI);
226 for (PostIncLoopSet::const_iterator
227 I = UI->PostIncLoops.begin(),
228 E = UI->PostIncLoops.end(); I != E; ++I) {
229 OS << " (post-inc with loop ";
230 WriteAsOperand(OS, (*I)->getHeader(), false);
234 UI->getUser()->print(OS, &Annotator);
239 void IVUsers::dump() const {
243 void IVUsers::releaseMemory() {
248 static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
249 if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
250 if (AR->getLoop() == L)
252 return findAddRecForLoop(AR->getStart(), L);
255 if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
256 for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
258 if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
266 const SCEV *IVStrideUse::getStride(const Loop *L) const {
267 if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(), L))
268 return AR->getStepRecurrence(*Parent->SE);
272 void IVStrideUse::transformToPostInc(const Loop *L) {
273 PostIncLoopSet Loops;
275 Expr = TransformForPostIncUse(Normalize, Expr,
276 getUser(), getOperandValToReplace(),
277 Loops, *Parent->SE, *Parent->DT);
278 PostIncLoops.insert(L);
281 void IVStrideUse::deleted() {
282 // Remove this user from the list.
283 Parent->IVUses.erase(this);