1//===- IVUsers.cpp - Induction Variable Users -------------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements bookkeeping for "interesting" users of expressions
11// computed from induction variables.
12//
13//===----------------------------------------------------------------------===//
14
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"
29#include <algorithm>
30using namespace llvm;
31
32char IVUsers::ID = 0;
33INITIALIZE_PASS_BEGIN(IVUsers, "iv-users",
34                      "Induction Variable Users", false, true)
35INITIALIZE_PASS_DEPENDENCY(LoopInfo)
36INITIALIZE_PASS_DEPENDENCY(DominatorTree)
37INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
38INITIALIZE_PASS_END(IVUsers, "iv-users",
39                      "Induction Variable Users", false, true)
40
41Pass *llvm::createIVUsersPass() {
42  return new IVUsers();
43}
44
45/// isInteresting - Test whether the given expression is "interesting" when
46/// used by the given expression, within the context of analyzing the
47/// given loop.
48static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
49                          ScalarEvolution *SE, LoopInfo *LI) {
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 unless they're
53    // only used outside the loop and we can simplify them.
54    if (AR->getLoop() == L)
55      return AR->isAffine() ||
56             (!L->contains(I) &&
57              SE->getSCEVAtScope(AR, LI->getLoopFor(I->getParent())) != AR);
58    // Otherwise recurse to see if the start value is interesting, and that
59    // the step value is not interesting, since we don't yet know how to
60    // do effective SCEV expansions for addrecs with interesting steps.
61    return isInteresting(AR->getStart(), I, L, SE, LI) &&
62          !isInteresting(AR->getStepRecurrence(*SE), I, L, SE, LI);
63  }
64
65  // An add is interesting if exactly one of its operands is interesting.
66  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
67    bool AnyInterestingYet = false;
68    for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
69         OI != OE; ++OI)
70      if (isInteresting(*OI, I, L, SE, LI)) {
71        if (AnyInterestingYet)
72          return false;
73        AnyInterestingYet = true;
74      }
75    return AnyInterestingYet;
76  }
77
78  // Nothing else is interesting here.
79  return false;
80}
81
82/// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
83/// reducible SCEV, recursively add its users to the IVUsesByStride set and
84/// return true.  Otherwise, return false.
85bool IVUsers::AddUsersIfInteresting(Instruction *I) {
86  if (!SE->isSCEVable(I->getType()))
87    return false;   // Void and FP expressions cannot be reduced.
88
89  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
90  // Also avoid creating IVs of non-native types. For example, we don't want a
91  // 64-bit IV in 32-bit code just because the loop has one 64-bit cast.
92  uint64_t Width = SE->getTypeSizeInBits(I->getType());
93  if (Width > 64 || (TD && !TD->isLegalInteger(Width)))
94    return false;
95
96  if (!Processed.insert(I))
97    return true;    // Instruction already handled.
98
99  // Get the symbolic expression for this instruction.
100  const SCEV *ISE = SE->getSCEV(I);
101
102  // If we've come to an uninteresting expression, stop the traversal and
103  // call this a user.
104  if (!isInteresting(ISE, I, L, SE, LI))
105    return false;
106
107  SmallPtrSet<Instruction *, 4> UniqueUsers;
108  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
109       UI != E; ++UI) {
110    Instruction *User = cast<Instruction>(*UI);
111    if (!UniqueUsers.insert(User))
112      continue;
113
114    // Do not infinitely recurse on PHI nodes.
115    if (isa<PHINode>(User) && Processed.count(User))
116      continue;
117
118    // Descend recursively, but not into PHI nodes outside the current loop.
119    // It's important to see the entire expression outside the loop to get
120    // choices that depend on addressing mode use right, although we won't
121    // consider references outside the loop in all cases.
122    // If User is already in Processed, we don't want to recurse into it again,
123    // but do want to record a second reference in the same instruction.
124    bool AddUserToIVUsers = false;
125    if (LI->getLoopFor(User->getParent()) != L) {
126      if (isa<PHINode>(User) || Processed.count(User) ||
127          !AddUsersIfInteresting(User)) {
128        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
129                     << "   OF SCEV: " << *ISE << '\n');
130        AddUserToIVUsers = true;
131      }
132    } else if (Processed.count(User) || !AddUsersIfInteresting(User)) {
133      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
134                   << "   OF SCEV: " << *ISE << '\n');
135      AddUserToIVUsers = true;
136    }
137
138    if (AddUserToIVUsers) {
139      // Okay, we found a user that we cannot reduce.
140      IVUses.push_back(new IVStrideUse(this, User, I));
141      IVStrideUse &NewUse = IVUses.back();
142      // Autodetect the post-inc loop set, populating NewUse.PostIncLoops.
143      // The regular return value here is discarded; instead of recording
144      // it, we just recompute it when we need it.
145      ISE = TransformForPostIncUse(NormalizeAutodetect,
146                                   ISE, User, I,
147                                   NewUse.PostIncLoops,
148                                   *SE, *DT);
149      DEBUG(if (SE->getSCEV(I) != ISE)
150              dbgs() << "   NORMALIZED TO: " << *ISE << '\n');
151    }
152  }
153  return true;
154}
155
156IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
157  IVUses.push_back(new IVStrideUse(this, User, Operand));
158  return IVUses.back();
159}
160
161IVUsers::IVUsers()
162    : LoopPass(ID) {
163  initializeIVUsersPass(*PassRegistry::getPassRegistry());
164}
165
166void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
167  AU.addRequired<LoopInfo>();
168  AU.addRequired<DominatorTree>();
169  AU.addRequired<ScalarEvolution>();
170  AU.setPreservesAll();
171}
172
173bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
174
175  L = l;
176  LI = &getAnalysis<LoopInfo>();
177  DT = &getAnalysis<DominatorTree>();
178  SE = &getAnalysis<ScalarEvolution>();
179  TD = getAnalysisIfAvailable<TargetData>();
180
181  // Find all uses of induction variables in this loop, and categorize
182  // them by stride.  Start by finding all of the PHI nodes in the header for
183  // this loop.  If they are induction variables, inspect their uses.
184  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
185    (void)AddUsersIfInteresting(I);
186
187  return false;
188}
189
190void IVUsers::print(raw_ostream &OS, const Module *M) const {
191  OS << "IV Users for loop ";
192  WriteAsOperand(OS, L->getHeader(), false);
193  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
194    OS << " with backedge-taken count "
195       << *SE->getBackedgeTakenCount(L);
196  }
197  OS << ":\n";
198
199  for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
200       E = IVUses.end(); UI != E; ++UI) {
201    OS << "  ";
202    WriteAsOperand(OS, UI->getOperandValToReplace(), false);
203    OS << " = " << *getReplacementExpr(*UI);
204    for (PostIncLoopSet::const_iterator
205         I = UI->PostIncLoops.begin(),
206         E = UI->PostIncLoops.end(); I != E; ++I) {
207      OS << " (post-inc with loop ";
208      WriteAsOperand(OS, (*I)->getHeader(), false);
209      OS << ")";
210    }
211    OS << " in  ";
212    UI->getUser()->print(OS);
213    OS << '\n';
214  }
215}
216
217void IVUsers::dump() const {
218  print(dbgs());
219}
220
221void IVUsers::releaseMemory() {
222  Processed.clear();
223  IVUses.clear();
224}
225
226/// getReplacementExpr - Return a SCEV expression which computes the
227/// value of the OperandValToReplace.
228const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
229  return SE->getSCEV(IU.getOperandValToReplace());
230}
231
232/// getExpr - Return the expression for the use.
233const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
234  return
235    TransformForPostIncUse(Normalize, getReplacementExpr(IU),
236                           IU.getUser(), IU.getOperandValToReplace(),
237                           const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
238                           *SE, *DT);
239}
240
241static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
242  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
243    if (AR->getLoop() == L)
244      return AR;
245    return findAddRecForLoop(AR->getStart(), L);
246  }
247
248  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
249    for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
250         I != E; ++I)
251      if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
252        return AR;
253    return 0;
254  }
255
256  return 0;
257}
258
259const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
260  if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
261    return AR->getStepRecurrence(*SE);
262  return 0;
263}
264
265void IVStrideUse::transformToPostInc(const Loop *L) {
266  PostIncLoops.insert(L);
267}
268
269void IVStrideUse::deleted() {
270  // Remove this user from the list.
271  Parent->IVUses.erase(this);
272  // this now dangles!
273}
274