IVUsers.cpp revision 191bd64a39490fa75d35b9aaecdd57b00c7a8b5f 
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/Assembly/AsmAnnotationWriter.h"
25#include "llvm/ADT/STLExtras.h"
26#include "llvm/Support/Debug.h"
27#include "llvm/Support/raw_ostream.h"
28#include <algorithm>
29using namespace llvm;
30
31char IVUsers::ID = 0;
32INITIALIZE_PASS(IVUsers, "iv-users", "Induction Variable Users", false, true);
33
34Pass *llvm::createIVUsersPass() {
35  return new IVUsers();
36}
37
38/// isInteresting - Test whether the given expression is "interesting" when
39/// used by the given expression, within the context of analyzing the
40/// given loop.
41static bool isInteresting(const SCEV *S, const Instruction *I, const Loop *L,
42                          ScalarEvolution *SE) {
43  // An addrec is interesting if it's affine or if it has an interesting start.
44  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
45    // Keep things simple. Don't touch loop-variant strides.
46    if (AR->getLoop() == L)
47      return AR->isAffine() || !L->contains(I);
48    // Otherwise recurse to see if the start value is interesting, and that
49    // the step value is not interesting, since we don't yet know how to
50    // do effective SCEV expansions for addrecs with interesting steps.
51    return isInteresting(AR->getStart(), I, L, SE) &&
52          !isInteresting(AR->getStepRecurrence(*SE), I, L, SE);
53  }
54
55  // An add is interesting if exactly one of its operands is interesting.
56  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
57    bool AnyInterestingYet = false;
58    for (SCEVAddExpr::op_iterator OI = Add->op_begin(), OE = Add->op_end();
59         OI != OE; ++OI)
60      if (isInteresting(*OI, I, L, SE)) {
61        if (AnyInterestingYet)
62          return false;
63        AnyInterestingYet = true;
64      }
65    return AnyInterestingYet;
66  }
67
68  // Nothing else is interesting here.
69  return false;
70}
71
72/// AddUsersIfInteresting - Inspect the specified instruction.  If it is a
73/// reducible SCEV, recursively add its users to the IVUsesByStride set and
74/// return true.  Otherwise, return false.
75bool IVUsers::AddUsersIfInteresting(Instruction *I) {
76  if (!SE->isSCEVable(I->getType()))
77    return false;   // Void and FP expressions cannot be reduced.
78
79  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
80  if (SE->getTypeSizeInBits(I->getType()) > 64)
81    return false;
82
83  if (!Processed.insert(I))
84    return true;    // Instruction already handled.
85
86  // Get the symbolic expression for this instruction.
87  const SCEV *ISE = SE->getSCEV(I);
88
89  // If we've come to an uninteresting expression, stop the traversal and
90  // call this a user.
91  if (!isInteresting(ISE, I, L, SE))
92    return false;
93
94  SmallPtrSet<Instruction *, 4> UniqueUsers;
95  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
96       UI != E; ++UI) {
97    Instruction *User = cast<Instruction>(*UI);
98    if (!UniqueUsers.insert(User))
99      continue;
100
101    // Do not infinitely recurse on PHI nodes.
102    if (isa<PHINode>(User) && Processed.count(User))
103      continue;
104
105    // Descend recursively, but not into PHI nodes outside the current loop.
106    // It's important to see the entire expression outside the loop to get
107    // choices that depend on addressing mode use right, although we won't
108    // consider references outside the loop in all cases.
109    // If User is already in Processed, we don't want to recurse into it again,
110    // but do want to record a second reference in the same instruction.
111    bool AddUserToIVUsers = false;
112    if (LI->getLoopFor(User->getParent()) != L) {
113      if (isa<PHINode>(User) || Processed.count(User) ||
114          !AddUsersIfInteresting(User)) {
115        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
116                     << "   OF SCEV: " << *ISE << '\n');
117        AddUserToIVUsers = true;
118      }
119    } else if (Processed.count(User) ||
120               !AddUsersIfInteresting(User)) {
121      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
122                   << "   OF SCEV: " << *ISE << '\n');
123      AddUserToIVUsers = true;
124    }
125
126    if (AddUserToIVUsers) {
127      // Okay, we found a user that we cannot reduce.
128      IVUses.push_back(new IVStrideUse(this, User, I));
129      IVStrideUse &NewUse = IVUses.back();
130      // Transform the expression into a normalized form.
131      ISE = TransformForPostIncUse(NormalizeAutodetect,
132                                   ISE, User, I,
133                                   NewUse.PostIncLoops,
134                                   *SE, *DT);
135      DEBUG(dbgs() << "   NORMALIZED TO: " << *ISE << '\n');
136    }
137  }
138  return true;
139}
140
141IVStrideUse &IVUsers::AddUser(Instruction *User, Value *Operand) {
142  IVUses.push_back(new IVStrideUse(this, User, Operand));
143  return IVUses.back();
144}
145
146IVUsers::IVUsers()
147 : LoopPass(ID) {
148}
149
150void IVUsers::getAnalysisUsage(AnalysisUsage &AU) const {
151  AU.addRequired<LoopInfo>();
152  AU.addRequired<DominatorTree>();
153  AU.addRequired<ScalarEvolution>();
154  AU.setPreservesAll();
155}
156
157bool IVUsers::runOnLoop(Loop *l, LPPassManager &LPM) {
158
159  L = l;
160  LI = &getAnalysis<LoopInfo>();
161  DT = &getAnalysis<DominatorTree>();
162  SE = &getAnalysis<ScalarEvolution>();
163
164  // Find all uses of induction variables in this loop, and categorize
165  // them by stride.  Start by finding all of the PHI nodes in the header for
166  // this loop.  If they are induction variables, inspect their uses.
167  for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ++I)
168    (void)AddUsersIfInteresting(I);
169
170  return false;
171}
172
173void IVUsers::print(raw_ostream &OS, const Module *M) const {
174  OS << "IV Users for loop ";
175  WriteAsOperand(OS, L->getHeader(), false);
176  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
177    OS << " with backedge-taken count "
178       << *SE->getBackedgeTakenCount(L);
179  }
180  OS << ":\n";
181
182  // Use a default AssemblyAnnotationWriter to suppress the default info
183  // comments, which aren't relevant here.
184  AssemblyAnnotationWriter Annotator;
185  for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
186       E = IVUses.end(); UI != E; ++UI) {
187    OS << "  ";
188    WriteAsOperand(OS, UI->getOperandValToReplace(), false);
189    OS << " = " << *getReplacementExpr(*UI);
190    for (PostIncLoopSet::const_iterator
191         I = UI->PostIncLoops.begin(),
192         E = UI->PostIncLoops.end(); I != E; ++I) {
193      OS << " (post-inc with loop ";
194      WriteAsOperand(OS, (*I)->getHeader(), false);
195      OS << ")";
196    }
197    OS << " in  ";
198    UI->getUser()->print(OS, &Annotator);
199    OS << '\n';
200  }
201}
202
203void IVUsers::dump() const {
204  print(dbgs());
205}
206
207void IVUsers::releaseMemory() {
208  Processed.clear();
209  IVUses.clear();
210}
211
212/// getReplacementExpr - Return a SCEV expression which computes the
213/// value of the OperandValToReplace.
214const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &IU) const {
215  return SE->getSCEV(IU.getOperandValToReplace());
216}
217
218/// getExpr - Return the expression for the use.
219const SCEV *IVUsers::getExpr(const IVStrideUse &IU) const {
220  return
221    TransformForPostIncUse(Normalize, getReplacementExpr(IU),
222                           IU.getUser(), IU.getOperandValToReplace(),
223                           const_cast<PostIncLoopSet &>(IU.getPostIncLoops()),
224                           *SE, *DT);
225}
226
227static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
228  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
229    if (AR->getLoop() == L)
230      return AR;
231    return findAddRecForLoop(AR->getStart(), L);
232  }
233
234  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
235    for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
236         I != E; ++I)
237      if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
238        return AR;
239    return 0;
240  }
241
242  return 0;
243}
244
245const SCEV *IVUsers::getStride(const IVStrideUse &IU, const Loop *L) const {
246  if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(IU), L))
247    return AR->getStepRecurrence(*SE);
248  return 0;
249}
250
251void IVStrideUse::transformToPostInc(const Loop *L) {
252  PostIncLoops.insert(L);
253}
254
255void IVStrideUse::deleted() {
256  // Remove this user from the list.
257  Parent->IVUses.erase(this);
258  // this now dangles!
259}
260