IVUsers.cpp revision 86eeeaf87747912a6c2404c383a416b07233c748 
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;
32static RegisterPass<IVUsers>
33X("iv-users", "Induction Variable Users", false, true);
34
35Pass *llvm::createIVUsersPass() {
36  return new IVUsers();
37}
38
39/// isInteresting - Test whether the given expression is "interesting" when
40/// used by the given expression, within the context of analyzing the
41/// given loop.
42static 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))
45    return true;
46
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);
54  }
55
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();
59         OI != OE; ++OI)
60      if (isInteresting(*OI, I, L))
61        return true;
62    return false;
63  }
64
65  // Nothing else is interesting here.
66  return false;
67}
68
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.
72bool IVUsers::AddUsersIfInteresting(Instruction *I) {
73  if (!SE->isSCEVable(I->getType()))
74    return false;   // Void and FP expressions cannot be reduced.
75
76  // LSR is not APInt clean, do not touch integers bigger than 64-bits.
77  if (SE->getTypeSizeInBits(I->getType()) > 64)
78    return false;
79
80  if (!Processed.insert(I))
81    return true;    // Instruction already handled.
82
83  // Get the symbolic expression for this instruction.
84  const SCEV *ISE = SE->getSCEV(I);
85  if (isa<SCEVCouldNotCompute>(ISE)) return false;
86
87  // If we've come to an uninteresting expression, stop the traversal and
88  // call this a user.
89  if (!isInteresting(ISE, I, L))
90    return false;
91
92  SmallPtrSet<Instruction *, 4> UniqueUsers;
93  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
94       UI != E; ++UI) {
95    Instruction *User = cast<Instruction>(*UI);
96    if (!UniqueUsers.insert(User))
97      continue;
98
99    // Do not infinitely recurse on PHI nodes.
100    if (isa<PHINode>(User) && Processed.count(User))
101      continue;
102
103    // Descend recursively, but not into PHI nodes outside the current loop.
104    // It's important to see the entire expression outside the loop to get
105    // choices that depend on addressing mode use right, although we won't
106    // consider references outside the loop in all cases.
107    // If User is already in Processed, we don't want to recurse into it again,
108    // but do want to record a second reference in the same instruction.
109    bool AddUserToIVUsers = false;
110    if (LI->getLoopFor(User->getParent()) != L) {
111      if (isa<PHINode>(User) || Processed.count(User) ||
112          !AddUsersIfInteresting(User)) {
113        DEBUG(dbgs() << "FOUND USER in other loop: " << *User << '\n'
114                     << "   OF SCEV: " << *ISE << '\n');
115        AddUserToIVUsers = true;
116      }
117    } else if (Processed.count(User) ||
118               !AddUsersIfInteresting(User)) {
119      DEBUG(dbgs() << "FOUND USER: " << *User << '\n'
120                   << "   OF SCEV: " << *ISE << '\n');
121      AddUserToIVUsers = true;
122    }
123
124    if (AddUserToIVUsers) {
125      // Okay, we found a user that we cannot reduce.
126      IVUses.push_back(new IVStrideUse(this, ISE, User, I));
127      IVStrideUse &NewUse = IVUses.back();
128      // Transform the expression into a normalized form.
129      NewUse.Expr =
130        TransformForPostIncUse(NormalizeAutodetect, NewUse.Expr,
131                               User, I,
132                               NewUse.PostIncLoops,
133                               *SE, *DT);
134      DEBUG(dbgs() << "   NORMALIZED TO: " << *NewUse.Expr << '\n');
135    }
136  }
137  return true;
138}
139
140IVStrideUse &IVUsers::AddUser(const SCEV *Expr,
141                              Instruction *User, Value *Operand) {
142  IVUses.push_back(new IVStrideUse(this, Expr, 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    AddUsersIfInteresting(I);
169
170  return false;
171}
172
173/// getReplacementExpr - Return a SCEV expression which computes the
174/// value of the OperandValToReplace of the given IVStrideUse.
175const SCEV *IVUsers::getReplacementExpr(const IVStrideUse &U) const {
176  PostIncLoopSet &Loops = const_cast<PostIncLoopSet &>(U.PostIncLoops);
177  return TransformForPostIncUse(Denormalize, U.getExpr(),
178                                U.getUser(), U.getOperandValToReplace(),
179                                Loops, *SE, *DT);
180}
181
182void IVUsers::print(raw_ostream &OS, const Module *M) const {
183  OS << "IV Users for loop ";
184  WriteAsOperand(OS, L->getHeader(), false);
185  if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
186    OS << " with backedge-taken count "
187       << *SE->getBackedgeTakenCount(L);
188  }
189  OS << ":\n";
190
191  // Use a default AssemblyAnnotationWriter to suppress the default info
192  // comments, which aren't relevant here.
193  AssemblyAnnotationWriter Annotator;
194  for (ilist<IVStrideUse>::const_iterator UI = IVUses.begin(),
195       E = IVUses.end(); UI != E; ++UI) {
196    OS << "  ";
197    WriteAsOperand(OS, UI->getOperandValToReplace(), false);
198    OS << " = "
199       << *getReplacementExpr(*UI);
200    for (PostIncLoopSet::const_iterator
201         I = UI->PostIncLoops.begin(),
202         E = UI->PostIncLoops.end(); I != E; ++I) {
203      OS << " (post-inc with loop ";
204      WriteAsOperand(OS, (*I)->getHeader(), false);
205      OS << ")";
206    }
207    OS << " in  ";
208    UI->getUser()->print(OS, &Annotator);
209    OS << '\n';
210  }
211}
212
213void IVUsers::dump() const {
214  print(dbgs());
215}
216
217void IVUsers::releaseMemory() {
218  Processed.clear();
219  IVUses.clear();
220}
221
222static const SCEVAddRecExpr *findAddRecForLoop(const SCEV *S, const Loop *L) {
223  if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
224    if (AR->getLoop() == L)
225      return AR;
226    return findAddRecForLoop(AR->getStart(), L);
227  }
228
229  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
230    for (SCEVAddExpr::op_iterator I = Add->op_begin(), E = Add->op_end();
231         I != E; ++I)
232      if (const SCEVAddRecExpr *AR = findAddRecForLoop(*I, L))
233        return AR;
234    return 0;
235  }
236
237  return 0;
238}
239
240const SCEV *IVStrideUse::getStride(const Loop *L) const {
241  if (const SCEVAddRecExpr *AR = findAddRecForLoop(getExpr(), L))
242    return AR->getStepRecurrence(*Parent->SE);
243  return 0;
244}
245
246void IVStrideUse::transformToPostInc(const Loop *L) {
247  PostIncLoopSet Loops;
248  Loops.insert(L);
249  Expr = TransformForPostIncUse(Normalize, Expr,
250                                getUser(), getOperandValToReplace(),
251                                Loops, *Parent->SE, *Parent->DT);
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