ScalarEvolutionExpander.h revision 06cb8ed00696eb14d1b831921452e50ec0568ea2 
1//===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- 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 defines the classes used to generate code from scalar expressions.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ANALYSIS_SCALAREVOLUTION_EXPANDER_H
15#define LLVM_ANALYSIS_SCALAREVOLUTION_EXPANDER_H
16
17#include "llvm/IRBuilder.h"
18#include "llvm/Analysis/ScalarEvolutionExpressions.h"
19#include "llvm/Analysis/ScalarEvolutionNormalization.h"
20#include "llvm/Support/TargetFolder.h"
21#include "llvm/Support/ValueHandle.h"
22#include <set>
23
24namespace llvm {
25  class TargetLowering;
26
27  /// SCEVExpander - This class uses information about analyze scalars to
28  /// rewrite expressions in canonical form.
29  ///
30  /// Clients should create an instance of this class when rewriting is needed,
31  /// and destroy it when finished to allow the release of the associated
32  /// memory.
33  class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
34    ScalarEvolution &SE;
35
36    // New instructions receive a name to identifies them with the current pass.
37    const char* IVName;
38
39    std::map<std::pair<const SCEV *, Instruction *>, AssertingVH<Value> >
40      InsertedExpressions;
41    std::set<AssertingVH<Value> > InsertedValues;
42    std::set<AssertingVH<Value> > InsertedPostIncValues;
43
44    /// RelevantLoops - A memoization of the "relevant" loop for a given SCEV.
45    DenseMap<const SCEV *, const Loop *> RelevantLoops;
46
47    /// PostIncLoops - Addrecs referring to any of the given loops are expanded
48    /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
49    /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
50    /// as opposed to a new phi starting at 1. This is only supported in
51    /// non-canonical mode.
52    PostIncLoopSet PostIncLoops;
53
54    /// IVIncInsertPos - When this is non-null, addrecs expanded in the
55    /// loop it indicates should be inserted with increments at
56    /// IVIncInsertPos.
57    const Loop *IVIncInsertLoop;
58
59    /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
60    /// insert the IV increment at this position.
61    Instruction *IVIncInsertPos;
62
63    /// Phis that complete an IV chain. Reuse
64    std::set<AssertingVH<PHINode> > ChainedPhis;
65
66    /// CanonicalMode - When true, expressions are expanded in "canonical"
67    /// form. In particular, addrecs are expanded as arithmetic based on
68    /// a canonical induction variable. When false, expression are expanded
69    /// in a more literal form.
70    bool CanonicalMode;
71
72    /// When invoked from LSR, the expander is in "strength reduction" mode. The
73    /// only difference is that phi's are only reused if they are already in
74    /// "expanded" form.
75    bool LSRMode;
76
77    typedef IRBuilder<true, TargetFolder> BuilderType;
78    BuilderType Builder;
79
80#ifndef NDEBUG
81    const char *DebugType;
82#endif
83
84    friend struct SCEVVisitor<SCEVExpander, Value*>;
85
86  public:
87    /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
88    explicit SCEVExpander(ScalarEvolution &se, const char *name)
89      : SE(se), IVName(name), IVIncInsertLoop(0), IVIncInsertPos(0),
90        CanonicalMode(true), LSRMode(false),
91        Builder(se.getContext(), TargetFolder(se.TD)) {
92#ifndef NDEBUG
93      DebugType = "";
94#endif
95    }
96
97#ifndef NDEBUG
98    void setDebugType(const char* s) { DebugType = s; }
99#endif
100
101    /// clear - Erase the contents of the InsertedExpressions map so that users
102    /// trying to expand the same expression into multiple BasicBlocks or
103    /// different places within the same BasicBlock can do so.
104    void clear() {
105      InsertedExpressions.clear();
106      InsertedValues.clear();
107      InsertedPostIncValues.clear();
108      ChainedPhis.clear();
109    }
110
111    /// getOrInsertCanonicalInductionVariable - This method returns the
112    /// canonical induction variable of the specified type for the specified
113    /// loop (inserting one if there is none).  A canonical induction variable
114    /// starts at zero and steps by one on each iteration.
115    PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
116
117    /// getIVIncOperand - Return the induction variable increment's IV operand.
118    Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
119                                 bool allowScale);
120
121    /// hoistIVInc - Utility for hoisting an IV increment.
122    bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
123
124    /// replaceCongruentIVs - replace congruent phis with their most canonical
125    /// representative. Return the number of phis eliminated.
126    unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
127                                 SmallVectorImpl<WeakVH> &DeadInsts,
128                                 const TargetLowering *TLI = NULL);
129
130    /// expandCodeFor - Insert code to directly compute the specified SCEV
131    /// expression into the program.  The inserted code is inserted into the
132    /// specified block.
133    Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
134
135    /// setIVIncInsertPos - Set the current IV increment loop and position.
136    void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
137      assert(!CanonicalMode &&
138             "IV increment positions are not supported in CanonicalMode");
139      IVIncInsertLoop = L;
140      IVIncInsertPos = Pos;
141    }
142
143    /// setPostInc - Enable post-inc expansion for addrecs referring to the
144    /// given loops. Post-inc expansion is only supported in non-canonical
145    /// mode.
146    void setPostInc(const PostIncLoopSet &L) {
147      assert(!CanonicalMode &&
148             "Post-inc expansion is not supported in CanonicalMode");
149      PostIncLoops = L;
150    }
151
152    /// clearPostInc - Disable all post-inc expansion.
153    void clearPostInc() {
154      PostIncLoops.clear();
155
156      // When we change the post-inc loop set, cached expansions may no
157      // longer be valid.
158      InsertedPostIncValues.clear();
159    }
160
161    /// disableCanonicalMode - Disable the behavior of expanding expressions in
162    /// canonical form rather than in a more literal form. Non-canonical mode
163    /// is useful for late optimization passes.
164    void disableCanonicalMode() { CanonicalMode = false; }
165
166    void enableLSRMode() { LSRMode = true; }
167
168    /// clearInsertPoint - Clear the current insertion point. This is useful
169    /// if the instruction that had been serving as the insertion point may
170    /// have been deleted.
171    void clearInsertPoint() {
172      Builder.ClearInsertionPoint();
173    }
174
175    /// isInsertedInstruction - Return true if the specified instruction was
176    /// inserted by the code rewriter.  If so, the client should not modify the
177    /// instruction.
178    bool isInsertedInstruction(Instruction *I) const {
179      return InsertedValues.count(I) || InsertedPostIncValues.count(I);
180    }
181
182    void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
183
184  private:
185    LLVMContext &getContext() const { return SE.getContext(); }
186
187    /// InsertBinop - Insert the specified binary operator, doing a small amount
188    /// of work to avoid inserting an obviously redundant operation.
189    Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
190
191    /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
192    /// reusing an existing cast if a suitable one exists, moving an existing
193    /// cast if a suitable one exists but isn't in the right place, or
194    /// or creating a new one.
195    Value *ReuseOrCreateCast(Value *V, Type *Ty,
196                             Instruction::CastOps Op,
197                             BasicBlock::iterator IP);
198
199    /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
200    /// which must be possible with a noop cast, doing what we can to
201    /// share the casts.
202    Value *InsertNoopCastOfTo(Value *V, Type *Ty);
203
204    /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
205    /// instead of using ptrtoint+arithmetic+inttoptr.
206    Value *expandAddToGEP(const SCEV *const *op_begin,
207                          const SCEV *const *op_end,
208                          PointerType *PTy, Type *Ty, Value *V);
209
210    Value *expand(const SCEV *S);
211
212    /// expandCodeFor - Insert code to directly compute the specified SCEV
213    /// expression into the program.  The inserted code is inserted into the
214    /// SCEVExpander's current insertion point. If a type is specified, the
215    /// result will be expanded to have that type, with a cast if necessary.
216    Value *expandCodeFor(const SCEV *SH, Type *Ty = 0);
217
218    /// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
219    const Loop *getRelevantLoop(const SCEV *);
220
221    Value *visitConstant(const SCEVConstant *S) {
222      return S->getValue();
223    }
224
225    Value *visitTruncateExpr(const SCEVTruncateExpr *S);
226
227    Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
228
229    Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
230
231    Value *visitAddExpr(const SCEVAddExpr *S);
232
233    Value *visitMulExpr(const SCEVMulExpr *S);
234
235    Value *visitUDivExpr(const SCEVUDivExpr *S);
236
237    Value *visitAddRecExpr(const SCEVAddRecExpr *S);
238
239    Value *visitSMaxExpr(const SCEVSMaxExpr *S);
240
241    Value *visitUMaxExpr(const SCEVUMaxExpr *S);
242
243    Value *visitUnknown(const SCEVUnknown *S) {
244      return S->getValue();
245    }
246
247    void rememberInstruction(Value *I);
248
249    void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
250
251    bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
252
253    bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
254
255    Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
256    PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
257                                       const Loop *L,
258                                       Type *ExpandTy,
259                                       Type *IntTy);
260    Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
261                       Type *ExpandTy, Type *IntTy, bool useSubtract);
262  };
263}
264
265#endif
266