ScalarEvolutionExpander.h revision 725f1d12801109a3b1d081a6e1c9e44426b2cf34 
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 ScalarTargetTransformInfo;
26
27  /// Return true if the given expression is safe to expand in the sense that
28  /// all materialized values are safe to speculate.
29  bool isSafeToExpand(const SCEV *S);
30
31  /// SCEVExpander - This class uses information about analyze scalars to
32  /// rewrite expressions in canonical form.
33  ///
34  /// Clients should create an instance of this class when rewriting is needed,
35  /// and destroy it when finished to allow the release of the associated
36  /// memory.
37  class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
38    ScalarEvolution &SE;
39
40    // New instructions receive a name to identifies them with the current pass.
41    const char* IVName;
42
43    std::map<std::pair<const SCEV *, Instruction *>, AssertingVH<Value> >
44      InsertedExpressions;
45    std::set<AssertingVH<Value> > InsertedValues;
46    std::set<AssertingVH<Value> > InsertedPostIncValues;
47
48    /// RelevantLoops - A memoization of the "relevant" loop for a given SCEV.
49    DenseMap<const SCEV *, const Loop *> RelevantLoops;
50
51    /// PostIncLoops - Addrecs referring to any of the given loops are expanded
52    /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
53    /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
54    /// as opposed to a new phi starting at 1. This is only supported in
55    /// non-canonical mode.
56    PostIncLoopSet PostIncLoops;
57
58    /// IVIncInsertPos - When this is non-null, addrecs expanded in the
59    /// loop it indicates should be inserted with increments at
60    /// IVIncInsertPos.
61    const Loop *IVIncInsertLoop;
62
63    /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
64    /// insert the IV increment at this position.
65    Instruction *IVIncInsertPos;
66
67    /// Phis that complete an IV chain. Reuse
68    std::set<AssertingVH<PHINode> > ChainedPhis;
69
70    /// CanonicalMode - When true, expressions are expanded in "canonical"
71    /// form. In particular, addrecs are expanded as arithmetic based on
72    /// a canonical induction variable. When false, expression are expanded
73    /// in a more literal form.
74    bool CanonicalMode;
75
76    /// When invoked from LSR, the expander is in "strength reduction" mode. The
77    /// only difference is that phi's are only reused if they are already in
78    /// "expanded" form.
79    bool LSRMode;
80
81    typedef IRBuilder<true, TargetFolder> BuilderType;
82    BuilderType Builder;
83
84#ifndef NDEBUG
85    const char *DebugType;
86#endif
87
88    friend struct SCEVVisitor<SCEVExpander, Value*>;
89
90  public:
91    /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
92    explicit SCEVExpander(ScalarEvolution &se, const char *name)
93      : SE(se), IVName(name), IVIncInsertLoop(0), IVIncInsertPos(0),
94        CanonicalMode(true), LSRMode(false),
95        Builder(se.getContext(), TargetFolder(se.TD)) {
96#ifndef NDEBUG
97      DebugType = "";
98#endif
99    }
100
101#ifndef NDEBUG
102    void setDebugType(const char* s) { DebugType = s; }
103#endif
104
105    /// clear - Erase the contents of the InsertedExpressions map so that users
106    /// trying to expand the same expression into multiple BasicBlocks or
107    /// different places within the same BasicBlock can do so.
108    void clear() {
109      InsertedExpressions.clear();
110      InsertedValues.clear();
111      InsertedPostIncValues.clear();
112      ChainedPhis.clear();
113    }
114
115    /// getOrInsertCanonicalInductionVariable - This method returns the
116    /// canonical induction variable of the specified type for the specified
117    /// loop (inserting one if there is none).  A canonical induction variable
118    /// starts at zero and steps by one on each iteration.
119    PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
120
121    /// getIVIncOperand - Return the induction variable increment's IV operand.
122    Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
123                                 bool allowScale);
124
125    /// hoistIVInc - Utility for hoisting an IV increment.
126    bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
127
128    /// replaceCongruentIVs - replace congruent phis with their most canonical
129    /// representative. Return the number of phis eliminated.
130    unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
131                                 SmallVectorImpl<WeakVH> &DeadInsts,
132                                 const ScalarTargetTransformInfo *STTI = NULL);
133
134    /// expandCodeFor - Insert code to directly compute the specified SCEV
135    /// expression into the program.  The inserted code is inserted into the
136    /// specified block.
137    Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
138
139    /// setIVIncInsertPos - Set the current IV increment loop and position.
140    void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
141      assert(!CanonicalMode &&
142             "IV increment positions are not supported in CanonicalMode");
143      IVIncInsertLoop = L;
144      IVIncInsertPos = Pos;
145    }
146
147    /// setPostInc - Enable post-inc expansion for addrecs referring to the
148    /// given loops. Post-inc expansion is only supported in non-canonical
149    /// mode.
150    void setPostInc(const PostIncLoopSet &L) {
151      assert(!CanonicalMode &&
152             "Post-inc expansion is not supported in CanonicalMode");
153      PostIncLoops = L;
154    }
155
156    /// clearPostInc - Disable all post-inc expansion.
157    void clearPostInc() {
158      PostIncLoops.clear();
159
160      // When we change the post-inc loop set, cached expansions may no
161      // longer be valid.
162      InsertedPostIncValues.clear();
163    }
164
165    /// disableCanonicalMode - Disable the behavior of expanding expressions in
166    /// canonical form rather than in a more literal form. Non-canonical mode
167    /// is useful for late optimization passes.
168    void disableCanonicalMode() { CanonicalMode = false; }
169
170    void enableLSRMode() { LSRMode = true; }
171
172    /// clearInsertPoint - Clear the current insertion point. This is useful
173    /// if the instruction that had been serving as the insertion point may
174    /// have been deleted.
175    void clearInsertPoint() {
176      Builder.ClearInsertionPoint();
177    }
178
179    /// isInsertedInstruction - Return true if the specified instruction was
180    /// inserted by the code rewriter.  If so, the client should not modify the
181    /// instruction.
182    bool isInsertedInstruction(Instruction *I) const {
183      return InsertedValues.count(I) || InsertedPostIncValues.count(I);
184    }
185
186    void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
187
188  private:
189    LLVMContext &getContext() const { return SE.getContext(); }
190
191    /// InsertBinop - Insert the specified binary operator, doing a small amount
192    /// of work to avoid inserting an obviously redundant operation.
193    Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
194
195    /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
196    /// reusing an existing cast if a suitable one exists, moving an existing
197    /// cast if a suitable one exists but isn't in the right place, or
198    /// or creating a new one.
199    Value *ReuseOrCreateCast(Value *V, Type *Ty,
200                             Instruction::CastOps Op,
201                             BasicBlock::iterator IP);
202
203    /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
204    /// which must be possible with a noop cast, doing what we can to
205    /// share the casts.
206    Value *InsertNoopCastOfTo(Value *V, Type *Ty);
207
208    /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
209    /// instead of using ptrtoint+arithmetic+inttoptr.
210    Value *expandAddToGEP(const SCEV *const *op_begin,
211                          const SCEV *const *op_end,
212                          PointerType *PTy, Type *Ty, Value *V);
213
214    Value *expand(const SCEV *S);
215
216    /// expandCodeFor - Insert code to directly compute the specified SCEV
217    /// expression into the program.  The inserted code is inserted into the
218    /// SCEVExpander's current insertion point. If a type is specified, the
219    /// result will be expanded to have that type, with a cast if necessary.
220    Value *expandCodeFor(const SCEV *SH, Type *Ty = 0);
221
222    /// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
223    const Loop *getRelevantLoop(const SCEV *);
224
225    Value *visitConstant(const SCEVConstant *S) {
226      return S->getValue();
227    }
228
229    Value *visitTruncateExpr(const SCEVTruncateExpr *S);
230
231    Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
232
233    Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
234
235    Value *visitAddExpr(const SCEVAddExpr *S);
236
237    Value *visitMulExpr(const SCEVMulExpr *S);
238
239    Value *visitUDivExpr(const SCEVUDivExpr *S);
240
241    Value *visitAddRecExpr(const SCEVAddRecExpr *S);
242
243    Value *visitSMaxExpr(const SCEVSMaxExpr *S);
244
245    Value *visitUMaxExpr(const SCEVUMaxExpr *S);
246
247    Value *visitUnknown(const SCEVUnknown *S) {
248      return S->getValue();
249    }
250
251    void rememberInstruction(Value *I);
252
253    void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
254
255    bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
256
257    bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
258
259    Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
260    PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
261                                       const Loop *L,
262                                       Type *ExpandTy,
263                                       Type *IntTy);
264    Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
265                       Type *ExpandTy, Type *IntTy, bool useSubtract);
266  };
267}
268
269#endif
270