ScalarEvolutionExpander.h revision 365c9f1ff55bef134c6b9707f7df44d680ddabea 
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/Analysis/ScalarEvolutionExpressions.h"
18#include "llvm/Analysis/ScalarEvolutionNormalization.h"
19#include "llvm/Support/IRBuilder.h"
20#include "llvm/Support/TargetFolder.h"
21#include "llvm/Support/ValueHandle.h"
22#include <set>
23
24namespace llvm {
25  /// SCEVExpander - This class uses information about analyze scalars to
26  /// rewrite expressions in canonical form.
27  ///
28  /// Clients should create an instance of this class when rewriting is needed,
29  /// and destroy it when finished to allow the release of the associated
30  /// memory.
31  class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
32    ScalarEvolution &SE;
33
34    // New instructions receive a name to identifies them with the current pass.
35    const char* IVName;
36
37    std::map<std::pair<const SCEV *, Instruction *>, AssertingVH<Value> >
38      InsertedExpressions;
39    std::set<AssertingVH<Value> > InsertedValues;
40    std::set<AssertingVH<Value> > InsertedPostIncValues;
41
42    /// RelevantLoops - A memoization of the "relevant" loop for a given SCEV.
43    DenseMap<const SCEV *, const Loop *> RelevantLoops;
44
45    /// PostIncLoops - Addrecs referring to any of the given loops are expanded
46    /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
47    /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
48    /// as opposed to a new phi starting at 1. This is only supported in
49    /// non-canonical mode.
50    PostIncLoopSet PostIncLoops;
51
52    /// IVIncInsertPos - When this is non-null, addrecs expanded in the
53    /// loop it indicates should be inserted with increments at
54    /// IVIncInsertPos.
55    const Loop *IVIncInsertLoop;
56
57    /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
58    /// insert the IV increment at this position.
59    Instruction *IVIncInsertPos;
60
61    /// CanonicalMode - When true, expressions are expanded in "canonical"
62    /// form. In particular, addrecs are expanded as arithmetic based on
63    /// a canonical induction variable. When false, expression are expanded
64    /// in a more literal form.
65    bool CanonicalMode;
66
67    /// When invoked from LSR, the expander is in "strength reduction" mode. The
68    /// only difference is that phi's are only reused if they are already in
69    /// "expanded" form.
70    bool LSRMode;
71
72    typedef IRBuilder<true, TargetFolder> BuilderType;
73    BuilderType Builder;
74
75#ifndef NDEBUG
76    const char *DebugType;
77#endif
78
79    friend struct SCEVVisitor<SCEVExpander, Value*>;
80
81  public:
82    /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
83    explicit SCEVExpander(ScalarEvolution &se, const char *name)
84      : SE(se), IVName(name), IVIncInsertLoop(0), IVIncInsertPos(0),
85        CanonicalMode(true), LSRMode(false),
86        Builder(se.getContext(), TargetFolder(se.TD)) {
87#ifndef NDEBUG
88      DebugType = "";
89#endif
90    }
91
92#ifndef NDEBUG
93    void setDebugType(const char* s) { DebugType = s; }
94#endif
95
96    /// clear - Erase the contents of the InsertedExpressions map so that users
97    /// trying to expand the same expression into multiple BasicBlocks or
98    /// different places within the same BasicBlock can do so.
99    void clear() {
100      InsertedExpressions.clear();
101      InsertedValues.clear();
102      InsertedPostIncValues.clear();
103    }
104
105    /// getOrInsertCanonicalInductionVariable - This method returns the
106    /// canonical induction variable of the specified type for the specified
107    /// loop (inserting one if there is none).  A canonical induction variable
108    /// starts at zero and steps by one on each iteration.
109    PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
110
111    /// hoistStep - Utility for hoisting an IV increment.
112    static bool hoistStep(Instruction *IncV, Instruction *InsertPos,
113                          const DominatorTree *DT);
114
115    /// replaceCongruentIVs - replace congruent phis with their most canonical
116    /// representative. Return the number of phis eliminated.
117    unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
118                                 SmallVectorImpl<WeakVH> &DeadInsts);
119
120    /// expandCodeFor - Insert code to directly compute the specified SCEV
121    /// expression into the program.  The inserted code is inserted into the
122    /// specified block.
123    Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
124
125    /// setIVIncInsertPos - Set the current IV increment loop and position.
126    void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
127      assert(!CanonicalMode &&
128             "IV increment positions are not supported in CanonicalMode");
129      IVIncInsertLoop = L;
130      IVIncInsertPos = Pos;
131    }
132
133    /// setPostInc - Enable post-inc expansion for addrecs referring to the
134    /// given loops. Post-inc expansion is only supported in non-canonical
135    /// mode.
136    void setPostInc(const PostIncLoopSet &L) {
137      assert(!CanonicalMode &&
138             "Post-inc expansion is not supported in CanonicalMode");
139      PostIncLoops = L;
140    }
141
142    /// clearPostInc - Disable all post-inc expansion.
143    void clearPostInc() {
144      PostIncLoops.clear();
145
146      // When we change the post-inc loop set, cached expansions may no
147      // longer be valid.
148      InsertedPostIncValues.clear();
149    }
150
151    /// disableCanonicalMode - Disable the behavior of expanding expressions in
152    /// canonical form rather than in a more literal form. Non-canonical mode
153    /// is useful for late optimization passes.
154    void disableCanonicalMode() { CanonicalMode = false; }
155
156    void enableLSRMode() { LSRMode = true; }
157
158    /// clearInsertPoint - Clear the current insertion point. This is useful
159    /// if the instruction that had been serving as the insertion point may
160    /// have been deleted.
161    void clearInsertPoint() {
162      Builder.ClearInsertionPoint();
163    }
164  private:
165    LLVMContext &getContext() const { return SE.getContext(); }
166
167    /// InsertBinop - Insert the specified binary operator, doing a small amount
168    /// of work to avoid inserting an obviously redundant operation.
169    Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
170
171    /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
172    /// reusing an existing cast if a suitable one exists, moving an existing
173    /// cast if a suitable one exists but isn't in the right place, or
174    /// or creating a new one.
175    Value *ReuseOrCreateCast(Value *V, Type *Ty,
176                             Instruction::CastOps Op,
177                             BasicBlock::iterator IP);
178
179    /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
180    /// which must be possible with a noop cast, doing what we can to
181    /// share the casts.
182    Value *InsertNoopCastOfTo(Value *V, Type *Ty);
183
184    /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
185    /// instead of using ptrtoint+arithmetic+inttoptr.
186    Value *expandAddToGEP(const SCEV *const *op_begin,
187                          const SCEV *const *op_end,
188                          PointerType *PTy, Type *Ty, Value *V);
189
190    Value *expand(const SCEV *S);
191
192    /// expandCodeFor - Insert code to directly compute the specified SCEV
193    /// expression into the program.  The inserted code is inserted into the
194    /// SCEVExpander's current insertion point. If a type is specified, the
195    /// result will be expanded to have that type, with a cast if necessary.
196    Value *expandCodeFor(const SCEV *SH, Type *Ty = 0);
197
198    /// isInsertedInstruction - Return true if the specified instruction was
199    /// inserted by the code rewriter.  If so, the client should not modify the
200    /// instruction.
201    bool isInsertedInstruction(Instruction *I) const {
202      return InsertedValues.count(I) || InsertedPostIncValues.count(I);
203    }
204
205    /// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
206    const Loop *getRelevantLoop(const SCEV *);
207
208    Value *visitConstant(const SCEVConstant *S) {
209      return S->getValue();
210    }
211
212    Value *visitTruncateExpr(const SCEVTruncateExpr *S);
213
214    Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
215
216    Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
217
218    Value *visitAddExpr(const SCEVAddExpr *S);
219
220    Value *visitMulExpr(const SCEVMulExpr *S);
221
222    Value *visitUDivExpr(const SCEVUDivExpr *S);
223
224    Value *visitAddRecExpr(const SCEVAddRecExpr *S);
225
226    Value *visitSMaxExpr(const SCEVSMaxExpr *S);
227
228    Value *visitUMaxExpr(const SCEVUMaxExpr *S);
229
230    Value *visitUnknown(const SCEVUnknown *S) {
231      return S->getValue();
232    }
233
234    void rememberInstruction(Value *I);
235
236    void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
237
238    bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
239
240    bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
241
242    Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
243    PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
244                                       const Loop *L,
245                                       Type *ExpandTy,
246                                       Type *IntTy);
247  };
248}
249
250#endif
251