ScalarEvolutionExpander.h revision 485c43fc478d5e16c55e14cb2586b56cc1c4c91f 
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 <set>
22
23namespace llvm {
24  /// SCEVExpander - This class uses information about analyze scalars to
25  /// rewrite expressions in canonical form.
26  ///
27  /// Clients should create an instance of this class when rewriting is needed,
28  /// and destroy it when finished to allow the release of the associated
29  /// memory.
30  class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
31    ScalarEvolution &SE;
32    std::map<std::pair<const SCEV *, Instruction *>, AssertingVH<Value> >
33      InsertedExpressions;
34    std::set<Value*> InsertedValues;
35    std::set<Value*> InsertedPostIncValues;
36
37    /// PostIncLoops - Addrecs referring to any of the given loops are expanded
38    /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
39    /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
40    /// as opposed to a new phi starting at 1. This is only supported in
41    /// non-canonical mode.
42    PostIncLoopSet PostIncLoops;
43
44    /// IVIncInsertPos - When this is non-null, addrecs expanded in the
45    /// loop it indicates should be inserted with increments at
46    /// IVIncInsertPos.
47    const Loop *IVIncInsertLoop;
48
49    /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
50    /// insert the IV increment at this position.
51    Instruction *IVIncInsertPos;
52
53    /// CanonicalMode - When true, expressions are expanded in "canonical"
54    /// form. In particular, addrecs are expanded as arithmetic based on
55    /// a canonical induction variable. When false, expression are expanded
56    /// in a more literal form.
57    bool CanonicalMode;
58
59    typedef IRBuilder<true, TargetFolder> BuilderType;
60    BuilderType Builder;
61
62    friend struct SCEVVisitor<SCEVExpander, Value*>;
63
64  public:
65    /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
66    explicit SCEVExpander(ScalarEvolution &se)
67      : SE(se), IVIncInsertLoop(0), CanonicalMode(true),
68        Builder(se.getContext(), TargetFolder(se.TD)) {}
69
70    /// clear - Erase the contents of the InsertedExpressions map so that users
71    /// trying to expand the same expression into multiple BasicBlocks or
72    /// different places within the same BasicBlock can do so.
73    void clear() { InsertedExpressions.clear(); }
74
75    /// getOrInsertCanonicalInductionVariable - This method returns the
76    /// canonical induction variable of the specified type for the specified
77    /// loop (inserting one if there is none).  A canonical induction variable
78    /// starts at zero and steps by one on each iteration.
79    Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty);
80
81    /// expandCodeFor - Insert code to directly compute the specified SCEV
82    /// expression into the program.  The inserted code is inserted into the
83    /// specified block.
84    Value *expandCodeFor(const SCEV *SH, const Type *Ty, Instruction *I);
85
86    /// setIVIncInsertPos - Set the current IV increment loop and position.
87    void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
88      assert(!CanonicalMode &&
89             "IV increment positions are not supported in CanonicalMode");
90      IVIncInsertLoop = L;
91      IVIncInsertPos = Pos;
92    }
93
94    /// setPostInc - Enable post-inc expansion for addrecs referring to the
95    /// given loops. Post-inc expansion is only supported in non-canonical
96    /// mode.
97    void setPostInc(const PostIncLoopSet &L) {
98      assert(!CanonicalMode &&
99             "Post-inc expansion is not supported in CanonicalMode");
100      PostIncLoops = L;
101    }
102
103    /// clearPostInc - Disable all post-inc expansion.
104    void clearPostInc() {
105      PostIncLoops.clear();
106
107      // When we change the post-inc loop set, cached expansions may no
108      // longer be valid.
109      InsertedPostIncValues.clear();
110    }
111
112    /// disableCanonicalMode - Disable the behavior of expanding expressions in
113    /// canonical form rather than in a more literal form. Non-canonical mode
114    /// is useful for late optimization passes.
115    void disableCanonicalMode() { CanonicalMode = false; }
116
117    /// clearInsertPoint - Clear the current insertion point. This is useful
118    /// if the instruction that had been serving as the insertion point may
119    /// have been deleted.
120    void clearInsertPoint() {
121      Builder.ClearInsertionPoint();
122    }
123
124  private:
125    LLVMContext &getContext() const { return SE.getContext(); }
126
127    /// InsertBinop - Insert the specified binary operator, doing a small amount
128    /// of work to avoid inserting an obviously redundant operation.
129    Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
130
131    /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
132    /// reusing an existing cast if a suitable one exists, moving an existing
133    /// cast if a suitable one exists but isn't in the right place, or
134    /// or creating a new one.
135    Value *ReuseOrCreateCast(Value *V, const Type *Ty,
136                             Instruction::CastOps Op,
137                             BasicBlock::iterator IP);
138
139    /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
140    /// which must be possible with a noop cast, doing what we can to
141    /// share the casts.
142    Value *InsertNoopCastOfTo(Value *V, const Type *Ty);
143
144    /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
145    /// instead of using ptrtoint+arithmetic+inttoptr.
146    Value *expandAddToGEP(const SCEV *const *op_begin,
147                          const SCEV *const *op_end,
148                          const PointerType *PTy, const Type *Ty, Value *V);
149
150    Value *expand(const SCEV *S);
151
152    /// expandCodeFor - Insert code to directly compute the specified SCEV
153    /// expression into the program.  The inserted code is inserted into the
154    /// SCEVExpander's current insertion point. If a type is specified, the
155    /// result will be expanded to have that type, with a cast if necessary.
156    Value *expandCodeFor(const SCEV *SH, const Type *Ty = 0);
157
158    /// isInsertedInstruction - Return true if the specified instruction was
159    /// inserted by the code rewriter.  If so, the client should not modify the
160    /// instruction.
161    bool isInsertedInstruction(Instruction *I) const {
162      return InsertedValues.count(I) || InsertedPostIncValues.count(I);
163    }
164
165    Value *visitConstant(const SCEVConstant *S) {
166      return S->getValue();
167    }
168
169    Value *visitTruncateExpr(const SCEVTruncateExpr *S);
170
171    Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
172
173    Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
174
175    Value *visitAddExpr(const SCEVAddExpr *S);
176
177    Value *visitMulExpr(const SCEVMulExpr *S);
178
179    Value *visitUDivExpr(const SCEVUDivExpr *S);
180
181    Value *visitAddRecExpr(const SCEVAddRecExpr *S);
182
183    Value *visitSMaxExpr(const SCEVSMaxExpr *S);
184
185    Value *visitUMaxExpr(const SCEVUMaxExpr *S);
186
187    Value *visitUnknown(const SCEVUnknown *S) {
188      return S->getValue();
189    }
190
191    void rememberInstruction(Value *I);
192
193    void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
194
195    Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
196    PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
197                                       const Loop *L,
198                                       const Type *ExpandTy,
199                                       const Type *IntTy);
200  };
201}
202
203#endif
204