1 //===- ConstantFolder.h - Constant folding helper ---------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the ConstantFolder class, a helper for IRBuilder.
10 // It provides IRBuilder with a set of methods for creating constants
11 // with minimal folding.  For general constant creation and folding,
12 // use ConstantExpr and the routines in llvm/Analysis/ConstantFolding.h.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #ifndef LLVM_IR_CONSTANTFOLDER_H
17 #define LLVM_IR_CONSTANTFOLDER_H
18 
19 #include "llvm/ADT/ArrayRef.h"
20 #include "llvm/ADT/STLExtras.h"
21 #include "llvm/IR/Constants.h"
22 #include "llvm/IR/ConstantFold.h"
23 #include "llvm/IR/IRBuilderFolder.h"
24 #include "llvm/IR/Instruction.h"
25 #include "llvm/IR/Operator.h"
26 
27 namespace llvm {
28 
29 /// ConstantFolder - Create constants with minimum, target independent, folding.
30 class ConstantFolder final : public IRBuilderFolder {
31   virtual void anchor();
32 
33 public:
34   explicit ConstantFolder() = default;
35 
36   //===--------------------------------------------------------------------===//
37   // Value-based folders.
38   //
39   // Return an existing value or a constant if the operation can be simplified.
40   // Otherwise return nullptr.
41   //===--------------------------------------------------------------------===//
42 
FoldBinOp(Instruction::BinaryOps Opc,Value * LHS,Value * RHS)43   Value *FoldBinOp(Instruction::BinaryOps Opc, Value *LHS,
44                    Value *RHS) const override {
45     auto *LC = dyn_cast<Constant>(LHS);
46     auto *RC = dyn_cast<Constant>(RHS);
47     if (LC && RC) {
48       if (ConstantExpr::isDesirableBinOp(Opc))
49         return ConstantExpr::get(Opc, LC, RC);
50       return ConstantFoldBinaryInstruction(Opc, LC, RC);
51     }
52     return nullptr;
53   }
54 
FoldExactBinOp(Instruction::BinaryOps Opc,Value * LHS,Value * RHS,bool IsExact)55   Value *FoldExactBinOp(Instruction::BinaryOps Opc, Value *LHS, Value *RHS,
56                         bool IsExact) const override {
57     auto *LC = dyn_cast<Constant>(LHS);
58     auto *RC = dyn_cast<Constant>(RHS);
59     if (LC && RC) {
60       if (ConstantExpr::isDesirableBinOp(Opc))
61         return ConstantExpr::get(Opc, LC, RC,
62                                  IsExact ? PossiblyExactOperator::IsExact : 0);
63       return ConstantFoldBinaryInstruction(Opc, LC, RC);
64     }
65     return nullptr;
66   }
67 
FoldNoWrapBinOp(Instruction::BinaryOps Opc,Value * LHS,Value * RHS,bool HasNUW,bool HasNSW)68   Value *FoldNoWrapBinOp(Instruction::BinaryOps Opc, Value *LHS, Value *RHS,
69                          bool HasNUW, bool HasNSW) const override {
70     auto *LC = dyn_cast<Constant>(LHS);
71     auto *RC = dyn_cast<Constant>(RHS);
72     if (LC && RC) {
73       if (ConstantExpr::isDesirableBinOp(Opc)) {
74         unsigned Flags = 0;
75         if (HasNUW)
76           Flags |= OverflowingBinaryOperator::NoUnsignedWrap;
77         if (HasNSW)
78           Flags |= OverflowingBinaryOperator::NoSignedWrap;
79         return ConstantExpr::get(Opc, LC, RC, Flags);
80       }
81       return ConstantFoldBinaryInstruction(Opc, LC, RC);
82     }
83     return nullptr;
84   }
85 
FoldBinOpFMF(Instruction::BinaryOps Opc,Value * LHS,Value * RHS,FastMathFlags FMF)86   Value *FoldBinOpFMF(Instruction::BinaryOps Opc, Value *LHS, Value *RHS,
87                       FastMathFlags FMF) const override {
88     return FoldBinOp(Opc, LHS, RHS);
89   }
90 
FoldUnOpFMF(Instruction::UnaryOps Opc,Value * V,FastMathFlags FMF)91   Value *FoldUnOpFMF(Instruction::UnaryOps Opc, Value *V,
92                       FastMathFlags FMF) const override {
93     if (Constant *C = dyn_cast<Constant>(V))
94       return ConstantFoldUnaryInstruction(Opc, C);
95     return nullptr;
96   }
97 
FoldICmp(CmpInst::Predicate P,Value * LHS,Value * RHS)98   Value *FoldICmp(CmpInst::Predicate P, Value *LHS, Value *RHS) const override {
99     auto *LC = dyn_cast<Constant>(LHS);
100     auto *RC = dyn_cast<Constant>(RHS);
101     if (LC && RC)
102       return ConstantExpr::getCompare(P, LC, RC);
103     return nullptr;
104   }
105 
106   Value *FoldGEP(Type *Ty, Value *Ptr, ArrayRef<Value *> IdxList,
107                  bool IsInBounds = false) const override {
108     if (!ConstantExpr::isSupportedGetElementPtr(Ty))
109       return nullptr;
110 
111     if (auto *PC = dyn_cast<Constant>(Ptr)) {
112       // Every index must be constant.
113       if (any_of(IdxList, [](Value *V) { return !isa<Constant>(V); }))
114         return nullptr;
115 
116       if (IsInBounds)
117         return ConstantExpr::getInBoundsGetElementPtr(Ty, PC, IdxList);
118       else
119         return ConstantExpr::getGetElementPtr(Ty, PC, IdxList);
120     }
121     return nullptr;
122   }
123 
FoldSelect(Value * C,Value * True,Value * False)124   Value *FoldSelect(Value *C, Value *True, Value *False) const override {
125     auto *CC = dyn_cast<Constant>(C);
126     auto *TC = dyn_cast<Constant>(True);
127     auto *FC = dyn_cast<Constant>(False);
128     if (CC && TC && FC)
129       return ConstantFoldSelectInstruction(CC, TC, FC);
130     return nullptr;
131   }
132 
FoldExtractValue(Value * Agg,ArrayRef<unsigned> IdxList)133   Value *FoldExtractValue(Value *Agg,
134                           ArrayRef<unsigned> IdxList) const override {
135     if (auto *CAgg = dyn_cast<Constant>(Agg))
136       return ConstantFoldExtractValueInstruction(CAgg, IdxList);
137     return nullptr;
138   };
139 
FoldInsertValue(Value * Agg,Value * Val,ArrayRef<unsigned> IdxList)140   Value *FoldInsertValue(Value *Agg, Value *Val,
141                          ArrayRef<unsigned> IdxList) const override {
142     auto *CAgg = dyn_cast<Constant>(Agg);
143     auto *CVal = dyn_cast<Constant>(Val);
144     if (CAgg && CVal)
145       return ConstantFoldInsertValueInstruction(CAgg, CVal, IdxList);
146     return nullptr;
147   }
148 
FoldExtractElement(Value * Vec,Value * Idx)149   Value *FoldExtractElement(Value *Vec, Value *Idx) const override {
150     auto *CVec = dyn_cast<Constant>(Vec);
151     auto *CIdx = dyn_cast<Constant>(Idx);
152     if (CVec && CIdx)
153       return ConstantExpr::getExtractElement(CVec, CIdx);
154     return nullptr;
155   }
156 
FoldInsertElement(Value * Vec,Value * NewElt,Value * Idx)157   Value *FoldInsertElement(Value *Vec, Value *NewElt,
158                            Value *Idx) const override {
159     auto *CVec = dyn_cast<Constant>(Vec);
160     auto *CNewElt = dyn_cast<Constant>(NewElt);
161     auto *CIdx = dyn_cast<Constant>(Idx);
162     if (CVec && CNewElt && CIdx)
163       return ConstantExpr::getInsertElement(CVec, CNewElt, CIdx);
164     return nullptr;
165   }
166 
FoldShuffleVector(Value * V1,Value * V2,ArrayRef<int> Mask)167   Value *FoldShuffleVector(Value *V1, Value *V2,
168                            ArrayRef<int> Mask) const override {
169     auto *C1 = dyn_cast<Constant>(V1);
170     auto *C2 = dyn_cast<Constant>(V2);
171     if (C1 && C2)
172       return ConstantExpr::getShuffleVector(C1, C2, Mask);
173     return nullptr;
174   }
175 
FoldCast(Instruction::CastOps Op,Value * V,Type * DestTy)176   Value *FoldCast(Instruction::CastOps Op, Value *V,
177                   Type *DestTy) const override {
178     if (auto *C = dyn_cast<Constant>(V)) {
179       if (ConstantExpr::isDesirableCastOp(Op))
180         return ConstantExpr::getCast(Op, C, DestTy);
181       return ConstantFoldCastInstruction(Op, C, DestTy);
182     }
183     return nullptr;
184   }
185 
186   //===--------------------------------------------------------------------===//
187   // Cast/Conversion Operators
188   //===--------------------------------------------------------------------===//
189 
CreatePointerCast(Constant * C,Type * DestTy)190   Constant *CreatePointerCast(Constant *C, Type *DestTy) const override {
191     return ConstantExpr::getPointerCast(C, DestTy);
192   }
193 
CreatePointerBitCastOrAddrSpaceCast(Constant * C,Type * DestTy)194   Constant *CreatePointerBitCastOrAddrSpaceCast(Constant *C,
195                                                 Type *DestTy) const override {
196     return ConstantExpr::getPointerBitCastOrAddrSpaceCast(C, DestTy);
197   }
198 
199   //===--------------------------------------------------------------------===//
200   // Compare Instructions
201   //===--------------------------------------------------------------------===//
202 
CreateFCmp(CmpInst::Predicate P,Constant * LHS,Constant * RHS)203   Constant *CreateFCmp(CmpInst::Predicate P, Constant *LHS,
204                        Constant *RHS) const override {
205     return ConstantExpr::getCompare(P, LHS, RHS);
206   }
207 };
208 
209 } // end namespace llvm
210 
211 #endif // LLVM_IR_CONSTANTFOLDER_H
212