1 //===-- ConstantFolding.h - Fold instructions into constants ----*- 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 declares routines for folding instructions into constants when all
11 // operands are constants, for example "sub i32 1, 0" -> "1".
12 //
13 // Also, to supplement the basic VMCore ConstantExpr simplifications,
14 // this file declares some additional folding routines that can make use of
15 // DataLayout information. These functions cannot go in VMCore due to library
16 // dependency issues.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #ifndef LLVM_ANALYSIS_CONSTANTFOLDING_H
21 #define LLVM_ANALYSIS_CONSTANTFOLDING_H
22 
23 namespace llvm {
24   class Constant;
25   class ConstantExpr;
26   class Instruction;
27   class DataLayout;
28   class TargetLibraryInfo;
29   class Function;
30   class Type;
31   template<typename T>
32   class ArrayRef;
33 
34 /// ConstantFoldInstruction - Try to constant fold the specified instruction.
35 /// If successful, the constant result is returned, if not, null is returned.
36 /// Note that this fails if not all of the operands are constant.  Otherwise,
37 /// this function can only fail when attempting to fold instructions like loads
38 /// and stores, which have no constant expression form.
39   Constant *ConstantFoldInstruction(Instruction *I, const DataLayout &DL,
40                                     const TargetLibraryInfo *TLI = nullptr);
41 
42 /// ConstantFoldConstantExpression - Attempt to fold the constant expression
43 /// using the specified DataLayout.  If successful, the constant result is
44 /// result is returned, if not, null is returned.
45   Constant *
46   ConstantFoldConstantExpression(const ConstantExpr *CE, const DataLayout &DL,
47                                  const TargetLibraryInfo *TLI = nullptr);
48 
49 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
50 /// specified operands.  If successful, the constant result is returned, if not,
51 /// null is returned.  Note that this function can fail when attempting to
52 /// fold instructions like loads and stores, which have no constant expression
53 /// form.
54 ///
55   Constant *ConstantFoldInstOperands(unsigned Opcode, Type *DestTy,
56                                      ArrayRef<Constant *> Ops,
57                                      const DataLayout &DL,
58                                      const TargetLibraryInfo *TLI = nullptr);
59 
60 /// ConstantFoldCompareInstOperands - Attempt to constant fold a compare
61 /// instruction (icmp/fcmp) with the specified operands.  If it fails, it
62 /// returns a constant expression of the specified operands.
63 ///
64   Constant *
65   ConstantFoldCompareInstOperands(unsigned Predicate, Constant *LHS,
66                                   Constant *RHS, const DataLayout &DL,
67                                   const TargetLibraryInfo *TLI = nullptr);
68 
69 /// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue
70 /// instruction with the specified operands and indices.  The constant result is
71 /// returned if successful; if not, null is returned.
72 Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val,
73                                              ArrayRef<unsigned> Idxs);
74 
75 /// \brief Attempt to constant fold an extractvalue instruction with the
76 /// specified operands and indices.  The constant result is returned if
77 /// successful; if not, null is returned.
78 Constant *ConstantFoldExtractValueInstruction(Constant *Agg,
79                                               ArrayRef<unsigned> Idxs);
80 
81 /// \brief Attempt to constant fold an extractelement instruction with the
82 /// specified operands and indices.  The constant result is returned if
83 /// successful; if not, null is returned.
84 Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx);
85 
86 /// ConstantFoldLoadFromConstPtr - Return the value that a load from C would
87 /// produce if it is constant and determinable.  If this is not determinable,
88 /// return null.
89 Constant *ConstantFoldLoadFromConstPtr(Constant *C, const DataLayout &DL);
90 
91 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
92 /// getelementptr constantexpr, return the constant value being addressed by the
93 /// constant expression, or null if something is funny and we can't decide.
94 Constant *ConstantFoldLoadThroughGEPConstantExpr(Constant *C, ConstantExpr *CE);
95 
96 /// ConstantFoldLoadThroughGEPIndices - Given a constant and getelementptr
97 /// indices (with an *implied* zero pointer index that is not in the list),
98 /// return the constant value being addressed by a virtual load, or null if
99 /// something is funny and we can't decide.
100 Constant *ConstantFoldLoadThroughGEPIndices(Constant *C,
101                                             ArrayRef<Constant*> Indices);
102 
103 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
104 /// the specified function.
105 bool canConstantFoldCallTo(const Function *F);
106 
107 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
108 /// with the specified arguments, returning null if unsuccessful.
109 Constant *ConstantFoldCall(Function *F, ArrayRef<Constant *> Operands,
110                            const TargetLibraryInfo *TLI = nullptr);
111 }
112 
113 #endif
114