1//===-- ConstantFolding.h - Fold instructions into constants ----*- 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 declares routines for folding instructions into constants when all
10// operands are constants, for example "sub i32 1, 0" -> "1".
11//
12// Also, to supplement the basic VMCore ConstantExpr simplifications,
13// this file declares some additional folding routines that can make use of
14// DataLayout information. These functions cannot go in VMCore due to library
15// dependency issues.
16//
17//===----------------------------------------------------------------------===//
18
19#ifndef LLVM_ANALYSIS_CONSTANTFOLDING_H
20#define LLVM_ANALYSIS_CONSTANTFOLDING_H
21
22#include <stdint.h>
23
24namespace llvm {
25
26namespace Intrinsic {
27using ID = unsigned;
28}
29
30class APInt;
31template <typename T> class ArrayRef;
32class CallBase;
33class Constant;
34class DSOLocalEquivalent;
35class DataLayout;
36class Function;
37class GlobalValue;
38class GlobalVariable;
39class Instruction;
40class TargetLibraryInfo;
41class Type;
42
43/// If this constant is a constant offset from a global, return the global and
44/// the constant. Because of constantexprs, this function is recursive.
45/// If the global is part of a dso_local_equivalent constant, return it through
46/// `Equiv` if it is provided.
47bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, APInt &Offset,
48 const DataLayout &DL,
49 DSOLocalEquivalent **DSOEquiv = nullptr);
50
51/// ConstantFoldInstruction - Try to constant fold the specified instruction.
52/// If successful, the constant result is returned, if not, null is returned.
53/// Note that this fails if not all of the operands are constant. Otherwise,
54/// this function can only fail when attempting to fold instructions like loads
55/// and stores, which have no constant expression form.
56Constant *ConstantFoldInstruction(Instruction *I, const DataLayout &DL,
57 const TargetLibraryInfo *TLI = nullptr);
58
59/// ConstantFoldConstant - Fold the constant using the specified DataLayout.
60/// This function always returns a non-null constant: Either the folding result,
61/// or the original constant if further folding is not possible.
62Constant *ConstantFoldConstant(const Constant *C, const DataLayout &DL,
63 const TargetLibraryInfo *TLI = nullptr);
64
65/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
66/// specified operands. If successful, the constant result is returned, if not,
67/// null is returned. Note that this function can fail when attempting to
68/// fold instructions like loads and stores, which have no constant expression
69/// form.
70///
71Constant *ConstantFoldInstOperands(Instruction *I, ArrayRef<Constant *> Ops,
72 const DataLayout &DL,
73 const TargetLibraryInfo *TLI = nullptr);
74
75/// Attempt to constant fold a compare instruction (icmp/fcmp) with the
76/// specified operands. Returns null or a constant expression of the specified
77/// operands on failure.
78/// Denormal inputs may be flushed based on the denormal handling mode.
79Constant *ConstantFoldCompareInstOperands(
80 unsigned Predicate, Constant *LHS, Constant *RHS, const DataLayout &DL,
81 const TargetLibraryInfo *TLI = nullptr, const Instruction *I = nullptr);
82
83/// Attempt to constant fold a unary operation with the specified operand.
84/// Returns null on failure.
85Constant *ConstantFoldUnaryOpOperand(unsigned Opcode, Constant *Op,
86 const DataLayout &DL);
87
88/// Attempt to constant fold a binary operation with the specified operands.
89/// Returns null or a constant expression of the specified operands on failure.
90Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS,
91 Constant *RHS, const DataLayout &DL);
92
93/// Attempt to constant fold a floating point binary operation with the
94/// specified operands, applying the denormal handling mod to the operands.
95/// Returns null or a constant expression of the specified operands on failure.
96Constant *ConstantFoldFPInstOperands(unsigned Opcode, Constant *LHS,
97 Constant *RHS, const DataLayout &DL,
98 const Instruction *I);
99
100/// Attempt to flush float point constant according to denormal mode set in the
101/// instruction's parent function attributes. If so, return a zero with the
102/// correct sign, otherwise return the original constant. Inputs and outputs to
103/// floating point instructions can have their mode set separately, so the
104/// direction is also needed.
105///
106/// If the calling function's "denormal-fp-math" input mode is "dynamic" for the
107/// floating-point type, returns nullptr for denormal inputs.
108Constant *FlushFPConstant(Constant *Operand, const Instruction *I,
109 bool IsOutput);
110
111/// Attempt to constant fold a select instruction with the specified
112/// operands. The constant result is returned if successful; if not, null is
113/// returned.
114Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1,
115 Constant *V2);
116
117/// Attempt to constant fold a cast with the specified operand. If it
118/// fails, it returns a constant expression of the specified operand.
119Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy,
120 const DataLayout &DL);
121
122/// Constant fold a zext, sext or trunc, depending on IsSigned and whether the
123/// DestTy is wider or narrower than C. Returns nullptr on failure.
124Constant *ConstantFoldIntegerCast(Constant *C, Type *DestTy, bool IsSigned,
125 const DataLayout &DL);
126
127/// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue
128/// instruction with the specified operands and indices. The constant result is
129/// returned if successful; if not, null is returned.
130Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val,
131 ArrayRef<unsigned> Idxs);
132
133/// Attempt to constant fold an extractvalue instruction with the
134/// specified operands and indices. The constant result is returned if
135/// successful; if not, null is returned.
136Constant *ConstantFoldExtractValueInstruction(Constant *Agg,
137 ArrayRef<unsigned> Idxs);
138
139/// Attempt to constant fold an insertelement instruction with the
140/// specified operands and indices. The constant result is returned if
141/// successful; if not, null is returned.
142Constant *ConstantFoldInsertElementInstruction(Constant *Val,
143 Constant *Elt,
144 Constant *Idx);
145
146/// Attempt to constant fold an extractelement instruction with the
147/// specified operands and indices. The constant result is returned if
148/// successful; if not, null is returned.
149Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx);
150
151/// Attempt to constant fold a shufflevector instruction with the
152/// specified operands and mask. See class ShuffleVectorInst for a description
153/// of the mask representation. The constant result is returned if successful;
154/// if not, null is returned.
155Constant *ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2,
156 ArrayRef<int> Mask);
157
158/// Extract value of C at the given Offset reinterpreted as Ty. If bits past
159/// the end of C are accessed, they are assumed to be poison.
160Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty, const APInt &Offset,
161 const DataLayout &DL);
162
163/// Extract value of C reinterpreted as Ty. Same as previous API with zero
164/// offset.
165Constant *ConstantFoldLoadFromConst(Constant *C, Type *Ty,
166 const DataLayout &DL);
167
168/// Return the value that a load from C with offset Offset would produce if it
169/// is constant and determinable. If this is not determinable, return null.
170Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, APInt Offset,
171 const DataLayout &DL);
172
173/// Return the value that a load from C would produce if it is constant and
174/// determinable. If this is not determinable, return null.
175Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty,
176 const DataLayout &DL);
177
178/// If C is a uniform value where all bits are the same (either all zero, all
179/// ones, all undef or all poison), return the corresponding uniform value in
180/// the new type. If the value is not uniform or the result cannot be
181/// represented, return null.
182Constant *ConstantFoldLoadFromUniformValue(Constant *C, Type *Ty,
183 const DataLayout &DL);
184
185/// canConstantFoldCallTo - Return true if its even possible to fold a call to
186/// the specified function.
187bool canConstantFoldCallTo(const CallBase *Call, const Function *F);
188
189/// ConstantFoldCall - Attempt to constant fold a call to the specified function
190/// with the specified arguments, returning null if unsuccessful.
191Constant *ConstantFoldCall(const CallBase *Call, Function *F,
192 ArrayRef<Constant *> Operands,
193 const TargetLibraryInfo *TLI = nullptr);
194
195Constant *ConstantFoldBinaryIntrinsic(Intrinsic::ID ID, Constant *LHS,
196 Constant *RHS, Type *Ty,
197 Instruction *FMFSource);
198
199/// ConstantFoldLoadThroughBitcast - try to cast constant to destination type
200/// returning null if unsuccessful. Can cast pointer to pointer or pointer to
201/// integer and vice versa if their sizes are equal.
202Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
203 const DataLayout &DL);
204
205/// Check whether the given call has no side-effects.
206/// Specifically checks for math routimes which sometimes set errno.
207bool isMathLibCallNoop(const CallBase *Call, const TargetLibraryInfo *TLI);
208
209Constant *ReadByteArrayFromGlobal(const GlobalVariable *GV, uint64_t Offset);
210}
211
212#endif
213

source code of llvm/include/llvm/Analysis/ConstantFolding.h