include/llvm/Analysis/ConstantFolding.h

   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 namespace llvm {
  23 class APInt;
  24 template <typename T> class ArrayRef;
  25 class CallBase;
  26 class Constant;
  27 class ConstantExpr;
  28 class ConstantVector;
  29 class DataLayout;
  30 class Function;
  31 class GlobalValue;
  32 class Instruction;
  33 class TargetLibraryInfo;
  34 class Type;
  35
  36 /// If this constant is a constant offset from a global, return the global and
  37 /// the constant. Because of constantexprs, this function is recursive.
  38 bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, APInt &Offset,
  39                                 const DataLayout &DL);
  40
  41 /// ConstantFoldInstruction - Try to constant fold the specified instruction.
  42 /// If successful, the constant result is returned, if not, null is returned.
  43 /// Note that this fails if not all of the operands are constant.  Otherwise,
  44 /// this function can only fail when attempting to fold instructions like loads
  45 /// and stores, which have no constant expression form.
  46 Constant *ConstantFoldInstruction(Instruction *I, const DataLayout &DL,
  47                                   const TargetLibraryInfo *TLI = nullptr);
  48
  49 /// ConstantFoldConstant - Attempt to fold the constant using the
  50 /// specified DataLayout.
  51 /// If successful, the constant result is returned, if not, null is returned.
  52 Constant *ConstantFoldConstant(const Constant *C, const DataLayout &DL,
  53                                const TargetLibraryInfo *TLI = nullptr);
  54
  55 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
  56 /// specified operands.  If successful, the constant result is returned, if not,
  57 /// null is returned.  Note that this function can fail when attempting to
  58 /// fold instructions like loads and stores, which have no constant expression
  59 /// form.
  60 ///
  61 Constant *ConstantFoldInstOperands(Instruction *I, ArrayRef<Constant *> Ops,
  62                                    const DataLayout &DL,
  63                                    const TargetLibraryInfo *TLI = nullptr);
  64
  65 /// ConstantFoldCompareInstOperands - Attempt to constant fold a compare
  66 /// instruction (icmp/fcmp) with the specified operands.  If it fails, it
  67 /// returns a constant expression of the specified operands.
  68 ///
  69 Constant *
  70 ConstantFoldCompareInstOperands(unsigned Predicate, Constant *LHS,
  71                                 Constant *RHS, const DataLayout &DL,
  72                                 const TargetLibraryInfo *TLI = nullptr);
  73
  74 /// Attempt to constant fold a binary operation with the specified
  75 /// operands.  If it fails, it returns a constant expression of the specified
  76 /// operands.
  77 Constant *ConstantFoldBinaryOpOperands(unsigned Opcode, Constant *LHS,
  78                                        Constant *RHS, const DataLayout &DL);
  79
  80 /// Attempt to constant fold a select instruction with the specified
  81 /// operands. The constant result is returned if successful; if not, null is
  82 /// returned.
  83 Constant *ConstantFoldSelectInstruction(Constant *Cond, Constant *V1,
  84                                         Constant *V2);
  85
  86 /// Attempt to constant fold a cast with the specified operand.  If it
  87 /// fails, it returns a constant expression of the specified operand.
  88 Constant *ConstantFoldCastOperand(unsigned Opcode, Constant *C, Type *DestTy,
  89                                   const DataLayout &DL);
  90
  91 /// ConstantFoldInsertValueInstruction - Attempt to constant fold an insertvalue
  92 /// instruction with the specified operands and indices.  The constant result is
  93 /// returned if successful; if not, null is returned.
  94 Constant *ConstantFoldInsertValueInstruction(Constant *Agg, Constant *Val,
  95                                              ArrayRef<unsigned> Idxs);
  96
  97 /// Attempt to constant fold an extractvalue instruction with the
  98 /// specified operands and indices.  The constant result is returned if
  99 /// successful; if not, null is returned.
 100 Constant *ConstantFoldExtractValueInstruction(Constant *Agg,
 101                                               ArrayRef<unsigned> Idxs);
 102
 103 /// Attempt to constant fold an insertelement instruction with the
 104 /// specified operands and indices.  The constant result is returned if
 105 /// successful; if not, null is returned.
 106 Constant *ConstantFoldInsertElementInstruction(Constant *Val,
 107                                                Constant *Elt,
 108                                                Constant *Idx);
 109
 110 /// Attempt to constant fold an extractelement instruction with the
 111 /// specified operands and indices.  The constant result is returned if
 112 /// successful; if not, null is returned.
 113 Constant *ConstantFoldExtractElementInstruction(Constant *Val, Constant *Idx);
 114
 115 /// Attempt to constant fold a shufflevector instruction with the
 116 /// specified operands and indices.  The constant result is returned if
 117 /// successful; if not, null is returned.
 118 Constant *ConstantFoldShuffleVectorInstruction(Constant *V1, Constant *V2,
 119                                                Constant *Mask);
 120
 121 /// ConstantFoldLoadFromConstPtr - Return the value that a load from C would
 122 /// produce if it is constant and determinable.  If this is not determinable,
 123 /// return null.
 124 Constant *ConstantFoldLoadFromConstPtr(Constant *C, Type *Ty, const DataLayout &DL);
 125
 126 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
 127 /// getelementptr constantexpr, return the constant value being addressed by the
 128 /// constant expression, or null if something is funny and we can't decide.
 129 Constant *ConstantFoldLoadThroughGEPConstantExpr(Constant *C, ConstantExpr *CE);
 130
 131 /// ConstantFoldLoadThroughGEPIndices - Given a constant and getelementptr
 132 /// indices (with an *implied* zero pointer index that is not in the list),
 133 /// return the constant value being addressed by a virtual load, or null if
 134 /// something is funny and we can't decide.
 135 Constant *ConstantFoldLoadThroughGEPIndices(Constant *C,
 136                                             ArrayRef<Constant *> Indices);
 137
 138 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
 139 /// the specified function.
 140 bool canConstantFoldCallTo(const CallBase *Call, const Function *F);
 141
 142 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
 143 /// with the specified arguments, returning null if unsuccessful.
 144 Constant *ConstantFoldCall(const CallBase *Call, Function *F,
 145                            ArrayRef<Constant *> Operands,
 146                            const TargetLibraryInfo *TLI = nullptr);
 147
 148 /// ConstantFoldLoadThroughBitcast - try to cast constant to destination type
 149 /// returning null if unsuccessful. Can cast pointer to pointer or pointer to
 150 /// integer and vice versa if their sizes are equal.
 151 Constant *ConstantFoldLoadThroughBitcast(Constant *C, Type *DestTy,
 152                                          const DataLayout &DL);
 153
 154 /// Check whether the given call has no side-effects.
 155 /// Specifically checks for math routimes which sometimes set errno.
 156 bool isMathLibCallNoop(const CallBase *Call, const TargetLibraryInfo *TLI);
 157 }
 158
 159 #endif