include/llvm/Analysis/Loads.h

   1 //===- Loads.h - Local load analysis --------------------------------------===//
   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 simple local analyses for load instructions.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_ANALYSIS_LOADS_H
  14 #define LLVM_ANALYSIS_LOADS_H
  15
  16 #include "llvm/Analysis/AliasAnalysis.h"
  17 #include "llvm/IR/BasicBlock.h"
  18 #include "llvm/Support/CommandLine.h"
  19
  20 namespace llvm {
  21
  22 class DataLayout;
  23 class MDNode;
  24
  25 /// Return true if this is always a dereferenceable pointer. If the context
  26 /// instruction is specified perform context-sensitive analysis and return true
  27 /// if the pointer is dereferenceable at the specified instruction.
  28 bool isDereferenceablePointer(const Value *V, Type *Ty,
  29                               const DataLayout &DL,
  30                               const Instruction *CtxI = nullptr,
  31                               const DominatorTree *DT = nullptr);
  32
  33 /// Returns true if V is always a dereferenceable pointer with alignment
  34 /// greater or equal than requested. If the context instruction is specified
  35 /// performs context-sensitive analysis and returns true if the pointer is
  36 /// dereferenceable at the specified instruction.
  37 bool isDereferenceableAndAlignedPointer(const Value *V, Type *Ty,
  38                                         unsigned Align, const DataLayout &DL,
  39                                         const Instruction *CtxI = nullptr,
  40                                         const DominatorTree *DT = nullptr);
  41
  42 /// Returns true if V is always dereferenceable for Size byte with alignment
  43 /// greater or equal than requested. If the context instruction is specified
  44 /// performs context-sensitive analysis and returns true if the pointer is
  45 /// dereferenceable at the specified instruction.
  46 bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align,
  47                                         const APInt &Size, const DataLayout &DL,
  48                                         const Instruction *CtxI = nullptr,
  49                                         const DominatorTree *DT = nullptr);
  50
  51 /// Return true if we know that executing a load from this value cannot trap.
  52 ///
  53 /// If DT and ScanFrom are specified this method performs context-sensitive
  54 /// analysis and returns true if it is safe to load immediately before ScanFrom.
  55 ///
  56 /// If it is not obviously safe to load from the specified pointer, we do a
  57 /// quick local scan of the basic block containing ScanFrom, to determine if
  58 /// the address is already accessed.
  59 bool isSafeToLoadUnconditionally(Value *V, unsigned Align, APInt &Size,
  60                                  const DataLayout &DL,
  61                                  Instruction *ScanFrom = nullptr,
  62                                  const DominatorTree *DT = nullptr);
  63
  64 /// Return true if we know that executing a load from this value cannot trap.
  65 ///
  66 /// If DT and ScanFrom are specified this method performs context-sensitive
  67 /// analysis and returns true if it is safe to load immediately before ScanFrom.
  68 ///
  69 /// If it is not obviously safe to load from the specified pointer, we do a
  70 /// quick local scan of the basic block containing ScanFrom, to determine if
  71 /// the address is already accessed.
  72 bool isSafeToLoadUnconditionally(Value *V, Type *Ty, unsigned Align,
  73                                  const DataLayout &DL,
  74                                  Instruction *ScanFrom = nullptr,
  75                                  const DominatorTree *DT = nullptr);
  76
  77 /// The default number of maximum instructions to scan in the block, used by
  78 /// FindAvailableLoadedValue().
  79 extern cl::opt<unsigned> DefMaxInstsToScan;
  80
  81 /// Scan backwards to see if we have the value of the given load available
  82 /// locally within a small number of instructions.
  83 ///
  84 /// You can use this function to scan across multiple blocks: after you call
  85 /// this function, if ScanFrom points at the beginning of the block, it's safe
  86 /// to continue scanning the predecessors.
  87 ///
  88 /// Note that performing load CSE requires special care to make sure the
  89 /// metadata is set appropriately.  In particular, aliasing metadata needs
  90 /// to be merged.  (This doesn't matter for store-to-load forwarding because
  91 /// the only relevant load gets deleted.)
  92 ///
  93 /// \param Load The load we want to replace.
  94 /// \param ScanBB The basic block to scan.
  95 /// \param [in,out] ScanFrom The location to start scanning from. When this
  96 /// function returns, it points at the last instruction scanned.
  97 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
  98 /// is zero, the whole block will be scanned.
  99 /// \param AA Optional pointer to alias analysis, to make the scan more
 100 /// precise.
 101 /// \param [out] IsLoadCSE Whether the returned value is a load from the same
 102 /// location in memory, as opposed to the value operand of a store.
 103 ///
 104 /// \returns The found value, or nullptr if no value is found.
 105 Value *FindAvailableLoadedValue(LoadInst *Load,
 106                                 BasicBlock *ScanBB,
 107                                 BasicBlock::iterator &ScanFrom,
 108                                 unsigned MaxInstsToScan = DefMaxInstsToScan,
 109                                 AliasAnalysis *AA = nullptr,
 110                                 bool *IsLoadCSE = nullptr,
 111                                 unsigned *NumScanedInst = nullptr);
 112
 113 /// Scan backwards to see if we have the value of the given pointer available
 114 /// locally within a small number of instructions.
 115 ///
 116 /// You can use this function to scan across multiple blocks: after you call
 117 /// this function, if ScanFrom points at the beginning of the block, it's safe
 118 /// to continue scanning the predecessors.
 119 ///
 120 /// \param Ptr The pointer we want the load and store to originate from.
 121 /// \param AccessTy The access type of the pointer.
 122 /// \param AtLeastAtomic Are we looking for at-least an atomic load/store ? In
 123 /// case it is false, we can return an atomic or non-atomic load or store. In
 124 /// case it is true, we need to return an atomic load or store.
 125 /// \param ScanBB The basic block to scan.
 126 /// \param [in,out] ScanFrom The location to start scanning from. When this
 127 /// function returns, it points at the last instruction scanned.
 128 /// \param MaxInstsToScan The maximum number of instructions to scan. If this
 129 /// is zero, the whole block will be scanned.
 130 /// \param AA Optional pointer to alias analysis, to make the scan more
 131 /// precise.
 132 /// \param [out] IsLoad Whether the returned value is a load from the same
 133 /// location in memory, as opposed to the value operand of a store.
 134 ///
 135 /// \returns The found value, or nullptr if no value is found.
 136 Value *FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy, bool AtLeastAtomic,
 137                                  BasicBlock *ScanBB,
 138                                  BasicBlock::iterator &ScanFrom,
 139                                  unsigned MaxInstsToScan, AliasAnalysis *AA,
 140                                  bool *IsLoad, unsigned *NumScanedInst);
 141 }
 142
 143 #endif