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