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