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 /// isDereferenceablePointer - Return true if this is always a dereferenceable 27 /// pointer. If the context instruction is specified perform context-sensitive 28 /// analysis and return true if the pointer is dereferenceable at the 29 /// specified instruction. 30 bool isDereferenceablePointer(const Value *V, const DataLayout &DL, 31 const Instruction *CtxI = nullptr, 32 const DominatorTree *DT = nullptr); 33 34 /// Returns true if V is always a dereferenceable pointer with alignment 35 /// greater or equal than requested. If the context instruction is specified 36 /// performs context-sensitive analysis and returns true if the pointer is 37 /// dereferenceable at the specified instruction. 38 bool isDereferenceableAndAlignedPointer(const Value *V, unsigned Align, 39 const DataLayout &DL, 40 const Instruction *CtxI = nullptr, 41 const DominatorTree *DT = nullptr); 42 43 /// isSafeToLoadUnconditionally - Return true if we know that executing a load 44 /// from this value cannot trap. 45 /// 46 /// If DT and ScanFrom are specified this method performs context-sensitive 47 /// analysis and returns true if it is safe to load immediately before ScanFrom. 48 /// 49 /// If it is not obviously safe to load from the specified pointer, we do a 50 /// quick local scan of the basic block containing ScanFrom, to determine if 51 /// the address is already accessed. 52 bool isSafeToLoadUnconditionally(Value *V, unsigned Align, 53 const DataLayout &DL, 54 Instruction *ScanFrom = nullptr, 55 const DominatorTree *DT = nullptr); 56 57 /// DefMaxInstsToScan - the default number of maximum instructions 58 /// to scan in the block, used by FindAvailableLoadedValue(). 59 extern cl::opt<unsigned> DefMaxInstsToScan; 60 61 /// \brief Scan backwards to see if we have the value of the given load 62 /// available locally within a small number of instructions. 63 /// 64 /// You can use this function to scan across multiple blocks: after you call 65 /// this function, if ScanFrom points at the beginning of the block, it's safe 66 /// to continue scanning the predecessors. 67 /// 68 /// Note that performing load CSE requires special care to make sure the 69 /// metadata is set appropriately. In particular, aliasing metadata needs 70 /// to be merged. (This doesn't matter for store-to-load forwarding because 71 /// the only relevant load gets deleted.) 72 /// 73 /// \param Load The load we want to replace. 74 /// \param ScanBB The basic block to scan. FIXME: This is redundant. 75 /// \param [in,out] ScanFrom The location to start scanning from. When this 76 /// function returns, it points at the last instruction scanned. 77 /// \param MaxInstsToScan The maximum number of instructions to scan. If this 78 /// is zero, the whole block will be scanned. 79 /// \param AA Optional pointer to alias analysis, to make the scan more 80 /// precise. 81 /// \param [out] AATags The aliasing metadata for the operation which produced 82 /// the value. FIXME: This is basically useless. 83 /// \param [out] IsLoadCSE Whether the returned value is a load from the same 84 /// location in memory, as opposed to the value operand of a store. 85 /// 86 /// \returns The found value, or nullptr if no value is found. 87 Value *FindAvailableLoadedValue(LoadInst *Load, 88 BasicBlock *ScanBB, 89 BasicBlock::iterator &ScanFrom, 90 unsigned MaxInstsToScan = DefMaxInstsToScan, 91 AliasAnalysis *AA = nullptr, 92 AAMDNodes *AATags = nullptr, 93 bool *IsLoadCSE = nullptr); 94 95 } 96 97 #endif 98
