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 21namespace llvm { 22 23class DataLayout; 24class 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. 30bool 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. 38bool 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. 52bool 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(). 59extern 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. 87Value *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