include/llvm/Analysis/CaptureTracking.h

   1 //===----- llvm/Analysis/CaptureTracking.h - Pointer capture ----*- C++ -*-===//
   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 contains routines that help determine which pointers are captured.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_ANALYSIS_CAPTURETRACKING_H
  14 #define LLVM_ANALYSIS_CAPTURETRACKING_H
  15
  16 namespace llvm {
  17
  18   class Value;
  19   class Use;
  20   class Instruction;
  21   class DominatorTree;
  22   class OrderedBasicBlock;
  23
  24   /// The default value for MaxUsesToExplore argument. It's relatively small to
  25   /// keep the cost of analysis reasonable for clients like BasicAliasAnalysis,
  26   /// where the results can't be cached.
  27   /// TODO: we should probably introduce a caching CaptureTracking analysis and
  28   /// use it where possible. The caching version can use much higher limit or
  29   /// don't have this cap at all.
  30   unsigned constexpr DefaultMaxUsesToExplore = 20;
  31
  32   /// PointerMayBeCaptured - Return true if this pointer value may be captured
  33   /// by the enclosing function (which is required to exist).  This routine can
  34   /// be expensive, so consider caching the results.  The boolean ReturnCaptures
  35   /// specifies whether returning the value (or part of it) from the function
  36   /// counts as capturing it or not.  The boolean StoreCaptures specified
  37   /// whether storing the value (or part of it) into memory anywhere
  38   /// automatically counts as capturing it or not.
  39   /// MaxUsesToExplore specifies how many uses should the analysis explore for
  40   /// one value before giving up due too "too many uses".
  41   bool PointerMayBeCaptured(const Value *V,
  42                             bool ReturnCaptures,
  43                             bool StoreCaptures,
  44                             unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
  45
  46   /// PointerMayBeCapturedBefore - Return true if this pointer value may be
  47   /// captured by the enclosing function (which is required to exist). If a
  48   /// DominatorTree is provided, only captures which happen before the given
  49   /// instruction are considered. This routine can be expensive, so consider
  50   /// caching the results.  The boolean ReturnCaptures specifies whether
  51   /// returning the value (or part of it) from the function counts as capturing
  52   /// it or not.  The boolean StoreCaptures specified whether storing the value
  53   /// (or part of it) into memory anywhere automatically counts as capturing it
  54   /// or not. Captures by the provided instruction are considered if the
  55   /// final parameter is true. An ordered basic block in \p OBB could be used
  56   /// to speed up capture-tracker queries.
  57   /// MaxUsesToExplore specifies how many uses should the analysis explore for
  58   /// one value before giving up due too "too many uses".
  59   bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
  60                                   bool StoreCaptures, const Instruction *I,
  61                                   const DominatorTree *DT, bool IncludeI = false,
  62                                   OrderedBasicBlock *OBB = nullptr,
  63                                   unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
  64
  65   /// This callback is used in conjunction with PointerMayBeCaptured. In
  66   /// addition to the interface here, you'll need to provide your own getters
  67   /// to see whether anything was captured.
  68   struct CaptureTracker {
  69     virtual ~CaptureTracker();
  70
  71     /// tooManyUses - The depth of traversal has breached a limit. There may be
  72     /// capturing instructions that will not be passed into captured().
  73     virtual void tooManyUses() = 0;
  74
  75     /// shouldExplore - This is the use of a value derived from the pointer.
  76     /// To prune the search (ie., assume that none of its users could possibly
  77     /// capture) return false. To search it, return true.
  78     ///
  79     /// U->getUser() is always an Instruction.
  80     virtual bool shouldExplore(const Use *U);
  81
  82     /// captured - Information about the pointer was captured by the user of
  83     /// use U. Return true to stop the traversal or false to continue looking
  84     /// for more capturing instructions.
  85     virtual bool captured(const Use *U) = 0;
  86   };
  87
  88   /// PointerMayBeCaptured - Visit the value and the values derived from it and
  89   /// find values which appear to be capturing the pointer value. This feeds
  90   /// results into and is controlled by the CaptureTracker object.
  91   /// MaxUsesToExplore specifies how many uses should the analysis explore for
  92   /// one value before giving up due too "too many uses".
  93   void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
  94                             unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
  95 } // end namespace llvm
  96
  97 #endif