llvm/lib/Transforms/ObjCARC/PtrState.h

   1 //===- PtrState.h - ARC State for a Ptr -------------------------*- 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 declarations for the ARC state associated with a ptr. It
  10 //  is only used by the ARC Sequence Dataflow computation. By separating this
  11 //  from the actual dataflow, it is easier to consider the mechanics of the ARC
  12 //  optimization separate from the actual predicates being used.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #ifndef LLVM_LIB_TRANSFORMS_OBJCARC_PTRSTATE_H
  17 #define LLVM_LIB_TRANSFORMS_OBJCARC_PTRSTATE_H
  18
  19 #include "llvm/ADT/SmallPtrSet.h"
  20 #include "llvm/Analysis/ObjCARCInstKind.h"
  21 #include "llvm/Support/Compiler.h"
  22
  23 namespace llvm {
  24
  25 class BasicBlock;
  26 class Instruction;
  27 class MDNode;
  28 class raw_ostream;
  29 class Value;
  30
  31 namespace objcarc {
  32
  33 class ARCMDKindCache;
  34 class BundledRetainClaimRVs;
  35 class ProvenanceAnalysis;
  36
  37 /// \enum Sequence
  38 ///
  39 /// A sequence of states that a pointer may go through in which an
  40 /// objc_retain and objc_release are actually needed.
  41 enum Sequence {
  42   S_None,
  43   S_Retain,        ///< objc_retain(x).
  44   S_CanRelease,    ///< foo(x) -- x could possibly see a ref count decrement.
  45   S_Use,           ///< any use of x.
  46   S_Stop,          ///< code motion is stopped.
  47   S_MovableRelease ///< objc_release(x), !clang.imprecise_release.
  48 };
  49
  50 raw_ostream &operator<<(raw_ostream &OS,
  51                         const Sequence S) LLVM_ATTRIBUTE_UNUSED;
  52
  53 /// Unidirectional information about either a
  54 /// retain-decrement-use-release sequence or release-use-decrement-retain
  55 /// reverse sequence.
  56 struct RRInfo {
  57   /// After an objc_retain, the reference count of the referenced
  58   /// object is known to be positive. Similarly, before an objc_release, the
  59   /// reference count of the referenced object is known to be positive. If
  60   /// there are retain-release pairs in code regions where the retain count
  61   /// is known to be positive, they can be eliminated, regardless of any side
  62   /// effects between them.
  63   ///
  64   /// Also, a retain+release pair nested within another retain+release
  65   /// pair all on the known same pointer value can be eliminated, regardless
  66   /// of any intervening side effects.
  67   ///
  68   /// KnownSafe is true when either of these conditions is satisfied.
  69   bool KnownSafe = false;
  70
  71   /// True of the objc_release calls are all marked with the "tail" keyword.
  72   bool IsTailCallRelease = false;
  73
  74   /// If the Calls are objc_release calls and they all have a
  75   /// clang.imprecise_release tag, this is the metadata tag.
  76   MDNode *ReleaseMetadata = nullptr;
  77
  78   /// For a top-down sequence, the set of objc_retains or
  79   /// objc_retainBlocks. For bottom-up, the set of objc_releases.
  80   SmallPtrSet<Instruction *, 2> Calls;
  81
  82   /// The set of optimal insert positions for moving calls in the opposite
  83   /// sequence.
  84   SmallPtrSet<Instruction *, 2> ReverseInsertPts;
  85
  86   /// If this is true, we cannot perform code motion but can still remove
  87   /// retain/release pairs.
  88   bool CFGHazardAfflicted = false;
  89
  90   RRInfo() = default;
  91
  92   void clear();
  93
  94   /// Conservatively merge the two RRInfo. Returns true if a partial merge has
  95   /// occurred, false otherwise.
  96   bool Merge(const RRInfo &Other);
  97 };
  98
  99 /// This class summarizes several per-pointer runtime properties which
 100 /// are propagated through the flow graph.
 101 class PtrState {
 102 protected:
 103   /// True if the reference count is known to be incremented.
 104   bool KnownPositiveRefCount = false;
 105
 106   /// True if we've seen an opportunity for partial RR elimination, such as
 107   /// pushing calls into a CFG triangle or into one side of a CFG diamond.
 108   bool Partial = false;
 109
 110   /// The current position in the sequence.
 111   unsigned char Seq : 8;
 112
 113   /// Unidirectional information about the current sequence.
 114   RRInfo RRI;
 115
 116   PtrState() : Seq(S_None) {}
 117
 118 public:
 119   bool IsKnownSafe() const { return RRI.KnownSafe; }
 120
 121   void SetKnownSafe(const bool NewValue) { RRI.KnownSafe = NewValue; }
 122
 123   bool IsTailCallRelease() const { return RRI.IsTailCallRelease; }
 124
 125   void SetTailCallRelease(const bool NewValue) {
 126     RRI.IsTailCallRelease = NewValue;
 127   }
 128
 129   bool IsTrackingImpreciseReleases() const {
 130     return RRI.ReleaseMetadata != nullptr;
 131   }
 132
 133   const MDNode *GetReleaseMetadata() const { return RRI.ReleaseMetadata; }
 134
 135   void SetReleaseMetadata(MDNode *NewValue) { RRI.ReleaseMetadata = NewValue; }
 136
 137   bool IsCFGHazardAfflicted() const { return RRI.CFGHazardAfflicted; }
 138
 139   void SetCFGHazardAfflicted(const bool NewValue) {
 140     RRI.CFGHazardAfflicted = NewValue;
 141   }
 142
 143   void SetKnownPositiveRefCount();
 144   void ClearKnownPositiveRefCount();
 145
 146   bool HasKnownPositiveRefCount() const { return KnownPositiveRefCount; }
 147
 148   void SetSeq(Sequence NewSeq);
 149
 150   Sequence GetSeq() const { return static_cast<Sequence>(Seq); }
 151
 152   void ClearSequenceProgress() { ResetSequenceProgress(S_None); }
 153
 154   void ResetSequenceProgress(Sequence NewSeq);
 155   void Merge(const PtrState &Other, bool TopDown);
 156
 157   void InsertCall(Instruction *I) { RRI.Calls.insert(I); }
 158
 159   void InsertReverseInsertPt(Instruction *I) { RRI.ReverseInsertPts.insert(I); }
 160
 161   void ClearReverseInsertPts() { RRI.ReverseInsertPts.clear(); }
 162
 163   bool HasReverseInsertPts() const { return !RRI.ReverseInsertPts.empty(); }
 164
 165   const RRInfo &GetRRInfo() const { return RRI; }
 166 };
 167
 168 struct BottomUpPtrState : PtrState {
 169   BottomUpPtrState() = default;
 170
 171   /// (Re-)Initialize this bottom up pointer returning true if we detected a
 172   /// pointer with nested releases.
 173   bool InitBottomUp(ARCMDKindCache &Cache, Instruction *I);
 174
 175   /// Return true if this set of releases can be paired with a release. Modifies
 176   /// state appropriately to reflect that the matching occurred if it is
 177   /// successful.
 178   ///
 179   /// It is assumed that one has already checked that the RCIdentity of the
 180   /// retain and the RCIdentity of this ptr state are the same.
 181   bool MatchWithRetain();
 182
 183   void HandlePotentialUse(BasicBlock *BB, Instruction *Inst, const Value *Ptr,
 184                           ProvenanceAnalysis &PA, ARCInstKind Class);
 185   bool HandlePotentialAlterRefCount(Instruction *Inst, const Value *Ptr,
 186                                     ProvenanceAnalysis &PA, ARCInstKind Class);
 187 };
 188
 189 struct TopDownPtrState : PtrState {
 190   TopDownPtrState() = default;
 191
 192   /// (Re-)Initialize this bottom up pointer returning true if we detected a
 193   /// pointer with nested releases.
 194   bool InitTopDown(ARCInstKind Kind, Instruction *I);
 195
 196   /// Return true if this set of retains can be paired with the given
 197   /// release. Modifies state appropriately to reflect that the matching
 198   /// occurred.
 199   bool MatchWithRelease(ARCMDKindCache &Cache, Instruction *Release);
 200
 201   void HandlePotentialUse(Instruction *Inst, const Value *Ptr,
 202                           ProvenanceAnalysis &PA, ARCInstKind Class);
 203
 204   bool HandlePotentialAlterRefCount(Instruction *Inst, const Value *Ptr,
 205                                     ProvenanceAnalysis &PA, ARCInstKind Class,
 206                                     const BundledRetainClaimRVs &BundledRVs);
 207 };
 208
 209 } // end namespace objcarc
 210
 211 } // end namespace llvm
 212
 213 #endif // LLVM_LIB_TRANSFORMS_OBJCARC_PTRSTATE_H