include/llvm/MC/MCCodePadder.h

   1 //===- llvm/MC/MCCodePadder.h - MC Code Padder ------------------*- 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 #ifndef LLVM_MC_MCCODEPADDER_H
  10 #define LLVM_MC_MCCODEPADDER_H
  11
  12 #include "MCFragment.h"
  13 #include "llvm/ADT/DenseMap.h"
  14 #include "llvm/ADT/SmallPtrSet.h"
  15 #include "llvm/ADT/SmallVector.h"
  16
  17 namespace llvm {
  18
  19 class MCAsmLayout;
  20 class MCCodePaddingPolicy;
  21 class MCFragment;
  22 class MCInst;
  23 class MCObjectStreamer;
  24 class MCSection;
  25
  26 typedef SmallVector<const MCPaddingFragment *, 8> MCPFRange;
  27
  28 struct MCCodePaddingContext {
  29   bool IsPaddingActive;
  30   bool IsBasicBlockReachableViaFallthrough;
  31   bool IsBasicBlockReachableViaBranch;
  32 };
  33
  34 /// Target-independent base class incharge of all code padding decisions for a
  35 /// target. During encoding it determines if and where MCPaddingFragments will
  36 /// be located, as later on, when layout information is available, it determines
  37 /// their sizes.
  38 class MCCodePadder {
  39   MCCodePadder(const MCCodePadder &) = delete;
  40   void operator=(const MCCodePadder &) = delete;
  41
  42   /// Determines if the MCCodePaddingPolicies are active.
  43   bool ArePoliciesActive;
  44
  45   /// All the supported MCCodePaddingPolicies.
  46   SmallPtrSet<MCCodePaddingPolicy *, 4> CodePaddingPolicies;
  47
  48   /// A pointer to the fragment of the instruction whose padding is currently
  49   /// done for.
  50   MCPaddingFragment *CurrHandledInstFragment;
  51
  52   /// A map holding the jurisdiction for each padding fragment. Key: padding
  53   /// fragment. Value: The fragment's jurisdiction. A jurisdiction is a vector
  54   /// of padding fragments whose conditions are being controlled by another
  55   /// fragment, the key fragment.
  56   DenseMap<MCPaddingFragment *, MCPFRange> FragmentToJurisdiction;
  57   MCPFRange &getJurisdiction(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
  58
  59   /// A map holding the maximal instruction window size relevant for a padding
  60   /// fragment.
  61   DenseMap<MCPaddingFragment *, uint64_t> FragmentToMaxWindowSize;
  62   uint64_t getMaxWindowSize(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
  63
  64 protected:
  65   /// The current streamer, used to stream code padding.
  66   MCObjectStreamer *OS;
  67
  68   bool addPolicy(MCCodePaddingPolicy *Policy);
  69
  70   virtual bool
  71   basicBlockRequiresInsertionPoint(const MCCodePaddingContext &Context) {
  72     return false;
  73   }
  74
  75   virtual bool instructionRequiresInsertionPoint(const MCInst &Inst) {
  76     return false;
  77   }
  78
  79   virtual bool usePoliciesForBasicBlock(const MCCodePaddingContext &Context) {
  80     return Context.IsPaddingActive;
  81   }
  82
  83 public:
  84   MCCodePadder()
  85       : ArePoliciesActive(false), CurrHandledInstFragment(nullptr),
  86         OS(nullptr) {}
  87   virtual ~MCCodePadder();
  88
  89   /// Handles all target related code padding when starting to write a new
  90   /// basic block to an object file.
  91   ///
  92   /// \param OS The streamer used for writing the padding data and function.
  93   /// \param Context the context of the padding, Embeds the basic block's
  94   /// parameters.
  95   void handleBasicBlockStart(MCObjectStreamer *OS,
  96                              const MCCodePaddingContext &Context);
  97   /// Handles all target related code padding when done writing a block to an
  98   /// object file.
  99   ///
 100   /// \param Context the context of the padding, Embeds the basic block's
 101   /// parameters.
 102   void handleBasicBlockEnd(const MCCodePaddingContext &Context);
 103   /// Handles all target related code padding before writing a new instruction
 104   /// to an object file.
 105   ///
 106   /// \param Inst the instruction.
 107   void handleInstructionBegin(const MCInst &Inst);
 108   /// Handles all target related code padding after writing an instruction to an
 109   /// object file.
 110   ///
 111   /// \param Inst the instruction.
 112   void handleInstructionEnd(const MCInst &Inst);
 113
 114   /// Relaxes a fragment (changes the size of the padding) according to target
 115   /// requirements. The new size computation is done w.r.t a layout.
 116   ///
 117   /// \param Fragment The fragment to relax.
 118   /// \param Layout Code layout information.
 119   ///
 120   /// \returns true iff any relaxation occurred.
 121   bool relaxFragment(MCPaddingFragment *Fragment, MCAsmLayout &Layout);
 122 };
 123
 124 /// The base class for all padding policies, i.e. a rule or set of rules to pad
 125 /// the generated code.
 126 class MCCodePaddingPolicy {
 127   MCCodePaddingPolicy() = delete;
 128   MCCodePaddingPolicy(const MCCodePaddingPolicy &) = delete;
 129   void operator=(const MCCodePaddingPolicy &) = delete;
 130
 131 protected:
 132   /// A mask holding the kind of this policy, i.e. only the i'th bit will be set
 133   /// where i is the kind number.
 134   const uint64_t KindMask;
 135   /// Instruction window size relevant to this policy.
 136   const uint64_t WindowSize;
 137   /// A boolean indicating which byte of the instruction determies its
 138   /// instruction window. If true - the last byte of the instructions, o.w. -
 139   /// the first byte of the instruction.
 140   const bool InstByteIsLastByte;
 141
 142   MCCodePaddingPolicy(uint64_t Kind, uint64_t WindowSize,
 143                       bool InstByteIsLastByte)
 144       : KindMask(UINT64_C(1) << Kind), WindowSize(WindowSize),
 145         InstByteIsLastByte(InstByteIsLastByte) {}
 146
 147   /// Computes and returns the offset of the consecutive fragment of a given
 148   /// fragment.
 149   ///
 150   /// \param Fragment The fragment whose consecutive offset will be computed.
 151   /// \param Layout Code layout information.
 152   ///
 153   /// \returns the offset of the consecutive fragment of \p Fragment.
 154   static uint64_t getNextFragmentOffset(const MCFragment *Fragment,
 155                                         const MCAsmLayout &Layout);
 156   /// Returns the instruction byte of an instruction pointed by a given
 157   /// MCPaddingFragment. An instruction byte is the address of the byte of an
 158   /// instruction which determines its instruction window.
 159   ///
 160   /// \param Fragment The fragment pointing to the instruction.
 161   /// \param Layout Code layout information.
 162   ///
 163   /// \returns the instruction byte of an instruction pointed by \p Fragment.
 164   uint64_t getFragmentInstByte(const MCPaddingFragment *Fragment,
 165                                MCAsmLayout &Layout) const;
 166   uint64_t computeWindowEndAddress(const MCPaddingFragment *Fragment,
 167                                    uint64_t Offset, MCAsmLayout &Layout) const;
 168
 169   /// Computes and returns the penalty weight of a first instruction window in a
 170   /// range. This requires a special function since the first window does not
 171   /// contain all the padding fragments in that window. It only contains all the
 172   /// padding fragments starting from the relevant insertion point.
 173   ///
 174   /// \param Window The first window.
 175   /// \param Offset The offset of the parent section relative to the beginning
 176   /// of the file, mod the window size.
 177   /// \param Layout Code layout information.
 178   ///
 179   /// \returns the penalty weight of a first instruction window in a range, \p
 180   /// Window.
 181   double computeFirstWindowPenaltyWeight(const MCPFRange &Window,
 182                                          uint64_t Offset,
 183                                          MCAsmLayout &Layout) const;
 184   /// Computes and returns the penalty caused by an instruction window.
 185   ///
 186   /// \param Window The instruction window.
 187   /// \param Offset The offset of the parent section relative to the beginning
 188   /// of the file, mod the window size.
 189   /// \param Layout Code layout information.
 190   ///
 191   /// \returns the penalty caused by \p Window.
 192   virtual double computeWindowPenaltyWeight(const MCPFRange &Window,
 193                                             uint64_t Offset,
 194                                             MCAsmLayout &Layout) const = 0;
 195
 196 public:
 197   virtual ~MCCodePaddingPolicy() {}
 198
 199   /// Returns the kind mask of this policy -  A mask holding the kind of this
 200   /// policy, i.e. only the i'th bit will be set where i is the kind number.
 201   uint64_t getKindMask() const { return KindMask; }
 202   /// Returns the instruction window size relevant to this policy.
 203   uint64_t getWindowSize() const { return WindowSize; }
 204   /// Returns true if the last byte of an instruction determines its instruction
 205   /// window, or false if the first of an instruction determines it.
 206   bool isInstByteLastByte() const { return InstByteIsLastByte; }
 207
 208   /// Returns true iff this policy needs padding for a given basic block.
 209   ///
 210   /// \param Context the context of the padding, Embeds the basic block's
 211   /// parameters.
 212   ///
 213   /// \returns true iff this policy needs padding for the basic block.
 214   virtual bool
 215   basicBlockRequiresPaddingFragment(const MCCodePaddingContext &Context) const {
 216     return false;
 217   }
 218   /// Returns true iff this policy needs padding for a given instruction.
 219   ///
 220   /// \param Inst The given instruction.
 221   ///
 222   /// \returns true iff this policy needs padding for \p Inst.
 223   virtual bool instructionRequiresPaddingFragment(const MCInst &Inst) const {
 224     return false;
 225   }
 226   /// Computes and returns the penalty caused by a range of instruction windows.
 227   /// The weight is computed for each window separelty and then accumulated.
 228   ///
 229   /// \param Range The range.
 230   /// \param Offset The offset of the parent section relative to the beginning
 231   /// of the file, mod the window size.
 232   /// \param Layout Code layout information.
 233   ///
 234   /// \returns the penalty caused by \p Range.
 235   double computeRangePenaltyWeight(const MCPFRange &Range, uint64_t Offset,
 236                                    MCAsmLayout &Layout) const;
 237 };
 238
 239 } // namespace llvm
 240
 241 #endif // LLVM_MC_MCCODEPADDER_H