lib/Target/ARM/ARMBasicBlockInfo.h

   1 //===-- ARMBasicBlockInfo.h - Basic Block Information -----------*- 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 // Utility functions and data structure for computing block size.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
  14 #define LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
  15
  16 #include "ARMBaseInstrInfo.h"
  17 #include "ARMMachineFunctionInfo.h"
  18 #include "llvm/Support/MathExtras.h"
  19 #include <algorithm>
  20 #include <cstdint>
  21
  22 namespace llvm {
  23
  24 using BBInfoVector = SmallVectorImpl<BasicBlockInfo>;
  25
  26 /// UnknownPadding - Return the worst case padding that could result from
  27 /// unknown offset bits.  This does not include alignment padding caused by
  28 /// known offset bits.
  29 ///
  30 /// @param Alignment alignment
  31 /// @param KnownBits Number of known low offset bits.
  32 inline unsigned UnknownPadding(Align Alignment, unsigned KnownBits) {
  33   if (KnownBits < Log2(Alignment))
  34     return Alignment.value() - (1ull << KnownBits);
  35   return 0;
  36 }
  37
  38 /// BasicBlockInfo - Information about the offset and size of a single
  39 /// basic block.
  40 struct BasicBlockInfo {
  41   /// Offset - Distance from the beginning of the function to the beginning
  42   /// of this basic block.
  43   ///
  44   /// Offsets are computed assuming worst case padding before an aligned
  45   /// block. This means that subtracting basic block offsets always gives a
  46   /// conservative estimate of the real distance which may be smaller.
  47   ///
  48   /// Because worst case padding is used, the computed offset of an aligned
  49   /// block may not actually be aligned.
  50   unsigned Offset = 0;
  51
  52   /// Size - Size of the basic block in bytes.  If the block contains
  53   /// inline assembly, this is a worst case estimate.
  54   ///
  55   /// The size does not include any alignment padding whether from the
  56   /// beginning of the block, or from an aligned jump table at the end.
  57   unsigned Size = 0;
  58
  59   /// KnownBits - The number of low bits in Offset that are known to be
  60   /// exact.  The remaining bits of Offset are an upper bound.
  61   uint8_t KnownBits = 0;
  62
  63   /// Unalign - When non-zero, the block contains instructions (inline asm)
  64   /// of unknown size.  The real size may be smaller than Size bytes by a
  65   /// multiple of 1 << Unalign.
  66   uint8_t Unalign = 0;
  67
  68   /// PostAlign - When > 1, the block terminator contains a .align
  69   /// directive, so the end of the block is aligned to PostAlign bytes.
  70   Align PostAlign;
  71
  72   BasicBlockInfo() = default;
  73
  74   /// Compute the number of known offset bits internally to this block.
  75   /// This number should be used to predict worst case padding when
  76   /// splitting the block.
  77   unsigned internalKnownBits() const {
  78     unsigned Bits = Unalign ? Unalign : KnownBits;
  79     // If the block size isn't a multiple of the known bits, assume the
  80     // worst case padding.
  81     if (Size & ((1u << Bits) - 1))
  82       Bits = countTrailingZeros(Size);
  83     return Bits;
  84   }
  85
  86   /// Compute the offset immediately following this block.  If Align is
  87   /// specified, return the offset the successor block will get if it has
  88   /// this alignment.
  89   unsigned postOffset(Align Alignment = Align::None()) const {
  90     unsigned PO = Offset + Size;
  91     const Align PA = std::max(PostAlign, Alignment);
  92     if (PA == Align::None())
  93       return PO;
  94     // Add alignment padding from the terminator.
  95     return PO + UnknownPadding(PA, internalKnownBits());
  96   }
  97
  98   /// Compute the number of known low bits of postOffset.  If this block
  99   /// contains inline asm, the number of known bits drops to the
 100   /// instruction alignment.  An aligned terminator may increase the number
 101   /// of know bits.
 102   /// If LogAlign is given, also consider the alignment of the next block.
 103   unsigned postKnownBits(Align Align = Align::None()) const {
 104     return std::max(Log2(std::max(PostAlign, Align)), internalKnownBits());
 105   }
 106 };
 107
 108 class ARMBasicBlockUtils {
 109
 110 private:
 111   MachineFunction &MF;
 112   bool isThumb = false;
 113   const ARMBaseInstrInfo *TII = nullptr;
 114   SmallVector<BasicBlockInfo, 8> BBInfo;
 115
 116 public:
 117   ARMBasicBlockUtils(MachineFunction &MF) : MF(MF) {
 118     TII =
 119       static_cast<const ARMBaseInstrInfo*>(MF.getSubtarget().getInstrInfo());
 120     isThumb = MF.getInfo<ARMFunctionInfo>()->isThumbFunction();
 121   }
 122
 123   void computeAllBlockSizes() {
 124     BBInfo.resize(MF.getNumBlockIDs());
 125     for (MachineBasicBlock &MBB : MF)
 126       computeBlockSize(&MBB);
 127   }
 128
 129   void computeBlockSize(MachineBasicBlock *MBB);
 130
 131   unsigned getOffsetOf(MachineInstr *MI) const;
 132
 133   unsigned getOffsetOf(MachineBasicBlock *MBB) const {
 134     return BBInfo[MBB->getNumber()].Offset;
 135   }
 136
 137   void adjustBBOffsetsAfter(MachineBasicBlock *MBB);
 138
 139   void adjustBBSize(MachineBasicBlock *MBB, int Size) {
 140     BBInfo[MBB->getNumber()].Size += Size;
 141   }
 142
 143   bool isBBInRange(MachineInstr *MI, MachineBasicBlock *DestBB,
 144                    unsigned MaxDisp) const;
 145
 146   void insert(unsigned BBNum, BasicBlockInfo BBI) {
 147     BBInfo.insert(BBInfo.begin() + BBNum, BBI);
 148   }
 149
 150   void clear() { BBInfo.clear(); }
 151
 152   BBInfoVector &getBBInfo() { return BBInfo; }
 153
 154 };
 155
 156 } // end namespace llvm
 157
 158 #endif // LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H