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ARMBasicBlockInfo.h
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1 //===-- ARMBasicBlockInfo.h - Basic Block Information -----------*- C++ -*-===//
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 // Utility functions and data structure for computing block size.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
15 #define LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
16 
18 #include <algorithm>
19 #include <cstdint>
20 
21 namespace llvm {
22 
23 /// UnknownPadding - Return the worst case padding that could result from
24 /// unknown offset bits. This does not include alignment padding caused by
25 /// known offset bits.
26 ///
27 /// @param LogAlign log2(alignment)
28 /// @param KnownBits Number of known low offset bits.
29 inline unsigned UnknownPadding(unsigned LogAlign, unsigned KnownBits) {
30  if (KnownBits < LogAlign)
31  return (1u << LogAlign) - (1u << KnownBits);
32  return 0;
33 }
34 
35 /// BasicBlockInfo - Information about the offset and size of a single
36 /// basic block.
38  /// Offset - Distance from the beginning of the function to the beginning
39  /// of this basic block.
40  ///
41  /// Offsets are computed assuming worst case padding before an aligned
42  /// block. This means that subtracting basic block offsets always gives a
43  /// conservative estimate of the real distance which may be smaller.
44  ///
45  /// Because worst case padding is used, the computed offset of an aligned
46  /// block may not actually be aligned.
47  unsigned Offset = 0;
48 
49  /// Size - Size of the basic block in bytes. If the block contains
50  /// inline assembly, this is a worst case estimate.
51  ///
52  /// The size does not include any alignment padding whether from the
53  /// beginning of the block, or from an aligned jump table at the end.
54  unsigned Size = 0;
55 
56  /// KnownBits - The number of low bits in Offset that are known to be
57  /// exact. The remaining bits of Offset are an upper bound.
58  uint8_t KnownBits = 0;
59 
60  /// Unalign - When non-zero, the block contains instructions (inline asm)
61  /// of unknown size. The real size may be smaller than Size bytes by a
62  /// multiple of 1 << Unalign.
63  uint8_t Unalign = 0;
64 
65  /// PostAlign - When non-zero, the block terminator contains a .align
66  /// directive, so the end of the block is aligned to 1 << PostAlign
67  /// bytes.
68  uint8_t PostAlign = 0;
69 
70  BasicBlockInfo() = default;
71 
72  /// Compute the number of known offset bits internally to this block.
73  /// This number should be used to predict worst case padding when
74  /// splitting the block.
75  unsigned internalKnownBits() const {
76  unsigned Bits = Unalign ? Unalign : KnownBits;
77  // If the block size isn't a multiple of the known bits, assume the
78  // worst case padding.
79  if (Size & ((1u << Bits) - 1))
80  Bits = countTrailingZeros(Size);
81  return Bits;
82  }
83 
84  /// Compute the offset immediately following this block. If LogAlign is
85  /// specified, return the offset the successor block will get if it has
86  /// this alignment.
87  unsigned postOffset(unsigned LogAlign = 0) const {
88  unsigned PO = Offset + Size;
89  unsigned LA = std::max(unsigned(PostAlign), LogAlign);
90  if (!LA)
91  return PO;
92  // Add alignment padding from the terminator.
93  return PO + UnknownPadding(LA, internalKnownBits());
94  }
95 
96  /// Compute the number of known low bits of postOffset. If this block
97  /// contains inline asm, the number of known bits drops to the
98  /// instruction alignment. An aligned terminator may increase the number
99  /// of know bits.
100  /// If LogAlign is given, also consider the alignment of the next block.
101  unsigned postKnownBits(unsigned LogAlign = 0) const {
102  return std::max(std::max(unsigned(PostAlign), LogAlign),
104  }
105 };
106 
107 } // end namespace llvm
108 
109 #endif // LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
GCNRegPressure max(const GCNRegPressure &P1, const GCNRegPressure &P2)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
unsigned Offset
Offset - Distance from the beginning of the function to the beginning of this basic block...
BasicBlockInfo - Information about the offset and size of a single basic block.
std::size_t countTrailingZeros(T Val, ZeroBehavior ZB=ZB_Width)
Count number of 0&#39;s from the least significant bit to the most stopping at the first 1...
Definition: MathExtras.h:112
unsigned postOffset(unsigned LogAlign=0) const
Compute the offset immediately following this block.
unsigned internalKnownBits() const
Compute the number of known offset bits internally to this block.
unsigned postKnownBits(unsigned LogAlign=0) const
Compute the number of known low bits of postOffset.
unsigned UnknownPadding(unsigned LogAlign, unsigned KnownBits)
UnknownPadding - Return the worst case padding that could result from unknown offset bits...
unsigned Size
Size - Size of the basic block in bytes.
uint8_t Unalign
Unalign - When non-zero, the block contains instructions (inline asm) of unknown size.
uint8_t KnownBits
KnownBits - The number of low bits in Offset that are known to be exact.
BasicBlockInfo()=default
uint8_t PostAlign
PostAlign - When non-zero, the block terminator contains a .align directive, so the end of the block ...