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
17 #include "llvm/Support/MathExtras.h"
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.
UnknownPadding(unsigned LogAlign,unsigned KnownBits)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.
37 struct BasicBlockInfo {
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.
internalKnownBitsBasicBlockInfo75 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),
103 internalKnownBits());
104 }
105 };
106
107 } // end namespace llvm
108
109 #endif // LLVM_LIB_TARGET_ARM_ARMBASICBLOCKINFO_H
110