1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
using ARMeilleure.IntermediateRepresentation;
using System;
using System.Numerics;
namespace ARMeilleure.CodeGen.Arm64
{
static class CodeGenCommon
{
public const int TcAddressRegister = 8;
public const int ReservedRegister = 17;
public static bool ConstFitsOnSImm7(int value, int scale)
{
return (((value >> scale) << 25) >> (25 - scale)) == value;
}
public static bool ConstFitsOnSImm9(int value)
{
return ((value << 23) >> 23) == value;
}
public static bool ConstFitsOnUImm12(int value)
{
return (value & 0xfff) == value;
}
public static bool ConstFitsOnUImm12(int value, OperandType type)
{
int scale = Assembler.GetScaleForType(type);
return (((value >> scale) & 0xfff) << scale) == value;
}
public static bool TryEncodeBitMask(Operand operand, out int immN, out int immS, out int immR)
{
ulong value = operand.Value;
if (operand.Type == OperandType.I32)
{
value |= value << 32;
}
return TryEncodeBitMask(value, out immN, out immS, out immR);
}
public static bool TryEncodeBitMask(ulong value, out int immN, out int immS, out int immR)
{
// Some special values also can't be encoded:
// 0 can't be encoded because we need to subtract 1 from onesCount (which would became negative if 0).
// A value with all bits set can't be encoded because it is reserved according to the spec, because:
// Any value AND all ones will be equal itself, so it's effectively a no-op.
// Any value OR all ones will be equal all ones, so one can just use MOV.
// Any value XOR all ones will be equal its inverse, so one can just use MVN.
if (value == ulong.MaxValue)
{
immN = 0;
immS = 0;
immR = 0;
return false;
}
int bitLength = CountSequence(value);
if ((value >> bitLength) != 0)
{
bitLength += CountSequence(value >> bitLength);
}
int bitLengthLog2 = BitOperations.Log2((uint)bitLength);
int bitLengthPow2 = 1 << bitLengthLog2;
if (bitLengthPow2 < bitLength)
{
bitLengthLog2++;
bitLengthPow2 <<= 1;
}
int selectedESize = 64;
int repetitions = 1;
int onesCount = BitOperations.PopCount(value);
if (bitLengthPow2 < 64 && (value >> bitLengthPow2) != 0)
{
for (int eSizeLog2 = bitLengthLog2; eSizeLog2 < 6; eSizeLog2++)
{
bool match = true;
int eSize = 1 << eSizeLog2;
ulong mask = (1UL << eSize) - 1;
ulong eValue = value & mask;
for (int e = 1; e < 64 / eSize; e++)
{
if (((value >> (e * eSize)) & mask) != eValue)
{
match = false;
break;
}
}
if (match)
{
selectedESize = eSize;
repetitions = 64 / eSize;
onesCount = BitOperations.PopCount(eValue);
break;
}
}
}
// Find rotation. We have two cases, one where the highest bit is 0
// and one where it is 1.
// If it's 1, we just need to count the number of 1 bits on the MSB to find the right rotation.
// If it's 0, we just need to count the number of 0 bits on the LSB to find the left rotation,
// then we can convert it to the right rotation shift by subtracting the value from the element size.
int rotation;
long vHigh = (long)(value << (64 - selectedESize));
if (vHigh < 0)
{
rotation = BitOperations.LeadingZeroCount(~(ulong)vHigh);
}
else
{
rotation = (selectedESize - BitOperations.TrailingZeroCount(value)) & (selectedESize - 1);
}
// Reconstruct value and see if it matches. If not, we can't encode.
ulong reconstructed = onesCount == 64 ? ulong.MaxValue : RotateRight((1UL << onesCount) - 1, rotation, selectedESize);
for (int bit = 32; bit >= selectedESize; bit >>= 1)
{
reconstructed |= reconstructed << bit;
}
if (reconstructed != value || onesCount == 0)
{
immN = 0;
immS = 0;
immR = 0;
return false;
}
immR = rotation;
// immN indicates that there are no repetitions.
// The MSB of immS indicates the amount of repetitions, and the LSB the number of bits set.
if (repetitions == 1)
{
immN = 1;
immS = 0;
}
else
{
immN = 0;
immS = (0xf80 >> BitOperations.Log2((uint)repetitions)) & 0x3f;
}
immS |= onesCount - 1;
return true;
}
private static int CountSequence(ulong value)
{
return BitOperations.TrailingZeroCount(value) + BitOperations.TrailingZeroCount(~value);
}
private static ulong RotateRight(ulong bits, int shift, int size)
{
return (bits >> shift) | ((bits << (size - shift)) & (size == 64 ? ulong.MaxValue : (1UL << size) - 1));
}
}
}
|
