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

//! Global values.

use crate::ir::immediates::{Imm64, Offset32};
use crate::ir::{ExternalName, GlobalValue, Type};
use crate::isa::TargetIsa;
use crate::machinst::RelocDistance;
use core::fmt;

#[cfg(feature = "enable-serde")]
use serde::{Deserialize, Serialize};

/// Information about a global value declaration.
#[derive(Clone, PartialEq, Hash)]
#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
pub enum GlobalValueData {
    /// Value is the address of the VM context struct.
    VMContext,

    /// Value is pointed to by another global value.
    ///
    /// The `base` global value is assumed to contain a pointer. This global value is computed
    /// by loading from memory at that pointer value. The memory must be accessible, and
    /// naturally aligned to hold a value of the type. The data at this address is assumed
    /// to never change while the current function is executing.
    Load {
        /// The base pointer global value.
        base: GlobalValue,

        /// Offset added to the base pointer before doing the load.
        offset: Offset32,

        /// Type of the loaded value.
        global_type: Type,

        /// Specifies whether the memory that this refers to is readonly, allowing for the
        /// elimination of redundant loads.
        readonly: bool,
    },

    /// Value is an offset from another global value.
    IAddImm {
        /// The base pointer global value.
        base: GlobalValue,

        /// Byte offset to be added to the value.
        offset: Imm64,

        /// Type of the iadd.
        global_type: Type,
    },

    /// Value is symbolic, meaning it's a name which will be resolved to an
    /// actual value later (eg. by linking). Cranelift itself does not interpret
    /// this name; it's used by embedders to link with other data structures.
    ///
    /// For now, symbolic values always have pointer type, and represent
    /// addresses, however in the future they could be used to represent other
    /// things as well.
    Symbol {
        /// The symbolic name.
        name: ExternalName,

        /// Offset from the symbol. This can be used instead of IAddImm to represent folding an
        /// offset into a symbol.
        offset: Imm64,

        /// Will this symbol be defined nearby, such that it will always be a certain distance
        /// away, after linking? If so, references to it can avoid going through a GOT. Note that
        /// symbols meant to be preemptible cannot be colocated.
        ///
        /// If `true`, some backends may use relocation forms that have limited range: for example,
        /// a +/- 2^27-byte range on AArch64. See the documentation for
        /// `RelocDistance` for more details.
        colocated: bool,

        /// Does this symbol refer to a thread local storage value?
        tls: bool,
    },

    /// Value is a multiple of how many instances of `vector_type` will fit in
    /// a target vector register.
    DynScaleTargetConst {
        /// Base vector type.
        vector_type: Type,
    },
}

impl GlobalValueData {
    /// Assume that `self` is an `GlobalValueData::Symbol` and return its name.
    pub fn symbol_name(&self) -> &ExternalName {
        match *self {
            Self::Symbol { ref name, .. } => name,
            _ => panic!("only symbols have names"),
        }
    }

    /// Return the type of this global.
    pub fn global_type(&self, isa: &dyn TargetIsa) -> Type {
        match *self {
            Self::VMContext { .. } | Self::Symbol { .. } => isa.pointer_type(),
            Self::IAddImm { global_type, .. } | Self::Load { global_type, .. } => global_type,
            Self::DynScaleTargetConst { .. } => isa.pointer_type(),
        }
    }

    /// If this global references a symbol, return an estimate of the relocation distance,
    /// based on the `colocated` flag.
    pub fn maybe_reloc_distance(&self) -> Option<RelocDistance> {
        match self {
            &GlobalValueData::Symbol {
                colocated: true, ..
            } => Some(RelocDistance::Near),
            &GlobalValueData::Symbol {
                colocated: false, ..
            } => Some(RelocDistance::Far),
            _ => None,
        }
    }
}

impl fmt::Display for GlobalValueData {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Self::VMContext => write!(f, "vmctx"),
            Self::Load {
                base,
                offset,
                global_type,
                readonly,
            } => write!(
                f,
                "load.{} notrap aligned {}{}{}",
                global_type,
                if readonly { "readonly " } else { "" },
                base,
                offset
            ),
            Self::IAddImm {
                global_type,
                base,
                offset,
            } => write!(f, "iadd_imm.{} {}, {}", global_type, base, offset),
            Self::Symbol {
                ref name,
                offset,
                colocated,
                tls,
            } => {
                write!(
                    f,
                    "symbol {}{}{}",
                    if colocated { "colocated " } else { "" },
                    if tls { "tls " } else { "" },
                    name.display(None)
                )?;
                let offset_val: i64 = offset.into();
                if offset_val > 0 {
                    write!(f, "+")?;
                }
                if offset_val != 0 {
                    write!(f, "{}", offset)?;
                }
                Ok(())
            }
            Self::DynScaleTargetConst { vector_type } => {
                write!(f, "dyn_scale_target_const.{}", vector_type)
            }
        }
    }
}