mijit 0.2.4

Experimental JIT compiler generator
Documentation 
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

/// Represents the address of an instruction that jumps to a `Label`.
#[derive(Debug, Copy, Clone)]
pub struct Patch(usize);

impl Patch {
    /// The address is expressed as a byte offset into the compiled code.
    pub fn new(address: usize) -> Self { Patch(address) }

    pub fn address(&self) -> usize { self.0 }
}

//-----------------------------------------------------------------------------

/// Represents a possibly unknown control-flow target, and accumulates a
/// set of instructions that jump to it. Undefined `Label`s can be resolved
/// using [`define()`]. The instructions that jump to a `Label`
/// can be redirected to another `Label` using [`steal()`].
///
/// There may be more than one `Label` targeting the same address; each can
/// be [`steal()`]ed separately. Each control-flow instruction targets
/// exactly one `Label`.
///
/// [`define()`]: super::Lower::define
/// [`steal()`]: super::Lower::steal
#[derive(Debug)]
pub struct Label {
    target: Option<usize>,
    patches: Vec<Patch>,
}

impl Label {
    /// Constructs an unused `Label`. See also [`here()`]
    ///  - target - the low-level target address of the `Label`, if known,
    ///    expressed as a byte offset into the compiled code.
    ///
    /// [`here()`]: super::Lower::here
    pub fn new(target: Option<usize>) -> Self {
        Label {target, patches: Vec::new()}
    }

    /// Returns the low-level target address of this `Label`, if known.
    pub fn target(&self) -> Option<usize> { self.target }

    /// Tests whether `label` has a known target address.
    pub fn is_defined(&self) -> bool {
        self.target().is_some()
    }

    /// Appends `patch` to the list of instructions that jump to `self`.
    pub fn push(&mut self, patch: Patch) {
        self.patches.push(patch);
    }

    /// Returns and forgets all the instructions that jump to `self`.
    pub fn drain(&mut self) -> impl Iterator<Item=Patch> + '_ {
        self.patches.drain(..)
    }
}

impl Default for Label {
    fn default() -> Self { Label::new(None) }
}