Struct cranelift_codegen::binemit::StackMap

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pub struct StackMap { /* private fields */ }
Expand description

Stack maps record which words in a stack frame contain live GC references at a given instruction pointer.

Logically, a set of stack maps for a function record a table of the form:

+---------------------+-------------------------------------------+
| Instruction Pointer | SP-Relative Offsets of Live GC References |
+---------------------+-------------------------------------------+
| 0x12345678          | 2, 6, 12                                  |
| 0x1234abcd          | 2, 6                                      |
| ...                 | ...                                       |
+---------------------+-------------------------------------------+

Where “instruction pointer” is an instruction pointer within the function, and “offsets of live GC references” contains the offsets (in units of words) from the frame’s stack pointer where live GC references are stored on the stack. Instruction pointers within the function that do not have an entry in this table are not GC safepoints.

Because

  • offsets of live GC references are relative from the stack pointer, and
  • stack frames grow down from higher addresses to lower addresses,

to get a pointer to a live reference at offset x within a stack frame, you add x from the frame’s stack pointer.

For example, to calculate the pointer to the live GC reference inside “frame 1” below, you would do frame_1_sp + x:

          Stack
        +-------------------+
        | Frame 0           |
        |                   |
   |    |                   |
   |    +-------------------+ <--- Frame 0's SP
   |    | Frame 1           |
 Grows  |                   |
 down   |                   |
   |    | Live GC reference | --+--
   |    |                   |   |
   |    |                   |   |
   V    |                   |   x = offset of live GC reference
        |                   |   |
        |                   |   |
        +-------------------+ --+--  <--- Frame 1's SP
        | Frame 2           |
        | ...               |

An individual StackMap is associated with just one instruction pointer within the function, contains the size of the stack frame, and represents the stack frame as a bitmap. There is one bit per word in the stack frame, and if the bit is set, then the word contains a live GC reference.

Note that a caller’s OutgoingArg stack slots and callee’s IncomingArg stack slots overlap, so we must choose which function’s stack maps record live GC references in these slots. We record the IncomingArgs in the callee’s stack map.

Implementations§

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impl StackMap

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pub fn from_slice(vec: &[bool]) -> Self

Create a vec of Bitsets from a slice of bools.

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pub fn get_bit(&self, bit_index: usize) -> bool

Returns a specified bit.

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pub fn as_slice(&self) -> &[BitSet<u32>]

Returns the raw bitmap that represents this stack map.

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pub fn mapped_words(&self) -> u32

Returns the number of words represented by this stack map.

Trait Implementations§

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impl Clone for StackMap

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fn clone(&self) -> StackMap

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for StackMap

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl PartialEq for StackMap

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fn eq(&self, other: &StackMap) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl Eq for StackMap

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impl StructuralPartialEq for StackMap

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.