cubecl_ir/
allocator.rs

1use alloc::{rc::Rc, vec::Vec};
2use core::cell::RefCell;
3
4use hashbrown::HashMap;
5use portable_atomic::{AtomicU32, Ordering};
6
7use crate::BarrierLevel;
8
9use super::{Item, Matrix, Variable, VariableKind};
10
11/// An allocator for local variables of a kernel.
12///
13/// A local variable is unique to a unit. That is, each unit have their own copy of a local variable.
14/// There are three types of local variables based on their capabilities.
15///     - An immutable local variable is obtained by calling [Allocator::create_local].
16///     - A mutable local variable is obtained by calling [Allocator::create_local_mut]. The allocator will reuse
17///       previously defined mutable variables if possible.
18///     - A restricted mutable local variable is obtained by calling [Allocator::create_local_restricted]. This a is
19///       mutable variable that cannot be reused. This is mostly used for loop indices.
20///
21/// # Performance tips
22///
23/// In order, prefer immutable local variables, then mutable, then restricted.
24///
25/// To enable many compiler optimizations, it is preferred to use the [static single-assignment] strategy for immutable variables.
26/// That is, each variable must be declared and used exactly once.
27///
28/// [static single-assignment](https://en.wikipedia.org/wiki/Static_single-assignment_form)
29#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
30#[derive(Clone, Debug, Default, TypeHash)]
31pub struct Allocator {
32    #[cfg_attr(feature = "serde", serde(skip))]
33    local_mut_pool: Rc<RefCell<HashMap<Item, Vec<ExpandElement>>>>,
34    next_id: Rc<AtomicU32>,
35}
36
37impl PartialEq for Allocator {
38    fn eq(&self, other: &Self) -> bool {
39        Rc::ptr_eq(&self.local_mut_pool, &other.local_mut_pool)
40            && Rc::ptr_eq(&self.next_id, &other.next_id)
41    }
42}
43impl Eq for Allocator {}
44
45impl Allocator {
46    /// Create a new immutable local variable of type specified by `item`.
47    pub fn create_local(&self, item: Item) -> ExpandElement {
48        let id = self.new_local_index();
49        let local = VariableKind::LocalConst { id };
50        ExpandElement::Plain(Variable::new(local, item))
51    }
52
53    /// Create a new mutable local variable of type specified by `item`.
54    /// Try to reuse a previously defined but unused mutable variable if possible.
55    /// Else, this define a new variable.
56    pub fn create_local_mut(&self, item: Item) -> ExpandElement {
57        if item.elem.is_atomic() {
58            self.create_local_restricted(item)
59        } else {
60            self.reuse_local_mut(item)
61                .unwrap_or_else(|| ExpandElement::Managed(self.add_local_mut(item)))
62        }
63    }
64
65    /// Create a new mutable restricted local variable of type specified by `item`.
66    pub fn create_local_restricted(&self, item: Item) -> ExpandElement {
67        let id = self.new_local_index();
68        let local = VariableKind::LocalMut { id };
69        ExpandElement::Plain(Variable::new(local, item))
70    }
71
72    pub fn create_local_array(&self, item: Item, array_size: u32) -> ExpandElement {
73        let id = self.new_local_index();
74        let local_array = Variable::new(
75            VariableKind::LocalArray {
76                id,
77                length: array_size,
78            },
79            item,
80        );
81        ExpandElement::Plain(local_array)
82    }
83
84    /// Create a slice variable
85    pub fn create_slice(&self, item: Item) -> ExpandElement {
86        let id = self.new_local_index();
87        let variable = Variable::new(VariableKind::Slice { id }, item);
88        ExpandElement::Plain(variable)
89    }
90
91    /// Create a matrix variable
92    pub fn create_matrix(&self, matrix: Matrix) -> ExpandElement {
93        let id = self.new_local_index();
94        let variable = Variable::new(
95            VariableKind::Matrix { id, mat: matrix },
96            Item::new(matrix.elem),
97        );
98        ExpandElement::Plain(variable)
99    }
100
101    pub fn create_pipeline(&self, item: Item, num_stages: u8) -> ExpandElement {
102        let id = self.new_local_index();
103        let variable = Variable::new(
104            VariableKind::Pipeline {
105                id,
106                item,
107                num_stages,
108            },
109            item,
110        );
111        ExpandElement::Plain(variable)
112    }
113
114    pub fn create_barrier(&self, item: Item, level: BarrierLevel) -> ExpandElement {
115        let id = self.new_local_index();
116        let variable = Variable::new(VariableKind::Barrier { id, item, level }, item);
117        ExpandElement::Plain(variable)
118    }
119
120    // Try to return a reusable mutable variable for the given `item` or `None` otherwise.
121    pub fn reuse_local_mut(&self, item: Item) -> Option<ExpandElement> {
122        // Among the candidates, take a variable if it's only referenced by the pool.
123        // Arbitrarily takes the first it finds in reversed order.
124        self.local_mut_pool.borrow().get(&item).and_then(|vars| {
125            vars.iter()
126                .rev()
127                .find(|var| matches!(var, ExpandElement::Managed(v) if Rc::strong_count(v) == 1))
128                .cloned()
129        })
130    }
131
132    /// Add a new variable to the pool with type specified by `item` for the given `scope`.
133    pub fn add_local_mut(&self, item: Item) -> Rc<Variable> {
134        let id = self.new_local_index();
135        let local = Variable::new(VariableKind::LocalMut { id }, item);
136        let var = Rc::new(local);
137        let expand = ExpandElement::Managed(var.clone());
138        let mut pool = self.local_mut_pool.borrow_mut();
139        let variables = pool.entry(item).or_default();
140        variables.push(expand);
141        var
142    }
143
144    pub fn new_local_index(&self) -> u32 {
145        self.next_id.fetch_add(1, Ordering::Release)
146    }
147
148    pub fn take_variables(&self) -> Vec<Variable> {
149        self.local_mut_pool
150            .borrow_mut()
151            .drain()
152            .flat_map(|it| it.1)
153            .map(|it| *it)
154            .collect()
155    }
156}
157
158use cubecl_macros_internal::TypeHash;
159pub use expand_element::*;
160
161mod expand_element {
162    use cubecl_common::{flex32, tf32};
163    use half::{bf16, f16};
164
165    use super::*;
166
167    /// Reference to a JIT variable
168    #[derive(Clone, Debug, TypeHash)]
169    pub enum ExpandElement {
170        /// Variable kept in the variable pool.
171        Managed(Rc<Variable>),
172        /// Variable not kept in the variable pool.
173        Plain(Variable),
174    }
175
176    impl core::ops::Deref for ExpandElement {
177        type Target = Variable;
178
179        fn deref(&self) -> &Self::Target {
180            match self {
181                ExpandElement::Managed(var) => var.as_ref(),
182                ExpandElement::Plain(var) => var,
183            }
184        }
185    }
186
187    impl From<ExpandElement> for Variable {
188        fn from(value: ExpandElement) -> Self {
189            match value {
190                ExpandElement::Managed(var) => *var,
191                ExpandElement::Plain(var) => var,
192            }
193        }
194    }
195
196    impl ExpandElement {
197        /// If the element can be mutated inplace, potentially reusing the register.
198        pub fn can_mut(&self) -> bool {
199            match self {
200                ExpandElement::Managed(var) => {
201                    if let VariableKind::LocalMut { .. } = var.as_ref().kind {
202                        Rc::strong_count(var) <= 2
203                    } else {
204                        false
205                    }
206                }
207                ExpandElement::Plain(_) => false,
208            }
209        }
210
211        /// Explicitly consume the element, freeing it for reuse if no other copies exist.
212        pub fn consume(self) -> Variable {
213            *self
214        }
215    }
216
217    macro_rules! impl_into_expand_element {
218        ($type:ty) => {
219            impl From<$type> for ExpandElement {
220                fn from(value: $type) -> Self {
221                    ExpandElement::Plain(Variable::from(value))
222                }
223            }
224        };
225    }
226
227    impl_into_expand_element!(u8);
228    impl_into_expand_element!(u16);
229    impl_into_expand_element!(u32);
230    impl_into_expand_element!(u64);
231    impl_into_expand_element!(usize);
232    impl_into_expand_element!(bool);
233    impl_into_expand_element!(flex32);
234    impl_into_expand_element!(f16);
235    impl_into_expand_element!(bf16);
236    impl_into_expand_element!(tf32);
237    impl_into_expand_element!(f32);
238    impl_into_expand_element!(i8);
239    impl_into_expand_element!(i16);
240    impl_into_expand_element!(i32);
241    impl_into_expand_element!(i64);
242}
cubecl_ir/allocator.rs

cubecl_ir/
allocator.rs
