winch_codegen/
regalloc.rs

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1use crate::{
2    codegen::CodeGenError,
3    isa::reg::{Reg, RegClass},
4    regset::{RegBitSet, RegSet},
5};
6
7use anyhow::{anyhow, Result};
8
9/// The register allocator.
10///
11/// The register allocator uses a single-pass algorithm;
12/// its implementation uses a bitset as a freelist
13/// to track per-class register availability.
14///
15/// If a particular register is not available upon request
16/// the register allocation will perform a "spill", essentially
17/// moving Local and Register values in the stack to memory.
18/// This process ensures that whenever a register is requested,
19/// it is going to be available.
20pub(crate) struct RegAlloc {
21    /// The register set.
22    regset: RegSet,
23}
24
25impl RegAlloc {
26    /// Create a register allocator from a bit set for each register class.
27    pub fn from(gpr: RegBitSet, fpr: RegBitSet) -> Self {
28        let rs = RegSet::new(gpr, fpr);
29        Self { regset: rs }
30    }
31
32    /// Allocate the next available register for the given class,
33    /// spilling if not available.
34    pub fn reg_for_class<F>(&mut self, class: RegClass, spill: &mut F) -> Result<Reg>
35    where
36        F: FnMut(&mut RegAlloc) -> Result<()>,
37    {
38        match self.regset.reg_for_class(class) {
39            Some(reg) => Ok(reg),
40            None => {
41                spill(self)?;
42                self.regset
43                    .reg_for_class(class)
44                    .ok_or_else(|| anyhow!(CodeGenError::expected_register_to_be_available()))
45            }
46        }
47    }
48
49    /// Returns true if the specified register is allocatable.
50    pub fn reg_available(&self, reg: Reg) -> bool {
51        self.regset.named_reg_available(reg)
52    }
53
54    /// Request a specific register, spilling if not available.
55    pub fn reg<F>(&mut self, named: Reg, mut spill: F) -> Result<Reg>
56    where
57        F: FnMut(&mut RegAlloc) -> Result<()>,
58    {
59        match self.regset.reg(named) {
60            Some(reg) => Ok(reg),
61            None => {
62                spill(self)?;
63                self.regset
64                    .reg(named)
65                    .ok_or_else(|| anyhow!(CodeGenError::expected_register_to_be_available()))
66            }
67        }
68    }
69
70    /// Free the given register.
71    pub fn free(&mut self, reg: Reg) {
72        self.regset.free(reg);
73    }
74}
winch_codegen/regalloc.rs

winch_codegen/
regalloc.rs
