Struct MachineEnv

pub struct MachineEnv {
    pub preferred_regs_by_class: [Vec<PReg>; 3],
    pub non_preferred_regs_by_class: [Vec<PReg>; 3],
    pub scratch_by_class: [Option<PReg>; 3],
    pub fixed_stack_slots: Vec<PReg>,
}

A machine environment tells the register allocator which registers are available to allocate and what register may be used as a scratch register for each class, and some other miscellaneous info as well.

Fields

preferred_regs_by_class: [Vec<PReg>; 3]

Preferred physical registers for each class. These are the registers that will be allocated first, if free.

If an explicit scratch register is provided in scratch_by_class then it must not appear in this list.

non_preferred_regs_by_class: [Vec<PReg>; 3]

Non-preferred physical registers for each class. These are the registers that will be allocated if a preferred register is not available; using one of these is considered suboptimal, but still better than spilling.

If an explicit scratch register is provided in scratch_by_class then it must not appear in this list.

scratch_by_class: [Option<PReg>; 3]

Optional dedicated scratch register per class. This is needed to perform moves between registers when cyclic move patterns occur. The register should not be placed in either the preferred or non-preferred list (i.e., it is not otherwise allocatable).

Note that the register allocator will freely use this register between instructions, but within the machine code generated by a single (regalloc-level) instruction, the client is free to use the scratch register. E.g., if one “instruction” causes the emission of two machine-code instructions, this lowering can use the scratch register between them.

If a scratch register is not provided then the register allocator will automatically allocate one as needed, spilling a value to the stack if necessary.

fixed_stack_slots: Vec<PReg>

Some PRegs can be designated as locations on the stack rather than actual registers. These can be used to tell the register allocator about pre-defined stack slots used for function arguments and return values.

PRegs in this list cannot be used as an allocatable or scratch register.

Trait Implementations

impl Clone for MachineEnv

fn clone(&self) -> MachineEnv

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for MachineEnv

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

Formats the value using the given formatter.

impl From<&MachineEnv> for PRegSet

fn from(env: &MachineEnv) -> Self

Converts to this type from the input type.