Struct regalloc2::MachineEnv

pub struct MachineEnv {
    pub preferred_regs_by_class: [Vec<PReg>; 2],
    pub non_preferred_regs_by_class: [Vec<PReg>; 2],
    pub scratch_by_class: [PReg; 2],
    pub fixed_stack_slots: Vec<PReg>,
}

A machine envrionment 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>; 2]

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

non_preferred_regs_by_class: [Vec<PReg>; 2]

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.

scratch_by_class: [PReg; 2]

One 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.

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 a scratch register or as an allocatable regsiter.

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.