Struct wasmtime_jit::trampoline::ir::MemFlags

pub struct MemFlags { /* private fields */ }

Flags for memory operations like load/store.

Each of these flags introduce a limited form of undefined behavior. The flags each enable certain optimizations that need to make additional assumptions. Generally, the semantics of a program does not change when a flag is removed, but adding a flag will.

In addition, the flags determine the endianness of the memory access. By default, any memory access uses the native endianness determined by the target ISA. This can be overridden for individual accesses by explicitly specifying little- or big-endian semantics via the flags.

Implementations

impl MemFlags

pub fn new() -> MemFlags

Create a new empty set of flags.

pub fn trusted() -> MemFlags

Create a set of flags representing an access from a “trusted” address, meaning it’s known to be aligned and non-trapping.

pub fn set_by_name(&mut self, name: &str) -> bool

Set a flag bit by name.

Returns true if the flag was found and set, false for an unknown flag name. Will also return false when trying to set inconsistent endianness flags.

pub fn endianness(self, native_endianness: Endianness) -> Endianness

Return endianness of the memory access. This will return the endianness explicitly specified by the flags if any, and will default to the native endianness otherwise. The native endianness has to be provided by the caller since it is not explicitly encoded in CLIF IR – this allows a front end to create IR without having to know the target endianness.

pub fn set_endianness(&mut self, endianness: Endianness)

Set endianness of the memory access.

pub fn notrap(self) -> bool

Test if the notrap flag is set.

Normally, trapping is part of the semantics of a load/store operation. If the platform would cause a trap when accessing the effective address, the Cranelift memory operation is also required to trap.

The notrap flag tells Cranelift that the memory is accessible, which means that accesses will not trap. This makes it possible to delete an unused load or a dead store instruction.

pub fn set_notrap(&mut self)

Set the notrap flag.

pub fn aligned(self) -> bool

Test if the aligned flag is set.

By default, Cranelift memory instructions work with any unaligned effective address. If the aligned flag is set, the instruction is permitted to trap or return a wrong result if the effective address is misaligned.

pub fn set_aligned(&mut self)

Set the aligned flag.

pub fn readonly(self) -> bool

Test if the readonly flag is set.

Loads with this flag have no memory dependencies. This results in undefined behavior if the dereferenced memory is mutated at any time between when the function is called and when it is exited.

pub fn set_readonly(&mut self)

Set the readonly flag.

Trait Implementations

impl Clone for MemFlags

pub fn clone(&self) -> MemFlags

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for MemFlags

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

Formats the value using the given formatter.

impl Display for MemFlags

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

Formats the value using the given formatter.

impl Hash for MemFlags

pub fn hash<__H>(&self, state: &mut __H) where
    __H: Hasher, 

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given Hasher.

impl PartialEq<MemFlags> for MemFlags

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

This method tests for self and other values to be equal, and is used by ==.

pub fn ne(&self, other: &MemFlags) -> bool

This method tests for !=.

impl Copy for MemFlags

impl Eq for MemFlags

impl StructuralEq for MemFlags

impl StructuralPartialEq for MemFlags