Struct rustc_mir_transform::large_enums::EnumSizeOpt

pub struct EnumSizeOpt {
    pub(crate) discrepancy: u64,
}

A pass that seeks to optimize unnecessary moves of large enum types, if there is a large enough discrepancy between them.

i.e. If there are two variants:

enum Example {
  Small,
  Large([u32; 1024]),
}

Instead of emitting moves of the large variant, Perform a memcpy instead. Based off of this HackMD.

In summary, what this does is at runtime determine which enum variant is active, and instead of copying all the bytes of the largest possible variant, copy only the bytes for the currently active variant.

Fields

discrepancy: u64

Implementations

impl EnumSizeOpt

fn candidate<'tcx>( &self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>, ty: Ty<'tcx>, alloc_cache: &mut FxHashMap<Ty<'tcx>, AllocId> ) -> Option<(AdtDef<'tcx>, usize, AllocId)>

fn optim<'tcx>(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)

Trait Implementations

impl<'tcx> MirPass<'tcx> for EnumSizeOpt

fn is_enabled(&self, sess: &Session) -> bool

Returns true if this pass is enabled with the current combination of compiler flags.

fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)

fn name(&self) -> &'static str

fn profiler_name(&self) -> &'static str

fn is_mir_dump_enabled(&self) -> bool

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 8 bytes