Struct rustc_mir_transform::nrvo::RenameReturnPlace
source · pub struct RenameReturnPlace;
Expand description
This pass looks for MIR that always copies the same local into the return place and eliminates
the copy by renaming all uses of that local to _0
.
This allows LLVM to perform an optimization similar to the named return value optimization
(NRVO) that is guaranteed in C++. This avoids a stack allocation and memcpy
for the
relatively common pattern of allocating a buffer on the stack, mutating it, and returning it by
value like so:
fn foo(init: fn(&mut [u8; 1024])) -> [u8; 1024] {
let mut buf = [0; 1024];
init(&mut buf);
buf
}
For now, this pass is very simple and only capable of eliminating a single copy. A more general version of copy propagation, such as the one based on non-overlapping live ranges in #47954 and #71003, could yield even more benefits.
Trait Implementations§
source§impl<'tcx> MirPass<'tcx> for RenameReturnPlace
impl<'tcx> MirPass<'tcx> for RenameReturnPlace
source§fn is_enabled(&self, sess: &Session) -> bool
fn is_enabled(&self, sess: &Session) -> bool
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
Auto Trait Implementations§
impl RefUnwindSafe for RenameReturnPlace
impl Send for RenameReturnPlace
impl Sync for RenameReturnPlace
impl Unpin for RenameReturnPlace
impl UnwindSafe for RenameReturnPlace
Blanket Implementations§
source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere T: ?Sized,
source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
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: 0 bytes