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work around compiler overhead around lambdas in generics by extracting them into free functions

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This commit is contained in:
The8472 2020-01-26 20:51:57 +01:00
parent 771b8ecc83
commit 872ab780c0
1 changed files with 39 additions and 34 deletions
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73
library/alloc/src/vec.rs
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@ -2212,6 +2212,34 @@ impl<T> SpecFrom<T, IntoIter<T>> for Vec<T> {
}
}
fn write_in_place<T>(src_end: *const T) -> impl FnMut(*mut T, T) -> Result<*mut T, !> {
move |mut dst, item| {
unsafe {
// the InPlaceIterable contract cannot be verified precisely here since
// try_fold has an exclusive reference to the source pointer
// all we can do is check if it's still in range
debug_assert!(dst as *const _ <= src_end, "InPlaceIterable contract violation");
ptr::write(dst, item);
dst = dst.add(1);
}
Ok(dst)
}
}
fn write_in_place_with_drop<T>(
src_end: *const T,
) -> impl FnMut(InPlaceDrop<T>, T) -> Result<InPlaceDrop<T>, !> {
move |mut sink, item| {
unsafe {
// same caveat as above
debug_assert!(sink.dst as *const _ <= src_end, "InPlaceIterable contract violation");
ptr::write(sink.dst, item);
sink.dst = sink.dst.add(1);
}
Ok(sink)
}
}
// Further specialization potential once
// https://github.com/rust-lang/rust/issues/62645 has been solved:
// T can be split into IN and OUT which only need to have the same size and alignment
@ -2230,46 +2258,23 @@ where
let inner = unsafe { iterator.as_inner().as_into_iter() };
(inner.buf.as_ptr(), inner.end, inner.cap)
};
let dst = src_buf;
// use try-fold
// - it vectorizes better for some iterator adapters
// - unlike most internal iteration methods methods it only takes a &mut self
// - lets us thread the write pointer through its innards and get it back in the end
let dst = if mem::needs_drop::<T>() {
// special-case drop handling since it prevents vectorization
let mut sink = InPlaceDrop { inner: src_buf, dst };
let _ = iterator.try_for_each::<_, Result<_, !>>(|item| {
unsafe {
debug_assert!(
sink.dst as *const _ <= src_end,
"InPlaceIterable contract violation"
);
ptr::write(sink.dst, item);
sink.dst = sink.dst.add(1);
}
Ok(())
});
// special-case drop handling since it forces us to lug that extra field around which
// can inhibit optimizations
let sink = InPlaceDrop { inner: src_buf, dst: src_buf };
let sink = iterator
.try_fold::<_, _, Result<_, !>>(sink, write_in_place_with_drop(src_end))
.unwrap();
// iteration succeeded, don't drop head
let sink = mem::ManuallyDrop::new(sink);
sink.dst
} else {
// use try-fold
// - it vectorizes better
// - unlike most internal iteration methods methods it only takes a &mut self
// - lets us thread the write pointer through its innards and get it back in the end
iterator
.try_fold::<_, _, Result<_, !>>(dst, move |mut dst, item| {
unsafe {
// the InPlaceIterable contract cannot be verified precisely here since
// try_fold has an exclusive reference to the source pointer
// all we can do is check if it's still in range
debug_assert!(
dst as *const _ <= src_end,
"InPlaceIterable contract violation"
);
ptr::write(dst, item);
dst = dst.add(1);
}
Ok(dst)
})
.unwrap()
iterator.try_fold::<_, _, Result<_, !>>(src_buf, write_in_place(src_end)).unwrap()
};
let src = unsafe { iterator.as_inner().as_into_iter() };