Beta backports #36591
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Beta backports #36591
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Go back on half the specialization, the part that changed the Zip
struct's fields themselves depending on the types of the iterators.
This means that the Zip iterator will always carry two usize fields,
which are unused. If a whole for loop using a .zip() iterator is
inlined, these are simply removed and have no effect.
The same improvement for Zip of for example slice iterators remain, and
they still optimize well. However, like when the specialization of zip
was merged, the compiler is still very sensistive to the exact context.
For example this code only autovectorizes if the function is used, not
if the code in zip_sum_i32 is inserted inline it was called:
```
fn zip_sum_i32(xs: &[i32], ys: &[i32]) -> i32 {
let mut s = 0;
for (&x, &y) in xs.iter().zip(ys) {
s += x * y;
}
s
}
fn zipdot_i32_default_zip(b: &mut test::Bencher)
{
let xs = vec![1; 1024];
let ys = vec![1; 1024];
b.iter(|| {
zip_sum_i32(&xs, &ys)
})
}
```
Include a test that checks that Zip<T, U> is covariant w.r.t. T and U.
|
@brson - the first three look good to me. Feel free to r=me |
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Beta backports
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Backports of these PRs:
These three don't apply cleanly and somebody else will need to backport:
adt::trans_constwhen translating constant closures and tuples #36406r? @nikomatsakis