Fix generator size regressions due to optimization #63034
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This actually exposed a latent bug related to uninhabitedness (basically #59972). I'm working on a PR to fix this, which this PR is blocked on. |
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This prevents uninhabited fields from "infecting" the abi and largest_niche of the generator layout. This fixes a latent bug, where an uninhabited field could be promoted to the generator prefix and cause the entire generator to become uninhabited.
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@tmandry Howdy from Triage! Is this PR still blocked? |
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Yes, on #63035 (I’ll rebase once I get an r+)
…On Fri, Aug 2, 2019 at 10:12 PM John Simon ***@***.***> wrote:
@tmandry <https://github.com/tmandry> Howdy from Triage! Is this PR still
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I tested the generator optimizations in rust-lang#60187 and rust-lang#61922 on the Fuchsia build, and noticed that some small generators (about 8% of the async fns in our build) increased in size slightly. This is because in rust-lang#60187 we split the fields into two groups, a "prefix" non-overlap region and an overlap region, and lay them out separately. This can introduce unnecessary padding bytes between the two groups. In every single case in the Fuchsia build, it was due to there being only a single variant being used in the overlap region. This means that we aren't doing any overlapping, period. So it's better to combine the two regions into one and lay out all the fields at once, which is what this change does.
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…ssions, r=cramertj Fix generator size regressions due to optimization I tested the generator optimizations in rust-lang#60187 and rust-lang#61922 on the Fuchsia build, and noticed that some small generators (about 8% of the async fns in our build) increased in size slightly. This is because in rust-lang#60187 we split the fields into two groups, a "prefix" non-overlap region and an overlap region, and lay them out separately. This can introduce unnecessary padding bytes between the two groups. In every single case in the Fuchsia build, it was due to there being only a single variant being used in the overlap region. This means that we aren't doing any overlapping, period. So it's better to combine the two regions into one and lay out all the fields at once, which is what this change does. r? @cramertj cc @eddyb @Zoxc
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Rollup of 9 pull requests Successful merges: - #63034 (Fix generator size regressions due to optimization) - #63035 (Use MaybeUninit to produce more correct layouts) - #63163 (add a pair of whitespace after remove parentheses) - #63294 (tests for async/await drop order) - #63307 (don't ignore mir_dump folder) - #63308 (PlaceRef's base is already a reference) - #63310 (Tests around moving parts of structs and tuples across await points) - #63314 (doc: the content has since been moved to the guide) - #63333 (Remove unnecessary features from compiler error code list) Failed merges: r? @ghost
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I tested the generator optimizations in #60187 and #61922 on the Fuchsia
build, and noticed that some small generators (about 8% of the async fns
in our build) increased in size slightly.
This is because in #60187 we split the fields into two groups, a
"prefix" non-overlap region and an overlap region, and lay them out
separately. This can introduce unnecessary padding bytes between the two
groups.
In every single case in the Fuchsia build, it was due to there being
only a single variant being used in the overlap region. This means that
we aren't doing any overlapping, period. So it's better to combine the
two regions into one and lay out all the fields at once, which is what
this change does.
r? @cramertj
cc @eddyb @Zoxc