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Don't allocate when creating an empty BTree #50352

Merged
merged 7 commits into from
May 12, 2018
Merged

Don't allocate when creating an empty BTree #50352

merged 7 commits into from
May 12, 2018

Commits on May 8, 2018

  1. Make LeafNode #[repr(C)] and put the metadata before generic items 

    This way we can safely statically allocate a LeafNode to use as the
placeholder before allocating, and any type accessing it will be able to
access the metadata at the same offset.
    @porglezomp
    porglezomp committed May 8, 2018
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  2. Add a statically allocated empty node for empty maps 

    This gives a pointer to that static empty node instead of allocating
a new node, and then whenever inserting makes sure that the root
isn't that empty node.
    @porglezomp
    porglezomp committed May 8, 2018
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  3. Don't drop the shared static node 

    We modify the drop implementation in IntoIter to not drop the shared root
    @porglezomp
    porglezomp committed May 8, 2018
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  4. Split into_slices() to avoid making extra slices 

    This splits into_slices() into into_key_slice() and into_val_slice(). While the
extra calls would get optimized out, this is a useful semantic change since we
call keys() while iterating, and we don't want to construct and out-of-bounds
val() pointer in the process if we happen to be pointing to the shared static
root.

This also paves the way for doing the alignment handling conditional differently
for the keys and values.
    @porglezomp
    porglezomp committed May 8, 2018
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  5. Make into_key_slice avoid taking out-of-bounds pointers

    @porglezomp
    porglezomp committed May 8, 2018
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  6. Add debug asserts and fix some violations

    @porglezomp
    porglezomp committed May 8, 2018
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  7. Make an ensure_root_is_owned method to reduce duplication 

    Also remove some unnecessary debug_assert! when creating the shared
root, since the root should be stored in the rodata and thus be
impossible to accidentally modify.
    @porglezomp
    porglezomp committed May 8, 2018
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