…ry cache.

The GNU C library (glibc) is documented to always allocate with an alignment
of at least 8 or 16 bytes, on 32-bit or 64-bit platforms:
https://www.gnu.org/software/libc/manual/html_node/Aligned-Memory-Blocks.html

This matches our use of `MIN_ALIGN` before this commit.
However, even when libc is glibc, the program might be linked
with another allocator that redefines the `malloc` symbol and friends.
(The `alloc_jemalloc` crate does, in some cases.)

So `alloc_system` doesn’t know which allocator it calls,
and needs to be conservative in assumptions it makes.

The C standard says:

https://port70.net/%7Ensz/c/c11/n1570.html#7.22.3
> The pointer returned if the allocation succeeds is suitably aligned
> so that it may be assigned to a pointer to any type of object
> with a fundamental alignment requirement

https://port70.net/~nsz/c/c11/n1570.html#6.2.8p2
> A fundamental alignment is represented by an alignment less than
> or equal to the greatest alignment supported by the implementation
> in all contexts, which is equal to `_Alignof (max_align_t)`.

`_Alignof (max_align_t)` depends on the ABI and doesn’t seem to have
a clear definition, but it seems to match our `MIN_ALIGN` in practice.

However, the size of objects is rounded up to the next multiple
of their alignment (since that size is also the stride used in arrays).
Conversely, the alignment of a non-zero-size object is at most its size.
So for example it seems ot be legal for `malloc(8)` to return a pointer
that’s only 8-bytes-aligned, even if `_Alignof (max_align_t)` is 16.

See previous commit’s message for what is expected of allocators
in general, and jemalloc/jemalloc#1072
for discussion of what jemalloc does specifically.

Most often, this code is used through the `std::heap::Heap`
and `#[gloabal_allocator]` indirection, so this branch is not
optimized out anymore.

Handles `pub use` of `extern { fn, static, type }`. Also plug in some more
`match` arms where handling `extern type` is reasonable.

Fixed #46098.

…ait.

This commit updates LLVM to fix #45511 (https://reviews.llvm.org/D39981) and
also reenables ThinLTO for libtest now that we shouldn't hit #45768. This also
opportunistically enables ThinLTO for libstd which was previously blocked
(#45661) on test failures related to debuginfo with a presumed cause of #45511.

Closes #45511

incr.comp.: Make sure we don't lose unused green results from the query cache.

In its current implementation, the query result cache works by bulk-writing the results of all cacheable queries into a monolithic binary file on disk. Prior to this PR, we would potentially lose query results during this process because only results that had already been loaded into memory were serialized. In contrast, results that were not needed during the given compilation session were not serialized again.

This PR will do one pass over all green `DepNodes` that represent a cacheable query and execute the corresponding query in order to make sure that the query result gets loaded into memory before cache serialization.

In the future we might want to look into a serialization format the can be updated in-place so that we don't have to load unchanged results just for immediately storing them again.

r? @nikomatsakis

Turns out ThinLTO was internalizing this symbol and eliminating it. Worse yet if
you compiled with LTO turns out no TLS destructors would run on Windows! The
`#[used]` annotation should be a more bulletproof implementation (in the face of
LTO) of preserving this symbol all the way through in LLVM and ensuring it makes
it all the way to the linker which will take care of it.

rustbuild: Update LLVM and enable ThinLTO

This commit updates LLVM to fix #45511 (https://reviews.llvm.org/D39981) and
also reenables ThinLTO for libtest now that we shouldn't hit #45768. This also
opportunistically enables ThinLTO for libstd which was previously blocked
(#45661) on test failures related to debuginfo with a presumed cause of #45511.

Closes #45511

Fix path search

Fixes #46015.

r? @QuietMisdreavus

allocators: don’t assume MIN_ALIGN for small sizes

See individual commit messages.

…, r=GuillaumeGomez

Properly handle reexport of foreign items.

Handles `pub use` of `extern { fn, static, type }`. Also plug in some more `match` arms where handling `extern type` is reasonable.

Fixed #46098.

rustc: don't mark lifetimes as early-bound in the presence of impl Trait.

This hack from the original implementation shouldn't be needed anymore, thanks to @cramertj.

r? @nikomatsakis

This commit alters how we compile LLVM by default enabling the WebAssembly
backend. This then also adds the wasm32-unknown-unknown target to get compiled
on the `cross` builder and distributed through rustup. Tests are not yet enabled
for this target but that should hopefully be coming soon!

rustbuild: Enable WebAssembly backend by default

This commit alters how we compile LLVM by default enabling the WebAssembly
backend. This then also adds the wasm32-unknown-unknown target to get compiled
on the `cross` builder and distributed through rustup. Tests are not yet enabled
for this target but that should hopefully be coming soon!