Now that LLVM has been updated, the only remaining roadblock to implementing
unwinding for MSVC is to fill out the runtime support in `std::rt::unwind::seh`.
This commit does precisely that, fixing up some other bits and pieces along the
way:
* The `seh` unwinding module now uses `RaiseException` to initiate a panic.
* The `rust_try.ll` file was rewritten for MSVC (as it's quite different) and is
located at `rust_try_msvc_64.ll`, only included on MSVC builds for now.
* The personality function for all landing pads generated by LLVM is hard-wired
to `__C_specific_handler` instead of the standard `rust_eh_personality` lang
item. This is required to get LLVM to emit SEH unwinding information instead
of DWARF unwinding information. This also means that on MSVC the
`rust_eh_personality` function is entirely unused (but is defined as it's a
lang item).
More details about how panicking works on SEH can be found in the
`rust_try_msvc_64.ll` or `seh.rs` files, but I'm always open to adding more
comments!
A key aspect of this PR is missing, however, which is that **unwinding is still
turned off by default for MSVC**. There is a [bug in llvm][llvm-bug] which
causes optimizations to inline enough landing pads that LLVM chokes. If the
compiler is optimized at `-O1` (where inlining isn't enabled) then it can
bootstrap with unwinding enabled, but when optimized at `-O2` (inlining is
enabled) then it hits a fatal LLVM error.
[llvm-bug]: https://llvm.org/bugs/show_bug.cgi?id=23884
I added it because it was easy (same a `char::to_lowercase`, just a different table), but it doesn’t make sense to have this in std but not str::to_titlecase, which would require https://github.com/unicode-rs/unicode-segmentation
At some point in the future this feature will be available (both on char and str) in a crates.io crate.
I added it because it was easy (same a `char::to_lowercase`,
just a different table), but it doesn’t make sense to have this
in std but not str::to_titlecase, which would require
https://github.com/unicode-rs/unicode-segmentation
At some point in the future this feature will be available
(both on char and str) in a crates.io crate.
This removes a footgun, since it is a reasonable assumption to make that
pointers to `T` will be aligned to `align_of::<T>()`. This also matches
the behaviour of C/C++. `min_align_of` is now deprecated.
Closes#21611.
This is needed to not drop performance, after the trait-based changes.
Force separate versions of the next method to be generated for the short
and long period cases.
In particular, I found that the disclaimer (promised in the second paragraph) doesn't stand out right now. I think the extra headers help with scanning this document, and making it easier to discern which steps are relevant to my particular flow through the options.
