Apply some fixes to cross-language LTO (especially when targeting MSVC)
This PR contains a few fixes that were needed in order to get Firefox compiling with Rust/C++ cross-language ThinLTO on Windows. The commits are self-contained and should be self-explanatory.
r? @alexcrichton
This commit tweaks the linker-level visibility of some lang items that rustc
uses and defines. Notably this means that `#[panic_implementation]` and
`#[alloc_error_handler]` functions are never marked as `internal`. It's up to
the linker to eliminate these, not rustc.
Additionally `#[global_allocator]` generated symbols are no longer forced to
`Default` visibility (fully exported), but rather they're relaxed to `Hidden`
visibility). This symbols are *not* needed across DLL boundaries, only as a
local implementation detail of the compiler-injected allocator symbols, so
`Hidden` should suffice.
Closes#51342Closes#52795
with ThinLTO and cross-lang-lto.
Normally, when compiling with whole-crate-graph ThinLTO, we expect
rustc's LTO step to "uplift" upstream object files/LLVM modules to
the current set of compilation artifacts. Therefore the staticlib
creation code skips this uplifting. However, when compiling with
"cross-language LTO" (i.e. defer LTO to the actual linker), the LTO
step in rustc is not performed, so we have to take care of copying
upstream object files during archive creation (like we already do
when compiling without any LTO).
Building librustc_codegen_llvm in a separate directory
This allows clearing it out and building it separately from the
compiler. Since it's essentially a different and separate crate this
makes sense to do, each cargo invocation should generally happen in its
own directory.
r? @alexcrichton
This allows clearing it out and building it separately from the
compiler. Since it's essentially a different and separate crate this
makes sense to do, each cargo invocation should generally happen in its
own directory.
Reintroduce `Undef` and properly check constant value sizes
r? @RalfJung
cc @eddyb
basically all kinds of silent failures that never occurred are assertions now
Disable debug sections when optimization flags is set for LLD.
Currently LLD does not error when optimization is set and debugging information sections are present. (See discussion at https://reviews.llvm.org/D47901)
Using `--strip-debug` along with the `-O` option.
Previously linker diagnostic were being hidden when two modules were linked
together but failed to link. This commit fixes the situation by ensuring that we
have a diagnostic handler installed and also adds support for handling linker
diagnostics.
