The idea here is that instead of the linker calling into codegen,
instead codegen should run before we touch the linker, and after MIR is
produced, it is sent to the linker. Aside from simplifying the call
graph (by preventing N linkers from each calling into M codegen
backends!), this has the huge benefit that it is possible to
parallellize codegen separately from linking. The threading model can
look like this:
* 1 semantic analysis thread, which generates AIR
* N codegen threads, which process AIR into MIR
* 1 linker thread, which emits MIR to the binary
The codegen threads are also responsible for `Air.Legalize` and
`Air.Liveness`; it's more efficient to do this work here instead of
blocking the main thread for this trivially parallel task.
I have repurposed the `Zcu.Feature.separate_thread` backend feature to
indicate support for this 1:N:1 threading pattern. This commit makes the
C backend support this feature, since it was relatively easy to divorce
from `link.C`: it just required eliminating some shared buffers. Other
backends don't currently support this feature. In fact, they don't even
compile -- the next few commits will fix them back up.
Nothing interesting here; literally just the bare minimum so I can work on this
on and off in a branch without worrying about merge conflicts in the non-backend
code.
Textual PTX is just assembly language like any other. And if we do ever add
support for emitting PTX object files after reverse engineering the bytecode
format, we'd be emitting ELF files like the CUDA toolchain. So there's really no
need for a special ObjectFormat tag here, nor linker code that treats it as a
distinct format.
This allows emitting object files for s390x-zos (GOFF) and powerpc(64)-aix
(XCOFF).
Note that GOFF emission in LLVM is still being worked on upstream for LLVM 21;
the resulting object files are useless right now. Also, -fstrip is required, or
LLVM will SIGSEGV during DWARF emission.
Previously, stepping from the single statement within the loop would
always exit the loop because all of the code unrolled from the loop is
associated with the same line and treated by the debugger as one line.
