rustc: Add `_imp_` symbols later in compilation
On MSVC targets rustc will add symbols prefixed with `_imp_` to LLVM modules to
"emulate" dllexported statics as that workaround is still in place after #27438
hasn't been solved otherwise. These statics, however, were getting gc'd by
ThinLTO accidentally which later would cause linking failures.
This commit updates the location we add such symbols to happen just before
codegen to ensure that (a) they're not eliminated by the optimizer and (b) the
optimizer doesn't even worry about them.
Closes#45347
On MSVC targets rustc will add symbols prefixed with `_imp_` to LLVM modules to
"emulate" dllexported statics as that workaround is still in place after #27438
hasn't been solved otherwise. These statics, however, were getting gc'd by
ThinLTO accidentally which later would cause linking failures.
This commit updates the location we add such symbols to happen just before
codegen to ensure that (a) they're not eliminated by the optimizer and (b) the
optimizer doesn't even worry about them.
Closes#45347
First the `addPreservedGUID` function forgot to take care of "alias" summaries.
I'm not 100% sure what this is but the current code now matches upstream. Next
the `computeDeadSymbols` return value wasn't actually being used, but it needed
to be used! Together these should...
Closes#45195
