Making it obvious which of the two operations is performed, reducing
call args and making sure a global isn't defined multiple times via
`defineGlobal()`.
The only [intended] functional change is in gen/trycatchfinally.cpp,
where I inserted a check for an existing __cpp_type_info_ptr global when
emitting a catch for C++ exceptions.
Not all type declarations yet (e.g., some TypeInfo subtypes are still
accessed directly), but those already wrapped as LazyType in the
gen/runtime.cpp module (with check and proper error msg in case object.d
doesn't contain a required declaration).
This fixes the 32-bit std.file unittests on Linux with enabled
optimizations. Quoting the SysV ABI docs:
> This is the only routine in the unwind library which is expected to be
> called directly by generated code: it will be called at the end of a
> landing pad in a "landing-pad" model.
The remaining LDC-specific ARM EABI wrapper (_d_eh_resume_unwind()) is
implemented in assembly (ldc/eh_asm.S), preserving registers apparently.
Previously assuming in the personality routine that encountering a C++ exception meant that catch clauses were raw std::type_info pointers was wrong in cases like:
try {
throwStdException(); // external C++ function throwing a std::exception
} catch (Throwable t) {
(...)
}
Generated __cpp_type_info_ptr constants receive the same mangling that they do within DMD.
Running a cleanup with a dummy target BB and later replacing all uses of
that dummy with the actual BB is buggy, as the cleanup keeps track of its
exit targets (via pointers) which aren't updated.
