[llvm-dev] Using C++ and sanitizer_common in profile runtime

[Petr Hosek via llvm-dev]

What are your thoughts on using C++ and sanitizer_common in profile runtime?

First, to clarify, I'm not suggesting using the standard C++ library. What
I'm suggesting is just using the C++ language akin to sanitizer runtimes or
memprof.

profile runtime is the last major runtime in compiler-rt that's implemented
in C and switching to C++ could make the compiler-rt codebase more uniform.
Beyond that, I think this could be beneficial for several reasons:

* _Reducing the duplication between profile runtime and sanitizer_common._
Both of these implement various polyfills for different platforms (for
example the mmap like interface) and it would be great if we could avoid
duplicating the effort and share a common implementation.

* _Avoiding potential cyclic dependencies in profile runtime._ The
implementation currently uses various libc functions, but if libc is
profile instrumented there is a risk of potentially entering an infinite
recursion. This could be avoided by using internal implementations of these
libc functions which sanitizer_common does, but if we wanted to take the
same approach for profile runtime, we would need to re-implement these
functions again further increasing duplication.

* _Simplifying the profile runtime implementation._ Some parts of the
runtime already use object-oriented style interfaces, that is structs with
function pointers, replacing these with classes would make the code
cleaner. Furthermore, we could use classes to abstract away some of the
platform implementation which currently relies on ifdefs. We could also
take the advantage of RAII for resource management.

If we decided to go ahead with this change, I'd suggest an incremental
transition rather than doing a major rewrite. We would start by ensuring
that all source files compile as C++. Then we would introduce the
sanitizer_common dependency and see which functions could be replaced by
sanitizer_common counterparts. Finally, we could refactor the
implementation and take advantage of C++ constructs where appropriate.
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