feat: add more optimization flags (no exception/no rtti) #182
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| @@ -78,6 +78,8 @@ macro(dynamic_project_options) | |||
| "ENABLE_CPPCHECK\;OFF\;${MAKEFILE_OR_NINJA}\;Enable cppcheck analysis during compilation" | |||
| "ENABLE_INTERPROCEDURAL_OPTIMIZATION\;OFF\;OFF\;Enable whole-program optimization (e.g. LTO)" | |||
| "ENABLE_NATIVE_OPTIMIZATION\;OFF\;OFF\;Enable the optimizations specific to the build machine (e.g. SSE4_1, AVX2, etc.)." | |||
| "DISABLE_EXCEPTIONS\;OFF\;OFF\;Disable Exceptions (no-exceptions flag)" | |||
| "DISABLE_RTTI\;OFF\;OFF\;Disable RTTI (no-rtti flag)" | |||
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These are interesting options for embedded targets. There's a third one that comes to mind -fno-threadsafe-statics.
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Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesn’t need to be thread-safe.
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-fno-threadsafe-statics
(interesting for shaving some extra bytes from the binary, haven't used this option, yet...)
if it's only one and only get used in GCC, I would just add this option with target_compile_options(mytarget INTERFACE $<$<CXX_COMPILER_ID:GNU,Clang>:-fno-threadsafe-statics>)
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The reason I mentioned that flag is because it may not be desirable (or possible at all) to have mutexes (or some other form of critical sections / disabling interrupts) when static variables are accessed on some systems. A quick google tells that MSVC has a /Zc:threadSafeInit- flag.
I took an interests in your pull request because I'm trying to do similar stuff. @aminya is probably in a better position to judge.
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Since this optimization is unsafe, I prefer that we do not add it. In general, it would be important not to hinder the safety/correctness of a program for minor performance improvements.
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If you are sure that one part of the code doesn't need to be thread-safe, you should use the thread_local attributes for that specific variable. You cannot assume that this is true for all the programs and your dependencies.
https://en.cppreference.com/w/cpp/language/storage_duration
thread_local size_t ABC = 1; 
Just to make life easier with MSVC- vs. GNU-flags.