Enabling compiler built-ins

From: 20.24.0

Many of the features or options in the ETL can be enhanced by the use of compiler built-ins.
If built-ins are available and the STL is not used, then many copy type algorithms may be declared as constexpr.
Also, some type traits can detect types more correctly.

Controlling Macros

If any of these are set to 1, then the ETL will use the compiler built-ins, were applicable.
Setting them to 0 will disable the use of the built-in.
Setting any of these in the project or etl_profile.h will override any later tests.

ETL_USE_BUILTIN_MEMCPY
ETL_USE_BUILTIN_MEMCMP
ETL_USE_BUILTIN_MEMMOVE
ETL_USE_BUILTIN_MEMSET

ETL_USE_BUILTIN_IS_ASSIGNABLE
ETL_USE_BUILTIN_IS_CONSTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_CONSTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_DESTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_COPYABLE

Defining macros

The use of built-ins can be controlled by macros.

If ETL_USING_MEM_BUILTINS is defined and the corresponding macro has not already been set, then following will be set to 1.

ETL_USE_BUILTIN_MEMCPY
ETL_USE_BUILTIN_MEMCMP
ETL_USE_BUILTIN_MEMMOVE
ETL_USE_BUILTIN_MEMSET

If ETL_USING_TYPE_TRAITS_BUILTINS is defined and the corresponding macro has not already been set, then following will be set to 1.

ETL_USE_BUILTIN_IS_ASSIGNABLE
ETL_USE_BUILTIN_IS_CONSTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_CONSTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_DESTRUCTIBLE
ETL_USE_BUILTIN_IS_TRIVIALLY_COPYABLE

Detection of built-ins

These tests occur after the above macro tests.
The ETL will attempt to check the availability of compiler built-ins.

If __has_builtin exists, then the existence of the following built-ins are checked.
If not already defined, the corresponding macro is set according to the result.

Sets ETL_USE_BUILTIN_MEMCPY = 1 if __builtin_memcmp exists, otherwise 0.

Sets ETL_USE_BUILTIN_MEMCPY = 1 if __builtin_memcpy exists, otherwise 0.

Sets ETL_USE_BUILTIN_MEMMOVE = 1 if __builtin_memmove exists, otherwise 0.

Sets ETL_USE_BUILTIN_MEMSET = 1 if __builtin_memset exists, otherwise 0.

Sets ETL_USE_BUILTIN_IS_ASSIGNABLE = 1 if __is_assignable exists, otherwise 0.

Sets ETL_USE_BUILTIN_IS_CONSTRUCTIBLE = 1 if __is_constructible exists, otherwise 0.

Sets ETL_USE_BUILTIN_IS_TRIVIALLY_CONSTRUCTIBLE = 1 if __has_trivial_constructor or __is_trivially_constructible exists, otherwise 0.

Sets ETL_USE_BUILTIN_IS_TRIVIALLY_DESTRUCTIBLE = 1 if __has_trivial_destructor or __is_trivially_destructible exists, otherwise 0.

Sets ETL_USE_BUILTIN_IS_TRIVIALLY_COPYABLE = 1 if __has_trivial_copy or __is_trivially_copyable exists, otherwise 0.

Default

Finally, any macro that has so far not been defined will be defined as 0.