The compiler-rt project consists of: - builtins - a simple library that provides an implementation of the low-level target-specific hooks required by code generation and other runtime components. For example, when compiling for a 32-bit target, converting a double to a 64-bit unsigned integer is compiling into a runtime call to the "__fixunsdfdi" function. The builtins library provides optimized implementations of this and other low-level routines, either in target-independent C form, or as a heavily-optimized assembly. - sanitizer runtimes - runtime libraries that are required to run the code with sanitizer instrumentation. This includes runtimes for: * AddressSanitizer * ThreadSanitizer * UndefinedBehaviorSanitizer * MemorySanitizer * LeakSanitizer * DataFlowSanitizer - profile - library which is used to collect coverage information. - BlocksRuntime - a target-independent implementation of Apple "Blocks" runtime interfaces.