The compiler-rt project is 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 compiler-rt library provides optimized implementations of this and other low-level routines.

the current feature set of compiler-rt is:

* full support for the libgcc interfaces on supported targets.
* high performance hand tuned implementations of commonly used functions
like __floatundidf in assembly that are dramatically faster than the
libgcc implementations.