check out :

http://sdcc.sourceforge.net/

This compiler is 100% and has a very good support. the current version also
supports 8051, DS390, Z80, GBZ80 (Gameboy), AVR is under construction.

This compiler is intended for uC like the 8051. SDCC stands for
Smal Device C Compiler.

There is lot of c-sources out there like the SDCC-OKR (OpenKnowledgeResource)
http://www.qsl.net/dl9sec/SDCC_OKR.htm

The compiler is open source.

is is fun. the code generated is very fast and lots of applications, a code generated by hand would not be faster, well maybe some 0.0..% The compiler does lots of optimizing. you do not need to worry much about the locations / overlaying as much is handled by the compiler.

i run a cpu with 5 external and lots of internal ints with int rates 1msec or less. lots of statemachines that have to handle structures inside structures while the serial io is at 57600Baud full interrupt driven Master-Slave IO.
Did i mention that the source of serveral 1000 lines is pure c code ? is is a larger project and the cpu still has time to enter the idle modes.

now, i do not see a need for asm. works fine, readable, everybody that can program c is able to support the code.

Michael