More info here:
http://www.mot.com/SPS/PowerPC/library/fact_sheet/mac_c.html

What's New in DR4.0 for Mac OS:

expanded details of optimizer's control variables
general porting tips to PPC
optimizing tips for PPC code/mcc usage tips
list of supported pragma's is included
new EDG C++ front end: 3.32
bug fixes
more aggressive optimizations
memset(), atan(), atan2() now in libmoto
new improved memcpy in libmoto
ability to selectively turn off warnings
pragma unused now supported
compiler supports profile driven feedback which allows the
compiler to use runtime information
to automatically optimize your apps
installation program for all Mac OS products
SPM preference panel
tracebacks for debugger now generated
produces output compatible with the Metrowerks Profiler (-p)