If you are compiling with the --multifile option, which in RVCT 4.0 is enabled by default at -O3 level, or --ltcg, it is possible for the compiler to perform automatic inlining for calls to functions that are defined in other translation units. --multifile is disabled by default in ARM Compiler 4.1 and later, regardless of the optimization level.

For --multifile, both translation units must be compiled in the same invocation of the compiler. For --ltcg, they are required only to be linked together.