If no optimization level is specified, the GCC default (-O0) is used.

If a GCC numeric optimization level (-O0 through -O3) is used, this is translated into -On -Otime for armcc. The GCC -Os option translates as -O3 -Ospace.

To force the use of a specific armcc optimization level, include the -Warmcc option. For example:

-Warmcc,-O1,-Ospace

Support for diagnostic control is limited. In particular, warnings are suppressed by default (similar to GCC) and are re-enabled with -W or -Wall. The -w option (lower case -w) is supported to suppress warnings, for example to override a -Wall earlier on the command line. Other GCC -W… options are ignored. If you require control of individual messages then you can use the normal compilation tools options, such as -Warmcc,--diag_suppress and -Warmcc,--diag_error.

Many GCC options do not have an equivalent in armcc. These include, for example, many of the -f... GCC options that control optimization phases that are specific to the GCC code generator, and are not applicable to armcc. Any GCC options that do not have an equivalent in armcc are silently ignored. To see the GCC options that are ignored, specify the options -Warmcc --remarks.