In general, compiler command-line options can appear in any
order in a single compiler invocation. However, the effects of some
options depend on the order they appear in the command line and
how they are combined with other related options, for example, optimization options
-O, or PreCompiled Header (PCH)
The compiler enables you to use multiple options even where these might conflict. This means that you can append new options to an existing command line, for example, in a makefile or a via file.
Where options override previous options on the same command line, the last option specified always takes precedence. For example:
armcc -O1 -O3 -Ospace -Otime ...
is executed by the compiler as:
armcc -O3 -Otime
The environment variable
be used to specify compiler command-line options. Options specified
on the command line take precedence over options specified in the environment
To see how the compiler has processed the command line, use
--show_cmdline option. This shows nondefault
options that the compiler used. The contents of any via files are
expanded. In the example used here, although the compiler executes
-O2 -Otime, the output from
-O2. This is because
the default optimization level, and
not show options that apply by default.
Introducing the ARM Compiler toolchain: