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3.3.5 GNU Compiler: Optimization

Figure 3-7 shows the MSP430 GCC Optimization settings window.

Figure 3-7 MSP430 GCC Settings: Optimization

Table 3-5 describes the options that are available for MSP430 GCC Optimization settings.

Table 3-5 MSP430 GCC Settings: Optimization

Option	Description
Optimization Level	Specifies the optimizations that the compiler applies to the generated object code. The options available are: None (O0): Disable optimizations. This setting is equivalent to specifying the -O0 command-line option. The compiler generates unoptimized linear assembly language code. Optimize (O1): The compiler performs all targets independent (that is, nonparallelized) optimizations, such as function inlining. This setting is equivalent to specifying the -O1 command-line option. The compiler omits all target-specific optimizations and generates linear assembly language code. Optimize more (O2): The compiler performs all optimizations (both target-independent and target-specific). This setting is equivalent to specifying the -O2 command-line option. The compiler outputs optimized nonlinear parallelized assembly language code. Optimize most (O3): The compiler performs all the level 2 optimizations, then the low-level optimizer performs global-algorithm register allocation. This setting is equivalent to specifying the -O3 command-line option. At this optimization level, the compiler generates code that is usually faster than the code generated from level 2 optimizations. Optimize for space rather than speed (-Os): Enables all -O2 optimizations that do not typically increase code size. The -Os option also performs further optimizations designed to reduce code size. Optimize for speed disregarding exact standards compliance (-Ofast): Enables all -O3 optimizations. The -Ofast option also enables optimizations that are not valid for all standard-compliant programs, such as -ffast-math.
Make 'char' unsigned by default (-funsigned-char)	Enable this option to ensure that the char is signed.
Place each function into its own section (-ffunction-sections)	Enable this option to place each function in its own section in the output file.
Place data items into their own section (-fdata-sections)	Enable this option to place each data item in its own section in the output file.
Convert floating point constants to single precision constants (-fsingle-precision-constant)	Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants.

Note:

Use the -ffunction-sections and -fdata-sections options in conjunction with the --gc-sections linker option to reduce code size by allowing the linker to remove unused sections.