ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Coding Practices
5.3 Compiler optimization levels and the debug view
The precise optimizations performed by the compiler depend both on the level of optimization
chosen, and whether you are optimizing for performance or code size.
The compiler supports the following optimization levels:
-O0 Minimum optimization. The compiler performs simple optimizations that do not
impair the debug view.
When debugging is enabled, this option gives the best possible debug view.
-O1 Restricted optimization.
When debugging is enabled, this option gives a generally satisfactory debug view
with good code density.
-O2 High optimization. This is the default optimization level.
When debugging is enabled, this option might give a less satisfactory debug view.
-O3 Maximum optimization. This is the most aggressive form of optimization
available. Specifying this option enables multifile compilation by default where
multiple files are specified on the command line.
When debugging is enabled, this option typically gives a poor debug view.
Because optimization affects the mapping of object code to source code, the choice of
optimization level with -Ospace and -Otime generally impacts the debug view.
The option -O0 is the best option to use if a simple debug view is needed. Selecting -O0 typically
increases the size of the ELF image by 7 to 15%. To reduce the size of your debug tables, use
the --remove_unneeded_entities option.
5.3.1 See also
Tasks
• Methods of reducing debug information in objects and libraries on page 5-20.
Concepts
• Benefits of reducing debug information in objects and libraries on page 5-19.
Reference
Compiler Reference:
• --debug, --no_debug on page 3-24
• --debug_macros, --no_debug_macros on page 3-24
• --dwarf2 on page 3-35
• --dwarf3 on page 3-35
• -Onum on page 3-71
• -Ospace on page 3-72
• -Otime on page 3-73
• --remove_unneeded_entities, --no_remove_unneeded_entities on page 3-82.
Other information
• ARM ELF File Format,
http://infocenter.arm.com/help/topic/com.arm.doc.dui0101-/index.html
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