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Optimization of algorithm on ARMCortex A8(using NEON)

Girisha SG
Note: This was originally posted on 1st June 2011 at http://forums.arm.com

I am new to code optimization for speed(is the main focus)/memory etc

I am looking out for ,

1. We have the algorithms implemented using floating point operations. As I understand NEON has floating point units & hence we dont have to rewrite the algorithms in fixed points, is there anything like floating point operations are slower than fixed point operations or they are same or any other differences with respect to final CPU load/speed?
2. Do we need to take any special care/special optimization techniques for NEON?
3. I would like to know optimization techniques for ARM Cortex A8 (except using intrinsics :), like cache/memory optimizations), do's & dont's.
4. Keywords/anything else to compiler/linker to instruct RVDS to generate optimized code
5. How can I instruct the complier/linker to use NEON accelarator?
6. Any other guidlines to speed optimization using RVDS & GCC compilers.
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  • Note: This was originally posted on 4th June 2011 at http://forums.arm.com

    If you are using GCC instead of ARM's RVDS compiler, then unfortunately you can't just enable compiler flags and expect it to produce efficient code, because the compiler almost never knows how to take advantage of NEON. So if you want to use NEON then my recommendation is to either buy the RVDS compiler and modify your C code slightly to take advantage of it and hope it will make a noticeable improvement (such as 1.5x or 2x speed boost), or learn ARM & NEON Assembly language.

    I have recently written a tutorial explaining some things about optimizing for ARM (using C/C++ libraries or ideally Assembly language), with an example for rotating an image or matrix, at: http://www.shervinemami.info/armAssembly.html

    Cheers,
    Shervin Emami.
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  • Note: This was originally posted on 4th June 2011 at http://forums.arm.com

    If you are using GCC instead of ARM's RVDS compiler, then unfortunately you can't just enable compiler flags and expect it to produce efficient code, because the compiler almost never knows how to take advantage of NEON. So if you want to use NEON then my recommendation is to either buy the RVDS compiler and modify your C code slightly to take advantage of it and hope it will make a noticeable improvement (such as 1.5x or 2x speed boost), or learn ARM & NEON Assembly language.

    I have recently written a tutorial explaining some things about optimizing for ARM (using C/C++ libraries or ideally Assembly language), with an example for rotating an image or matrix, at: http://www.shervinemami.info/armAssembly.html

    Cheers,
    Shervin Emami.
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