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Compilers and Libraries forum RVCT ARM compiler 3.1

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RVCT ARM compiler 3.1

Mallikarjun Shivappa Bidari over 11 years ago

Note: This was originally posted on 20th February 2009 at http://forums.arm.com

Hi,

Does RVCT 3.1 compiler is intelligent enough to identify which part of code can be NEON optimized and compiled in NEON?

Does it also give instruciotns while compiling, whether the code can be better optimized if we hand code it in NEON?

Regards,
Mallikarjun

0 Mallikarjun Shivappa Bidari over 11 years ago

Note: This was originally posted on 20th February 2009 at http://forums.arm.com

Thank you for the information.

I would like to know whether the compiler generates any information or not about which part of the code can be NEON optimized
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0 Mallikarjun Shivappa Bidari over 11 years ago
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0 Peter Harris over 11 years ago

Note: This was originally posted on 20th February 2009 at http://forums.arm.com

For most uses of NEON on Cortex-A8, such as codecs, which operate on complex packed structures it is generally better to hand code assembler. C isn't very good at expressing this kind of data manipulation.
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0 Peter Harris over 11 years ago

Note: This was originally posted on 21st February 2009 at http://forums.arm.com

> As per your example code, i could make out that, the compiler has given a message saying, " the line-10 of a function has been NEON optimized"

Yes, if you have the --remarks flag specified it will tell you what it has vectorized.
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0 Simon Craske over 11 years ago

Note: This was originally posted on 20th February 2009 at http://forums.arm.com

Mallikarjun,

It has a go if you request vectorizing, e.g.:

float vecmax(float *array) { int i; float max; max = array[0]; for(i=0;i<128;i=i+1) if(array[i] > max) max = array[i]; return max; }

armcc --cpu=cortex-a8 -O3 -Otime --vectorize --remarks -c vecmax.c

produces:
"vecmax.c", line 10: #1679-D: Optimization: Loop vectorized (i)

and generates vectorised floating-point Neon code.

hth
s.
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