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Arm Neon Intrinsics vs hand assembly

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https://web.archive.org/web/20170227190422/http://hilbert-space.de/?p=22 On this site which is quite dated it shows that hand written asm would give a much greater improvement then the intrinsics. I am wondering if this is the current truth even now in 2012. So has the compilation optimization improved for intrinsics using gnu cross compiler? My experience is that the intrinsics haven't really been worth the trouble. It's too easy for the compiler to inject extra register unload/load steps between your intrinsics. The effort to get it to stop doing that is more complicated than just writing

ARM Cortex-A8: Whats the difference between VFP and NEON

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问题 In ARM Cortex-A8 processor, I understand what NEON is, it is an SIMD co-processor. But is VFP(Vector Floating Point) unit, which is also a co-processor, works as a SIMD processor? If so which one is better to use? I read few links such as - Link1 Link2. But not really very clear what they mean. They say that VFP was never intended to be used for SIMD but on Wiki I read the following - " The VFP architecture also supports execution of short vector instructions but these operate on each vector

Methods to vectorise histogram in SIMD?

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问题 I am trying to implement histogram in Neon. Is it possible to vectorise ? 回答1: Histogramming is almost impossible to vectorize, unfortunately. You can probably optimise the scalar code somewhat however - a common trick is to use two histograms and then combine them at the end. This allows you to overlap loads/increments/stores and thereby bury some of the serial dependencies and associated latencies. Pseudo code: init histogram 1 to all 0s init histogram 2 to all 0s loop get input value 1 get

Android build system, NEON and non-NEON builds

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问题 I want to build my library for armv6, and there is some neon code that I enable at runtime if the device supports it. The neon code uses neon intrinsics, and to be able to compile it, I must enable armeabi-v7a, but that affects regular c-code (it becomes broken on some low-end devices). So, if the android build system wasn't excessively intrusive, I wouldn't have to ask questions, but it seems that there is no way for me to compile one file for armv6 and the other file for arm7-neon. Can

Using an union (encapsulated in a struct) to bypass conversions for neon data types

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问题 I made my first approach with vectorization intrinsics with SSE, where there is basically only one data type __m128i . Switching to Neon I found the data types and function prototypes to be much more specific, e.g. uint8x16_t (a vector of 16 unsigned char ), uint8x8x2_t (2 vectors with 8 unsigned char each), uint32x4_t (a vector with 4 uint32_t ) etc. First I was enthusiastic (much easier to find the exact function operating on the desired data type), then I saw what a mess it was when

Arm Neon Intrinsics vs hand assembly

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问题 https://web.archive.org/web/20170227190422/http://hilbert-space.de/?p=22 On this site which is quite dated it shows that hand written asm would give a much greater improvement then the intrinsics. I am wondering if this is the current truth even now in 2012. So has the compilation optimization improved for intrinsics using gnu cross compiler? 回答1: My experience is that the intrinsics haven't really been worth the trouble. It's too easy for the compiler to inject extra register unload/load