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by eliasmacpherson 5348 days ago
Although it's a poorly titled article, it was interesting to read. Surely the objective is to trick the compiler into generating the best code. I was surprised that the vectorisation it mentions was not performed automatically.

One other way would be to target different hardware than it's designed to work with via flags, or by using AMD with the intel compiler mentioned in the article. There was a very short discussion about this on reddit yesterday http://www.reddit.com/r/programming/comments/lj1ze/ask_rprog...
2 comments
froydnj 5348 days ago
> I was surprised that the vectorisation it mentions was not performed automatically.

The OP didn't mention what compiler was being used; GCC will certainly automatically vectorize this example (and ICC probably will as well). I used GCC 4.4 for x86 with -O3 -msse2.

Of course, there's a lot of compensation code inserted for unaligned pointers and aliased pointers and the like, but automatic vectorization is certainly doable.

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JoeAltmaier 5348 days ago
Depends entirely upon the compiler. Don't worry about this stuff in general unless you're doing embedded work, where the compilers are often problematical. Any desktop compiler will know more about generating code than you do.
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sliverstorm 5348 days ago
Embedded compilers are perfectly intelligent; I would hazard that you just wind up doing weird things more often, and/or you care more what exactly it does with this or that function because of your 32kHz clock and/or 1KB of program memory.
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tryp 5348 days ago
Many embedded compilers and assemblers are terribly buggy. Having worked with dozens, my impression is that the compilers targeting 8-bit microcontrollers are generally of similar quality to 80's x86 compilers. Emission of incorrect assembly given correct code is rare, but optimizations are incredibly weak and the compilers segfault relatively often.

Some of the DSP tool suites have solid compilers that optimize insightfully for their target architecture but whose in-circuit debuggers are tied to flaky IDEs. I'm currently working with an XDP debugger on a Sandy Bridge board that requires the debugger software to be restarted nearly hourly, often corrupting the project file requiring me to enter the memory map again.

Lately I've been thrilled to spec in ARM micros because I can just use GCC, an el-cheapo universal USB JTAG adapter through OpenOCD, and expect everything to work.

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