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Potentially both. Most compilers have vectorization optimizations if you compile for an architecture that supports it. However, a lot of software is compiled o
by habitue 4y ago
Potentially both. Most compilers have vectorization optimizations if you compile for an architecture that supports it.
However, a lot of software is compiled on one machine to be run on potentially many possible architectures, so they target a very lowest common denominator arch like x86-64. This will have some SIMD instructions but (I don't think) AVX-512.
So if a developer wants to ensure those instructions are used if they're supported, they'll write two code paths. one path will explicitly call the avx512 instructions with compiler intrinsics and then the other path will just use the manual code and let the compiler decide how to turn it into x86-64 safe instructions.
- readonlybarbie 4y agothanks for that! so it sounds like, if i purchase a chip that supports avx512, and run an operating system and compiler that supports avx512, i can write "plain old c code" with a minimal amount of compiler arguments and compile that code on my machine (aka not just running someone else's binary). and then the full power of avx512 is right there waiting for me? :)
- janwas 4y agoA compiler turning C(++) code into SIMD instructions is called "autovectorization". In my experience this works for simple loops such as dot products (even that requires special compiler flags to enable FMA and reorders), but unfortunately the wheels often fall off for more complex code. Also, I haven't seen the compiler generate the more exotic instructions.