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A comment on A 100LOC C impl of memset, that is faster than glibc's. Parent comment

Re:A 100LOC C impl of memset, that is faster than glibc's by ninkendo on Friday November 12, 2021 @09:02AM (#29199315)
Here's the code in godbolt:

gcc: https://godbolt.org/z/6xG5dKjj9

clang: https://godbolt.org/z/Mh9zozjvK

I'm no asm expert, but it doesn't look like a lot of vector instructions in the gcc compilation of this, while the clang compilation seems to have more calls with the 128-bit xmm registers (at least on x86_64.) You can also just see visibly how many more instructions the gcc version outputs.

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Re:A 100LOC C impl of memset, that is faster than glibc's by mananaysiempre on Friday November 12, 2021 @09:13AM (#29199399)
Thank you! Indeed GCC does not use SIMD here unless you set -O3 (... I seem to remember this enables some vectorization?) or allow it to use AVX with -mavx or -march=x86-64-v3. For some reason I’m unable to get it to use plain SSE (always available on x86-64) with any -mtune setting or even with -march=x86-64-v2.
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