nicula

5 ms·

1.
Claude Code's poor time awareness(nicula.xyz)
1 points by nicula 6mo ago|0 comments
2.
Auto-vectorizing operations on buffers of unknown length(nicula.xyz)
4 points by nicula 10mo ago|0 comments
3.
by nicula 2y ago
Yeah it's quite interesting. I don't think I've seen this come up in anything besides that talk which is about the HFT space. However, I did hear a few times about cases where you'd trade better average performance that
4.
Bypassing the Branch Predictor(nicula.xyz)
9 points by nicula 2y ago|2 comments
5.
by nicula 2y ago
Great observations, thanks! I wrote the code that you suggested (LMK if I understood your points): https://godbolt.org/z/jW4o3cnh3 And here's the benchmark output, on my machine: https://0x0.st/8Ss
6.
by nicula 2y ago
Thanks for looking into it! I modified the footnote to get rid of the misleading statements regarding the 'backfiring' of the optimization. :)
7.
by nicula 2y ago
> I'm not sure how "it can go the other way around too" -- in that case (assigning to a uint8_t local variable), it seems like that particular optimisation is just not being applied. So the case that you described has 2 la
8.
by nicula 2y ago
Some people already mentioned this in the r/cpp discussion. Small correction: 256 is not the correct number of iterations, since if all elements in that slice are even, then your 8-bit counter will wrap-around to zero, which can lead t
9.
by nicula 2y ago
Like @wffurr mentioned, this is indeed discussed in a footnote. I just added another remark to the same footnote: "It's also debatable whether or not Clang's 'optimization' results in better codegen in most cases th
10.
by nicula 2y ago
haha I didn't even notice that
11.
Improving on std:count_if()'s auto-vectorization(nicula.xyz)
134 points by nicula 2y ago|45 comments
12.
by nicula 2y ago
> So it's not a Clang regression per se, it's an issue with the LLVM core? Yes. > If you run LLVM 18's `opt` on bytecode generated by Clang 19 and then compile it, does it also generate the same bad assembly? No. If you
13.
by nicula 2y ago
This issue doesn't require large switch tables in order to show up. Even if you have 4 cases and the rest of them are default'ed, Clang 18 optimizes that to a switch, while Clang 19 does the (potentially) inefficient labels+jump
14.
Getting rid of unwanted branches in C/C++ code with __builtin_unreachable()(nicula.xyz)
2 points by nicula 2y ago|0 comments
15.
by nicula 2y ago
Oh wow didn't know about this. Somebody else posted it for me. Sorry for the dup:)
16.
A Clang regression related to switch statements and inlining(nicula.xyz)
21 points by nicula 2y ago|3 comments