| 1 Aug 2025 |
 emily | (this is the entire link the reddit post goes to) | 12:06:28 |
 dramforever | it's literally not the same instruction encodings | 12:07:41 |
| emily | RISC-V feels like the kind of architecture I would have produced as a teenager who was monomaniacally fixated on orthogonality and minimality in all things | 12:07:57 |
| emily | I guess this comparison is probably not using uhh RV32 or whatever though | 12:08:13 |
| emily | or whatever you're meant to be using now. the real architecture | 12:08:20 |
 K900 | It's literally like that | 12:08:26 |
| emily | yeah ok the reddit comments say as much | 12:08:34 |
| K900 | Their response to "why" is "just do more uop fusion lol" | 12:08:37 |
| emily | well, no | 12:09:02 |
| emily | https://godbolt.org/z/19jnvda7G | 12:09:03 |
| emily | it looks like rva23u64 beats MIPS there | 12:09:20 |
| emily | so it's just a dumb comparison | 12:09:27 |
| K900 | Well yeah I don't mean this specific case | 12:09:37 |
| K900 | I just mean in general | 12:09:39 |
| emily | although the fragmentation of the RISC-V instruction sets in general is its own kind of dumb I suppose | 12:09:39 |
| emily | but also the thing teenage me would have done | 12:09:45 |
| K900 | There's like | 12:09:46 |
| K900 | A List | 12:09:47 |
| K900 | Of like Officially Mandated Fusions You Must Do To Fast | 12:10:01 |
| K900 | That compilers also know | 12:10:07 |
| emily | I think x86 also involves known uop fusions that compilers take into account | 12:10:08 |
| emily | it's arguably better to write it down than not | 12:10:15 |
| K900 | Not really | 12:10:17 |
| K900 | (for x86) | 12:10:23 |
| K900 | x86 mostly just has scheduling fuckery because it's very wide | 12:10:37 |
| K900 | But then modern aarch64 is also very wide | 12:10:46 |
| K900 | So it's likely actually fast RISC-V will also be very wide | 12:10:55 |
| K900 | So you'd have to consider both scheduling AND uop fusion and this is when you get the real funni | 12:11:12 |
| emily | my opinion as someone with no ISA design experience and no right to be making any judgement is that it feels like nobody has actually made anything better than AArch64 so far | 12:11:17 |
| dramforever | x86 and arm64 absolutely fuse | 12:11:24 |
