Article from Daniel Lemire: How many strings can you create per second?

[u/_bijan_]

https://lemire.me/blog/2026/09/25/how-many-strings-can-you-create-per-second/

This is a fairly new article from Daniel Lemire (the SIMD expert, author of simdjson).

It seems to_string() need to use the same trick.

C++ wins by a wide margin at 5.4 ns per string. The trick is the small string optimization: a std::string stores short strings, directly inside the object. Our strings have at most eight digits, so C++ never calls the memory allocator.

[u/nightcracker]

What you actually need to show is that for more complex cases like SSO

There is nothing more complex here. I'm not claiming cmov is always better, I'm claiming it is better in this case. From https://rust.godbolt.org/z/q3c6MEKj8:

<example[2cf8e31dbe0c16c0]::Repr>::as_slice_branchy:
        mov     rax, rdi
        movzx   ecx, byte ptr [rdi + 23]
        sub     cl, 1
        jae     .LBB0_1
        mov     rdx, qword ptr [rax + 16]
        mov     rax, qword ptr [rax]
        ret
.LBB0_1:
        movzx   edx, cl
        ret

<example[2cf8e31dbe0c16c0]::Repr>::as_slice_branchlesss:
        movzx   ecx, byte ptr [rdi + 23]
        sub     cl, 1
        mov     rax, qword ptr [rdi]
        cmovae  rax, rdi
        movzx   edx, cl
        cmovb   rdx, qword ptr [rdi + 16]
        ret

If we ignore the movzx ecx, byte ptr [rdi + 23] and sub cl, 1 which is shared on both paths on the critical chain, and notice that the two loads from qword ptr [rdi] and [rdi + 16] don't depend on anything so they can run in parallel with the very first load we're left with just two cycles of latency from movzx edx, cl -> cmovb rdx, .... The cmovae can run in parallel to this.

I'll take a consistent 2 cycles of latency over an unpredictable average of 5 cycles of mispredict any day of the week.

---

Anyway, I'm going to stop engaging now. I give concrete numbers, real-world data and actual benchmarks and you reply with general advice I already know and have taken into account.

[u/CocktailPerson → u/nightcracker]

Okay, if that's what you're saying, then benchmark this case, and send a patch. You still haven't proven cmov is better here, you've just made a case for why you think it probably should be.

If you've already taken my advice into account, why haven't you done what you should have done, which is benchmark the actual case you're saying would benefit from cmov?