[Core] Optimize String::insert

[AThousandShips]

See also:

• [Core] Optimize String::join #92550
• [Core] Optimize String::replace methods #92546

[Calinou]

Tested locally (rebased on top of master c73ac74), it works as expected.

Testing project: test_pr_92555.zip

Benchmark

PC specifications

• CPU: Intel Core i9-13900K
• GPU: NVIDIA GeForce RTX 4090
• RAM: 64 GB (2×32 GB DDR5-5800 C30)
• SSD: Solidigm P44 Pro 2 TB
• OS: Linux (Fedora 40)

Using an optimized editor build (optimize=speed lto=full).

20 million iterations of String.insert() (10 million at the beginning of a string, 10 million at the end¹):

Before	After
2169 ms	952 ms

With much longer strings to insert into:

Before

insert(0) took 1222376 usecs
insert(5) took 3907256 usecs

After

insert(0) took 797245 usecs
insert(5) took 802382 usecs

Footnotes

1. These take more or less the same time to complete, I wanted to check performance of both cases just to be sure. ↩

[akien-mga]

Thanks!

[AThousandShips]

Thank you!