[Issue 18600] Regex performance enhancement for repeated matchFirst calls

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18600

--- Comment #2 from Jon Degenhardt <jrdemail2000-dlang at yahoo.com> ---
Phobos PR 6268 was included in LDC 1.10.0-beta1. For this release the standard
benchmark I used for the TSV Utilities improved as follows:

LDC 1.7.0 (before regression):     8.37 seconds
LDC 1.8.0 (after regression):     10.01 seconds
LDC 1.9.0 (first fixes):           9.44 seconds
LDC 1.10.0-beta1 (Phobos PR 6268):  5.85 seconds

First fixes: Phobos PR 5981, DMD PR 7599

The benchmark test used reads a TSV file line-by-line and checks individual
fields for regex matches. A significant amount of processing time is IO, so the
percentage gain on the regex portion is higher than the overall gain. The
overall gain from LDC 1.7.0 is 30%.

Test was run on MacOS, MacMini with 16GB RAM, SSD drives. The file used was
2.7GB, 14 million lines. Test info can be found here:
https://github.com/eBay/tsv-utils-dlang/blob/master/docs/ComparativeBenchmarks2018.md

Great result!

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