go/token: faster FileSet.Position implementation
- added a cache for last file looked up: avoids binary
search if the file matches
- don't look up extra line info if not present
(it is almost never present)
- inline one critical binary search call (inlining
provides almost 30% improvement in this case)
Together, these changes make the go/printer benchmark
more than twice as fast (53% improvement). gofmt also
sped up by about the same amount.
Also: removed an unused internal field from FileSet.
Measurements (always best of 5 runs):
* original:
printer.BenchmarkPrint 5
238354200 ns/op (100%)
* using last file cache:
printer.BenchmarkPrint 10
201796600 ns/op (85%)
* avoiding lookup of extra line info:
printer.BenchmarkPrint 10
157072700 ns/op (66%)
* inlining a critical binary search call:
printer.BenchmarkPrint 10
111523500 ns/op (47%)
gofmt (always best of 3 runs):
* before:
time gofmt -l src misc
real 0m33.316s
user 0m31.298s
sys 0m0.319s
* after:
time gofmt -l src misc
real 0m15.889s
user 0m14.596s
sys 0m0.224s
R=r, dfc, bradfitz, rsc1
CC=golang-dev
https://golang.org/cl/
4433086