cmd/gc: superlinear slow-down compiling slice of interface literal

[bradfitz]

As the number of elements in a slice of interface literal grows, cmd/gc slows down more
than linearly:

http://play.golang.org/p/5TDTCtaP3Q


package main

type I interface {
    foo()
}

type S string

func (S) foo() {}

var s = []I{
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
    S("foo"),
...


Observed times for "go build x.go":

  100   0.003s
 1000   0.187s
 2000   0.784s
 3000   1.593s
 4000   2.655s
 5000   4.016s
 6000   5.685s
 7000   7.600s
14000   29.234s

[bradfitz]

Comment 1:

It also happens with append:
var s [5000]I
func init() {
    _ = append(s[:],
                S("foo"),
                S("foo"),
                S("foo"),
        S("foo"),
        S("foo"),
        S("foo"),
        S("foo"),
.....

[gopherbot]

Comment 2:

CL https://golang.org/cl/125720043 mentions this issue.

[rsc]

Comment 3:

This issue was closed by revision 7aa3031.

Status changed to Fixed.

[bradfitz]

Comment 4:

Comparing tip to Go 1.3 (1.3.0):
With 5000 elements: 9.68x faster.
With 10000 elements: 17.95x faster.
5000:
mac:~ bradfitz$ time go13 build x.go
real    0m9.414s
user    0m9.135s
sys 0m0.211s
mac:~ bradfitz$ time go build x.go
real    0m0.972s
user    0m0.809s
sys 0m0.142s
10,000:
mac:~ bradfitz$ time go13 build x.go
real    0m52.722s
user    0m51.368s
sys 0m0.769s
mac:~ bradfitz$ time go build x.go
real    0m2.937s
user    0m2.441s
sys 0m0.397s

[rsc]

Comment 5:

Approved for Go 1.3.1 (CL 125720043).

Labels changed: added release-go1.3.1, removed release-go1.4.

[adg]

Comment 6:

This issue was closed by revision 23f1ebe74d90.

[adg]

Comment 7:

Applied to release-branch.go1.3.