strings: timeout in TestCompareStrings

[ianlancetaylor]

The builders have recently started showing a number of timeouts running TestCompareStrings. Why?

In case it's a compiler issue, CC @randall77 @josharian @martisch

2018-10-30T16:23:44-f570b54/solaris-amd64-oraclerel
2018-10-30T17:09:42-5168fcf/freebsd-amd64-12_0
2018-10-30T17:45:19-f14067f/darwin-amd64-10_10
2018-10-30T17:45:19-f14067f/freebsd-amd64-10_3
2018-10-31T13:47:42-49dafc7/darwin-amd64-10_11
2018-10-31T13:47:42-49dafc7/windows-amd64-race
2018-10-31T13:55:01-e8ffb8a/windows-amd64-race
2018-10-31T15:07:05-53856c4/darwin-amd64-10_12
2018-10-31T16:11:20-cb07f49/darwin-amd64-10_11
2018-10-31T16:11:20-cb07f49/darwin-amd64-10_12
2018-10-31T16:11:20-cb07f49/windows-amd64-race
2018-10-31T16:29:40-86ad85c/darwin-amd64-10_12
2018-10-31T19:29:56-f6f27bf/windows-amd64-race
2018-10-31T22:14:09-d086c5c/darwin-amd64-10_10
2018-10-31T22:48:13-4b05c01/freebsd-amd64-10_3
2018-11-01T00:54:46-01f0dbb/windows-amd64-race
2018-11-01T08:36:12-6c9b655/darwin-amd64-10_12
2018-11-01T14:38:45-21d2e15/darwin-amd64-10_11
2018-11-01T15:56:48-0ff6e5f/dragonfly-amd64
2018-11-02T00:52:46-914a25c/windows-amd64-race
2018-11-02T04:47:34-2182bb0/freebsd-amd64-10_3
2018-11-02T05:35:56-a70a2a8/darwin-amd64-race
2018-11-02T07:30:03-f108158/darwin-amd64-10_12
2018-11-02T07:30:03-f108158/freebsd-amd64-10_3
2018-11-02T07:30:03-f108158/freebsd-amd64-10_4
2018-11-02T12:48:25-86d3754/darwin-amd64-10_12
2018-11-02T12:48:25-86d3754/windows-amd64-race
2018-11-02T12:49:16-a86f549/solaris-amd64-oraclerel
2018-11-02T12:50:03-a1ee0a2/darwin-amd64-10_12
2018-11-02T12:50:03-a1ee0a2/solaris-amd64-oraclerel
2018-11-02T12:53:20-31e7842/darwin-amd64-10_10
2018-11-02T12:55:58-21f7f01/solaris-amd64-oraclerel
2018-11-02T13:21:12-cdad408/darwin-amd64-10_11
2018-11-02T13:44:27-bd4b6ca/darwin-amd64-10_12
2018-11-02T13:44:27-bd4b6ca/freebsd-amd64-12_0
2018-11-02T15:56:35-3a0d609/darwin-amd64-10_12
2018-11-02T15:56:35-3a0d609/solaris-amd64-oraclerel
2018-11-02T17:05:38-f08352b/darwin-amd64-10_11
2018-11-02T17:05:38-f08352b/darwin-amd64-10_12
2018-11-02T17:05:38-f08352b/solaris-amd64-oraclerel
2018-11-02T17:53:18-e8df7df/darwin-amd64-10_10
2018-11-02T17:53:18-e8df7df/solaris-amd64-oraclerel
2018-11-02T17:56:07-745ec8b/darwin-amd64-10_11
2018-11-02T17:56:07-745ec8b/darwin-amd64-10_12
2018-11-02T17:56:07-745ec8b/freebsd-amd64-10_3
2018-11-02T19:43:41-c5d78f5/darwin-amd64-10_12
2018-11-02T19:53:59-b2c397e/freebsd-amd64-10_3
2018-11-02T21:54:22-7aee799/freebsd-amd64-race
2018-11-02T21:54:38-ef21689/darwin-amd64-10_11
2018-11-02T21:54:52-84d6a7a/freebsd-amd64-12_0
2018-11-02T22:04:51-0663fe9/darwin-amd64-10_11
2018-11-02T22:04:51-0663fe9/darwin-amd64-10_12
2018-11-02T22:05:06-7f5dce0/windows-amd64-race
2018-11-02T22:05:52-ee7e443/freebsd-amd64-12_0
2018-11-02T22:07:02-4caa127/freebsd-amd64-12_0
2018-11-02T22:07:43-c21ba09/windows-amd64-race
2018-11-02T22:17:47-e25823e/dragonfly-amd64
2018-11-02T22:17:47-e25823e/freebsd-amd64-12_0
2018-11-02T22:47:58-3813edf/freebsd-amd64-12_0
2018-11-02T23:22:57-1645dfa/darwin-amd64-10_12

[randall77]

Strange. This is mostly a test of the garbage collector, not of strings.
Not sure why this would have changed recently.
I can whip up a CL that does unsafe shenanigans to get rid of most of the allocation.

[gopherbot]

Change https://golang.org/cl/147358 mentions this issue: strings: lower running time of TestCompareStrings