Currently, several important fields of a heap span are set by
heapBits.initSpan, which happens after the span has already been
published and returned from the locked region of alloc_m. In
particular, allocBits is set very late, which makes mspan.isFree
unsafe even if you were to lock the heap because it tries to access
allocBits.

This CL fixes this by populating these fields in alloc_m. The next CL
builds on this to only publish the span once it is fully initialized.
Together, they'll make it safe to check allocBits even if there is a
race with alloc_m.

For #10958, #24543, but a good fix in general.

Change-Id: I7fde90023af0f497e826b637efa4d19c32840c08
Reviewed-on: https://go-review.googlesource.com/c/go/+/203285
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Updates #35194

Change-Id: Ib854bc6250ddeb606d6ff6240179e23b98e4ac62
Reviewed-on: https://go-review.googlesource.com/c/go/+/203999
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Follow the recommandation from RFC 8422, section 5.1.2 of sending back the
ec_points_format extension when requested by the client. This is to fix
some clients declining the handshake if omitted.

Fixes #31943

Change-Id: I7b04dbac6f9af75cda094073defe081e1e9a295d
Reviewed-on: https://go-review.googlesource.com/c/go/+/176418
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Olivier Poitrey <rs@rhapsodyk.net>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This is a re-submission of CL 151157, since it was reverted in CL 190909
due to an introduced crash found by a fuzzer. The revert CL included
regression tests, while this CL includes a fixed version of the original
change.

In particular, what we forgot in the original optimization was that we
still need the length and trailing quote checks at the beginning of
unquoteBytes. Without those, we could end up in a crash later on.

We can work out how many bytes can be unquoted trivially in
rescanLiteral, which already iterates over a string's bytes.

Removing the extra loop in unquoteBytes simplifies the function and
speeds it up, especially when decoding simple strings, which are common.

While at it, we can remove the check that s[0]=='"', since all call
sites already meet that condition.

name           old time/op    new time/op    delta
CodeDecoder-8    10.6ms ± 2%    10.5ms ± 1%  -1.01%  (p=0.004 n=20+10)

name           old speed      new speed      delta
CodeDecoder-8   183MB/s ± 2%   185MB/s ± 1%  +1.02%  (p=0.003 n=20+10)

Updates #28923.

Change-Id: I8c6b13302bcd86a364bc998d72451332c0809cde
Reviewed-on: https://go-review.googlesource.com/c/go/+/190659
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>

Add some simple unit tests for these atomic operations. These can't
catch all the bugs that are possible with these operations but at
least they provide some coverage.

Change-Id: I94b9f451fcc9fecdb2a1448c5357b019563ad275
Reviewed-on: https://go-review.googlesource.com/c/go/+/204317
Run-TryBot: Michael Munday <mike.munday@ibm.com>
Reviewed-by: Austin Clements <austin@google.com>

No big changes in the runtime package benchmarks.

Changes in the time package benchmarks:

name                      old time/op  new time/op  delta
AfterFunc-12              1.57ms ± 1%  0.07ms ± 1%  -95.42%  (p=0.000 n=10+8)
After-12                  1.63ms ± 3%  0.11ms ± 1%  -93.54%  (p=0.000 n=9+10)
Stop-12                   78.3µs ± 3%  73.6µs ± 3%   -6.01%  (p=0.000 n=9+10)
SimultaneousAfterFunc-12   138µs ± 1%   111µs ± 1%  -19.57%  (p=0.000 n=10+9)
StartStop-12              28.7µs ± 1%  31.5µs ± 5%   +9.64%  (p=0.000 n=10+7)
Reset-12                  6.78µs ± 1%  4.24µs ± 7%  -37.45%  (p=0.000 n=9+10)
Sleep-12                   183µs ± 1%   125µs ± 1%  -31.67%  (p=0.000 n=10+9)
Ticker-12                 5.40ms ± 2%  0.03ms ± 1%  -99.43%  (p=0.000 n=10+10)
Sub-12                     114ns ± 1%   113ns ± 3%     ~     (p=0.069 n=9+10)
Now-12                    37.2ns ± 1%  36.8ns ± 3%     ~     (p=0.287 n=8+8)
NowUnixNano-12            38.1ns ± 2%  37.4ns ± 3%   -1.87%  (p=0.020 n=10+9)
Format-12                  252ns ± 2%   195ns ± 3%  -22.61%  (p=0.000 n=9+10)
FormatNow-12               234ns ± 1%   177ns ± 2%  -24.34%  (p=0.000 n=10+10)
MarshalJSON-12             320ns ± 2%   250ns ± 0%  -21.94%  (p=0.000 n=8+8)
MarshalText-12             320ns ± 2%   245ns ± 2%  -23.30%  (p=0.000 n=9+10)
Parse-12                   206ns ± 2%   208ns ± 4%     ~     (p=0.084 n=10+10)
ParseDuration-12          89.1ns ± 1%  86.6ns ± 3%   -2.78%  (p=0.000 n=10+10)
Hour-12                   4.43ns ± 2%  4.46ns ± 1%     ~     (p=0.324 n=10+8)
Second-12                 4.47ns ± 1%  4.40ns ± 3%     ~     (p=0.145 n=9+10)
Year-12                   14.6ns ± 1%  14.7ns ± 2%     ~     (p=0.112 n=9+9)
Day-12                    20.1ns ± 3%  20.2ns ± 1%     ~     (p=0.404 n=10+9)

Updates #6239
Updates #27707

Change-Id: I51e25a90f941574f1a9cf83a22e84ac8c678537d
Reviewed-on: https://go-review.googlesource.com/c/go/+/171883
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Flush the output log up to the root when a test panics. Prior to
this change, only the current test's output log was flushed to its
parent, resulting in no output when a subtest panics.

For the following test function:

	func Test(t *testing.T) {
		for i, test := range []int{1, 0, 2} {
			t.Run(fmt.Sprintf("%v/%v", i, test), func(t *testing.T) {
				_ = 1 / test
			})
		}
	}

Output before this change:

	panic: runtime error: integer divide by zero [recovered]
		panic: runtime error: integer divide by zero
	(stack trace follows)

Output after this change:

	--- FAIL: Test (0.00s)
	    --- FAIL: Test/1/0 (0.00s)
	panic: runtime error: integer divide by zero [recovered]
	(stack trace follows)

Fixes #32121

Change-Id: Ifee07ccc005f0493a902190a8be734943123b6b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/179599
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Also, fix the alert value sent when a signature by a client certificate
is invalid in TLS 1.0-1.2.

Fixes #35190

Change-Id: I2ae1d5593dfd5ee2b4d979664aec74aab4a8a704
Reviewed-on: https://go-review.googlesource.com/c/go/+/204157Reviewed-by: Katie Hockman <katie@golang.org>

The documentation for TokenReader suggests that implementations of the
interface may return a token and io.EOF together, indicating that it is
the last token in the stream. This is similar to io.Reader. However, if
you wrap such a TokenReader in a Decoder it complained about the EOF.
A test was added to ensure this behavior on Decoder's.

Change-Id: I9083c91d9626180d3bcf5c069a017050f3c7c4a8
Reviewed-on: https://go-review.googlesource.com/c/go/+/130556
Run-TryBot: Sam Whited <sam@samwhited.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates #6239
Updates #27707

Change-Id: I0a62c1374db485dd830bf02e59625997d9247fc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/203890
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fcntl can't be called using syscall.Syscall as it doesn't work on AIX.
Moreover, fcntl isn't exported by syscall package.

However, it can be accessed by exporting it from runtime package
using export_aix_test.go.

Change-Id: Ib6af66d9d7eacb9ca0525ebc4cd4c92951735f1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/204059
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: I2629711ce02d935130fb2aab29f9028b62ba9fe6
Reviewed-on: https://go-review.googlesource.com/c/go/+/204318
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

ENFILE is returned from accept when the whole system has run out of
file descriptors. Mark the error as temporary, so that accept loops
continue working.

Fixes #35131
Updates #1891

Change-Id: Idf44c084731898ff4c720d06c250d3b8a42de312
Reviewed-on: https://go-review.googlesource.com/c/go/+/203117
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The flags -headerpad, -Wl,-no_pie and -pagezero_size are incompatible with
the -fembed-bitcode flag used by `gomobile build`. Than McIntosh
suggested we might not need the offending flags; this change removes
the flags on darwin/arm64 and -headerpad, -pagezero_size on darwin/arm.

The -Wl,-no_pie flag is left for darwin/arm because linking fails
without it:

ld: warning: PIE disabled. Absolute addressing (perhaps -mdynamic-no-pic) not allowed in code signed PIE, but used in _runtime.rodata from /var/folders/qq/qxn86k813bn9fjxydm095rxw0000gp/T/workdir-host-darwin-amd64-zenly-ios/tmp/go-link-225285265/go.o. To fix this warning, don't compile with -mdynamic-no-pic or link with -Wl,-no_pie

Discussion: https://groups.google.com/d/msg/golang-dev/U1jK3xmmGAk/j0_ty46EDAAJ

I've verified the CL on the builders, built the "flappy" example from
gomobile with `gomobile build`, and verified that flappy runs on an
iPhone 5S.

Updates #32963

Change-Id: I783abc93ccf3c1d2b7ca00144b7164ba223d3529
Reviewed-on: https://go-review.googlesource.com/c/go/+/201358Reviewed-by: Cherry Zhang <cherryyz@google.com>

Number literal strings returned by the lexer (internal/syntax package) and other
arguments to SetString never contain leading whitespace. There's no need (anymore)
to trim the argument.

Change-Id: Ib060d109f46f79a364a5c8aa33c4f625fe849264
Reviewed-on: https://go-review.googlesource.com/c/go/+/203997Reviewed-by: Robert Griesemer <gri@golang.org>

This fixes the Plan 9 support for the new timer code.

Updates #6239
Updates #27707

Change-Id: Ia498c399b8924910b97fcde07545fae3588aad47
Reviewed-on: https://go-review.googlesource.com/c/go/+/204045Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

The C fnctl takes all int parameters, so consistently use int32.
We already used int32 on Darwin.

Change-Id: I69a012145d012771d7308d705d133159fc1aceaa
Reviewed-on: https://go-review.googlesource.com/c/go/+/204101
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

On some platforms (currently ARM and ARM64), when calling into
VDSO we store the G to the gsignal stack, if there is one, so if
we receive a signal during VDSO we can find the G.

When an M exits, it frees the gsignal stack. But m.gsignal.stack
still points to that stack. When we call nanotime on this M, we
will write to the already freed gsignal stack, which is bad.
Prevent this by unlinking the freed stack from the M.

Should fix #35235.

Change-Id: I338b1fc8ec62aae036f38afaca3484687e11a40d
Reviewed-on: https://go-review.googlesource.com/c/go/+/204158
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

For a discussion, see the issue.

Fixes #35189.

Change-Id: I46c87a45bddf2ea8c33bc101d58880b7922e0f78
Reviewed-on: https://go-review.googlesource.com/c/go/+/204044Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

The rules for extracting the interface data word don't leave
the result typed correctly. If I do i.([1]*int)[0], the result
should have type *int, not [1]*int. Using (IData x) for the result
keeps the typing of the original top-level Value.

I don't think this would ever cause a real codegen bug, bug fixing it
at least makes the typing shown in ssa.html more consistent.

Change-Id: I239d821c394e58347639387981b0510d13b2f7b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/204042
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This change deletes several internal packages, replaces imports to
them with the equivalent golang.org/x/mod packages, updates x/mod, and
re-runs 'go mod vendor'.

Packages are replaced as follows:

cmd/go/internal/modfile → golang.org/x/mod/modfile
cmd/go/internal/module → golang.org/x/mod/module
cmd/go/internal/semver → golang.org/x/mod/semver
cmd/go/internal/sumdb → golang.org/x/mod/sumdb
cmd/go/internal/dirhash → golang.org/x/mod/sumdb/dirhash
cmd/go/internal/note → golang.org/x/mod/sumdb/note
cmd/go/internal/tlog → golang.org/x/mod/sumdb/tlog

Updates #31761
Fixes #34924

Change-Id: Ie3bf677bb0be49af969f654a0214243a6547eb57
Reviewed-on: https://go-review.googlesource.com/c/go/+/202698
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

In my experimentation, I had found that most non-SSAable expressions were
converted to autotmp variables during AST evaluation. However, this was not true
generally, as witnessed by issue #35213, which has a non-SSAable field reference
of a struct that is not converted to an autotmp. So, I fixed openDeferSave() to
handle non-SSAable nodes more generally, and make sure that these non-SSAable
expressions are not evaluated more than once (which could incorrectly repeat side
effects).

Fixes #35213

Change-Id: I8043d5576b455e94163599e930ca0275e550d594
Reviewed-on: https://go-review.googlesource.com/c/go/+/203888
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This is a partial revert of CL 203218.

cmd/go/internal/modfile is about to be deleted and replaced with
golang.org/x/mod/modfile in CL 202698. cmd/internal/diff is not
visible from golang.org/x/mod/modfile, and it doesn't make sense to
extract it into a new package there.

Updates #31761

Change-Id: I3bbbc4cae81120020e1092c1138524729530b415
Reviewed-on: https://go-review.googlesource.com/c/go/+/204103
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

This is a follow-up on https://golang.org/cl/202581.

Updates #33649.

Change-Id: Ib078fed983792c5493bdbed6d33e21b86856894a
Reviewed-on: https://go-review.googlesource.com/c/go/+/204041
Run-TryBot: Robert Griesemer <gri@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

Previously, we were using srcDir, which would apply the wrong module
dependencies (including the wrong 'replace' and 'exclude' directives)
when locating an import path within a module.

Fixes #34860

Change-Id: Ie59dcc2075a7b51ba40f7cd2f62dae27bf58c9b0
Reviewed-on: https://go-review.googlesource.com/c/go/+/203820Reviewed-by: Jay Conrod <jayconrod@google.com>

Updates #25911
Fixes #35220

Change-Id: Id063722d181a12d926801d2e5bb1a9becb463a90
Reviewed-on: https://go-review.googlesource.com/c/go/+/204040
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Also remove unused test hook.

Updates #35117

Change-Id: I6f05ba234fb09e4b44e77c1539c02d1aed49910a
Reviewed-on: https://go-review.googlesource.com/c/go/+/204060Reviewed-by: Bryan C. Mills <bcmills@google.com>

Netpoll must be always be initialized when TestNetpollBreak is launched.
However, when it is run in standalone, it won't be the case, so it must
be forced.

Updates: #27707

Change-Id: I28147f3834f3d6aca982c6a298feadc09b55f66e
Reviewed-on: https://go-review.googlesource.com/c/go/+/204058
Run-TryBot: Clément Chigot <clement.chigot%atos.net@gtempaccount.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The connection count must only be decremented if the persistent
connection was also removed.

Fixes #34941

Change-Id: I5070717d5d9effec78016005fa4910593500c8cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/202087Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

When compiling for GOARCH=386 GOOS=android, the compiler was attaching
R_TLS_LE relocations inappropriately -- as of Go 1.13 the TLS access
recipe for Android refers to a runtime symbol and no longer needs this
type of relocation (which was causing a crash when the linker tried to
process it).

Updates #29674.
Fixes #34788.

Change-Id: Ida01875011b524586597b1f7e273aa14e11815d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/200337
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Elias Naur <mail@eliasnaur.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Change-Id: Ie6fc3e9789aea6e5949e66186db6f2b071b6fdff
Reviewed-on: https://go-review.googlesource.com/c/go/+/204037
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CL 203284 added a compiler intrinsics from atomic Load8 and Store8 on
several architectures, but missed the lowering on MIPS. This CL fixes
that.

Updates #10958, #24543.

Change-Id: I82e88971554fe8c33ad2bf195a633c44b9ac4cf7
Reviewed-on: https://go-review.googlesource.com/c/go/+/203977
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

TestPreemptM doesn't test preemptM, it tests signalM. Rename it and
co-locate it with the other tests related to signals.

Change-Id: I7b95f2ba96530c49cfa8d5bf33282946b5f2d9af
Reviewed-on: https://go-review.googlesource.com/c/go/+/203891
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

TestPreemptM tests signal delivery using SIGUSR1, but (for unknown
reasons) SIGUSR1 is blocked by default on android/arm and
android/arm64, causing the test to fail.

This fixes the test by ensuring that SIGUSR1 is unblocked for this
test.

Updates #10958, #24543.

Change-Id: I9f81fbab53f96c74622aabcb6f5276f79e2b6d33
Reviewed-on: https://go-review.googlesource.com/c/go/+/203957
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

As suggested by comments from the review of CL 168478, this adds
Go code to do reverse bytes and removes the asm code, as well
as making a few cosmetic changes.

Change-Id: I08276a11222e03c3b42f4c9dc0d10a371a418be7
Reviewed-on: https://go-review.googlesource.com/c/go/+/203937
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Munday <mike.munday@ibm.com>

Mostly replaced [:x] slice operation with [:x:x]. 

According to @mdempsky, compiler specially recognizes when you combine
a pointer conversion with a full slice operation in a single expression
and makes an exception.

Updates golang/go#34972

Change-Id: I07d9de3b31da254d55f50d14c18155f8fc8f3ece
Reviewed-on: https://go-review.googlesource.com/c/go/+/203442Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>

n.Opt() is used in walkCheckPtrArithmetic to prevent infinite loops. The
fact that it's used today because n.Opt() is not used for OCONVNOP
during walk.go. If that changes, then it's not safe to repalce it
anymore. So doing hard fail if that case happens, the author of new
changes will be noticed and must change the usage of n.Opt() inside
walkCheckPtrArithmetic, too.

Change-Id: Ic7094baa1759c647fc10e82457c19026099a0d47
Reviewed-on: https://go-review.googlesource.com/c/go/+/202497
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Windows uses '\' not '/'.

Fixes #35175.

Change-Id: Ib3d01dcf148fc0675496d5213f5bcc9cf210a6fc
Reviewed-on: https://go-review.googlesource.com/c/go/+/203889Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

The asm encoder generally assumes that the lowest 5 bits of the
REG_XX constants match the machine instruction encoding, i.e.
the lowest 5 bits is the register number. This was not true for
FCR registers and M registers. Make it so.

MOV Rx, FCRy was encoded as two machine instructions. The first
is unnecessary. Remove.

Change-Id: Ib988e6b109ba8f564337cdd31019c1a6f1881f5b
Reviewed-on: https://go-review.googlesource.com/c/go/+/203717
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

For #10958, #24543, but makes sense on its own.

Change-Id: I2a87dab66b82a1863e4b6512b1f8def51463ce2a
Reviewed-on: https://go-review.googlesource.com/c/go/+/203284
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>