Make the extended precision add-with-carry and sub-with-carry operations
take a constant amount of time to execute, regardless of input.

name             old time/op  new time/op  delta
Add-4            1.16ns ±11%  1.51ns ± 5%  +30.52%  (p=0.008 n=5+5)
Add32-4          1.08ns ± 0%  1.03ns ± 1%   -4.86%  (p=0.029 n=4+4)
Add64-4          1.09ns ± 1%  1.95ns ± 3%  +79.23%  (p=0.008 n=5+5)
Add64multiple-4  4.03ns ± 1%  4.55ns ±11%  +13.07%  (p=0.008 n=5+5)
Sub-4            1.08ns ± 1%  1.50ns ± 0%  +38.17%  (p=0.016 n=5+4)
Sub32-4          1.09ns ± 2%  1.53ns ±10%  +40.26%  (p=0.008 n=5+5)
Sub64-4          1.10ns ± 1%  1.47ns ± 1%  +33.39%  (p=0.008 n=5+5)
Sub64multiple-4  4.30ns ± 2%  4.08ns ± 4%   -5.07%  (p=0.032 n=5+5)

Fixes #31267

Change-Id: I1824b1b3ab8f09902ce8b5fef84ce2fdb8847ed9
Reviewed-on: https://go-review.googlesource.com/c/go/+/170758Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

callerName requested 2 PCs from Callers, and that causes
both to be looked up in the file/line mapping.
We really only need to do the work for one PC.
(And in fact the caller doesn't need file/line at all, but
the Callers API can't express that.)

We used to request 2 PCs because in 1.11 and earlier we
stored an inline skip count in the second entry.
That's not necessary any more (as of 1.12).

Fixes #32093

Change-Id: I7b272626ef6496e848ee8af388cdaafd2556857b
Reviewed-on: https://go-review.googlesource.com/c/go/+/177858
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Caleb Spare <cespare@gmail.com>

name        old alloc/op      new alloc/op      delta
Template         37.1MB ± 0%       36.8MB ± 0%  -0.57%  (p=0.008 n=5+5)
Unicode          28.1MB ± 0%       28.1MB ± 0%  -0.07%  (p=0.008 n=5+5)
GoTypes           125MB ± 0%        124MB ± 0%  -0.61%  (p=0.008 n=5+5)
Compiler          571MB ± 0%        568MB ± 0%  -0.60%  (p=0.008 n=5+5)
SSA              1.88GB ± 0%       1.86GB ± 0%  -0.82%  (p=0.008 n=5+5)
Flate            22.9MB ± 0%       22.8MB ± 0%  -0.59%  (p=0.008 n=5+5)
GoParser         27.5MB ± 0%       27.3MB ± 0%  -0.53%  (p=0.008 n=5+5)
Reflect          79.8MB ± 0%       79.5MB ± 0%  -0.40%  (p=0.008 n=5+5)
Tar              34.9MB ± 0%       34.7MB ± 0%  -0.44%  (p=0.008 n=5+5)
XML              45.7MB ± 0%       45.4MB ± 0%  -0.58%  (p=0.008 n=5+5)
[Geo mean]       80.3MB            79.9MB       -0.52%

name        old allocs/op     new allocs/op     delta
Template           380k ± 0%         378k ± 0%  -0.57%  (p=0.008 n=5+5)
Unicode            340k ± 0%         340k ± 0%  -0.08%  (p=0.008 n=5+5)
GoTypes           1.36M ± 0%        1.36M ± 0%  -0.44%  (p=0.008 n=5+5)
Compiler          5.52M ± 0%        5.49M ± 0%  -0.45%  (p=0.008 n=5+5)
SSA               17.6M ± 0%        17.5M ± 0%  -0.42%  (p=0.008 n=5+5)
Flate              235k ± 0%         234k ± 0%  -0.65%  (p=0.008 n=5+5)
GoParser           302k ± 0%         300k ± 0%  -0.70%  (p=0.008 n=5+5)
Reflect            982k ± 0%         978k ± 0%  -0.40%  (p=0.008 n=5+5)
Tar                353k ± 0%         351k ± 0%  -0.53%  (p=0.008 n=5+5)
XML                437k ± 0%         435k ± 0%  -0.48%  (p=0.008 n=5+5)
[Geo mean]         844k              840k       -0.47%

Updates #27739

Change-Id: I5d533013270cbbd7c0bad1b43da96c8499be76f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/177917
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

In TLS 1.3 session tickets are delivered after the handshake, and it
looks like now the Google servers wait until the first flight of data to
send them (or our timeout is too low). Cause some data to be sent so we
can avoid the guessing game.

Fixes #32090

Change-Id: I54af4acb3a89cc70c9e14a5dfe18a44c29a841a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/177877Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The motivation for doing so is to avoid making inaccurate claims.
Logging may not go to os.Stderr if anyone overrides the log package's
default output via https://godoc.org/log#SetOutput. Saying that
the standard logger is used should be sufficient to explain the
behavior, and users can infer that os.Stderr is used by default,
unless it's changed.

This change is the same as what was applied to http.Server.ErrorLog
documentation in CL 53950.

Change-Id: I32873fc548ceee573f8616b4d49b8a8b98881803
Reviewed-on: https://go-review.googlesource.com/c/go/+/176817Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

When we downgrade a module (using 'go get m@none' or similar), we
exclude versions of other modules that depend on it. We'll try
previous versions (in the "versions" list returned by the proxy or in
codeRepo.Versions for vcs) until we find a version that doesn't
require an excluded module version.

If older versions of a module are broken for some reason,
mvs.Downgrade currently panics. With this change, we ignore versions
with errors during downgrade.

A frequent cause of this is incompatible v2+ versions. These are
common if a repository tagged v2.0.0 before migrating to modules, then
tagged v2.0.1 with a go.mod file later. v2.0.0 is incorrectly
considered part of the v2 module.

Fixes #31942

Change-Id: Icaa75c5c93f73f18a400c22f18a8cc603aa4011a
Reviewed-on: https://go-review.googlesource.com/c/go/+/177337
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

The current example illustrates using As when the error is able to be
interpreted as an os.PathError, but elides the "else" case. This CL adds the
small extra else case to make it clear that it's not safe to assume As will
return true.

This CL also squash the err instantiation and the err nil check into one line
for brevity.

Change-Id: I3d3ab483ffb38fb2788d0498b3f03229a87dd7c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/177717Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Support for Ed25519 certificates was added in CL 175478, this wires them
up into the TLS stack according to RFC 8422 (TLS 1.2) and RFC 8446 (TLS 1.3).

RFC 8422 also specifies support for TLS 1.0 and 1.1, and I initially
implemented that, but even OpenSSL doesn't take the complexity, so I
just dropped it. It would have required keeping a buffer of the
handshake transcript in order to do the direct Ed25519 signatures. We
effectively need to support TLS 1.2 because it shares ClientHello
signature algorithms with TLS 1.3.

While at it, reordered the advertised signature algorithms in the rough
order we would want to use them, also based on what curves have fast
constant-time implementations.

Client and client auth tests changed because of the change in advertised
signature algorithms in ClientHello and CertificateRequest.

Fixes #25355

Change-Id: I9fdd839afde4fd6b13fcbc5cc7017fd8c35085ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/177698
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

A timespec on netbsd/amd64 is int64/int64, not int64/int32.
This bug appears to have been introduced in 7777bac6.

Spotted by Cherry Zhang while reviewing https://go-review.googlesource.com/c/go/+/177120.

Change-Id: I163c55d926965defd981bdbfd2511de7d9d4c542
Reviewed-on: https://go-review.googlesource.com/c/go/+/177637Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Benny Siegert <bsiegert@gmail.com>

Fix various bugs in the netbsd/arm64 runtime assembly.

Updates #30824.

Change-Id: I5ca10926ab663a8ff4df9973530e645e2469c1aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/177120Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

A cross C compiler should be specified when cross building go
for android on x86 host. This CL fixes the typo in README.

Change-Id: Ideda915364d9f7f0fcd53146abc1e74506a8a8e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/177777Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Elias Naur <mail@eliasnaur.com>

Change-Id: I44af6cd8baa8fcd2a666429467fae4bed5f21fa0
GitHub-Last-Rev: d0c9722f082114b356de55fc79ce138ede019636
GitHub-Pull-Request: golang/go#32052
Reviewed-on: https://go-review.googlesource.com/c/go/+/177277Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Update #28603

Change-Id: I8bdbea57b3661e15dcc760d27252b794daa476db
Reviewed-on: https://go-review.googlesource.com/c/go/+/177697Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

If a user runs 'go get mod@vers' where the module transitively
requires itself at a newer version, 'go get' attempts to perform a
downgrade, which necessarily excludes the requested version of the
module.

Previously, we called mvs.BuildList with the requested module
version as the target. This panicked because BuildList doesn't allow
the target module (typically the main module) to require a newer
version of itself.

With this change, when we lose an upgrade due to a downgrade, we call
mvs.BuildList through a wrapper that treats the lost module version as
requirement of a synthetic root module, rather than the target
module. This avoids the panic.

This change also starts reporting errors when an upgraded module is
lost entirely (downgrades caused the module to be completely removed
from the build list).

Fixes #31491

Change-Id: I70ca261c20af7553cad2d3b840a1eaf3d18a4191
Reviewed-on: https://go-review.googlesource.com/c/go/+/177602
Run-TryBot: Jay Conrod <jayconrod@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

On most platforms newly-mapped memory is untouched, meaning the pages
backing the region haven't been faulted in yet. However, we mark this
memory as unscavenged which means the background scavenger
aggressively "returns" this memory to the OS if the heap is small.

The only platform where newly-mapped memory is actually unscavenged (and
counts toward the application's RSS) is on Windows, since
(*mheap).sysAlloc commits the reservation. Instead of making a special
case for Windows, I change the requirements a bit for a sysReserve'd
region. It must now be both sysMap'd and sysUsed'd, with sysMap being a
no-op on Windows. Comments about memory allocation have been updated to
include a more up-to-date mental model of which states a region of memory
may be in (at a very low level) and how to transition between these
states.

Now this means we can correctly mark newly-mapped heap memory as
scavenged on every platform, reducing the load on the background
scavenger early on in the application for small heaps. As a result,
heap-growth scavenging is no longer necessary, since any actual RSS
growth will be accounted for on the allocation codepath.

Finally, this change also cleans up grow a little bit to avoid
pretending that it's freeing an in-use span and just does the necessary
operations directly.

Fixes #32012.
Fixes #31966.
Updates #26473.

Change-Id: Ie06061eb638162e0560cdeb0b8993d94cfb4d290
Reviewed-on: https://go-review.googlesource.com/c/go/+/177097
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

For:

    http2: track reused connections
    https://golang.org/cl/176720 (updates golang/go#31982)

Some x/sys/unix updates come along for the ride too.

I filed #32031 for making the bundling process less difficult and
error-prone in the future.

Change-Id: Ic822080991ffa2d50352c5f613e45648a327cf16
Reviewed-on: https://go-review.googlesource.com/c/go/+/177037
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #32060

Change-Id: I49ab48a9bdd64a7ed777a045e2d92d28a37b5c0b
Reviewed-on: https://go-review.googlesource.com/c/go/+/177600
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates #30790
Fixes #31960

Change-Id: Ib3ac074cf1f98fe69f53af82d2a0441582116570
Reviewed-on: https://go-review.googlesource.com/c/go/+/176925
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>

The compiler appears to have a latent bug:
fusePlain calls invalidateCFG when it changes block structure,
but fuseIf does not.

Fix this by hoisting the call to invalidateCFG to the top level.

Change-Id: Ic960fb3ac963b15b4a225aad84863d58efa954e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/177198
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

The CL 164718 mistyped the comparison flags. The rules for floating
point comparison should be GreaterThanF and GreaterEqualF. Fortunately,
the wrong optimizations were overwritten by other integer rules, so the
issue won't cause failure but just some performance impact.

The fixed CL optimizes the floating point test as follows.

source code: func foo(f float64) bool { return f > 4 || f < -4}
previous version: "FCMPD", "CSET\tGT", "CBZ"
fixed version: "FCMPD", BLE"

Add the test case.

Change-Id: Iea954fdbb8272b2d642dae0f816dc77286e6e1fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/177121Reviewed-by: Ben Shi <powerman1st@163.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This is CVE-2019-11888.

Previously, passing a nil environment but a non-nil token would result
in the new potentially unprivileged process inheriting the parent
potentially privileged environment, or would result in the new
potentially privileged process inheriting the parent potentially
unprivileged environment. Either way, it's bad. In the former case, it's
an infoleak. In the latter case, it's a possible EoP, since things like
PATH could be overwritten.

Not specifying an environment currently means, "use the existing
environment". This commit amends the behavior to be, "use the existing
environment of the token the process is being created for." The behavior
therefore stays the same when creating processes without specifying a
token. And it does the correct thing when creating processes when
specifying a token.

Fixes #32000

Change-Id: Ia57f6e89b97bdbaf7274d6a89c1d9948b6d40ef5
Reviewed-on: https://go-review.googlesource.com/c/go/+/176619
Run-TryBot: Jason Donenfeld <Jason@zx2c4.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

This is useful for debugging line number assignment and
also for making sense of pathological line number inputs.

Activated with
-gcflags=-d=ssa/number_lines/stats=1 (the bit matters)
-gcflags=-d=ssa/number_lines/debug

Stats:
"SUM_LINE_RANGE",
   SUM for f in files {MAX line in f {line}-MIN line in f {line}}
"MAXMIN_LINE_RANGE",
   MAX for f in files {MAX line in f {line}} -
   MIN for f in files {MIN line in f {line}}
"MAXFILE", maxfile,
   MAX for f in files {f}
"NFILES", len(entries)
   | files |

Change-Id: I8a7336e6370452fe2e3a62de17606db9bd6a6fd3
Reviewed-on: https://go-review.googlesource.com/c/go/+/174947
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This cuts the time for 'go test -short testing' from 0.9s to < 0.1s.

Change-Id: Ib8402f80239e1e96ea5221dfd5cd0db08170d85b
Reviewed-on: https://go-review.googlesource.com/c/go/+/177420
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CL 121936 added this diagnostic to avoid a panic accessing *short.
(Hence the "This shouldn't really be a panic" comment.)

That CL was right to produce a clearer error than a plain memory fault,
but I think wrong to print+exit instead of panicking. I just ran into
one of these in a real program, and there is no indication anywhere
of how the program reached this point. The panic will show that.
So change print+exit to a panic with a helpful message, in contrast
to the original panic with an unhelpful message and the current
helpful message without stack trace.

Change-Id: Ib2bae1dead4ccde92f00fa3a34c05241ff7690c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/177419
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This just makes all.bash a bit less chatty.

Change-Id: I7d2ecabf0c7d8df2065d7052718f611bb2907801
Reviewed-on: https://go-review.googlesource.com/c/go/+/177418
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

These tests take 20 seconds each to rebuild the entire world
in their respective modes. That's too much for short mode,
including all.bash on developer machines.

Keep doing it on builders and if someone runs 'go test' by hand
in that directory.

For #26473.

Change-Id: I3dc6955bc3aa7a20fd170efcde72a7d19b37bdbf
Reviewed-on: https://go-review.googlesource.com/c/go/+/177417
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Speeds up the "go test runtime -cpu=1,2,4 -short -quick" phase of all.bash.

For #26473.

Change-Id: I090f5a5aa754462b3253a2156dc31fa67ce7af2a
Reviewed-on: https://go-review.googlesource.com/c/go/+/177399
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

Was 50 seconds on unloaded Mac laptop; now 27.
Still longer than I would like, but every little bit helps.

For #26473.

Change-Id: Id4be016ee1555cbc3512eca0ae10236d7f06bd02
Reviewed-on: https://go-review.googlesource.com/c/go/+/177398
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

_go_testing is equally unlikely and much less concerning
than testing_xxxxxxxxxxxx if it appears in an error message
(as it does, for example, in https://storage.googleapis.com/go-build-log/0d543f89/linux-amd64_3467a10e.log).

Change-Id: I45dc3ebe2d3b6c9e53273cd21782ee11a53f5edb
Reviewed-on: https://go-review.googlesource.com/c/go/+/177197
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Add information about action and build IDs,
commands run, time spent in commands,
and overall time to -debug-actiongraph output.

Also avoid a terrible outcome in:

	go build -debug-actiongraph x.go

Change-Id: I7a3a638f4848d75f2bdc997517f4ab23656da4f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/177138
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

The work of running full vet on std and cmd during local development
has moved to go test, which of course runs during all.bash.

For errors in other GOOS/GOARCH combinations, the misc-compile
builders (running buildall.bash) also now run go vet std cmd.

The vetall builder need not do anything anymore.
Make it a no-op until it can be retired, and remove
cmd/vet/all and its special case in the go command.

Fixes #31916.

Change-Id: I8f30d184c382ea7c2c8f520e5618f680db633968
Reviewed-on: https://go-review.googlesource.com/c/go/+/176440
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Now that the main tree complies with 'go vet', enable all vet checks
during 'go test' in the main tree. This helps surface helpful errors
while developing, instead of having to wait for the misc-vet-vetall builder.

During 'go test', the additional vet checks are essentially free:
the vet invocations themselves take only 8 seconds total for the entire tree.

Also update buildall.bash (used by the misc-compile builders)
to run 'go vet std cmd' for each GOOS/GOARCH pair.
This is not as free, since in general it can require recompiling
packages with their tests included before invoking vet.
(That compilation was going on anyway in the 'go test' case.)

On my Mac laptop, ./buildall.bash freebsd used to take
68+16+17+18 = 119 seconds for make.bash and then
the builds of the three freebsd architectures.
Now it takes 68+16+23+17+23+18+24 = 189 seconds, 60% longer.
Some of this is spent doing unnecessary cgo work.
Still, this lets us shard the vet checks and match all.bash.

Fixes #20119.
For #31916.

Change-Id: I6b0c40bac47708a688463c7fca12c0fc23ab2751
Reviewed-on: https://go-review.googlesource.com/c/go/+/176439
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This updates the Go function declarations to match race_amd64.s.

Change-Id: I2b541a6b335ce732f4c31652aa615240ce7bb1c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/177397
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

When fmt.Errorf is provided with a %w verb with an error operand,
return an error implementing an Unwrap method returning that operand.

It is invalid to use %w with other formatting functions, to use %w
multiple times in a format string, or to use %w with a non-error
operand. When the Errorf format string contains an invalid use of %w,
the returned error does not implement Unwrap.

Change-Id: I534e20d3b163ab22c2b137b1c9095906dc243221
Reviewed-on: https://go-review.googlesource.com/c/go/+/176998Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

Reverts the following changes:

  https://go.googlesource.com/go/+/1f90d081391d4f5911960fd28d81d7ea5e554a8f
  https://go.googlesource.com/go/+/8bf18b56a47a98b9dd2fa03beb358312237a8c76
  https://go.googlesource.com/go/+/5402854c3557f87fa2741a52ffc15dfb1ef333cc
  https://go.googlesource.com/go/+/37f84817247d3b8e687a701ccb0d6bc7ffe3cb78
  https://go.googlesource.com/go/+/6be6f114e0d483a233101a67c9644cd72bd3ae7a

Partially reverts the followinng change, removing the errors.Opaque
function and the errors.Wrapper type definition:

  https://go.googlesource.com/go/+/62f5e8156ef56fa61e6af56f4ccc633bde1a9120

Updates documentation referencing the Wrapper type.

Change-Id: Ia622883e39cafb06809853e3fd90b21441124534
Reviewed-on: https://go-review.googlesource.com/c/go/+/176997
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

Based on RFC 8410.

Updates #25355

Change-Id: If7abb7eeb0ede10a9bb3d2004f2116e587c6207a
Reviewed-on: https://go-review.googlesource.com/c/go/+/175478
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

This allows the use of CLONE_VFORK and CLONE_VM for fork/exec, preventing
"fork/exec ...: cannot allocate memory" failures from occuring when attempting
to execute commands from a Go process that has a large memory footprint.
Additionally, this should reduce the latency of fork/exec on these platforms.

The same problem was addressed on linux/amd64 via issue #5838.

Updates #31936

Change-Id: I7ae0fbbeaa29cab944a49a11272a380d497eb2d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/175697
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Vet needs export data for the imports of the package it is analyzing.
Vet does not need export data for the package itself, since vet will
do its own type checking. Assuming that vet is just as good as the compiler
at detecting invalid programs, don't run the compiler unnecessarily.

This especially matters for tests without external test files or for
which the external test files do not import the test-augmented original
package. In that case, the test-augmented original package need not
be compiled at all.

Cuts time for 'go clean -cache && go vet -x cmd/compile/internal/ssa'
from 7.6r 24.3u 2.8s to 3.5r 8.5u 1.9s, by not running the compiler
on the augmented test package.

There is still more to be done here - if we do need to build a
test-augmented package, we rerun cgo unnecessarily.
But this is a big help.

Cuts time for 'go vet std cmd' by about 30%.

For #31916.

Change-Id: If6136b4d384f1da77aed90b43f1a6b95f09b5d86
Reviewed-on: https://go-review.googlesource.com/c/go/+/176438
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Picks up vet fix from CL 176357.

Change-Id: Ia77cd4a582c4edfbe59bbc311e6ce14046df0e83
Reviewed-on: https://go-review.googlesource.com/c/go/+/177137
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

For many patterns we can compute the minimum input length at compile time.
If the input is shorter, we can return early and get a huge speedup.

As pointed out by Damian Gryski, Perl's regex engine contains a number of
these kinds of fail-fast optimizations:
https://perldoc.perl.org/perlreguts.html#Peep-hole-Optimisation-and-Analysis

Benchmarks: (including new ones for compile time)

name               old time/op    new time/op    delta
Compile/Onepass-8    4.39µs ± 1%    4.40µs ± 0%  +0.34%  (p=0.029 n=9+8)
Compile/Medium-8     9.80µs ± 0%    9.91µs ± 0%  +1.17%  (p=0.000 n=10+10)
Compile/Hard-8       72.7µs ± 0%    73.5µs ± 0%  +1.10%  (p=0.000 n=9+10)

name                       old time/op    new time/op      delta
Match/Easy0/16-8             52.6ns ± 5%       4.9ns ± 0%     -90.68%  (p=0.000 n=10+9)
Match/Easy0/32-8             64.1ns ±10%      61.4ns ± 1%        ~     (p=0.188 n=10+9)
Match/Easy0/1K-8              280ns ± 1%       277ns ± 2%      -0.97%  (p=0.004 n=10+10)
Match/Easy0/32K-8            4.61µs ± 1%      4.55µs ± 1%      -1.49%  (p=0.000 n=9+10)
Match/Easy0/1M-8              229µs ± 0%       226µs ± 1%      -1.29%  (p=0.000 n=8+10)
Match/Easy0/32M-8            7.50ms ± 1%      7.47ms ± 1%        ~     (p=0.165 n=10+10)
Match/Easy0i/16-8             533ns ± 1%         5ns ± 2%     -99.07%  (p=0.000 n=10+10)
Match/Easy0i/32-8             950ns ± 0%       950ns ± 1%        ~     (p=0.920 n=10+9)
Match/Easy0i/1K-8            27.5µs ± 1%      27.5µs ± 0%        ~     (p=0.739 n=10+10)
Match/Easy0i/32K-8           1.13ms ± 0%      1.13ms ± 1%        ~     (p=0.079 n=9+10)
Match/Easy0i/1M-8            36.7ms ± 2%      36.1ms ± 0%      -1.64%  (p=0.000 n=10+9)
Match/Easy0i/32M-8            1.17s ± 0%       1.16s ± 1%      -0.80%  (p=0.004 n=8+9)
Match/Easy1/16-8             55.5ns ± 6%       4.9ns ± 1%     -91.19%  (p=0.000 n=10+9)
Match/Easy1/32-8             58.3ns ± 8%      56.6ns ± 1%        ~     (p=0.449 n=10+8)
Match/Easy1/1K-8              750ns ± 0%       748ns ± 1%        ~     (p=0.072 n=8+10)
Match/Easy1/32K-8            31.8µs ± 0%      31.6µs ± 1%      -0.50%  (p=0.035 n=10+9)
Match/Easy1/1M-8             1.10ms ± 1%      1.09ms ± 0%      -0.95%  (p=0.000 n=10+9)
Match/Easy1/32M-8            35.5ms ± 0%      35.2ms ± 1%      -1.05%  (p=0.000 n=9+10)
Match/Medium/16-8             442ns ± 2%         5ns ± 1%     -98.89%  (p=0.000 n=10+10)
Match/Medium/32-8             875ns ± 0%       878ns ± 1%        ~     (p=0.071 n=9+10)
Match/Medium/1K-8            26.1µs ± 0%      25.9µs ± 0%      -0.64%  (p=0.000 n=10+10)
Match/Medium/32K-8           1.09ms ± 1%      1.08ms ± 0%      -0.84%  (p=0.000 n=10+9)
Match/Medium/1M-8            34.9ms ± 0%      34.6ms ± 1%      -0.98%  (p=0.000 n=9+10)
Match/Medium/32M-8            1.12s ± 1%       1.11s ± 1%      -0.98%  (p=0.000 n=10+9)
Match/Hard/16-8               721ns ± 1%         5ns ± 0%     -99.32%  (p=0.000 n=10+9)
Match/Hard/32-8              1.32µs ± 1%      1.31µs ± 0%      -0.71%  (p=0.000 n=9+9)
Match/Hard/1K-8              39.8µs ± 1%      39.7µs ± 1%        ~     (p=0.165 n=10+10)
Match/Hard/32K-8             1.57ms ± 0%      1.56ms ± 0%      -0.70%  (p=0.000 n=10+9)
Match/Hard/1M-8              50.4ms ± 1%      50.1ms ± 1%      -0.57%  (p=0.007 n=10+10)
Match/Hard/32M-8              1.62s ± 1%       1.60s ± 0%      -0.98%  (p=0.000 n=10+10)
Match/Hard1/16-8             3.88µs ± 1%      3.86µs ± 0%        ~     (p=0.118 n=10+10)
Match/Hard1/32-8             7.44µs ± 1%      7.46µs ± 1%        ~     (p=0.109 n=10+10)
Match/Hard1/1K-8              232µs ± 1%       229µs ± 1%      -1.31%  (p=0.000 n=10+9)
Match/Hard1/32K-8            7.41ms ± 2%      7.41ms ± 0%        ~     (p=0.237 n=10+8)
Match/Hard1/1M-8              238ms ± 1%       238ms ± 0%        ~     (p=0.481 n=10+10)
Match/Hard1/32M-8             7.69s ± 1%       7.61s ± 0%      -1.00%  (p=0.000 n=10+10)

Fixes #31329

Change-Id: I04640e8c59178ec8b3106e13ace9b109b6bdbc25
Reviewed-on: https://go-review.googlesource.com/c/go/+/171023Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>