Address Russ's feedback from https://golang.org/cl/33244

TBR=See https://golang.org/cl/33244

Updates #17929

Change-Id: I708d71f519f6414ecec629d3c273d9e737d8ed50
Reviewed-on: https://go-review.googlesource.com/33656Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Tested by running

GOTRACEBACK=2 CGO_CFLAGS="-Wa,--elf-stt-common=yes" go test -ldflags=-linkmode=internal

in misc/cgo/test. That failed before this CL, succeeded after.

I don't think it's worth doing that as a regular test, though,
especially since only recent versions of the GNU binutils support the
--elf-stt-common option.

Fixes #18088.

Change-Id: I893d86181faee217b1504c054b0ed3f7c8d977d3
Reviewed-on: https://go-review.googlesource.com/33653
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Go 1.5 worked with Unicode console input but not ^Z.
Go 1.6 did not work with Unicode console input but did handle one ^Z case.
Go 1.7 did not work with Unicode console input but did handle one ^Z case.

The intent of this CL is for Go 1.8 to work with Unicode console input
and also handle all ^Z cases.

Here's a simple test program for reading from the console.
It prints a "> " prompt, calls read, prints what it gets, and repeats.

	package main

	import (
	    "fmt"
	    "os"
	)

	func main() {
	    p := make([]byte, 100)
	    fmt.Printf("> ")
	    for {
	        n, err := os.Stdin.Read(p)
	        fmt.Printf("[%d %q %v]\n> ", n, p[:n], err)
	    }
	}

On Unix, typing a ^D produces a break in the input stream.
If the ^D is at the beginning of a line, then the 0 bytes returned
appear as an io.EOF:

	$ go run /tmp/x.go
	> hello
	[6 "hello\n" <nil>]
	> hello^D[5 "hello" <nil>]
	> ^D[0 "" EOF]
	> ^D[0 "" EOF]
	> hello^Dworld
	[5 "hello" <nil>]
	> [6 "world\n" <nil>]
	>

On Windows, the EOF character is ^Z, not ^D, and there has
been a long-standing problem that in Go programs, ^Z on Windows
does not behave in the expected way, namely like ^D on Unix.
Instead, the ^Z come through as literal ^Z characters:

	C:\>c:\go1.5.4\bin\go run x.go
	> ^Z
	[3 "\x1a\r\n" <nil>]
	> hello^Zworld
	[13 "hello\x1aworld\r\n" <nil>]
	>

CL 4310 attempted to fix this bug, then known as #6303,
by changing the use of ReadConsole to ReadFile.
This CL was released as part of Go 1.6 and did fix the case
of a ^Z by itself, but not as part of a larger input:

	C:\>c:\go1.6.3\bin\go run x.go
	> ^Z
	[0 "" EOF]
	> hello^Zworld
	[13 "hello\x1aworld\r\n" <nil>]
	>

So the fix was incomplete.
Worse, the fix broke Unicode console input.

ReadFile does not handle Unicode console input correctly.
To handle Unicode correctly, programs must use ReadConsole.
Early versions of Go used ReadFile to read the console,
leading to incorrect Unicode handling, which was filed as #4760
and fixed in CL 7312053, which switched to ReadConsole
and was released as part of Go 1.1 and still worked as of Go 1.5:

	C:\>c:\go1.5.4\bin\go run x.go
	> hello
	[7 "hello\r\n" <nil>]
	> hello world™
	[16 "hello world™\r\n" <nil>]
	>

But in Go 1.6:

	C:\>c:\go1.6.3\bin\go run x.go
	> hello
	[7 "hello\r\n" <nil>]
	> hello world™
	[0 "" EOF]
	>

That is, changing back to ReadFile in Go 1.6 reintroduced #4760,
which has been refiled as #17097. (We have no automated test
for this because we don't know how to simulate console input
in a test: it appears that one must actually type at a keyboard
to use the real APIs. This CL at least adds a comment warning
not to reintroduce ReadFile again.)

CL 29493 attempted to fix #17097, but it was not a complete fix:
the hello world™ example above still fails, as does Shift-JIS input,
which was filed as #17939.

CL 29493 also broke ^Z handling, which was filed as #17427.

This CL attempts the never before successfully performed trick
of simultaneously fixing Unicode console input and ^Z handling.
It changes the console input to use ReadConsole again,
as in Go 1.5, which seemed to work for all known Unicode input.
Then it adds explicit handling of ^Z in the input stream.
(In the case where standard input is a redirected file, ^Z processing
should not happen, and it does not, because this code path is only
invoked when standard input is the console.)

With this CL:

	C:\>go run x.go
	> hello
	[7 "hello\r\n" <nil>]
	> hello world™
	[16 "hello world™\r\n" <nil>]
	> ^Z
	[0 "" EOF]
	> [2 "\r\n" <nil>]
	> hello^Zworld
	[5 "hello" <nil>]
	> [0 "" EOF]
	> [7 "world\r\n" <nil>]

This almost matches Unix:

	$ go run /tmp/x.go
	> hello
	[6 "hello\n" <nil>]
	> hello world™
	[15 "hello world™\n" <nil>]
	> ^D
	[0 "" EOF]
	> [1 "\n" <nil>]
	> hello^Dworld
	[5 "hello" <nil>]
	> [6 "world\n" <nil>]
	>

The difference is in the handling of hello^Dworld / hello^Zworld.
On Unix, hello^Dworld terminates the read of hello but does not
result in a zero-length read between reading hello and world.
This is dictated by the tty driver, not any special Go code.

On Windows, in this CL, hello^Zworld inserts a zero length read
result between hello and world, which is treated as an interior EOF.
This is implemented by the Go code in this CL, but it matches the
handling of ^Z on the console in other programs:

	C:\>copy con x.txt
	hello^Zworld
	        1 file(s) copied.

	C:\>type x.txt
	hello
	C:\>

A natural question is how to test all this. As noted above, we don't
know how to write automated tests using the actual Windows console.
CL 29493 introduced the idea of substituting a different syscall.ReadFile
implementation for testing; this CL continues that idea but substituting
for syscall.ReadConsole instead. To avoid the regression of putting
ReadFile back, this CL adds a comment warning against that.

Fixes #17427.
Fixes #17939.

Change-Id: Ibaabd0ceb2d7af501d44ac66d53f64aba3944142
Reviewed-on: https://go-review.googlesource.com/33451
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes the os test on the Android builder.

Change-Id: Ibb9db712156a620fcccf515e035475c5e2f535a5
Reviewed-on: https://go-review.googlesource.com/33650
Run-TryBot: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates #18082

Change-Id: I2e65b115b809c1e1bf813f538989d1a1f96b2876
Reviewed-on: https://go-review.googlesource.com/33636Reviewed-by: Ian Lance Taylor <iant@golang.org>

The pprof code discards all heap allocations made by runtime
routines. This caused it to discard heap allocations made by functions
called by reflect.Call, as the calls are made via the functions
`runtime.call32`, `runtime.call64`, etc. Fix the profiler to retain
these heap allocations.

Fixes #18077.

Change-Id: I8962d552f1d0b70fc7e6f7b2dbae8d5bdefb0735
Reviewed-on: https://go-review.googlesource.com/33635
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #18054

Change-Id: I6773943a95b92eebd7e347f8f7a80843b4827243
Reviewed-on: https://go-review.googlesource.com/33630Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Document that key in Header.Get(key) is case insensitive in
http.Header, mail.Header, textproto.Header.

Fixes #18019

Change-Id: Iba7932491e02e555190b6fce053088b580a853ef
Reviewed-on: https://go-review.googlesource.com/33530Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The element index needs to be placed in From3. Before this CL it
was impossible to write a VSTE instruction that could be
successfully parsed, so this won't affect existing assembly code.

Fixes #18075.

Change-Id: I5b71be4c6632b1d5a30820a529122f96fd1bc864
Reviewed-on: https://go-review.googlesource.com/33584
Run-TryBot: Michael Munday <munday@ca.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bill O'Farrell <billotosyr@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: Ic96fb52f37257e06e77cc08da5c73ea6f9ff158c
Reviewed-on: https://go-review.googlesource.com/33592Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #17982

Change-Id: I4884a6b57905420ac0e37210c411de98c582de1d
Reviewed-on: https://go-review.googlesource.com/33473Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The TestMain docs explain that flag.Parse() should be called if TestMain
itself depends on command-line flags.

The issue here is that the example implementation does not use any
flags, and thus the flag.Parse call is unnecessary. This leads to people
who use this example as a starting point for their own implementations
to forget that the call is not necessary in most cases.

Comment it out instead of removing the line to keep it as a reminder, as
suggested by Minux Ma.

Change-Id: I6ffc5413e7036366ae3cf0f069b7065e832a3b45
Reviewed-on: https://go-review.googlesource.com/33273Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Or they can use sql.Param instead.

Change-Id: Icf21dbcc87170635c3f5d3f49736429a37abe9da
Reviewed-on: https://go-review.googlesource.com/33576
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Minux Ma <minux@golang.org>

Change-Id: Ib936539946f43556a7dd501f8127054f6a27861f
Reviewed-on: https://go-review.googlesource.com/33553Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Ia27ca728bafcf20d001b477787b21d16ae12960d
Reviewed-on: https://go-review.googlesource.com/33552Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

When transitioning from C code to Go code we must respect the C
calling convention. On s390x this means that r6-r13, r15 and f8-f15
must be saved and restored by functions that use them.

On s390x we were saving the wrong set of floating point registers
(f0, f2, f4 and f6) rather than f8-f15 which means that Go code
could clobber registers that C code expects to be restored. This
CL modifies the crosscall functions on s390x to save/restore the
correct floating point registers.

Fixes #18035.

Change-Id: I5cc6f552c893a4e677669c8891521bf735492e97
Reviewed-on: https://go-review.googlesource.com/33571Reviewed-by: Ian Lance Taylor <iant@golang.org>

It was supposed to be testing SSA, not amd64.

For #18024

Change-Id: Ibe65d7eb6bed9bc4b3eda68e1eaec5fa39fe8f76
Reviewed-on: https://go-review.googlesource.com/33491Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

There is some code value too: types intending to implement
Source64 can write a conversion confirming that.

For #4254 and the Go 1.8 release notes.

Change-Id: I7fc350a84f3a963e4dab317ad228fa340dda5c66
Reviewed-on: https://go-review.googlesource.com/33456
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

TBR=See https://golang.org/cl/33244 and review there.

Updates #17929

Change-Id: I752ec7a6d086f370feaf3cf282708620e891079b
Reviewed-on: https://go-review.googlesource.com/33478Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #18026

Change-Id: Id510f427ceffb2441c3d6f5bb5c93244e46c6497
Reviewed-on: https://go-review.googlesource.com/33477
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

CL 32796 changes the SIGPIPE behaviour for c-archive and c-shared
programs. Add it to go1.8.txt.

Change-Id: I31200187033349c642965a4bb077bcc77d5329a3
Reviewed-on: https://go-review.googlesource.com/33397Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Sigh, forgot to run `git mail`.

Change-Id: Idc49be2bb20d6f0e392cb472a63267ffee2ca22c
Reviewed-on: https://go-review.googlesource.com/33476Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

Update #9401.
Fixes #18016.

Change-Id: Icc24dd10dab1ad8e5cf295e0727d437afa5025c0
Reviewed-on: https://go-review.googlesource.com/33475
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

TestPendingConnsAfterErr showed a failure on slower systems.
Wait and check for the database to close all connections
before pronouncing failure.

A more careful method was attempted but the connection pool
behavior is too dependent on the scheduler behavior to be
predictable.

Fixes #15684

Change-Id: Iafdbc90ba51170c76a079db04c3d5452047433a4
Reviewed-on: https://go-review.googlesource.com/33418Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I51180e1c685e488f7ea4c51a63fd035148671b05
Reviewed-on: https://go-review.googlesource.com/33470Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

TBR=See https://golang.org/cl/33244 and review there.

Updates #17929

Change-Id: I7cb0b666469dba35426d1f0ae1b185e0bdfeac05
Reviewed-on: https://go-review.googlesource.com/33474Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This changes makes the output of `go env` the same
as on other operating systems.

Fixes #18013.

Change-Id: I3079e14dcf7b30c75ec3fde6c78cb95721111320
Reviewed-on: https://go-review.googlesource.com/33396Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Applies the fix from CL 32920 to the new test TestSampledHeapAllocProfile
introduced in CL 33422. The test should be skipped rather than fail if
there is only one executable region of memory.

Updates #17852.

Change-Id: Id8c47b1f17ead14f02a58a024c9a04ebb8ec0429
Reviewed-on: https://go-review.googlesource.com/33453
Run-TryBot: Michael Munday <munday@ca.ibm.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The expected default behavior (no explicit GOTRACEBACK setting)
is for the stack trace to start in user code, eliding unnecessary runtime
frames that led up to the actual trace printing code. The idea was that
the first line number printed was the one that crashed.

For #5832 we added code to show 'panic' frames so that if code panics
and then starts running defers and then we trace from there, the panic
frame can help explain why the code seems to have made a call not
present in the code. But that's only needed for panics between two different
call frames, not the panic at the very top of the stack trace.
Fix the fix to again elide the runtime code at the very top of the stack trace.

Simple panic:

	package main

	func main() {
		var x []int
		println(x[1])
	}

Before this CL:

	panic: runtime error: index out of range

	goroutine 1 [running]:
	panic(0x1056980, 0x1091bf0)
		/Users/rsc/go/src/runtime/panic.go:531 +0x1cf
	main.main()
		/tmp/x.go:5 +0x5

After this CL:

	panic: runtime error: index out of range

	goroutine 1 [running]:
	main.main()
		/tmp/x.go:5 +0x5

Panic inside defer triggered by panic:

	package main

	func main() {
		var x []int
		defer func() {
			println(x[1])
		}()
		println(x[2])
	}

Before this CL:

	panic: runtime error: index out of range
		panic: runtime error: index out of range

	goroutine 1 [running]:
	panic(0x1056aa0, 0x1091bf0)
		/Users/rsc/go/src/runtime/panic.go:531 +0x1cf
	main.main.func1(0x0, 0x0, 0x0)
		/tmp/y.go:6 +0x62
	panic(0x1056aa0, 0x1091bf0)
		/Users/rsc/go/src/runtime/panic.go:489 +0x2cf
	main.main()
		/tmp/y.go:8 +0x59

The middle panic is important: it explains why main.main ended up calling main.main.func1 on a line that looks like a call to println. The top panic is noise.

After this CL:

	panic: runtime error: index out of range
		panic: runtime error: index out of range

	goroutine 1 [running]:
	main.main.func1(0x0, 0x0, 0x0)
		/tmp/y.go:6 +0x62
	panic(0x1056ac0, 0x1091bf0)
		/Users/rsc/go/src/runtime/panic.go:489 +0x2cf
	main.main()
		/tmp/y.go:8 +0x59

Fixes #17901.

Change-Id: Id6d7c76373f7a658a537a39ca32b7dc23e1e76aa
Reviewed-on: https://go-review.googlesource.com/33165
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

TBR=See https://golang.org/cl/33244 and review there.

Updates #17929

Change-Id: I37b49318a9203b16c0c788926039288b99a36ce5
Reviewed-on: https://go-review.googlesource.com/33450Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

When debug is 0, emit the compressed proto format.
The debug>0 format stays the same.

Updates #16093

Change-Id: I45aa1874a22d34cf44dd4aa78bbff9302381cb34
Reviewed-on: https://go-review.googlesource.com/33422
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Updates #17929

Change-Id: Ibc711d39d9ff83458d213778117493796b678aa7
Reviewed-on: https://go-review.googlesource.com/33437Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates #17929

Change-Id: Ie90736cfce3fc5f23cbe0a0f1971476705aac5f9
Reviewed-on: https://go-review.googlesource.com/33436Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Day 0 is as invalid as day 32.

Fixes #17874

Change-Id: I52109d12bafd6d957d00c44d540cb88389fff0a7
Reviewed-on: https://go-review.googlesource.com/33429
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

When I added t.Parallel to some tests earlier, I overlooked some using
the global "Get" func, which uses DefaultTransport.

The DefaultTransport can have its CloseIdleConnections called by other
parallel tests. Use a private Transport instead.

Fixes #18006

Change-Id: Ia4faca5bac235cfa95dcf2703c25f3627112a5e9
Reviewed-on: https://go-review.googlesource.com/33432
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

When we raise a signal that was delivered to C code, it's possible that
the kernel will not deliver it immediately. This is especially possible
on Darwin where we use send the signal to the entire process rather than
just the current thread. Sleep for a millisecond after sending the
signal to give it a chance to be delivered before we restore the Go
signal handler. In most real cases the program is going to crash at this
point, so sleeping is kind of irrelevant anyhow.

Fixes #14809.

Change-Id: Ib2c0d2c4e240977fb4535dc1dd2bdc50d430eb85
Reviewed-on: https://go-review.googlesource.com/33300
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

When CC is set in the environment, the mkEnv function sets its version
of CC to the first word $CC and sets GOGCCFLAGS to the remainder. That
worked since Go 1 but was broken accidentally by
https://golang.org/cl/6409, which changed the code such that `go env`
calls mkEnv twice. The second call to mkEnv would clobber GOGCCFLAGS
based on the value of CC set by the first call. Go back to the old
handling by only calling mkEnv once.

Fixes #15457.

Change-Id: I000a1ebcc48684667e48f2b9b24605867b9e06cd
Reviewed-on: https://go-review.googlesource.com/33293Reviewed-by: Russ Cox <rsc@golang.org>

Introduce R_WEAKADDROFF, a "weak" variation of the R_ADDROFF relocation
that will only reference the type described if it is in some other way
reachable.

Use this for the ptrToThis field in reflect type information where it
is safe to do so (that is, types that don't need to be included for
interface satisfaction, and types that won't cause the compiler to
recursively generate an endless series of ptr-to-ptr-to-ptr-to...
types).

Also fix a small bug in reflect, where StructOf was not clearing the
ptrToThis field of new types.

Fixes #17931

Change-Id: I4d3b53cb9c916c97b3b16e367794eee142247281
Reviewed-on: https://go-review.googlesource.com/33427
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

See issues for details. We can expand this test during the Go 1.9
cycle.

Updates #18008

Change-Id: I78b6b7e8dede414769be97898e29f969bc2a9651
Reviewed-on: https://go-review.googlesource.com/33430Reviewed-by: Cherry Zhang <cherryyz@google.com>

After x.ProbablyPrime(n) passes the n Miller-Rabin rounds,
add a Baillie-PSW test before declaring x probably prime.

Although the provable error bounds are unchanged, the empirical
error bounds drop dramatically: there are no known inputs
for which Baillie-PSW gives the wrong answer. For example,
before this CL, big.NewInt(443*1327).ProbablyPrime(1) == true.
Now it is (correctly) false.

The new Baillie-PSW test is two pieces: an added Miller-Rabin
round with base 2, and a so-called extra strong Lucas test.
(See the references listed in prime.go for more details.)
The Lucas test takes about 3.5x as long as the Miller-Rabin round,
which is close to theoretical expectations.

name                              time/op
ProbablyPrime/Lucas             2.91ms ± 2%
ProbablyPrime/MillerRabinBase2   850µs ± 1%
ProbablyPrime/n=0               3.75ms ± 3%

The speed of prime testing for a prime input does get slower:

name                  old time/op  new time/op   delta
ProbablyPrime/n=1    849µs ± 1%   4521µs ± 1%  +432.31%   (p=0.000 n=10+9)
ProbablyPrime/n=5   4.31ms ± 3%   7.87ms ± 1%   +82.70%  (p=0.000 n=10+10)
ProbablyPrime/n=10  8.52ms ± 3%  12.28ms ± 1%   +44.11%  (p=0.000 n=10+10)
ProbablyPrime/n=20  16.9ms ± 2%   21.4ms ± 2%   +26.35%   (p=0.000 n=9+10)

However, because the Baillie-PSW test is only added when the old
ProbablyPrime(n) would return true, testing composites runs at
the same speed as before, except in the case where the result
would have been incorrect and is now correct.

In particular, the most important use of this code is for
generating random primes in crypto/rand. That use spends
essentially all its time testing composites, so it is not
slowed down by the new Baillie-PSW check:

name                  old time/op  new time/op   delta
Prime                104ms ±22%    111ms ±16%      ~     (p=0.165 n=10+10)

Thanks to Serhat Şevki Dinçer for CL 20170, which this CL builds on.

Fixes #13229.

Change-Id: Id26dde9b012c7637c85f2e96355d029b6382812a
Reviewed-on: https://go-review.googlesource.com/30770
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>