Move all parse/format related functionality into strconv.go
and thoroughly test them. This also reduces the amount of noise
inside reader.go and writer.go.

There was zero functionality change other than moving code around.

Change-Id: I3bc288d10c20ebb3814b30b75d8acd7be62b85d7
Reviewed-on: https://go-review.googlesource.com/28470
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

RFC 6265, section 4.2.2 says:
<<<
Although cookies are serialized linearly in the Cookie header,
servers SHOULD NOT rely upon the serialization order.  In particular,
if the Cookie header contains two cookies with the same name (e.g.,
that were set with different Path or Domain attributes), servers
SHOULD NOT rely upon the order in which these cookies appear in the
header.
>>>

This statement seems to indicate that cookies should conceptually
be thought of as a map of keys to sets of values (map[key][]value).
However, in practice, everyone pretty much treats cookies as a
map[key]value and the API for Request.Cookie seems to indicate that.

We should update the documentation for Request.Cookie to warn the
user what happens when there is are multiple cookies with the same
key. I deliberately did not want to say *which* cookie is returned.

Change-Id: Id3e0e24b2b14ca2d9ea8b13f82ba739edaa71cf0
Reviewed-on: https://go-review.googlesource.com/29364Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I573278c9aee80e62463b2542774dabeec7c3b098
Reviewed-on: https://go-review.googlesource.com/29969
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

In https://golang.org/cl/28951 I cleaned up the lookupProtocol and
lookupPort paths to be consistently case-insensitive across operating
systems and to share the same baked-in maps of port & proto values
that can be relied on to exist on any platform.

I missed the fallback to the baked-in maps on Windows, though, which
broke Windows XP. This should fix it.

Fixes #17175

Change-Id: Iecd434fb684304137ee27f5521cfaa8c351a1bde
Reviewed-on: https://go-review.googlesource.com/29968
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

IntLiteral was only called by the gins functions in
cmd/compile/internal/{arm64,mips64,ppc64}/gsubr.go
but CL 29220 (cmd/compile: remove gins) deleted them,
so IntLiteral is now unused.

Change-Id: I2652b6d2ace6fdadc1982f65e749f3982513371e
Reviewed-on: https://go-review.googlesource.com/29996Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #17276

Change-Id: I0188cf9bc5fdb48c71ad929cc54206d03e0b96e4
Reviewed-on: https://go-review.googlesource.com/29995Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This makes function fit in 16 bytes, saving 16 bytes.

Change-Id: Iac5d2add42f6dae985b2a5cbe19ad4bd4bcc92ec
Reviewed-on: https://go-review.googlesource.com/29151
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

When offset < 0 and -offset fits in instruction, generate SUB
instruction, instead of ADD with constant from the pool.

Fixes #13280.

Change-Id: I57d97fe9300fe1f6554365e2262393ef50acbdd3
Reviewed-on: https://go-review.googlesource.com/30014
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Remove duplicate vars, commented out code  and duplicate lines.
When choosing between 2 aliases, on with more uses was chosen.

Change-Id: I7bc15f1693de3f6d378cef9c09469970a659db40
Reviewed-on: https://go-review.googlesource.com/29152
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Fixes #17270.

Change-Id: I4affa57e10baf1a758bc0977265d160f220b2945
Reviewed-on: https://go-review.googlesource.com/29960
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Also add compiler debug ouput and add a test.

Fixes #15390.

Change-Id: Iceba1414c29bcc213b87837387bf8ded1f3157f1
Reviewed-on: https://go-review.googlesource.com/30011
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

This change adds support for decoding and encoding the bool type. The
encoding is a single byte, with a zero value for false and a non-zero
value for true.

Closes #16856.

Change-Id: I1d1114b320263691473bb100cad0f380e0204186
Reviewed-on: https://go-review.googlesource.com/28514Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I6d413f747e6a6c30c5e0e9afdffd5ec18dce7e08
Reviewed-on: https://go-review.googlesource.com/29974Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This change reverts CL 18814 which is a workaroud for older DragonFly
BSD kernels, and fixes #13945 and #13947 in a more general way the
same as other platforms except NetBSD.

This is a followup to CL 29491.

Updates #16329.

Change-Id: I771670bc672c827f2b3dbc7fd7417c49897cb991
Reviewed-on: https://go-review.googlesource.com/29971
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change setsig, setsigstack, getsig, raise, raiseproc to take uint32 for
signal number parameter, as that is the type mostly used for signal
numbers.  Same for dieFromSignal, sigInstallGoHandler, raisebadsignal.

Remove setsig restart parameter, as it is always either true or
irrelevant.

Don't check the handler in setsigstack, as the only caller does that
anyhow.

Don't bother to convert the handler from sigtramp to sighandler in
getsig, as it will never be called when the handler is sigtramp or
sighandler.

Don't check the return value from rt_sigaction in the GNU/Linux version
of setsigstack; no other setsigstack checks it, and it never fails.

Change-Id: I6bbd677e048a77eddf974dd3d017bc3c560fbd48
Reviewed-on: https://go-review.googlesource.com/29953
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #17231

Change-Id: I0d6007ab504f2277cb6affc9e2050157a6ad4d5e
Reviewed-on: https://go-review.googlesource.com/29970Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This change replaces the use of CryptGenRandom with RtlGenRandom in
Windows to generate cryptographically random numbers during process
startup. RtlGenRandom uses the same RNG as CryptGenRandom, but it has many
fewer DLL dependencies and so does not affect process startup time as
much.

This makes running simple Go program on my computers faster.

Windows XP:
benchmark                      old ns/op     new ns/op     delta
BenchmarkRunningGoProgram-2     47408573      10784148      -77.25%

Windows 7 (VM):
benchmark                    old ns/op     new ns/op     delta
BenchmarkRunningGoProgram     16260390      12792150      -21.33%

Windows 7:
benchmark                      old ns/op     new ns/op     delta
BenchmarkRunningGoProgram-2     13600778      10050574      -26.10%

Fixes #15589

Change-Id: I2816239a2056e3d4a6dcd86a6fa2bb619c6008fe
Reviewed-on: https://go-review.googlesource.com/29700Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Mark nil check operations as faulting if their arg is zero.
This lets the late nilcheck pass remove duplicates.

Fixes #17242.

Change-Id: I4c9938d8a5a1e43edd85b4a66f0b34004860bcd9
Reviewed-on: https://go-review.googlesource.com/29952
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Also add GP<->FP move addressing mode to FMOVS, FMOVD
instructions.

Ceil-8                 37.1ns ± 0%   7.9ns ± 0%  -78.64%          (p=0.000 n=4+5)
Dim-8                  20.9ns ± 1%  11.3ns ± 0%  -45.93%          (p=0.008 n=5+5)
Floor-8                22.9ns ± 0%   7.9ns ± 0%  -65.41%          (p=0.029 n=4+4)
Gamma-8                 117ns ± 0%    94ns ± 1%  -19.50%          (p=0.016 n=4+5)
PowInt-8                121ns ± 0%   108ns ± 1%  -11.07%          (p=0.008 n=5+5)
PowFrac-8               331ns ± 0%   318ns ± 0%   -3.93%          (p=0.000 n=5+4)
Trunc-8                18.8ns ± 0%   7.9ns ± 0%  -57.83%          (p=0.016 n=4+5)

Change-Id: I709b7f1a914b28adc27414522db551e2630cfb92
Reviewed-on: https://go-review.googlesource.com/29734
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

It wasn't lowercasing the string, folding widths, and putting strings
into NFC form. Do those.

Fixes #13835

Change-Id: Ia3de6159417cacec203b48e206e51d79f945df58
Reviewed-on: https://go-review.googlesource.com/29860
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

Add golang.org/x/text/unicode/norm from x/text git rev a7c02369.

Needed by net/http for IDNA normalization.

Updates #13835

Change-Id: I8b024e179d573f2b093c209a4b9e4f71f7d4a1f2
Reviewed-on: https://go-review.googlesource.com/29859
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

    Documentation made reference to an unknown entity "DisableHTMLEscaping,"
    but I think it actually meant the method "Encoder.SetEscapeHTML."

    Fixes #17255

Change-Id: I18fda76f8066110caef85fd33698de83d632e646
Reviewed-on: https://go-review.googlesource.com/29931Reviewed-by: Ian Lance Taylor <iant@golang.org>

The OS-independent sigmask type was not pulling its weight. Replace it
with the OS-dependent sigset type. This requires adding an OS-specific
sigaddset function, but permits removing the OS-specific sigmaskToSigset
function.

Change-Id: I43307b512b0264ec291baadaea902f05ce212305
Reviewed-on: https://go-review.googlesource.com/29950
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Add context methods to sql and sql/driver methods. If
the driver doesn't implement context methods the connection
pool will still handle timeouts when a query fails to return
in time or when a connection is not available from the pool
in time.

There will be a follow-up CL that will add support for
context values that specify transaction levels and modes
that a driver can use.

Fixes #15123

Change-Id: Ia99f3957aa3f177b23044dd99d4ec217491a30a7
Reviewed-on: https://go-review.googlesource.com/29381Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

IsPredeclared allows simplifying src/golang.org/x/tools/godoc/linkify.go

Change-Id: I56b3223896f844630bc2e940255572d1682f0d06
Reviewed-on: https://go-review.googlesource.com/29870Reviewed-by: Robert Griesemer <gri@golang.org>

Change the two calls to signalstack(nil) to inline the code
instead (it's two lines).

Change-Id: Ie92a05494f924f279e40ac159f1b677fda18f281
Reviewed-on: https://go-review.googlesource.com/29854
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The SetFinalizer documentation states that

"The argument obj must be a pointer to an object allocated by calling
new or by taking the address of a composite literal."

which precludes pointers to local variables. According to a comment
on #6591, this case is expected to work. This CL updates the documentation
for SetFinalizer accordingly.

Fixes #6591

Change-Id: Id861b3436bc1c9521361ea2d51c1ce74a121c1af
Reviewed-on: https://go-review.googlesource.com/29592
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

This commit makes the assembler frontend reorder the operands so that
they are in the order the backend expects. The index should be first
for consistency with the other vector instructions.

Before this commit no operand order would have been accepted so this
isn't a breaking change.

Change-Id: I188d57eeb338d27fa1fa6845de0d6d1521b7a6c3
Reviewed-on: https://go-review.googlesource.com/29855
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: Brad Fitzpatrick <bradfitz@golang.org>

These instructions are the same as BLT and BLE except that they
also branch if the 'unordered' bit is set in the condition code.

They are already used by the SSA backend. This change allows them
to be used in hand-written assembly code.

Change-Id: Ie9b5985a5e87ea22e8043567a286e09dce16a2db
Reviewed-on: https://go-review.googlesource.com/29930
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: Brad Fitzpatrick <bradfitz@golang.org>

Use the A{,G}HI instructions where possible (4 bytes instead of 6 bytes
for A{,G}FI). Also, use 32-bit operations where appropriate for
multiplication.

Change-Id: I4041781cda26be52b54e4804a9e71552310762d0
Reviewed-on: https://go-review.googlesource.com/29733
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: Brad Fitzpatrick <bradfitz@golang.org>

Use an MVC loop to copy arguments in runtime.call* rather than copying
bytes individually.

I've added the benchmark CallArgCopy to test the speed of Value.Call
for various argument sizes.

name                    old speed      new speed       delta
CallArgCopy/size=128     439MB/s ± 1%    582MB/s ± 1%   +32.41%  (p=0.000 n=10+10)
CallArgCopy/size=256     695MB/s ± 1%   1172MB/s ± 1%   +68.67%  (p=0.000 n=10+10)
CallArgCopy/size=1024    573MB/s ± 8%   4175MB/s ± 2%  +628.11%  (p=0.000 n=10+10)
CallArgCopy/size=4096   1.46GB/s ± 2%  10.19GB/s ± 1%  +600.52%  (p=0.000 n=10+10)
CallArgCopy/size=65536  1.51GB/s ± 0%  12.30GB/s ± 1%  +716.30%   (p=0.000 n=9+10)

Change-Id: I87dae4809330e7964f6cb4a9e40e5b3254dd519d
Reviewed-on: https://go-review.googlesource.com/28096
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: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: I9b2e6c45f7e83543a06d0aafd08a911f7b6485fd
Reviewed-on: https://go-review.googlesource.com/29874Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

When allocating registers, before kicking out the existing value,
copy it to a spare register if there is one. So later use of this
value can be found in register instead of reload from spill. This
is very helpful for instructions of which the input and/or output
can only be in specific registers, e.g. DIV on x86, MUL/DIV on
MIPS. May also be helpful in general.

For "go build -a cmd/go" on AMD64, reduce "spilled value remains"
by 1% (not including args, which almost certainly remain).

For the code in issue #16061 on AMD64:
MaxRem-12   111µs ± 1%    94µs ± 0%  -15.38%  (p=0.008 n=5+5)

Go1 benchmark on AMD64:
BinaryTree17-12              2.32s ± 2%     2.30s ± 1%    ~     (p=0.421 n=5+5)
Fannkuch11-12                2.52s ± 0%     2.44s ± 0%  -3.44%  (p=0.008 n=5+5)
FmtFprintfEmpty-12          39.9ns ± 3%    39.8ns ± 0%    ~     (p=0.635 n=5+4)
FmtFprintfString-12          114ns ± 1%     113ns ± 1%    ~     (p=0.905 n=5+5)
FmtFprintfInt-12             102ns ± 6%      98ns ± 1%    ~     (p=0.087 n=5+5)
FmtFprintfIntInt-12          146ns ± 5%     147ns ± 1%    ~     (p=0.238 n=5+5)
FmtFprintfPrefixedInt-12     155ns ± 2%     151ns ± 1%  -2.58%  (p=0.008 n=5+5)
FmtFprintfFloat-12           231ns ± 1%     232ns ± 1%    ~     (p=0.286 n=5+5)
FmtManyArgs-12               657ns ± 1%     649ns ± 0%  -1.31%  (p=0.008 n=5+5)
GobDecode-12                6.35ms ± 0%    6.29ms ± 1%    ~     (p=0.056 n=5+5)
GobEncode-12                5.38ms ± 1%    5.45ms ± 1%    ~     (p=0.056 n=5+5)
Gzip-12                      209ms ± 0%     209ms ± 1%    ~     (p=0.690 n=5+5)
Gunzip-12                   31.2ms ± 1%    31.1ms ± 1%    ~     (p=0.548 n=5+5)
HTTPClientServer-12          123µs ± 4%     130µs ± 8%    ~     (p=0.151 n=5+5)
JSONEncode-12               14.0ms ± 1%    14.0ms ± 1%    ~     (p=0.421 n=5+5)
JSONDecode-12               41.2ms ± 1%    41.1ms ± 2%    ~     (p=0.421 n=5+5)
Mandelbrot200-12            3.96ms ± 1%    3.98ms ± 0%    ~     (p=0.421 n=5+5)
GoParse-12                  2.88ms ± 1%    2.88ms ± 1%    ~     (p=0.841 n=5+5)
RegexpMatchEasy0_32-12      68.0ns ± 3%    66.6ns ± 1%  -2.00%  (p=0.024 n=5+5)
RegexpMatchEasy0_1K-12       728ns ± 8%     682ns ± 1%  -6.26%  (p=0.008 n=5+5)
RegexpMatchEasy1_32-12      66.8ns ± 2%    66.0ns ± 1%    ~     (p=0.302 n=5+5)
RegexpMatchEasy1_1K-12       291ns ± 2%     288ns ± 1%    ~     (p=0.111 n=5+5)
RegexpMatchMedium_32-12      103ns ± 2%     100ns ± 0%  -2.53%  (p=0.016 n=5+4)
RegexpMatchMedium_1K-12     31.9µs ± 1%    31.3µs ± 0%  -1.75%  (p=0.008 n=5+5)
RegexpMatchHard_32-12       1.59µs ± 2%    1.59µs ± 1%    ~     (p=0.548 n=5+5)
RegexpMatchHard_1K-12       48.3µs ± 2%    47.7µs ± 1%    ~     (p=0.222 n=5+5)
Revcomp-12                   340ms ± 1%     338ms ± 1%    ~     (p=0.421 n=5+5)
Template-12                 46.3ms ± 1%    46.5ms ± 1%    ~     (p=0.690 n=5+5)
TimeParse-12                 252ns ± 1%     247ns ± 0%  -1.91%  (p=0.000 n=5+4)
TimeFormat-12                277ns ± 1%     267ns ± 0%  -3.82%  (p=0.008 n=5+5)
[Geo mean]                  48.8µs         48.3µs       -0.93%

It has very little effect on binary size and compiler speed.
compilebench:
Template       230ms ±10%      231ms ± 8%    ~             (p=0.546 n=9+9)
Unicode        123ms ± 6%      124ms ± 9%    ~           (p=0.481 n=10+10)
GoTypes        742ms ± 6%      755ms ± 3%    ~           (p=0.123 n=10+10)
Compiler       3.10s ± 3%      3.08s ± 1%    ~           (p=0.631 n=10+10)

Fixes #16061.

Change-Id: Id99cdc7a182ee10a704fa0f04e8e0d0809b2ac56
Reviewed-on: https://go-review.googlesource.com/29732
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Change-Id: I8984eac30e5df78d4b94f19412135d3cc36969f8
Reviewed-on: https://go-review.googlesource.com/29910
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Compression of paletted images is more efficient if they are not filtered.
This patch skips filtering for cbP8 images.
The improvements are demonstrated at https://github.com/olt/compressbench

Fixes #16196

Change-Id: Ie973aad287cacf9057e394bb01cf0e4448a77618
Reviewed-on: https://go-review.googlesource.com/29872Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Realign multi-line comments that got misaligned by the c->go
conversion.

Change-Id: I584b902e95cf588aa14febf1e0b6dfa499c303c2
Reviewed-on: https://go-review.googlesource.com/29871Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Change-Id: Idffb82cdcba4985954d061bdb021217f47ff4985
Reviewed-on: https://go-review.googlesource.com/29850Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #16984

Change-Id: I3a330e82941a068ca6097985af4ab221275fd336
Reviewed-on: https://go-review.googlesource.com/29299
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

This optimizes deferproc and deferreturn in various ways.

The most important optimization is that it more carefully arranges to
prevent preemption or stack growth. Currently we do this by switching
to the system stack on every deferproc and every deferreturn. While we
need to be on the system stack for the slow path of allocating and
freeing defers, in the common case we can fit in the nosplit stack.
Hence, this change pushes the system stack switch down into the slow
paths and makes everything now exposed to the user stack nosplit. This
also eliminates the need for various acquirem/releasem pairs, since we
are now preventing preemption by preventing stack split checks.

As another smaller optimization, we special case the common cases of
zero-sized and pointer-sized defer frames to respectively skip the
copy and perform the copy in line instead of calling memmove.

This speeds up the runtime defer benchmark by 42%:

name           old time/op  new time/op  delta
Defer-4        75.1ns ± 1%  43.3ns ± 1%  -42.31%   (p=0.000 n=8+10)

In reality, this speeds up defer by about 2.2X. The two benchmarks
below compare a Lock/defer Unlock pair (DeferLock) with a Lock/Unlock
pair (NoDeferLock). NoDeferLock establishes a baseline cost, so these
two benchmarks together show that this change reduces the overhead of
defer from 61.4ns to 27.9ns.

name           old time/op  new time/op  delta
DeferLock-4    77.4ns ± 1%  43.9ns ± 1%  -43.31%  (p=0.000 n=10+10)
NoDeferLock-4  16.0ns ± 0%  15.9ns ± 0%   -0.39%    (p=0.000 n=9+8)

This also shaves 34ns off cgo calls:

name       old time/op  new time/op  delta
CgoNoop-4   122ns ± 1%  88.3ns ± 1%  -27.72%  (p=0.000 n=8+9)

Updates #14939, #16051.

Change-Id: I2baa0dea378b7e4efebbee8fca919a97d5e15f38
Reviewed-on: https://go-review.googlesource.com/29656Reviewed-by: Keith Randall <khr@golang.org>

This makes it possible to inline getcallersp. getcallersp is on the
hot path of defers, so this slightly speeds up defer:

name           old time/op  new time/op  delta
Defer-4        78.3ns ± 2%  75.1ns ± 1%  -4.00%   (p=0.000 n=9+8)

Updates #14939.

Change-Id: Icc1cc4cd2f0a81fc4c8344432d0b2e783accacdd
Reviewed-on: https://go-review.googlesource.com/29655
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>