Like the indexed MOVW (MOVWloadidx/MOVWstoreidx) used in current
ARM backend, the indexed MOVB/MOVBU/MOVH/MOVHU can also be used to
generate further optimized ARM code.

My patch implements this optimization. Here are some contrast test
results against the original go compiler.

1. The total size of all .a files in pkg/ shrinks by 0.03%.

2. The compilecmp benchmark shows a little decline.
name        old time/op       new time/op       delta
Template          2.35s ± 1%        2.37s ± 3%  +0.94%  (p=0.006 n=19+19)
Unicode           1.33s ± 3%        1.33s ± 2%    ~     (p=0.158 n=20+18)
GoTypes           7.86s ± 2%        7.84s ± 1%    ~     (p=0.284 n=19+18)
Compiler          37.5s ± 1%        37.7s ± 2%    ~     (p=0.101 n=20+19)
SSA               83.4s ± 2%        83.6s ± 2%    ~     (p=0.231 n=20+20)
Flate             1.46s ± 2%        1.45s ± 1%    ~     (p=0.097 n=20+17)
GoParser          1.86s ± 2%        1.86s ± 4%    ~     (p=0.738 n=20+20)
Reflect           5.10s ± 1%        5.11s ± 1%    ~     (p=0.290 n=20+18)
Tar               1.78s ± 2%        1.77s ± 2%    ~     (p=0.166 n=19+20)
XML               2.61s ± 2%        2.61s ± 2%    ~     (p=0.665 n=19+19)
[Geo mean]        4.67s             4.68s       +0.16%

name        old user-time/op  new user-time/op  delta
Template          2.79s ± 3%        2.80s ± 2%    ~     (p=0.662 n=20+20)
Unicode           1.62s ± 3%        1.64s ± 4%    ~     (p=0.252 n=20+20)
GoTypes           9.58s ± 2%        9.62s ± 2%    ~     (p=0.250 n=20+20)
Compiler          46.2s ± 1%        46.2s ± 1%    ~     (p=0.602 n=20+19)
SSA                108s ± 1%         108s ± 2%    ~     (p=0.242 n=18+20)
Flate             1.69s ± 3%        1.69s ± 4%    ~     (p=0.470 n=20+20)
GoParser          2.16s ± 3%        2.20s ± 4%  +1.70%  (p=0.005 n=19+20)
Reflect           6.02s ± 2%        6.02s ± 2%    ~     (p=0.700 n=20+17)
Tar               2.11s ± 2%        2.11s ± 3%    ~     (p=0.480 n=18+20)
XML               3.07s ± 2%        3.11s ± 4%  +1.50%  (p=0.043 n=20+20)
[Geo mean]        5.61s             5.64s       +0.55%

name        old text-bytes    new text-bytes    delta
HelloSize         586kB ± 0%        586kB ± 0%    ~     (all equal)

name        old data-bytes    new data-bytes    delta
HelloSize        5.46kB ± 0%       5.46kB ± 0%    ~     (all equal)

name        old bss-bytes     new bss-bytes     delta
HelloSize        72.9kB ± 0%       72.9kB ± 0%    ~     (all equal)

name        old exe-bytes     new exe-bytes     delta
HelloSize        1.03MB ± 0%       1.03MB ± 0%    ~     (all equal)

3. The go1 benchmark shows improvement totally, and even more than 10%
improvement in the test case Revcomp. 
name                     old time/op    new time/op    delta
BinaryTree17-4              42.0s ± 1%     41.5s ± 1%   -1.32%  (p=0.000 n=39+40)
Fannkuch11-4                24.1s ± 1%     23.6s ± 0%   -2.38%  (p=0.000 n=40+40)
FmtFprintfEmpty-4           843ns ± 0%     839ns ± 1%   -0.46%  (p=0.000 n=33+40)
FmtFprintfString-4         1.44µs ± 1%    1.37µs ± 1%   -5.48%  (p=0.000 n=40+35)
FmtFprintfInt-4            1.44µs ± 1%    1.41µs ± 2%   -1.50%  (p=0.000 n=40+40)
FmtFprintfIntInt-4         2.07µs ± 1%    2.06µs ± 0%   -0.78%  (p=0.000 n=40+40)
FmtFprintfPrefixedInt-4    2.50µs ± 1%    2.33µs ± 1%   -6.85%  (p=0.000 n=40+40)
FmtFprintfFloat-4          4.36µs ± 1%    4.34µs ± 0%   -0.39%  (p=0.017 n=40+40)
FmtManyArgs-4              8.11µs ± 0%    8.00µs ± 0%   -1.37%  (p=0.000 n=40+40)
GobDecode-4                 105ms ± 2%     103ms ± 2%   -2.17%  (p=0.000 n=39+39)
GobEncode-4                90.1ms ± 2%    88.6ms ± 1%   -1.67%  (p=0.000 n=40+39)
Gzip-4                      4.18s ± 1%     4.09s ± 1%   -2.03%  (p=0.000 n=40+40)
Gunzip-4                    608ms ± 1%     603ms ± 1%   -0.86%  (p=0.000 n=40+34)
HTTPClientServer-4          674µs ± 3%     661µs ± 2%   -1.82%  (p=0.000 n=40+39)
JSONEncode-4                256ms ± 1%     243ms ± 0%   -5.11%  (p=0.000 n=39+31)
JSONDecode-4                915ms ± 1%     904ms ± 1%   -1.18%  (p=0.000 n=40+36)
Mandelbrot200-4            49.2ms ± 0%    49.3ms ± 0%     ~     (p=0.254 n=34+40)
GoParse-4                  46.9ms ± 2%    46.9ms ± 1%     ~     (p=0.737 n=40+39)
RegexpMatchEasy0_32-4      1.28µs ± 1%    1.27µs ± 1%   -0.71%  (p=0.000 n=40+40)
RegexpMatchEasy0_1K-4      7.86µs ± 4%    7.67µs ± 4%   -2.46%  (p=0.000 n=38+40)
RegexpMatchEasy1_32-4      1.28µs ± 1%    1.28µs ± 1%   -0.54%  (p=0.000 n=40+40)
RegexpMatchEasy1_1K-4      10.4µs ± 2%    10.3µs ± 2%   -0.88%  (p=0.003 n=40+39)
RegexpMatchMedium_32-4     2.05µs ± 0%    2.04µs ± 0%   -0.34%  (p=0.000 n=40+33)
RegexpMatchMedium_1K-4      541µs ± 1%     535µs ± 1%   -1.02%  (p=0.000 n=40+38)
RegexpMatchHard_32-4       29.3µs ± 1%    29.1µs ± 1%   -0.51%  (p=0.000 n=40+40)
RegexpMatchHard_1K-4        881µs ± 1%     871µs ± 1%   -1.15%  (p=0.000 n=40+40)
Revcomp-4                  81.7ms ± 2%    67.5ms ± 2%  -17.37%  (p=0.000 n=39+39)
Template-4                  1.05s ± 1%     1.08s ± 2%   +3.67%  (p=0.000 n=40+40)
TimeParse-4                7.24µs ± 1%    7.09µs ± 1%   -2.13%  (p=0.000 n=40+40)
TimeFormat-4               13.2µs ± 1%    13.1µs ± 0%   -0.31%  (p=0.007 n=40+31)
[Geo mean]                  733µs          718µs        -2.03%

name                     old speed      new speed      delta
GobDecode-4              7.28MB/s ± 2%  7.44MB/s ± 2%   +2.23%  (p=0.000 n=39+39)
GobEncode-4              8.52MB/s ± 2%  8.67MB/s ± 1%   +1.70%  (p=0.000 n=40+39)
Gzip-4                   4.65MB/s ± 1%  4.74MB/s ± 1%   +1.94%  (p=0.000 n=37+40)
Gunzip-4                 31.9MB/s ± 1%  32.2MB/s ± 1%   +0.90%  (p=0.000 n=40+36)
JSONEncode-4             7.57MB/s ± 1%  7.98MB/s ± 0%   +5.41%  (p=0.000 n=40+31)
JSONDecode-4             2.12MB/s ± 1%  2.15MB/s ± 1%   +1.23%  (p=0.000 n=40+40)
GoParse-4                1.23MB/s ± 1%  1.23MB/s ± 1%     ~     (p=0.769 n=39+40)
RegexpMatchEasy0_32-4    25.0MB/s ± 1%  25.2MB/s ± 1%   +0.71%  (p=0.000 n=40+40)
RegexpMatchEasy0_1K-4     130MB/s ± 5%   134MB/s ± 4%   +2.53%  (p=0.000 n=38+40)
RegexpMatchEasy1_32-4    24.9MB/s ± 1%  25.1MB/s ± 1%   +0.55%  (p=0.000 n=40+40)
RegexpMatchEasy1_1K-4    98.5MB/s ± 2%  99.4MB/s ± 2%   +0.88%  (p=0.003 n=40+39)
RegexpMatchMedium_32-4    490kB/s ± 0%   490kB/s ± 0%     ~     (all equal)
RegexpMatchMedium_1K-4   1.89MB/s ± 1%  1.91MB/s ± 1%   +1.02%  (p=0.000 n=40+38)
RegexpMatchHard_32-4     1.10MB/s ± 1%  1.10MB/s ± 0%   +0.41%  (p=0.000 n=40+33)
RegexpMatchHard_1K-4     1.16MB/s ± 1%  1.17MB/s ± 1%   +1.21%  (p=0.000 n=40+40)
Revcomp-4                31.1MB/s ± 2%  37.6MB/s ± 2%  +21.03%  (p=0.000 n=39+39)
Template-4               1.86MB/s ± 1%  1.79MB/s ± 1%   -3.51%  (p=0.000 n=40+38)
[Geo mean]               6.66MB/s       6.80MB/s        +2.13%

fixes #21492

Change-Id: Ia26e7ca393f0a5f31de240e8ff9a220453ca7e0d
Reviewed-on: https://go-review.googlesource.com/58450Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Current documentation lacks simple examples for functions Regexp.Expand
and Regexp.ExpandString whose usage is unclear from description alone.
This commit adds examples that demonstrate usage in practical way.

Fixes #21649

Change-Id: I7b2c06c8ab747f69a6578f0595bf0f3c742ac479
Reviewed-on: https://go-review.googlesource.com/59470Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fixes #19157

Change-Id: Ieea286e8dc03929c3645f3113c33df569f8e26f3
Reviewed-on: https://go-review.googlesource.com/58930Reviewed-by: Cherry Zhang <cherryyz@google.com>

Most of these are return values that were part of a receiving parameter,
so they're still accessible.

A few others are not, but those have never had a use.

Found with github.com/mvdan/unparam, after Kevin Burke's suggestion that
the tool should also warn about unused result parameters.

Change-Id: Id8b5ed89912a99db22027703a88bd94d0b292b8b
Reviewed-on: https://go-review.googlesource.com/55910
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

* use bool instead of int if it's adequate.
* remove blank lines.

Change-Id: Ic4a5644a33ed9fc7ce388ef8ba15f1732446fcfc
Reviewed-on: https://go-review.googlesource.com/59375
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Change-Id: I9882488e69565dc9da6814fefbdba3621daf74fe
Reviewed-on: https://go-review.googlesource.com/59332
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com>

The PKCS #1 v2.2 document has been moved to an EMC
website with a new URL. This CL updates the reference to the document to
the new URL.

The new URL is referenced under https://en.wikipedia.org/wiki/PKCS_1

Fixes #21642

Change-Id: Ib8738b0c4c3bb9ec427bebea20c4aacd607ba0db
Reviewed-on: https://go-review.googlesource.com/59351Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This has been supported since Go 1 and there's even a test for it.
The documentation was missing.

Fixes #21409.

Change-Id: I5813488f6a98c1b4506c239e968d43344b91be12
Reviewed-on: https://go-review.googlesource.com/59412Reviewed-by: Ian Lance Taylor <iant@golang.org>

The IsMetaPackage function was made exported when it was moved from
cmd/go to cmd/go/internal/load in CL 36196. Its documentation wasn't
updated accordingly. This change fixes that, resolving a golint issue.

Updates #18653.

Change-Id: Icf89461000754d0f09e6617b11c838e4c050d5a6
Reviewed-on: https://go-review.googlesource.com/59430Reviewed-by: Dave Cheney <dave@cheney.net>

Change-Id: If27f7fbf94ede6f9a57f2520aaf75e6506e0b3f8
Reviewed-on: https://go-review.googlesource.com/59374
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

One example of a heavily-used zero-size value is encoding/binary.BigEndian.

Change-Id: I8e873c447e154ab2ca61b7315df774693891270c
Reviewed-on: https://go-review.googlesource.com/59330
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

Went mainly for the ones that make no sense, such as the ones
mid-sentence or after commas.

Change-Id: Ie245d2c19cc7428a06295635cf6a9482ade25ff0
Reviewed-on: https://go-review.googlesource.com/57293Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Many aspects of the package is woefully undocumented.
With the recent flurry of improvements, the package is now at feature
parity with the GNU and TAR tools. Thoroughly all of the public API
and perform some minor stylistic cleanup in some code segments.

Change-Id: Ic892fd72c587f30dfe91d1b25b88c9c8048cc389
Reviewed-on: https://go-review.googlesource.com/59210
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The PAX specification says the following:
<<<
'g' represents global extended header records for the following files in the archive.
The format of these extended header records shall be as described in pax Extended Header.
Each value shall affect all subsequent files that do not override that value
in their own extended header record and until another global extended header record
is reached that provides another value for the same field.
>>>

This CL adds support for parsing and composing global PAX records,
but intentionally does not provide support for automatically
persisting the global state across files.

Changes made:
* When Reader encounters a TypeXGlobalRecord header, it parses the
PAX records and returns them to the user ad-verbatim. Reader does not
store them in its state, ensuring it has no effect on future Next calls.
* When Writer receives a TypeXGlobalRecord header, it writes the
PAX records to the archive ad-verbatim. It does not store them in
its state, ensuring it has no effect on future WriteHeader calls.
* The restriction regarding empty record values is lifted since this
value is used to represent deletion in global headers.

Why provide raw support only:
* Some archives in the wild have a global header section (often empty)
and it is the user's responsibility to manually read and discard it's body.
The logic added here allows users to more easily skip over these sections.
* For users that do care about global headers, having access to the raw
records allows them to implement the functionality of global headers themselves
and manually persist the global state across files.
* We can still upgrade to a full implementation in the future.

Why we don't provide full support:
* Even though the PAX specification describes their operation in detail,
both the GNU and BSD tar tools (which are the most common implementations)
do not have a consistent interpretation of many details.
* Global headers were a controversial feature in PAX, by admission of the
specification itself:
  <<<
  The concept of a global extended header (typeflag g) was controversial.

  The typeflag g global headers should not be used with interchange media that
  could suffer partial data loss in transporting the archive.
  >>>
* Having state persist from entry-to-entry complicates the implementation
for a feature that is not widely used and not well supported.

Change-Id: I1d904cacc2623ddcaa91525a5470b7dbe226c7e8
Reviewed-on: https://go-review.googlesource.com/59190Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>

Change-Id: I6cb0ed9b726da34106ba239b57e2da732a8e1b71
Reviewed-on: https://go-review.googlesource.com/50730Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Avelino <t@avelino.xxx>

Otherwise, if there are any parallel tests, it will hang and panic with
"all goroutines are asleep - deadlock!".

Do not use flag.Uint to handle the error for us because we also want to
error on N==0, and because it would make setting the default to
GOMAXPROCS(0) more difficult, since it's an int.

Check for it right after flag.Parse, and mimic flag errors by printing
the usage and returning exit code 2.

Fixes #20542.

Change-Id: I0c9d4587f83d406a8f5e42ed74e40be46d639ffb
Reviewed-on: https://go-review.googlesource.com/54150
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This addresses the case of a -timeout panic, but not the more
general case of a signal arriving. See CL 48370 and CL 44352
for recent difficulties in that area.

"-timeout" here means flag usage to distinguish from the
default timeout termination which uses signals.

Fixes #19394

Change-Id: I5452d5422c0c080e940cbcc8c6606049975268c6
Reviewed-on: https://go-review.googlesource.com/48491Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Closes #21519

Change-Id: I1247e9435de93aae7e4db2b6e8e5be1b010c296b
Reviewed-on: https://go-review.googlesource.com/56832Reviewed-by: Avelino <t@avelino.xxx>
Reviewed-by: Adam Langley <agl@golang.org>

This CL adds the following new publicly visible API:
	type Header struct { ...; PAXRecords map[string]string }

The new Header.PAXRecords field is a map of all PAX extended header records.

We suggest (but do not enforce) that users use VENDOR-prefixed keys
according to the following in the PAX specification:
<<<
The standard developers have reserved keyword name space for vendor extensions.
It is suggested that the format to be used is:
	VENDOR.keyword
where VENDOR is the name of the vendor or organization in all uppercase letters.
>>>

When reading, the Header.PAXRecords is populated with all PAX records
encountered so far, including basic ones (e.g., "path", "mtime", etc).
When writing, the fields of Header will be merged into PAXRecords,
overwriting any records that may conflict.

Since PAXRecords is a more expressive feature than Xattrs and
is entirely a superset of Xattrs, we mark Xattrs as deprecated,
and steer users towards the new PAXRecords API.

The issue has a discussion about adding a Header.SetPAXRecord method
to help validate records and keep the Header fields in sync.
However, we do not include that in this CL since that helper
method can always be added in the future.

There is no support for global records.

Fixes #14472

Change-Id: If285a52749acc733476cf75a2c7ad15bc1542071
Reviewed-on: https://go-review.googlesource.com/58390
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Add this early in the cycle so that we can start regression testing
of the master toolchain.

Change-Id: Ida3ccad6e9642648f489babd12877fc8a5eca07a
Reviewed-on: https://go-review.googlesource.com/59151Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I8e8a3a118b1216f191c9076b70a88f6f3f19f79f
Reviewed-on: https://go-review.googlesource.com/59150
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #21570

Change-Id: Ia0734929a04fbce8fdd5fbcb1b7baff9a8bbe39e
Reviewed-on: https://go-review.googlesource.com/58030Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

If Less(a, b) returns true when a is less than b, the correct way to
check if a is greater than b is to use Less(b, a). It is wrong to use
!Less(a, b) because that checks if a is greater than *or equal to* b.

1. The decreasingDistance function in Example_sortKeys makes this
   mistake. Fix it.

2. The documentation of multiSorter.Less says it loops along the less
   functions until it finds a comparison "that is either Less or
   !Less". This is nonsense, because (Less(a, b) or !Less(a, b)) is
   always true. Fix the documentation to say that it finds a
   comparison "that discriminates between the two items (one is less
   than the other)". The implementation already does this correctly.

Change-Id: If52b79f68e4fdb0d1095edf29bdecdf154a61b8d
Reviewed-on: https://go-review.googlesource.com/57752Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The current code treats the type of SIMD&FP register as C_REG incorrectly.

The fix code converts C_REG type into C_FREG type.

Uncomment fcsels/fcseld test cases.

Fixes #21582
Change-Id: I754c51f72a0418bd352cbc0f7740f14cc599c72d
Reviewed-on: https://go-review.googlesource.com/58350Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fix two small but serious bugs in the DWARF location list code that
should have been caught by the automated tests I didn't write.

After emitting debug information for a user variable, mark it as done
so that it doesn't get emitted again. Otherwise it would be written once
per slot it was decomposed into.

Correct a merge error in CL 44350: the location list abbreviations need
to have DW_AT_decl_line too, otherwise the resulting DWARF is gibberish.

Change-Id: I6ab4b8b32b7870981dac80eadf0ebfc4015ccb01
Reviewed-on: https://go-review.googlesource.com/59070
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Change-Id: Ic3ce2f3c055f2636ec8fc9cec8592e596b18dc05
Reviewed-on: https://go-review.googlesource.com/54771
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Use "STP (ZR, ZR), O(R)" instead of "MOVD ZR, O(R)" to implement memory clearing.
Also improve assembler supports to STP/LDP.
Results (A57@2GHzx8):

benchmark                   old ns/op     new ns/op     delta
BenchmarkClearFat8-8        1.00          1.00          +0.00%
BenchmarkClearFat12-8       1.01          1.01          +0.00%
BenchmarkClearFat16-8       1.01          1.01          +0.00%
BenchmarkClearFat24-8       1.52          1.52          +0.00%
BenchmarkClearFat32-8       3.00          2.02          -32.67%
BenchmarkClearFat40-8       3.50          2.52          -28.00%
BenchmarkClearFat48-8       3.50          3.03          -13.43%
BenchmarkClearFat56-8       4.00          3.50          -12.50%
BenchmarkClearFat64-8       4.25          4.00          -5.88%
BenchmarkClearFat128-8      8.01          8.01          +0.00%
BenchmarkClearFat256-8      16.1          16.0          -0.62%
BenchmarkClearFat512-8      32.1          32.0          -0.31%
BenchmarkClearFat1024-8     64.1          64.1          +0.00%

Change-Id: Ie5f5eac271ff685884775005825f206167a5c146
Reviewed-on: https://go-review.googlesource.com/55610
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Sometimes (often for calls) we generate code like this:

MOVQ  (addr),AX
MOVQ  8(addr),BX
MOVQ  AX,(otheraddr)
MOVQ  BX,8(otheraddr)

Replace it with

MOVUPS (addr),X0
MOVUPS X0,(otheraddr)

For completeness do the same for 8,16,32-bit loads/stores too.
Shaves 1% from code sections of go tool.

/localdisk/itocar/golang/bin/go 10293917
go_old 10334877 [40960 bytes]

read-only data = 682 bytes (0.040769%)
global text (code) = 38961 bytes (1.036503%)
Total difference 39643 bytes (0.674628%)

Updates #6853

Change-Id: I1f0d2f60273a63a079b58927cd1c4e3429d2e7ae
Reviewed-on: https://go-review.googlesource.com/57130
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Throughout the spec we use the notion of a constant x being
representable by a value of type T. While intuitively clear,
at least for floating-point and complex constants types, the
concept was not well-defined. In the section on Conversions
there was an extra rule for floating-point types only and it
missed the case of floating-point values overflowing to an
infinity after rounding.

Since the concept is important to Go, and a compiler most
certainly will have a function to test "representability",
it seems warranted to define the term explicitly in the spec.

This change introduces a new entry "Representability" under
the section on "Properties of types and values", and defines
the term explicitly, together with examples.

The phrase used is "representable by" rather than "representable as"
because the former use is prevalent in the spec.

Additionally, it clarifies that a floating-point constant
that overflows to an infinity after rounding is never
representable by a value of a floating-point type, even though
infinities are valid values of IEEE floating point types.
This is required because there are not infinite value constants
in the language (like there is also no -0.0) and representability
also matters for constant conversions. This is not a language
change, and type-checkers have been following this rule before.

The change also introduces links throughout the spec to the new
section as appropriate and removes duplicate text and examples
elsewhere (Constants and Conversions sections), leading to
simplifications in the relevant paragraphs.

Fixes #15389.

Change-Id: I8be0e071552df0f18998ef4c5ef521f64ffe8c44
Reviewed-on: https://go-review.googlesource.com/57530Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Prior to this change, we use typedmemmove to write the key
value to its new location in mapassign_fast32 and mapassign_fast64.
(The use of typedmemmove was a last-minute fix in the 1.9 cycle;
see #21297 and CL 53414.)

This is significantly less inefficient than direct assignment or
calling writebarrierptr directly.

Fortunately, there aren't many cases to consider.

On systems with 32 bit pointers:

* A 32 bit AMEM value either is a single pointer or has no pointers.
* A 64 bit AMEM value may contain a pointer at the beginning,
  a pointer at 32 bits, or two pointers.

On systems with 64 bit pointers:

* A 32 bit AMEM value contains no pointers.
* A 64 bit AMEM value either is a single pointer or has no pointers.

All combinations except the 32 bit pointers / 64 bit AMEM value are
cheap and easy to handle, and the problematic case is likely rare.
The most popular map keys appear to be ints and pointers.

So we handle them exhaustively. The sys.PtrSize checks are constant branches
and are eliminated by the compiler.

An alternative fix would be to return a pointer to the key,
and have the calling code do the assignment, at which point the compiler
would have full type information.

Initial tests suggest that the performance difference between these
strategies is negligible, and this fix is considerably simpler,
and has much less impact on binary size.

Fixes #21321

Change-Id: Ib03200e89e2324dd3c76d041131447df66f22bfe
Reviewed-on: https://go-review.googlesource.com/59110
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Follow-up to CL 58371.

Change-Id: I3d2aaec84ee6db3ef1bd4fcfcaf46cc297c7176b
Reviewed-on: https://go-review.googlesource.com/58610
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Implement int reg <-> fp reg moves on amd64.
If we see a load to int reg followed by an int->fp move, then we can just
load to the fp reg instead.  Same for stores.

math.Abs is now:

MOVQ	"".x+8(SP), AX
SHLQ	$1, AX
SHRQ	$1, AX
MOVQ	AX, "".~r1+16(SP)

math.Copysign is now:

MOVQ	"".x+8(SP), AX
SHLQ	$1, AX
SHRQ	$1, AX
MOVQ	"".y+16(SP), CX
SHRQ	$63, CX
SHLQ	$63, CX
ORQ	CX, AX
MOVQ	AX, "".~r2+24(SP)

math.Float64bits is now:

MOVSD	"".x+8(SP), X0
MOVSD	X0, "".~r1+16(SP)
(it would be nicer to use a non-SSE reg for this, nothing is perfect)

And due to the fix for #21440, the inlined version of these improve as well.

name      old time/op  new time/op  delta
Abs       1.38ns ± 5%  0.89ns ±10%  -35.54%  (p=0.000 n=10+10)
Copysign  1.56ns ± 7%  1.35ns ± 6%  -13.77%  (p=0.000 n=9+10)

Fixes #13095

Change-Id: Ibd7f2792412a6668608780b0688a77062e1f1499
Reviewed-on: https://go-review.googlesource.com/58732
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>

Make it dead simple to see visually what the function outputs in
various scenarios.

Change-Id: I8f6fcd72fa1515361481f0510412cde221e1d4e3
Reviewed-on: https://go-review.googlesource.com/51630
Run-TryBot: Kevin Burke <kev@inburke.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Hiroshi Ioka <hirochachacha@gmail.com>

CL 36428 changed the way nanotime works so on Darwin and Windows it
now depends on runtime.startNano, which is computed at runtime.init
time. Unfortunately, the `runtimeInitTime = nanotime()` initialization
happened *before* runtime.init, so on these platforms runtimeInitTime
is set incorrectly. The one (and only) consequence of this is that the
start time printed in gctrace lines is bogus:

gc 1 18446653480.186s 0%: 0.092+0.47+0.038 ms clock, 0.37+0.15/0.81/1.8+0.15 ms cpu, 4->4->1 MB, 5 MB goal, 8 P

To fix this, this commit moves the runtimeInitTime initialization to
shortly after runtime.init, at which point nanotime is safe to use.

This also requires changing the condition in newproc1 that currently
uses runtimeInitTime != 0 simply to detect whether or not the main M
has started. Since runtimeInitTime could genuinely be 0 now, this
introduces a separate flag to newproc1.

Fixes #21554.

Change-Id: Id874a4b912d3fa3d22f58d01b31ffb3548266d3b
Reviewed-on: https://go-review.googlesource.com/58690
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Generated with
 github.com/catapult/tracing/bin/vulcanize_trace_viewer
catapult @ ab4d571fa

Renamed trace_viewer_lean.html to trace_viewer_full.html
to make it clear we are using the full version of trace viewer
(waiting for https://github.com/catapult-project/catapult/issues/2247
to be fixed).

Update #15302

Change-Id: Ice808bb27ab79a1dec9fc863e0c5a761027ebfbe
Reviewed-on: https://go-review.googlesource.com/58750Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

Updates #21486

Change-Id: I78ca76490d8e9b52e055c1f0b8d10bdb227e3a80
Reviewed-on: https://go-review.googlesource.com/56331Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Fix debugger printing of uint that mistakenly
invoked .int64() instead of .uint64()

Fixes #21392

Change-Id: I107a7e87e0efbb06303c1e627dee76c369f75d1e
Reviewed-on: https://go-review.googlesource.com/54750Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Benchmark results on GOOS=linux:

GOARCH=amd64

name              old time/op  new time/op  delta
Atoi/Pos/7bit-4   20.1ns ± 2%   8.6ns ± 1%  -57.34%  (p=0.000 n=10+10)
Atoi/Pos/26bit-4  25.8ns ± 7%  11.9ns ± 0%  -53.91%  (p=0.000 n=10+8)
Atoi/Pos/31bit-4  27.3ns ± 2%  13.2ns ± 1%  -51.56%  (p=0.000 n=10+10)
Atoi/Pos/56bit-4  37.2ns ± 5%  18.2ns ± 1%  -51.26%  (p=0.000 n=10+10)
Atoi/Pos/63bit-4  38.7ns ± 1%  38.6ns ± 1%     ~     (p=0.297 n=9+10)
Atoi/Neg/7bit-4   17.6ns ± 1%   7.2ns ± 0%  -59.22%  (p=0.000 n=10+10)
Atoi/Neg/26bit-4  24.4ns ± 1%  12.4ns ± 1%  -49.28%  (p=0.000 n=10+10)
Atoi/Neg/31bit-4  26.9ns ± 0%  14.0ns ± 1%  -47.88%  (p=0.000 n=7+10)
Atoi/Neg/56bit-4  36.2ns ± 1%  19.5ns ± 0%  -46.24%  (p=0.000 n=10+9)
Atoi/Neg/63bit-4  38.9ns ± 1%  38.8ns ± 1%     ~     (p=0.385 n=9+10)

GOARCH=386

name              old time/op  new time/op  delta
Atoi/Pos/7bit-4   89.6ns ± 1%   8.2ns ± 1%  -90.84%  (p=0.000 n=9+10)
Atoi/Pos/26bit-4   187ns ± 2%    12ns ± 1%  -93.71%  (p=0.000 n=10+9)
Atoi/Pos/31bit-4   225ns ± 1%   225ns ± 1%     ~     (p=0.995 n=10+10)
Atoi/Neg/7bit-4   86.2ns ± 1%   8.5ns ± 1%  -90.14%  (p=0.000 n=10+10)
Atoi/Neg/26bit-4   183ns ± 1%    13ns ± 1%  -92.77%  (p=0.000 n=9+10)
Atoi/Neg/31bit-4   223ns ± 0%   223ns ± 0%     ~     (p=0.247 n=8+9)

Fixes #20557

Change-Id: Ib6245d88cffd4b037419e2bf8e4a71b86c6d773f
Reviewed-on: https://go-review.googlesource.com/44692Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Since golang.org/cl/31670, we've stopped using the 'embedded' function
for handling struct embeddings within package export data. Now the
only remaining use is for Go source files, which allows for some
substantial simplifications:

1. CenterDot never appears within Go source files, so that logic can
simply be removed.

2. The field name will always be declared in the local package.

Passes toolstash-check.

Change-Id: I59505f62824206dd5de0782918f98fbef6e93224
Reviewed-on: https://go-review.googlesource.com/58790
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

The enumeration of numeric types missed the complex types.
Clarify by removing the explicit enumeration and referring
to numeric types instead.

Fixes #21579.

Change-Id: If36c2421f8501eeec82a07f442ac2e16a35927ba
Reviewed-on: https://go-review.googlesource.com/58491Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Rob Pike <r@golang.org>