Fixes #27731

Change-Id: Ifb4d57923b1bba0210ec1f623d779d7b5f442812
Reviewed-on: https://go-review.googlesource.com/135995
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

The -mod=release flag is not supported, so this appears to be a
documentation mistake.

Fixes #27354.

Change-Id: I895e8d5b4918adcb1f605361773173f312fa7b65
GitHub-Last-Rev: 42bfe0c11e38c90e76887771654ea81af98d50ec
GitHub-Pull-Request: golang/go#27358
Reviewed-on: https://go-review.googlesource.com/132116
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

Makes use of bounded shift information to generate
more efficient shift instructions.

Updates #25167 for ppc64x

Change-Id: I7fc8d49a3fb3e0f273cc51bc767470b239cbdca7
Reviewed-on: https://go-review.googlesource.com/135380
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Munday <mike.munday@ibm.com>

Fixes missing commas where it wasn't immediately apparent whether
"requests" was being used as a verb or a noun.

Change-Id: Ic8c99b4f46475f40a6160d26a3cd11c215940dd5
GitHub-Last-Rev: 1becf6fabeb6f928e37526e96297dd60397ccf9b
GitHub-Pull-Request: golang/go#27649
Reviewed-on: https://go-review.googlesource.com/135135Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

Change-Id: Idcd79788e64947a927af662b6394ac7218e62ba8
Reviewed-on: https://go-review.googlesource.com/135836Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

According to AMD64.rules, BTS&BTR&BTC use arg1 as the bit index,
while BT uses arg0. This CL fixes the wrong comment message in
AMD64Ops.go, which indicates all bit indexes are in arg0.

Change-Id: Idb78f4d39f7ef5ea78065ad8bc651324597e2a8a
Reviewed-on: https://go-review.googlesource.com/135419Reviewed-by: Keith Randall <khr@golang.org>

If a cyclic declaration uses a non-type object where it expects
a type, don't report the cycle error in favor of the clearer and
more informative error about the missing type.

Fixes #25790.

Change-Id: If937078383def878efb4c69686e5b4b2a495fd5d
Reviewed-on: https://go-review.googlesource.com/135700Reviewed-by: Alan Donovan <adonovan@google.com>

Change-Id: Ia32d40cc272cb049c0a7c9d5f8ef4329bdefc7fe
Reviewed-on: https://go-review.googlesource.com/135699
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

Fixes: #27298

Change-Id: Icfc6992b470136bb25a77912f670a25883642316
Reviewed-on: https://go-review.googlesource.com/132095Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Use float <-> int register moves without conversion instead of stores
and loads to move float <-> int values.

Math package benchmark results.
name                 old time/op  new time/op  delta
Acosh                 153ns ± 0%   147ns ± 0%   -3.92%  (p=0.000 n=10+10)
Asinh                 183ns ± 0%   177ns ± 0%   -3.28%  (p=0.000 n=10+10)
Atanh                 157ns ± 0%   155ns ± 0%   -1.27%  (p=0.000 n=10+10)
Atan2                 118ns ± 0%   117ns ± 1%   -0.59%  (p=0.003 n=10+10)
Cbrt                  119ns ± 0%   114ns ± 0%   -4.20%  (p=0.000 n=10+10)
Copysign             7.51ns ± 0%  6.51ns ± 0%  -13.32%  (p=0.000 n=9+10)
Cos                  73.1ns ± 0%  70.6ns ± 0%   -3.42%  (p=0.000 n=10+10)
Cosh                  119ns ± 0%   121ns ± 0%   +1.68%  (p=0.000 n=10+9)
ExpGo                 154ns ± 0%   149ns ± 0%   -3.05%  (p=0.000 n=9+10)
Expm1                 101ns ± 0%    99ns ± 0%   -1.88%  (p=0.000 n=10+10)
Exp2Go                150ns ± 0%   146ns ± 0%   -2.67%  (p=0.000 n=10+10)
Abs                  7.01ns ± 0%  6.01ns ± 0%  -14.27%  (p=0.000 n=10+9)
Mod                   234ns ± 0%   212ns ± 0%   -9.40%  (p=0.000 n=9+10)
Frexp                34.5ns ± 0%  30.0ns ± 0%  -13.04%  (p=0.000 n=10+10)
Gamma                 112ns ± 0%   111ns ± 0%   -0.89%  (p=0.000 n=10+10)
Hypot                73.6ns ± 0%  68.6ns ± 0%   -6.79%  (p=0.000 n=10+10)
HypotGo              77.1ns ± 0%  72.1ns ± 0%   -6.49%  (p=0.000 n=10+10)
Ilogb                31.0ns ± 0%  28.0ns ± 0%   -9.68%  (p=0.000 n=10+10)
J0                    437ns ± 0%   434ns ± 0%   -0.62%  (p=0.000 n=10+10)
J1                    433ns ± 0%   431ns ± 0%   -0.46%  (p=0.000 n=10+10)
Jn                    927ns ± 0%   922ns ± 0%   -0.54%  (p=0.000 n=10+10)
Ldexp                41.5ns ± 0%  37.0ns ± 0%  -10.84%  (p=0.000 n=9+10)
Log                   124ns ± 0%   118ns ± 0%   -4.84%  (p=0.000 n=10+9)
Logb                 34.0ns ± 0%  32.0ns ± 0%   -5.88%  (p=0.000 n=10+10)
Log1p                 110ns ± 0%   108ns ± 0%   -1.82%  (p=0.000 n=10+10)
Log10                 136ns ± 0%   132ns ± 0%   -2.94%  (p=0.000 n=10+10)
Log2                 51.6ns ± 0%  47.1ns ± 0%   -8.72%  (p=0.000 n=10+10)
Nextafter32          33.0ns ± 0%  30.5ns ± 0%   -7.58%  (p=0.000 n=10+10)
Nextafter64          29.0ns ± 0%  26.5ns ± 0%   -8.62%  (p=0.000 n=10+10)
PowInt                169ns ± 0%   160ns ± 0%   -5.33%  (p=0.000 n=10+10)
PowFrac               375ns ± 0%   361ns ± 0%   -3.73%  (p=0.000 n=10+10)
RoundToEven          14.0ns ± 0%  12.5ns ± 0%  -10.71%  (p=0.000 n=10+10)
Remainder             206ns ± 0%   192ns ± 0%   -6.80%  (p=0.000 n=10+9)
Signbit              6.01ns ± 0%  5.51ns ± 0%   -8.32%  (p=0.000 n=10+9)
Sin                  70.1ns ± 0%  69.6ns ± 0%   -0.71%  (p=0.000 n=10+10)
Sincos               99.1ns ± 0%  99.6ns ± 0%   +0.50%  (p=0.000 n=9+10)
SqrtGoLatency         178ns ± 0%   146ns ± 0%  -17.70%  (p=0.000 n=8+10)
SqrtPrime            9.19µs ± 0%  9.20µs ± 0%   +0.01%  (p=0.000 n=9+9)
Tanh                  125ns ± 1%   127ns ± 0%   +1.36%  (p=0.000 n=10+10)
Y0                    428ns ± 0%   426ns ± 0%   -0.47%  (p=0.000 n=10+10)
Y1                    431ns ± 0%   429ns ± 0%   -0.46%  (p=0.000 n=10+9)
Yn                    906ns ± 0%   901ns ± 0%   -0.55%  (p=0.000 n=10+10)
Float64bits          4.50ns ± 0%  3.50ns ± 0%  -22.22%  (p=0.000 n=10+10)
Float64frombits      4.00ns ± 0%  3.50ns ± 0%  -12.50%  (p=0.000 n=10+9)
Float32bits          4.50ns ± 0%  3.50ns ± 0%  -22.22%  (p=0.002 n=8+10)
Float32frombits      4.00ns ± 0%  3.50ns ± 0%  -12.50%  (p=0.000 n=10+10)

Change-Id: Iba829e15d5624962fe0c699139ea783efeefabc2
Reviewed-on: https://go-review.googlesource.com/129715Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

For sweep events, we used to modify the ViewerEvent returned from
ctx.emitSlice later in order to embed more details about the sweep
operation. The trick no longer works after the change
https://golang.org/cl/92375 and caused a regression.

ctx.emit method encodes the ViewerEvent, so any modification to the
ViewerEvent object after ctx.emit returns will not be reflected.

Refactor ctx.emitSlice, so ctx.makeSlice can be used when producing
slices for SWEEP. ctx.emit* methods are meant to truely emit
ViewerEvents.

Fixes #27711

Change-Id: I0b733ebbbfd4facd8714db0535809ec3cab0833d
Reviewed-on: https://go-review.googlesource.com/135775Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: If0e8fbb05c09ee7c64e1aa6b0aa2ade35a70df8a
Reviewed-on: https://go-review.googlesource.com/135696Reviewed-by: Alan Donovan <adonovan@google.com>

Check the size of uintptr instead of listing GOARCHes explicitly. This
will make the test also run on linux/mips{,le}.

Change-Id: I649f15d293002afc1360b1913910202c3e5188b7
Reviewed-on: https://go-review.googlesource.com/135715
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The CMPconstload opcodes take a ValAndOff as their AuxInt, not just
an offset.

Originally introduced in CL 135379.

Change-Id: I244b2d56ef2e99d2975faa2e97f4291ec97c64b7
Reviewed-on: https://go-review.googlesource.com/135418
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>

Change-Id: Ib0544adc1444a473f8edcb9dd92aefa9fcbc7330
Reviewed-on: https://go-review.googlesource.com/134656Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Use the new custom truncate/extension code when storing or extracting
float32 values from AuxInts to avoid the value being changed by the
host platform's floating point conversion instructions (e.g. sNaN ->
qNaN).

Updates #27516.

Change-Id: Id39650f1431ef74af088c895cf4738ea5fa87974
Reviewed-on: https://go-review.googlesource.com/134855
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Instead of skipping all OSLICEARR, skip only ones with non-pointer
array type. For pointers to arrays, it's safe to apply the
self-assignment slicing optimizations.

Refactored the matching code into separate function for readability.

This is an extension to already existing optimization.

On its own, it does not improve any code under std, but
it opens some new optimization opportunities. One
of them is described in the referenced issue.

Updates #7921

Change-Id: I08ac660d3ef80eb15fd7933fb73cf53ded9333ad
Reviewed-on: https://go-review.googlesource.com/133375
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

OLEN and OCAP can't affect memory state as long as their
arguments don't.

Re-organized case bodies to avoid duplicating same branches for
recursive invocations.

Change-Id: I30407143429f7dd1891badb70df88969ed267535
Reviewed-on: https://go-review.googlesource.com/133555
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Removes a redundant err check and replaces some returns in a testing
loop with continue to prevent skipping unrelated test cases when
a failure is encountered.

Change-Id: Ic1a560751b95bb0ef8dfa957e057e0fa0c2b281d
Reviewed-on: https://go-review.googlesource.com/134236
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

It's worth clarifying that the language is called "Go".

Fixes #27616.

Change-Id: Ie4a9cb5e7e6afa437c60e06914125ef7490f27d0
Reviewed-on: https://go-review.googlesource.com/135517Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Clarify the behavior of splice on older kernels, merge comments so
control flow becomes more obvious, as discussed in CL 133575.

Change-Id: I95855991bd0b1fa1c78a900b39c4382f65d83468
Reviewed-on: https://go-review.googlesource.com/135436Reviewed-by: Ian Lance Taylor <iant@golang.org>

This makes Android consistent with the change in CL 121877.

Updates #20969

Change-Id: I1f114556fd1d4654c8e4e6a59513bddd5dc3d1a0
Reviewed-on: https://go-review.googlesource.com/135416
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Elias Naur <elias.naur@gmail.com>

The cmd/compile/internal/ld/go.go file not exist, actually cmd/link/internal/ld/go.go.
Also, write line number is not good because it changes every commit of the file.

Change-Id: Id2b9f2c9904390adb011dab357716ee8e2fe84fc
Reviewed-on: https://go-review.googlesource.com/135516Reviewed-by: Ian Lance Taylor <iant@golang.org>

Gracefully fallback to a userspace copy when the kernel does not support
splice(2) on a unix domain socket. EINVAL is returned by the splice
syscall if it does not support unix domain sockets. Keeping the handled
return value as false when the first splice call fails with EINVAL will
cause the caller to fall back to a userspace copy.

Fixes #27513

Change-Id: I4b10c1900ba3c096cb32edb7c8a6044f468efb52
Reviewed-on: https://go-review.googlesource.com/133575
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

In Go 1.11, cmd/go gained support for the GOFLAGS environment variable.
It was added and described in detail in CL 126656.
Mention it in the Go 1.11 release notes, link to the cmd/go documentation,
and add more details there.

Fixes #27282.

Change-Id: Ifc35bfe3e0886a145478d36dde8e80aedd8ec68e
Reviewed-on: https://go-review.googlesource.com/135035Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Rob Pike <r@golang.org>

Currently, when a tz file was being checked inside a zoneInfo dir,
a syscall.ENOENT error was being returned, which caused it to look
in the zoneinfo.zip file and return an error for that case.

We return a syscall.ENOENT error for the zip file case too, so that
it falls through to the end of the loop and returns an uniform error
for both cases.

Fixes #20969

Change-Id: If1de068022ac7693caabb5cffd1c929878460140
Reviewed-on: https://go-review.googlesource.com/121877
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This makes TestRuntimePanic keep most of the existing environment,
just as the other runtime tests do.

Change-Id: I7944abfeee292d41716dca14483134a50d75f081
Reviewed-on: https://go-review.googlesource.com/135376
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Makes go binary smaller by 0.2%.

I noticed this in autogenerated equal methods, and there are
probably a lot of those.

Change-Id: I4e04eb3653fbceb9dd6a4eee97ceab1fa4d10b72
Reviewed-on: https://go-review.googlesource.com/135379Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>

The GNU assembler for ARM treats @ as a comment character, so section
types must be written using % instead.

Fixes https://gcc.gnu.org/PR87260.

Change-Id: I5461e4bf5b20793db321f540c7f25a9e6e12b6f4
Reviewed-on: https://go-review.googlesource.com/135297
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

The 387 unit always quietens float64 and float32 signaling NaNs,
even when just loading and storing them. This makes it difficult
to propagate such values in the compiler. This is a hard problem
to fix and it is also very obscure.

Updates #27516.

Change-Id: I03d88e31f14c86fa682fcea4b6d1fba18968aee8
Reviewed-on: https://go-review.googlesource.com/135195Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

For a relative symlink in the root directory, such as /tmp ->
private/tmp, we were dropping the leading slash.

No test because we can't create a symlink in the root directory.
The test TestGZIPFilesHaveZeroMTimes was failing on the Darwin builders.

Updates #19922
Updates #20506

Change-Id: Ic83cb6d97ad0cb628fc551ac772a44fb3e20f038
Reviewed-on: https://go-review.googlesource.com/135295
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

CL 135015 added TestSpuriousWakeupsNeverHangSemasleep.
However, this test is failing on Plan 9 because
syscall.SIGIO is not defined.

This change excludes semasleep_test.go on Plan 9

Fixes #27662.

Change-Id: I52f9f0fe9ec3c70da5d2f586a95debbc1fe568a1
Reviewed-on: https://go-review.googlesource.com/135315
Run-TryBot: David du Colombier <0intro@gmail.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

When a zip archive for a module contains an unexpected file, the error
message removes the last character in the version number, e.g. an invalid
archive for "somemod@v1.2.3" would generate the following error:
"zip for somemod@1.2. has unexpected file..."

Change-Id: I366622df16a71fa7467a4bc62cb696e3e83a2942
GitHub-Last-Rev: f172283bcdffd45b485b1e8fd99795eb93fef726
GitHub-Pull-Request: golang/go#27279
Reviewed-on: https://go-review.googlesource.com/131635
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

This adds some improvements to the rules for PPC64 to eliminate
unnecessary zero or sign extends, and fix some rule for truncates
which were not always using the correct sign instruction.

This reduces of size of many functions by 1 or 2 instructions and
can improve performance in cases where the execution time depends
on small loops where at least 1 instruction was removed and where that
loop contributes a significant amount of the total execution time.

Included is a testcase for codegen to verify the sign/zero extend
instructions are omitted.

An example of the improvement (strings):
IndexAnyASCII/256:1-16     392ns ± 0%   369ns ± 0%  -5.79%  (p=0.000 n=1+10)
IndexAnyASCII/256:2-16     397ns ± 0%   376ns ± 0%  -5.23%  (p=0.000 n=1+9)
IndexAnyASCII/256:4-16     405ns ± 0%   384ns ± 0%  -5.19%  (p=1.714 n=1+6)
IndexAnyASCII/256:8-16     427ns ± 0%   403ns ± 0%  -5.57%  (p=0.000 n=1+10)
IndexAnyASCII/256:16-16    441ns ± 0%   418ns ± 1%  -5.33%  (p=0.000 n=1+10)
IndexAnyASCII/4096:1-16   5.62µs ± 0%  5.27µs ± 1%  -6.31%  (p=0.000 n=1+10)
IndexAnyASCII/4096:2-16   5.67µs ± 0%  5.29µs ± 0%  -6.67%  (p=0.222 n=1+8)
IndexAnyASCII/4096:4-16   5.66µs ± 0%  5.28µs ± 1%  -6.66%  (p=0.000 n=1+10)
IndexAnyASCII/4096:8-16   5.66µs ± 0%  5.31µs ± 1%  -6.10%  (p=0.000 n=1+10)
IndexAnyASCII/4096:16-16  5.70µs ± 0%  5.33µs ± 1%  -6.43%  (p=0.182 n=1+10)

Change-Id: I739a6132b505936d39001aada5a978ff2a5f0500
Reviewed-on: https://go-review.googlesource.com/129875Reviewed-by: David Chase <drchase@google.com>

Change-Id: I24c4b08091bf3b8734f5dcdb9eac1a3582a4daa8
Reviewed-on: https://go-review.googlesource.com/135116Reviewed-by: Alan Donovan <adonovan@google.com>

Printing of scopes was horribly wrong: If a scope contained
no object declarations, it would abort printing even if the
scope had children scopes. Also, the line breaks were not
inserted consistently. The actual test case (ExampleScope)
was incorrect as well.

Fixed and simplified printing, and adjusted example which
tests the printing output.

Change-Id: If21c1d4ad71b15a517d4a54da16de5e6228eb4b5
Reviewed-on: https://go-review.googlesource.com/135115
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

This failure occurs randomly on arm64.

13:10:32 --- FAIL: TestGcSys (0.06s)
13:10:32 gc_test.go:30: expected "OK\n", but got "using too much memory: 71401472 bytes\n"
13:10:32 FAIL

Updates #27636

Change-Id: Ifd4cfce167d8054dc6f037bd34368d63c7f68ed4
Reviewed-on: https://go-review.googlesource.com/135155
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Rather than try to work around Clean and Join on intermediate steps,
which can remove ".." components unexpectedly, just do everything in
walkSymlinks. Use a single loop over path components.

Fixes #23444

Change-Id: I4f15e50d0df32349cc4fd55e3d224ec9ab064379
Reviewed-on: https://go-review.googlesource.com/121676
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

Change-Id: I628aad9a3abe9cc0c3233f476960e53bd291eca9
Reviewed-on: https://go-review.googlesource.com/135235Reviewed-by: Ralph Corderoy <ralph@inputplus.co.uk>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This change compares the first two characters instead of the first one,
and if they match, the entire string is compared. Comparing the first two
characters helps to filter out the case where the first character matches
but the subsequent characters do not match, thereby improving the substring
search speed in this case.

Benchmarks with no effect or minimal impact (less than 5%) is not listed,
the following are improved benchmarks:
On arm64:
strings:
IndexPeriodic/IndexPeriodic16-8   172890.00ns +- 2%   124156.20ns +- 0%  -28.19%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic32-8    78092.80ns +- 0%    65138.60ns +- 0%  -16.59%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic64-8    42322.20ns +- 0%    34661.60ns +- 0%  -18.10%  (p=0.008 n=5+5)
bytes:
IndexPeriodic/IndexPeriodic16-8     183468.20ns +- 6%     123759.00ns +- 0%  -32.54%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic32-8      84776.40ns +- 0%      63907.80ns +- 0%  -24.62%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic64-8      45835.60ns +- 0%      34194.20ns +- 0%  -25.40%  (p=0.008 n=5+5)

On amd64:
strings:
IndexPeriodic/IndexPeriodic8-16    219499.00ns +- 0%   178123.40ns +- 0%  -18.85%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic16-16   109760.20ns +- 0%    88957.80ns +- 0%  -18.95%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic32-16    54943.00ns +- 0%    44573.80ns +- 0%  -18.87%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic64-16    29804.80ns +- 0%    24417.80ns +- 0%  -18.07%  (p=0.008 n=5+5)
bytes:
IndexPeriodic/IndexPeriodic8-16     226592.60ns +- 0%    181183.20ns +- 0%  -20.04%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic16-16    111432.60ns +- 0%     90634.60ns +- 0%  -18.66%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic32-16     55640.60ns +- 0%     45433.00ns +- 0%  -18.35%  (p=0.008 n=5+5)
IndexPeriodic/IndexPeriodic64-16     30833.00ns +- 0%     24784.20ns +- 0%  -19.62%  (p=0.008 n=5+5)

Change-Id: I2d9e7e138d29e960d20a203eb74dc2ec976a9d71
Reviewed-on: https://go-review.googlesource.com/131177
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>