Change-Id: If1d08a84c9295816489b1cfdd031ba12892ae963
Reviewed-on: https://go-review.googlesource.com/31598Reviewed-by: Matthew Dempsky <mdempsky@google.com>

This makes grayModel and gray16Model in color.go use the exact same
formula as RGBToYCbCr in ycbcr.go. They were the same formula in theory,
but in practice the color.go versions used a divide by 1000 and the
ycbcr.go versions used a (presumably faster) shift by 16.

This implies the nice property that converting an image.RGBA to an
image.YCbCr and then taking only the Y channel is equivalent to
converting an image.RGBA directly to an image.Gray.

The difference between the two formulae is non-zero, but small:
https://play.golang.org/p/qG7oe-eqHI

Updates #16251

Change-Id: I288ecb957fd6eceb9626410bd1a8084d2e4f8198
Reviewed-on: https://go-review.googlesource.com/31538Reviewed-by: Rob Pike <r@golang.org>

For very large input files, use of GOSSAFUNC to obtain a dump
after compilation steps can lead to both unwieldy large output
files and unwieldy larger processes (because the output is
buffered in a string).  This flag

  -d=ssa/<phase>/dump:<function name>

provides finer control of what is dumped, into a smaller
file, and with less memory overhead in the running compiler.
The special phase name "build" is added to allow printing
of the just-built ssa before any transformations are applied.

This was helpful in making sense of the gogo/protobuf
problems.

The output format was tweaked to remove gratuitous spaces,
and a crude -d=ssa/help help text was added.

Change-Id: If7516e22203420eb6ed3614f7cee44cb9260f43e
Reviewed-on: https://go-review.googlesource.com/23044
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Fixes #16076

Change-Id: I91fa87b642592ee4604537dd8c3197cd61ec8b31
Reviewed-on: https://go-review.googlesource.com/31516
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Closes #17528.

Change-Id: I2ba55ad4e41077808f882ed67a0549f0a00e25d0
Reviewed-on: https://go-review.googlesource.com/31596
Run-TryBot: Michael Munday <munday@ca.ibm.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Account for changes in https://golang.org/cl/31233.

Change-Id: I3311c6850a3c714d18209fdff500dd817e9dfcb2
Reviewed-on: https://go-review.googlesource.com/31594Reviewed-by: Matthew Dempsky <mdempsky@google.com>

This change updates the vendored copy of x/crypto/poly1305, specifically
to include the following changes:
  3ded668 poly1305: enable assembly for ARM in Go 1.6.
  dec8741 poly1305: fix stack handling in sum_arm.s

Fixes #17499.

Change-Id: I8f152da9599bd15bb976f630b0ef602be05143d3
Reviewed-on: https://go-review.googlesource.com/31592
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Uncommented 4 comparison rules of this form:
(NE (CMPWconst [0] (FLessThan cc)) yes no) -> (FLT cc yes no)

Fixes #17507.

Change-Id: I74f34f13526aeee619711c8281a66652d90a962a
Reviewed-on: https://go-review.googlesource.com/31612
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

This issue has been fixed in CL 31390.

Fixes #9554.

Change-Id: Ib8ff4cb1ffcb7cdbf117510b98b4a7e13e4efd2b
Reviewed-on: https://go-review.googlesource.com/31520
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: David du Colombier <0intro@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

CVTSL2SS, CVTSQ2SS, CVTSL2SD, CVTSQ2SD preserve upper part of xmm register,
introducing false dependency on a previous value.
Break it by xoring destination with itself.
Increases size of go executable by 320 bytes, but shows nice improvement on go1.
Also fixes performance degradation introduced by 1.7.

name                     old time/op    new time/op    delta
BinaryTree17-4              2.20s ± 1%     2.19s ± 0%  -0.36%        (p=0.000 n=18+16)
Fannkuch11-4                2.44s ± 1%     2.45s ± 2%  +0.47%        (p=0.030 n=20+20)
FmtFprintfEmpty-4          40.9ns ± 7%    40.5ns ± 1%    ~           (p=0.531 n=20+16)
FmtFprintfString-4          111ns ± 2%     111ns ± 1%    ~           (p=0.510 n=18+19)
FmtFprintfInt-4            98.3ns ± 3%    99.3ns ± 1%  +1.01%        (p=0.003 n=20+18)
FmtFprintfIntInt-4          148ns ± 3%     147ns ± 1%    ~           (p=0.919 n=20+17)
FmtFprintfPrefixedInt-4     149ns ± 1%     152ns ± 0%  +1.73%        (p=0.000 n=19+17)
FmtFprintfFloat-4           231ns ± 0%     231ns ± 1%    ~           (p=0.678 n=18+19)
FmtManyArgs-4               667ns ± 1%     672ns ± 1%  +0.73%        (p=0.005 n=20+20)
GobDecode-4                5.60ms ± 0%    5.61ms ± 0%  +0.24%        (p=0.000 n=20+20)
GobEncode-4                4.74ms ± 0%    4.73ms ± 1%  -0.20%        (p=0.002 n=20+20)
Gzip-4                      199ms ± 0%     199ms ± 1%  +0.35%        (p=0.000 n=19+20)
Gunzip-4                   31.8ms ± 1%    31.5ms ± 1%  -0.89%        (p=0.000 n=20+20)
HTTPClientServer-4         38.1µs ± 1%    38.0µs ± 1%    ~           (p=0.117 n=19+18)
JSONEncode-4               14.2ms ± 1%    13.4ms ± 0%  -5.73%        (p=0.000 n=20+20)
JSONDecode-4               42.7ms ± 0%    42.7ms ± 1%  +0.18%        (p=0.019 n=18+19)
Mandelbrot200-4            3.26ms ± 0%    2.99ms ± 0%  -8.38%        (p=0.000 n=19+19)
GoParse-4                  2.76ms ± 1%    2.76ms ± 1%    ~           (p=0.583 n=20+20)
RegexpMatchEasy0_32-4      69.5ns ± 0%    69.6ns ± 0%  +0.10%        (p=0.017 n=16+17)
RegexpMatchEasy0_1K-4       703ns ± 0%     708ns ± 3%  +0.65%        (p=0.000 n=17+18)
RegexpMatchEasy1_32-4      68.2ns ± 1%    68.2ns ± 2%    ~           (p=0.094 n=18+20)
RegexpMatchEasy1_1K-4       288ns ± 1%     288ns ± 0%    ~           (p=0.403 n=17+18)
RegexpMatchMedium_32-4      104ns ± 2%     103ns ± 1%    ~           (p=0.110 n=20+16)
RegexpMatchMedium_1K-4     31.7µs ± 3%    31.7µs ± 3%    ~           (p=0.091 n=19+20)
RegexpMatchHard_32-4       1.59µs ± 2%    1.58µs ± 2%    ~           (p=0.083 n=20+20)
RegexpMatchHard_1K-4       48.1µs ± 3%    47.9µs ± 2%    ~           (p=0.461 n=20+19)
Revcomp-4                   344ms ± 0%     345ms ± 0%  +0.08%        (p=0.009 n=18+17)
Template-4                 44.8ms ± 1%    44.7ms ± 1%    ~           (p=0.277 n=20+20)
TimeParse-4                 258ns ± 0%     258ns ± 0%    ~     (all samples are equal)
TimeFormat-4                275ns ± 0%     273ns ± 0%  -0.64%        (p=0.000 n=20+18)

name                     old speed      new speed      delta
GobDecode-4               137MB/s ± 0%   137MB/s ± 0%  -0.24%        (p=0.000 n=20+20)
GobEncode-4               162MB/s ± 0%   162MB/s ± 0%  +0.20%        (p=0.002 n=20+20)
Gzip-4                   97.6MB/s ± 0%  97.3MB/s ± 1%  -0.35%        (p=0.000 n=19+20)
Gunzip-4                  610MB/s ± 1%   615MB/s ± 1%  +0.89%        (p=0.000 n=20+20)
JSONEncode-4              136MB/s ± 1%   145MB/s ± 0%  +6.08%        (p=0.000 n=20+20)
JSONDecode-4             45.5MB/s ± 0%  45.4MB/s ± 1%  -0.17%        (p=0.017 n=18+19)
GoParse-4                21.0MB/s ± 1%  21.0MB/s ± 1%    ~           (p=0.578 n=20+20)
RegexpMatchEasy0_32-4     460MB/s ± 0%   460MB/s ± 0%  -0.09%        (p=0.031 n=16+17)
RegexpMatchEasy0_1K-4    1.46GB/s ± 0%  1.45GB/s ± 3%  -0.64%        (p=0.000 n=17+18)
RegexpMatchEasy1_32-4     469MB/s ± 0%   469MB/s ± 2%  +0.06%        (p=0.043 n=18+20)
RegexpMatchEasy1_1K-4    3.55GB/s ± 1%  3.55GB/s ± 0%    ~           (p=0.057 n=17+18)
RegexpMatchMedium_32-4   9.61MB/s ± 2%  9.64MB/s ± 2%    ~           (p=0.856 n=20+20)
RegexpMatchMedium_1K-4   32.3MB/s ± 3%  32.3MB/s ± 3%    ~           (p=0.085 n=19+20)
RegexpMatchHard_32-4     20.1MB/s ± 2%  20.2MB/s ± 2%    ~           (p=0.086 n=20+20)
RegexpMatchHard_1K-4     21.3MB/s ± 3%  21.4MB/s ± 2%    ~           (p=0.578 n=20+20)
Revcomp-4                 738MB/s ± 0%   737MB/s ± 0%  -0.08%        (p=0.009 n=18+17)
Template-4               43.3MB/s ± 1%  43.4MB/s ± 1%    ~           (p=0.274 n=20+20)

Fixes #16982

Change-Id: If574d66f39f4183a9b1d5ffff0339909cc73f59d
Reviewed-on: https://go-review.googlesource.com/31490
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

Add VBROADCASTSD, BROADCASTSS, MOVDDUP, MOVSHDUP, MOVSLDUP,
VMOVDDUP, VMOVSHDUP, VMOVSLDUP.

Fixes #16007

Change-Id: I9614e58eed6c1b6f299d9b4f0b1a7750aa7c1725
Reviewed-on: https://go-review.googlesource.com/31491
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

Missing the DB mutex unlock on an early return after checking
if the context has expired.

Fixes #17518

Change-Id: I247cafcef62623d813f534a941f3d5a3744f0738
Reviewed-on: https://go-review.googlesource.com/31494Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: Ie6258602554c5bb6685c9de42ccda84d297af1e2
Reviewed-on: https://go-review.googlesource.com/31515
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Issues fixed:
* Could not handle quantity of seconds greater than 1<<31 on
32bit machines since strconv.ParseInt did not treat integers as 64b.
* Did not handle negative timestamps properly if nanoseconds were used.
Note that "-123.456" should result in a call to time.Unix(-123, -456000000).
* Incorrectly allowed a '-' right after the '.' (e.g., -123.-456)
* Did not detect invalid input after the truncation point (e.g., 123.123456789badbadbad).

Note that negative timestamps are allowed by PAX, but are not guaranteed
to be portable. See the relevant specification:
<<<
If pax encounters a file with a negative timestamp in copy or write mode,
it can reject the file, substitute a non-negative timestamp, or generate
a non-portable timestamp with a leading '-'.
>>>

Since the previous behavior already partially supported negative timestamps,
we are bound by Go's compatibility rules to keep support for them.
However, we should at least make sure we handle them properly.

Change-Id: I5686997708bfb59110ea7981175427290be737d1
Reviewed-on: https://go-review.googlesource.com/31441
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #17491

Change-Id: Ic070cbed60fa893fed568e8fac448b86cd3e0cbc
Reviewed-on: https://go-review.googlesource.com/31411Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

This is a more robust method for obtaining the availability of vx.
Since this variable may be checked frequently I've also now
padded it so that it will be in its own cache line.

I've kept the other check (in hash/crc32) the same for now until
I can figure out the best way to update it.

Updates #15403.

Change-Id: I74eed651afc6f6a9c5fa3b88fa6a2b0c9ecf5875
Reviewed-on: https://go-review.googlesource.com/31149Reviewed-by: Austin Clements <austin@google.com>

oneNewExtraM creates a spare M and G for use with cgo callbacks. The G
doesn't run right away, but goes directly into syscall status. For the
garbage collector, it's marked as "scan valid" and not on the rescan
list, but I forgot to also mark it as "scan done". As a result,
gcMarkRootCheck thinks that the goroutine hasn't been scanned and
panics.

This only affects GODEBUG=gccheckmark=1 mode, since we otherwise skip
the gcMarkRootCheck.

Fixes #17473.

Change-Id: I94f5671c42eb44bd5ea7dc68fbf85f0c19e2e52c
Reviewed-on: https://go-review.googlesource.com/31139
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

Change-Id: I79ebccdaefc434c47b77bd545cc3c50723c18b61
Reviewed-on: https://go-review.googlesource.com/31135
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

Updating the heap profile stats is one of the most expensive parts of
mark termination other than stack rescanning, but there's really no
need to do this with the world stopped. Move it to right after we've
started the world back up. This creates a *very* small window where
allocations from the next cycle can slip into the profile, but the
exact point where mark termination happens is so non-deterministic
already that a slight reordering here is unimportant.

Change-Id: I2f76f22c70329923ad6a594a2c26869f0736d34e
Reviewed-on: https://go-review.googlesource.com/31363
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

The only reason these flushes are still necessary at all is that
gcmarknewobject doesn't flush its gcWork stats like it's supposed to.
By changing gcmarknewobject to follow the standard protocol, the
flushes become completely unnecessary because mark 2 ensures caches
are flushed (and stay flushed) before we ever enter mark termination.

In the garbage benchmark, this takes roughly 50 µs, which is
surprisingly long for doing nothing. We still double-check after
draining that they are in fact empty.

Change-Id: Ia1c7cf98a53f72baa513792eb33eca6a0b4a7128
Reviewed-on: https://go-review.googlesource.com/31134
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

The pointer checking code needs to know the exact type of the parameter
expected by the C function, so that it can use a type assertion to
convert the empty interface returned by cgoCheckPointer to the correct
type. Previously this was done by using a type conversion, but that
meant that the code accepted arguments that were convertible to the
parameter type, rather than arguments that were assignable as in a
normal function call. In other words, some code that should not have
passed type checking was accepted.

This CL changes cgo to always use a function literal for pointer
checking. Now the argument is passed to the function literal, which has
the correct argument type, so type checking is performed just as for a
function call as it should be.

Since we now always use a function literal, simplify the checking code
to run as a statement by itself. It now no longer needs to return a
value, and we no longer need a type assertion.

This does have the cost of introducing another function call into any
call to a C function that requires pointer checking, but the cost of the
additional call should be minimal compared to the cost of pointer
checking.

Fixes #16591.

Change-Id: I220165564cf69db9fd5f746532d7f977a5b2c989
Reviewed-on: https://go-review.googlesource.com/31233
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Just happened to notice that these names (funcAlign and friends) are
never referenced outside their package, so no need to export them.

Change-Id: I4bbdaa4b0ef330c3c3ef50a2ca39593977a83545
Reviewed-on: https://go-review.googlesource.com/31496
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

mkbuiltin.go now generates builtin.go using go/ast instead of running
the compiler, so we don't need the -A flag anymore.

Passes toolstash -cmp.

Change-Id: Ifa70f4f3c9feae10c723cbec81a0a47c39610090
Reviewed-on: https://go-review.googlesource.com/31497Reviewed-by: Robert Griesemer <gri@golang.org>

Generating binary export data requires a working Go compiler. Even
trickier to change the export data format itself requires a careful
bootstrapping procedure.

Instead, simply generate normal Go code that lets us directly
construct the builtin runtime declarations.

Passes toolstash -cmp.

Fixes #17508.

Change-Id: I4f6078a3c7507ba40072580695d57c87a5604baf
Reviewed-on: https://go-review.googlesource.com/31493
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

Fixes #16965

Change-Id: I3638fe280a5b1063ff589e6e1ff8a97c74b77c66
Reviewed-on: https://go-review.googlesource.com/30359Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Relevant PAX specification:
<<<
If the <value> field is zero length, it shall delete any header
block field, previously entered extended header value, or
global extended header value of the same name.
>>>

We don't delete global extender headers since the Reader doesn't
even support global headers (which the specification admits was
a controversial feature).

Change-Id: I2125a5c907b23a3dc439507ca90fa5dc47d474a9
Reviewed-on: https://go-review.googlesource.com/31440
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Took this opportunity to also embed tables in the functions
that they are actually used in and other stylistic cleanups.

There was no logical changes to the tests.

Change-Id: Ifa724060532175f6f4407d6cedc841891efd8f7b
Reviewed-on: https://go-review.googlesource.com/31436
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Add support for passing reflect.Values to and returning reflect.Values from
any registered functions in the FuncMap, much as if they were
interface{} values. Keeping the reflect.Value instead of round-tripping
to interface{} preserves addressability of the value, which is important
for method lookup.

Change index and a few other built-in functions to use reflect.Values,
making a loop using explicit indexing now match the semantics that
range has always had.

Fixes #14916.

Change-Id: Iae1a2fd9bb426886a7fcd9204f30a2d6ad4646ad
Reviewed-on: https://go-review.googlesource.com/31462Reviewed-by: Rob Pike <r@golang.org>

The GNU format does not have a prefix field, so we should make
no attempt to read it. It does however have atime and ctime fields.
Since Go previously placed incorrect values here, we liberally
read the atime and ctime fields and ignore errors so that old tar
files written by Go can at least be partially read.

This fixes half of #12594. The Writer is much harder to fix.

Updates #12594

Change-Id: Ia32845e2f262ee53366cf41dfa935f4d770c7a30
Reviewed-on: https://go-review.googlesource.com/31444
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The panic leaves the lock in an unusable state.
Trying to panic with a usable state makes the lock significantly
less efficient and scalable (see early CL patch sets and discussion).

Instead, use runtime.throw, which will crash the program directly.

In general throw is reserved for when the runtime detects truly
serious, unrecoverable problems. This problem is certainly serious,
and, without a significant performance hit, is unrecoverable.

Fixes #13879.

Change-Id: I41920d9e2317270c6f909957d195bd8b68177f8d
Reviewed-on: https://go-review.googlesource.com/31359Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Before: ... appears in an ambiguous URL context.
After:  ... appears in an ambiguous context within a URL.

It's a minor point, but it's confused multiple people.
Try to make clearer that the ambiguity is "where exactly inside the URL?"

Fixes #17319.

Change-Id: Id834868d1275578036c1b00c2bdfcd733d9d2b7b
Reviewed-on: https://go-review.googlesource.com/31465
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Change-Id: I4270bf81511a5bf80ed146f5e66e4f8aeede2aa2
Reviewed-on: https://go-review.googlesource.com/31463Reviewed-by: Ian Lance Taylor <iant@golang.org>

For #17428.

Change-Id: Ia902b50cf0c40e3c2167fb573a39d328331c38c7
Reviewed-on: https://go-review.googlesource.com/31449Reviewed-by: Ian Lance Taylor <iant@golang.org>

Updates #14892

Change-Id: I640c6e1635ccdf611f219521a7d297a9885c4cb3
Reviewed-on: https://go-review.googlesource.com/31446
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

This CL makes NewRequest set Body nil for known-zero bodies, and makes
the http1 Transport not peek-Read a byte to determine whether there's
a body.

Background:

Many fields of the Request struct have different meanings for whether
they're outgoing (via the Transport) or incoming (via the Server).

For outgoing requests, ContentLength and Body are documented as:

	// Body is the request's body.
	//
	// For client requests a nil body means the request has no
	// body, such as a GET request. The HTTP Client's Transport
	// is responsible for calling the Close method.
	Body io.ReadCloser

	// ContentLength records the length of the associated content.
	// The value -1 indicates that the length is unknown.
	// Values >= 0 indicate that the given number of bytes may
	// be read from Body.
	// For client requests, a value of 0 with a non-nil Body is
	// also treated as unknown.
	ContentLength int64

Because of the ambiguity of what ContentLength==0 means, the http1 and
http2 Transports previously Read the first byte of a non-nil Body when
the ContentLength was 0 to determine whether there was an actual body
(with a non-zero length) and ContentLength just wasn't populated, or
it was actually empty.

That byte-sniff has been problematic and gross (see #17480, #17071)
and was removed for http2 in a previous commit.

That means, however, that users doing:

    req, _ := http.NewRequest("POST", url, strings.NewReader(""))

... would not send a Content-Length header in their http2 request,
because the size of the reader (even though it was known, being one of
the three common recognized types from NewRequest) was zero, and so
the HTTP Transport thought it was simply unset.

To signal explicitly-zero vs unset-zero, this CL changes NewRequest to
signal explicitly-zero by setting the Body to nil, instead of the
strings.NewReader("") or other zero-byte reader.

This CL also removes the byte sniff from the http1 Transport, like
https://golang.org/cl/31326 did for http2.

Updates #17480
Updates #17071

Change-Id: I329f02f124659bf7d8bc01e2c9951ebdd236b52a
Reviewed-on: https://go-review.googlesource.com/31445
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Fixes #16531.

Change-Id: I41ec8123f2d3fbe063fd3b09a9366e69722793e5
Reviewed-on: https://go-review.googlesource.com/31355Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #17092.

Change-Id: If203d802a919e00594ddc1282782fc59a083fd63
Reviewed-on: https://go-review.googlesource.com/31458Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This was supposed to be in CL 31354
but was dropped due to a Git usage error.

For #16573.

Change-Id: I3d99087c8efc8cbc016c55e8365d0005f79d1b2f
Reviewed-on: https://go-review.googlesource.com/31461Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Make two important points clearer:

 - Giving a template definition containing
   nothing but spaces has no effect.
 - Giving a template definition containing
   non-spaces can only be done once per template.

Fixes #16912.
Fixes #16913.
Fixes #17360.

Change-Id: Ie3971b83ab148b7c8bb800fe4a21579566378e3e
Reviewed-on: https://go-review.googlesource.com/31459
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

Noted in CL 31358 after submit.

Change-Id: I76ddad9b9e27dd6a03c1c4f49153213747fe0a61
Reviewed-on: https://go-review.googlesource.com/31365
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>