cmd/gc: don't hash nor compare struct padding or blank fields.

Fixes issue 4585.

R=rsc, golang-dev
CC=golang-dev
https://codereview.appspot.com/7142052
doc/contribute.html: mention hg mail during hg change discussion

People keep not reading all the way to the bottom of the doc
and not running hg mail.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7137057
compress/flate: Performance improvement for inflate

Decode as much as possible of a Huffman symbol in a single table
lookup (much like the zlib implementation), filling more bits
(conservatively, so we don't consume past the end of the stream)
when the code prefix indicates more bits are needed. This
results in about a 50% performance gain in speed benchmarks.
The following set is benchcmp done on a retina MacBook Pro:

benchmark                            old MB/s     new MB/s  speedup
BenchmarkDecodeDigitsSpeed1e4           28.41        42.79    1.51x
BenchmarkDecodeDigitsSpeed1e5           30.18        47.62    1.58x
BenchmarkDecodeDigitsSpeed1e6           30.81        48.14    1.56x
BenchmarkDecodeDigitsDefault1e4         30.28        44.61    1.47x
BenchmarkDecodeDigitsDefault1e5         32.18        51.94    1.61x
BenchmarkDecodeDigitsDefault1e6         35.57        53.28    1.50x
BenchmarkDecodeDigitsCompress1e4        30.39        44.83    1.48x
BenchmarkDecodeDigitsCompress1e5        33.05        51.64    1.56x
BenchmarkDecodeDigitsCompress1e6        35.69        53.04    1.49x
BenchmarkDecodeTwainSpeed1e4            25.90        43.04    1.66x
BenchmarkDecodeTwainSpeed1e5            29.97        48.19    1.61x
BenchmarkDecodeTwainSpeed1e6            31.36        49.43    1.58x
BenchmarkDecodeTwainDefault1e4          28.79        45.02    1.56x
BenchmarkDecodeTwainDefault1e5          37.12        55.65    1.50x
BenchmarkDecodeTwainDefault1e6          39.28        58.16    1.48x
BenchmarkDecodeTwainCompress1e4         28.64        44.90    1.57x
BenchmarkDecodeTwainCompress1e5         37.40        55.98    1.50x
BenchmarkDecodeTwainCompress1e6         39.35        58.06    1.48x

R=rsc, dave, minux.ma, bradfitz, nigeltao
CC=golang-dev
https://codereview.appspot.com/6872063

Committer: Russ Cox <rsc@golang.org>
build: change GO386=sse to GO386=sse2

sse2 is a more precise description of the requirement,
and it matches what people will see in, for example
        grep sse2 /proc/cpuinfo # linux
        sysctl hw.optional.sse2 # os x

R=golang-dev, dsymonds, iant
CC=golang-dev
https://codereview.appspot.com/7057050
cmd/dist: update for new flag parsing on Plan 9

R=golang-dev, seed, rsc
CC=golang-dev
https://codereview.appspot.com/7069053

Committer: Russ Cox <rsc@golang.org>
time: add note about Parse()'s choice of default year

R=rsc
CC=golang-dev
https://codereview.appspot.com/7101046
cmd/go: diagnose un-bootstrapped runtime

Fixes issue 4665.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7132057
cmd/gc: allow registerization of temporaries created by inlining.

Names beginning with a dot are ignored by optimizers.

R=rsc, lvd, golang-dev, dave
CC=golang-dev
https://codereview.appspot.com/7098049
cmd/6c: Improve peep hole optimization of rotate and shift instructions.

Update issue 4629.

$ cat shift2.c
unsigned int
shift(unsigned int x, unsigned int y)
{
        x = (x << 3);
        y = (y << 5);
        x = (x << 7);
        y = (y << 9);
        return x ^ y;
}

## BEFORE
$ go tool 6c -S shift2.c
(shift2.c:2)	TEXT	shift+0(SB),$0-8
(shift2.c:4)	MOVL	x+0(FP),!!AX
(shift2.c:4)	SALL	$3,!!AX
(shift2.c:4)	MOVL	AX,!!DX
(shift2.c:5)	MOVL	y+4(FP),!!AX
(shift2.c:5)	SALL	$5,!!AX
(shift2.c:5)	MOVL	AX,!!CX
(shift2.c:6)	MOVL	DX,!!AX
(shift2.c:6)	SALL	$7,!!AX
(shift2.c:6)	MOVL	AX,!!DX
(shift2.c:7)	MOVL	CX,!!AX
(shift2.c:7)	SALL	$9,!!AX
(shift2.c:7)	MOVL	AX,!!CX
(shift2.c:8)	MOVL	DX,!!AX
(shift2.c:8)	XORL	CX,!!AX
(shift2.c:8)	RET	,!!
(shift2.c:8)	RET	,!!
(shift2.c:8)	END	,!!

## AFTER
$ go tool 6c -S shift2.c
(shift2.c:2)	TEXT	shift+0(SB),$0-8
(shift2.c:4)	MOVL	x+0(FP),!!AX
(shift2.c:4)	SALL	$3,!!AX
(shift2.c:5)	MOVL	y+4(FP),!!CX
(shift2.c:5)	SALL	$5,!!CX
(shift2.c:6)	SALL	$7,!!AX
(shift2.c:7)	SALL	$9,!!CX
(shift2.c:8)	XORL	CX,!!AX
(shift2.c:8)	RET	,!!
(shift2.c:8)	RET	,!!
(shift2.c:8)	END	,!!

R=rsc, minux.ma, dave, nigeltao
CC=golang-dev
https://codereview.appspot.com/7066055

Committer: Russ Cox <rsc@golang.org>
cmd/gc, cmd/6g: fix error on large stacks.

Fixes issue 4666.

R=golang-dev, daniel.morsing, rsc
CC=golang-dev
https://codereview.appspot.com/7141047
runtime: faster mcentral alloc.

Reduce individual object handling by anticipating how much of them are servable.

Not a chunked transfer cache, but decent enough to make sure the bottleneck is not here.

Mac OSX, median of 10 runs:

benchmark                 old ns/op    new ns/op    delta
BenchmarkBinaryTree17    5358937333   4892813012   -8.70%
BenchmarkFannkuch11      3257752475   3315436116   +1.77%
BenchmarkGobDecode         23277349     23001114   -1.19%
BenchmarkGobEncode         14367327     14262925   -0.73%
BenchmarkGzip             441045541    440451719   -0.13%
BenchmarkGunzip           139117663    139622494   +0.36%
BenchmarkJSONEncode        45715854     45687802   -0.06%
BenchmarkJSONDecode       103949570    106530032   +2.48%
BenchmarkMandelbrot200      4542462      4548290   +0.13%
BenchmarkParse              7790558      7557540   -2.99%
BenchmarkRevcomp          831436684    832510381   +0.13%
BenchmarkTemplate         133789824    133007337   -0.58%

benchmark                  old MB/s     new MB/s  speedup
BenchmarkGobDecode            32.82        33.33    1.02x
BenchmarkGobEncode            53.42        53.86    1.01x
BenchmarkGzip                 43.70        44.01    1.01x
BenchmarkGunzip              139.09       139.14    1.00x
BenchmarkJSONEncode           42.69        42.56    1.00x
BenchmarkJSONDecode           18.78        17.91    0.95x
BenchmarkParse                 7.37         7.67    1.04x
BenchmarkRevcomp             306.83       305.70    1.00x
BenchmarkTemplate             14.57        14.56    1.00x

R=rsc, dvyukov
CC=golang-dev
https://codereview.appspot.com/7005055

Committer: Russ Cox <rsc@golang.org>
cmd/5a, cmd/5c, cmd/6a, cmd/6c, cmd/8a, cmd/8c, cmd/ld: update reference

Reference the 80386 compiler documentation now that the
documentation for the 68020 is offline.

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/7127053
cmd/gc: fix handling of struct padding in hash/eq.

The test case of issue 4585 was not passing due to
miscalculation of memequal args, and the previous fix
does not handle padding at the end of a struct.

Handling of padding at end of structs also fixes the case
of [n]T where T is such a padded struct.

Fixes issue 4585.
(again)

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/7133059
syscall, os: fix a fork-exec/wait race in Plan 9.

On Plan 9, only the parent of a given process can enter its wait
queue. When a Go program tries to fork-exec a child process
and subsequently waits for it to finish, the goroutines doing
these two tasks do not necessarily tie themselves to the same
(or any single) OS thread. In the case that the fork and the wait
system calls happen on different OS threads (say, due to a
goroutine being rescheduled somewhere along the way), the
wait() will either return an error or end up waiting for a
completely different child than was intended.

This change forces the fork and wait syscalls to happen in the
same goroutine and ties that goroutine to its OS thread until
the child exits. The PID of the child is recorded upon fork and
exit, and de-queued once the child's wait message has been read.
The Wait API, then, is translated into a synthetic implementation
that simply waits for the requested PID to show up in the queue
and then reads the associated stats.

R=rsc, rminnich, npe, mirtchovski, ality
CC=golang-dev
https://codereview.appspot.com/6545051

Committer: Russ Cox <rsc@golang.org>
cmd/gc: more robust checking of OIND nodes.

Fixes issue 4610.

R=golang-dev, remyoudompheng, rsc
CC=golang-dev, nigeltao
https://codereview.appspot.com/7058057
test: re-enable issue4348.go.

The test array is too large to fit a stack frame
but can be a global.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7127059
runtime: try to determine the actual type during garbage collection

If the scanned block has no typeinfo the garbage collector will attempt
to get the actual type of the block.

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://codereview.appspot.com/7093045

Committer: Russ Cox <rsc@golang.org>
spec: clarify lhs syntax for range and select

Fixes issue 4653.

R=rsc, r, iant, ken, thakis
CC=golang-dev
https://codereview.appspot.com/7135058
encoding/xml: fix decoding of attributes in to pointer fields.
Fixes issue 3719.

R=anacrolix, rsc
CC=golang-dev
https://codereview.appspot.com/7131052

Committer: Russ Cox <rsc@golang.org>
cmd/6c: Optimize rotate expressions to use rotate instructions.

For simplicity, only recognizes expressions of the exact form
"(x << a) | (x >> b)" where x is a variable and a and b are
integer constant expressions that add to x's bit width.

Fixes issue 4629.

$ cat rotate.c
unsigned int
rotate(unsigned int x)
{
        x = (x << 3) | (x >> (sizeof(x) * 8 - 3));
        return x;
}

## BEFORE
$ go tool 6c -S rotate.c
(rotate.c:2)	TEXT	rotate+0(SB),$0-8
(rotate.c:2)	MOVL	x+0(FP),!!DX
(rotate.c:4)	MOVL	DX,!!AX
(rotate.c:4)	SALL	$3,!!AX
(rotate.c:4)	MOVL	DX,!!CX
(rotate.c:4)	SHRL	$29,!!CX
(rotate.c:4)	ORL	CX,!!AX
(rotate.c:5)	RET	,!!
(rotate.c:5)	RET	,!!
(rotate.c:5)	END	,!!

## AFTER
$ go tool 6c -S rotate.c
(rotate.c:2)	TEXT	rotate+0(SB),$0-8
(rotate.c:4)	MOVL	x+0(FP),!!AX
(rotate.c:4)	ROLL	$3,!!AX
(rotate.c:5)	RET	,!!
(rotate.c:5)	RET	,!!
(rotate.c:5)	END	,!!

R=rsc, minux.ma
CC=golang-dev
https://codereview.appspot.com/7069056

Committer: Russ Cox <rsc@golang.org>