Fixes windows build.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/127510043

Fixes #8431.

LGTM=r
R=golang-codereviews, r, minux
CC=golang-codereviews
https://golang.org/cl/130830043

Fixes #8140.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/131900044

TBR=iant
CC=golang-codereviews
https://golang.org/cl/131900043

It was incorrectly encoded as ASETLS.

LGTM=ruiu, rsc
R=rsc, ruiu
CC=golang-codereviews
https://golang.org/cl/126400043

We need to change the interface value representation for
concurrent garbage collection, so that there is no ambiguity
about whether the data word holds a pointer or scalar.

This CL does NOT make any representation changes.

Instead, it removes representation assumptions from
various pieces of code throughout the tree.
The isdirectiface function in cmd/gc/subr.c is now
the only place that decides that policy.
The policy propagates out from there in the reflect
metadata, as a new flag in the internal kind value.

A follow-up CL will change the representation by
changing the isdirectiface function. If that CL causes
problems, it will be easy to roll back.

Update #8405.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, r
https://golang.org/cl/129090043

CC=golang-codereviews
https://golang.org/cl/124580043

LGTM=rminnich, iant
R=golang-codereviews, rminnich, iant
CC=golang-codereviews, r
https://golang.org/cl/125140043

The change to pc-relative addressing will make this illegal.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, r
https://golang.org/cl/129890043

Update #8527

Fixes, cmd/6g/reg.c:847:24: runtime error: left shift of 1 by 31 places cannot be represented in type 'int'

LGTM=minux, rsc
R=minux, rsc
CC=dvyukov, golang-codereviews
https://golang.org/cl/129290043

type T byte
func (T) String() string { return "X" }

fmt.Sprintf("%s", []T{97, 98, 99, 100}) == "abcd"
fmt.Sprintf("%x", []T{97, 98, 99, 100}) == "61626364"
fmt.Sprintf("%v", []T{97, 98, 99, 100}) == "[X X X X]"

This change makes the last case print correctly.
Before, it would have been "[97 98 99 100]".

Fixes #8360.

LGTM=r
R=r, dan.kortschak
CC=golang-codereviews
https://golang.org/cl/129330043

Improve performance of move-to-front by using cache-friendly
copies instead of doubly-linked list. Simplify so that the
underlying slice is the object. Remove the n=0 special case,
      which was actually slower with the copy approach.

benchmark                 old ns/op     new ns/op     delta
BenchmarkDecodeDigits     26429714      23859699      -9.72%
BenchmarkDecodeTwain      76684510      67591946      -11.86%

benchmark                 old MB/s     new MB/s     speedup
BenchmarkDecodeDigits     1.63         1.81         1.11x
BenchmarkDecodeTwain      1.63         1.85         1.13x

Updates #6754.

LGTM=adg, agl, josharian
R=adg, agl, josharian
CC=golang-codereviews
https://golang.org/cl/131840043

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/130210043

LGTM=r, bradfitz
R=r, bradfitz
CC=golang-codereviews
https://golang.org/cl/127470043

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews, khr, rlh, rsc
https://golang.org/cl/125420043

Added in linux commit eb6452537b28

LGTM=agl
R=agl
CC=golang-codereviews
https://golang.org/cl/130170043

Currently we do the following dance after sweeping a span:
1. lock mcentral
2. remove the span from a list
3. unlock mcentral
4. unmark span
5. lock mheap
6. insert the span into heap
7. unlock mheap
8. lock mcentral
9. observe empty list
10. unlock mcentral
11. lock mheap
12. grab the span
13. unlock mheap
14. mark span
15. lock mcentral
16. insert the span into empty list
17. unlock mcentral

This change short-circuits this sequence to nothing,
that is, we just cache and use the span after sweeping.

This gives us functionality similar (even better) to tcmalloc's transfer cache.

benchmark            old ns/op     new ns/op     delta
BenchmarkMalloc8     22.2          19.5          -12.16%
BenchmarkMalloc16    31.0          26.6          -14.19%

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/119550043

Fixes #8530.

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rsc
https://golang.org/cl/124440043

Mallocgc must be atomic wrt GC, but for performance reasons
don't acquirem/releasem on fast path. The code does not have
split stack checks, so it can't be preempted by GC.
Functions like roundup/add are inlined. And onM/racemalloc are nosplit.
Also add debug code that checks these assumptions.

benchmark                     old ns/op     new ns/op     delta
BenchmarkMalloc8              20.5          17.2          -16.10%
BenchmarkMalloc16             29.5          27.0          -8.47%
BenchmarkMallocTypeInfo8      31.5          27.6          -12.38%
BenchmarkMallocTypeInfo16     34.7          30.9          -10.95%

LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/123100043

Perf builders show 3-5% GC pause increase with GOMAXPROCS=1 when marking with atomic ops:
http://goperfd.appspot.com/perfdetail?commit=a8a6e765d6a87f7ccb71fd85a60eb5a821151f85&commit0=3b864e02b987171e05e2e9d0840b85b5b6476386&kind=builder&builder=linux-amd64&benchmark=http

LGTM=rlh
R=golang-codereviews, rlh
CC=dave, golang-codereviews, khr, rsc
https://golang.org/cl/128340043

Fixes #8480.

This CL reapplies CL 114420043. This attempt doesn't blow up when encountering hidden symbols.

LGTM=minux
R=minux
CC=golang-codereviews
https://golang.org/cl/128310043

LGTM=rsc
R=gobot, dave
CC=golang-codereviews, iant, rsc
https://golang.org/cl/114420043

In retrospect this should've been a variable instead of a type,
but oh well.

LGTM=agl
R=agl
CC=golang-codereviews
https://golang.org/cl/129250044

When building golang, the environment variable GOROOT_FINAL can be set
to indicate a different installation location from the build
location. This works fine, except that the goc2c build step embeds
line numbers in the resulting c source files that refer to the build
location, no the install location.

This would not be a big deal, except that in turn the linker uses the
location of runtime/string.goc to embed the gdb script in the
resulting binary and as a net result, the debugger now complains that
the script is outside its load path (it has the install location
configured).

See https://code.google.com/p/go/issues/detail?id=8524 for the full
description.

Fixes #8524.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/128230046

Generated by a+c.

R=gobot
CC=golang-codereviews
https://golang.org/cl/130140043

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/127410043

Fixes #8512.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/130090043

bv.data is an array of uint32s but the code was using
offsets computed for an array of bytes.
Add a test for stack GC info.
Fixes #8531.

LGTM=rsc
R=golang-codereviews
CC=golang-codereviews, khr, rsc
https://golang.org/cl/124450043

Fixes #7760.

LGTM=iant
R=iant, remyoudompheng
CC=golang-codereviews
https://golang.org/cl/130720043

LGTM=dave, minux
R=golang-codereviews, dave, minux
CC=golang-codereviews, rsc
https://golang.org/cl/122570043

Fixes #8492

LGTM=alex.brainman
R=golang-codereviews, alex.brainman
CC=golang-codereviews
https://golang.org/cl/122200043

LGTM=minux, adg
R=golang-codereviews, minux, adg
CC=golang-codereviews
https://golang.org/cl/129180043

On the go.benchmarks/garbage benchmark with GOMAXPROCS=16:
                   old ns/op     new ns/op     delta
time               1392254       1353170       -2.81%
cputime            21995751      21373999      -2.83%
gc-pause-one       15044812      13050524      -13.26%
gc-pause-total     213636        185317        -13.26%

LGTM=rlh
R=golang-codereviews, rlh
CC=golang-codereviews, khr, rsc
https://golang.org/cl/123380043

E.g., here's the new "go build" output:

$ go build misc/cgo/errors/issue8442.go
# command-line-arguments
could not determine kind of name for C.issue8442foo

gcc errors for preamble:
misc/cgo/errors/issue8442.go:11:19: error: unknown type name 'UNDEF'

Fixes #8442.

LGTM=iant
R=iant, alex.brainman
CC=golang-codereviews
https://golang.org/cl/129160043

CC=golang-codereviews
https://golang.org/cl/129130043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/123390043

In cgo, now that recursive calls to typeConv.Type() always work,
we can more robustly calculate the array sizes based on the size
of our element type.

Also, in debug/dwarf, the decision to call zeroType is made
based on a type's usage	within a particular struct, but dwarf.Type
values are cached in typeCache, so the modification might affect
uses of the type in other structs.  Current compilers don't appear
to share DWARF type entries for "[]foo" and "[0]foo", but they also
don't consistently share type entries in other cases.  Arguably
modifying the types is an improvement in some cases, but varying
translated types according to compiler whims seems like a bad idea.

Lastly, also in debug/dwarf, zeroType only needs to rewrite the
top-level dimension, and only if the rest of the array size is
non-zero.

Fixes #8428.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/127980043

Restore https://golang.org/cl/41040043 after GC rewrite.
Original description:
On the plus side, we don't need to change the bits on malloc and free.
On the downside, we need to mark objects in the free lists during GC.
But the free lists are small at GC time, so it should be a net win.

benchmark             old ns/op     new ns/op     delta
BenchmarkMalloc8      21.9          20.4          -6.85%
BenchmarkMalloc16     31.1          29.6          -4.82%

LGTM=khr
R=khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/122280043

Basically this cleanup replaces all the usage usages of strcmp() == 0,
found by the following command line:

$ grep -R strcmp cmd/dist | grep "0"

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/123330043

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/128170043