Overall:

plugin build mode & package (many CLs)
Many ppc64, s390x, arm, arm64 optimizations
New frontend
Improvements to binary size, runtime speed, compile speed.
Hybrid barrier. <100us GC pauses.

Language:

When explicitly converting structs, tags are ignored for structural type identity (CL 24190).

Tools:

compile: SSA for 386, nacl, arm, arm64, ppc64, ppc64le, s390x ... (many CLs)
yacc: "go tool yacc" is removed. now at golang.org/x/tools/cmd/goyacc (CL 27324, CL 27325)
go: -buildmode=c-archive now builds PIC on ELF (CL 24180)
go: mobile pkg dir change, recommend using go list in scripts (CL 24930, CL 27929)
go, dist: can set default pkg-config tool using PKG_CONFIG env var (CL 29991)
go: can set secure/insecure GIT schemes using GIT_ALLOW_PROTOCOL env var (CL 30135)

Ports:

dragonfly: go1.8 requires DragonFly BSD 4.4.4 or above (CL 29491)
plan9: various fixes (Close unblocks Read, I/O deadline maybe?)
mips, mipsle

API additions and behavior changes:

all: freeze net/rpc and reword the 'frozen' message in other frozen packages (CL 32112)
archive/tar: fix and cleanup readOldGNUSparseMap (CL 28471)
archive/tar: fix parsePAX to be POSIX.1-2001 compliant (CL 31440)
archive/tar: fix parsePAXTime (CL 31441)
archive/tar: make Reader handle GNU format properly (CL 31444)
archive/tar: reapply Header.Size to regFileReader after merging (CL 28418)
archive/tar: validate sparse headers in parsePAX (CL 31439)
archive/zip: handle mtime in NTFS/UNIX/ExtendedTS extra fields (CL 18274)
archive/zip: only use Extended Timestamp on non-zero MS-DOS timestamps (CL 30811)
cmd/cgo: add -srcdir option (CL 32354)
cmd/cgo: fix line info in _cgo_gotypes.go (CL 29713)
cmd/cgo: throw if C.malloc returns nil (CL 31768)
cmd/compile, runtime, etc: get rid of constant FP registers (CL 28095)
cmd/compile, runtime: add go:yeswritebarrierrec pragma (CL 30938)
cmd/compile/internal/gc: add runtime/trace support (CL 25354)
cmd/compile/internal/gc: enable new parser by default (CL 27203)
cmd/compile/internal/syntax: fast Go syntax trees, initial commit (CL 27195)
cmd/compile: add SSA backend for s390x and enable by default (CL 28978)
cmd/compile: add compiler phase timing (CL 24462)
cmd/compile: add go:notinheap type pragma (CL 30939)
cmd/compile: add inline explainer (CL 22782)
cmd/compile: args no longer live until end of function - use runtime.KeepAlive instead (CL 28310)
cmd/compile: enable flag-specified dump of specific phase+function (CL 23044)
cmd/compile: fail gracefully on export format skew (CL 27814)
cmd/compile: import/export of alias declarations (CL 32090)
cmd/compile: inline convI2E (CL 31260)
cmd/compile: make ssa compilation unconditional (CL 29155)
cmd/compile: remove -A flag (CL 31497)
cmd/compile: remove old lexer and parser (CL 32020)
cmd/compile: remove support for textual export format (CL 27171)
cmd/cover: Fix compiler directives handling (CL 30161)
cmd/cover: handle gotos (CL 30977)
cmd/dist, go/build: make CGO_ENABLED during make.bash sticky (CL 31141)
cmd/dist: enable plugin test on darwin/amd64 (CL 29396)
cmd/dist: test PIE internal linking on linux/amd64 (CL 28545)
cmd/doc: ensure summaries truly are only one line (CL 25420)
cmd/doc: perform type grouping for constants and variables (CL 25419)
cmd/doc: show documentation for interface methods when requested explicitly (CL 31852)
cmd/fix: add golang.org/x/net/context fix (CL 28872)
cmd/go, testing: indicate when no tests are run (CL 22341)
cmd/go: add bug command (CL 28485)
cmd/go: add distribution-specific info for Linux to bug command (CL 28581)
cmd/go: apply import restrictions to test code too (CL 31821)
cmd/go: diagnose non-canonical import paths before compilation (CL 31668)
cmd/go: enable -buildmode=plugin on darwin/amd64 (CL 29395)
cmd/go: for -msan build runtime/cgo with -fsanitize=memory (CL 24855)
cmd/go: make bug subcommand open the browser (CL 29210)
cmd/go: make go test -i -o x.test actually write x.test (CL 31352)
cmd/go: print more env variables in "go env" (CL 31330)
cmd/go: referee another vendor vs symlink fight (CL 31665)
cmd/internal/obj, cmd/link: darwin dynlink support (CL 29393)
cmd/internal/objfile: add ppc64/ppc64le disassembler support (CL 9682)
cmd/link, cmd/go: delay linking of mingwex and mingw32 until very end (CL 26670)
cmd/link: R_ADDR dynamic relocs for internal PIE (CL 29118)
cmd/link: add trampolines for too far calls in ppc64x (CL 30850)
cmd/link: allow internal PIE linking (CL 28543)
cmd/link: fix -X importpath.name=value when import path needs escaping (CL 31970)
cmd/link: fix -buildmode=pie / -linkshared combination (CL 28996)
cmd/link: insert trampolines for too-far jumps on ARM (CL 29397)
cmd/link: non-executable stack support for Solaris (CL 24142)
cmd/link: plugin support on darwin/amd64 (CL 29394)
cmd/link: put text at address 0x1000000 on darwin/amd64 (CL 32185)
cmd/link: remove the -shared flag (CL 28852)
cmd/link: split large elf text sections on ppc64x (CL 27790)
cmd/link: trampoline support for external linking on ARM (CL 31143)
cmd/objdump: implement objdump of .o files (CL 24818)
cmd/pprof: instruction-level granularity in callgrind output (CL 23781)
cmd/trace: add option to output pprof files (CL 23324)
cmd/trace: fix a runnable goroutine count bug (CL 25552)
cmd/trace: move process-wide GC events to their own row (CL 30017)
cmd/vet: accept space-separated tag lists for compatibility with cmd/go (CL 32030)
cmd/vet: allow ^& uintptr arithmetic (CL 27156)
cmd/vet: allow any printf verb with any interface (CL 27127)
cmd/vet: check for copying of array of locks (CL 24340)
cmd/vet: check for duplicate json, xml struct field tags (CL 16704)
cmd/vet: diagnose non-space-separated struct tag like `json:"x",xml:"y"` (CL 32031)
cmd/vet: improve asmdecl parameter handling (CL 27150)
cmd/vet: properly handle indexed arguments in printf (CL 24391)
cmd/vet: skip printf check for non-constant format string during failed import (CL 29014)
compress/flate: always return uncompressed data in the event of error (CL 28216)
compress/flate: level 1 (best speed) match across blocks (CL 31640)
compress/flate: make compression level 0 consistent (CL 31174)
compress/flate: tighten the BestSpeed max match offset bound. (CL 32149)
compress/gzip, compress/zlib: add HuffmanOnly as compression levels. (CL 31186)
compress/gzip: only encode MTIME if it is valid (CL 32325)
context: make DeadlineExceeded implement net.Error (CL 30370)
crypto/cipher: enforce message size limits for GCM (CL 28410)
crypto/rsa: ensure that generating toy RSA keys doesn't loop (CL 28969)
crypto/tls: add CloseWrite method to Conn (CL 25159)
crypto/tls: add CloseWrite method to Conn (CL 31318)
crypto/tls: add Config.Clone (CL 28075)
crypto/tls: add Config.GetConfigForClient (CL 30790)
crypto/tls: add GetClientCertificate callback (CL 32115)
crypto/tls: add KeyLogWriter for debugging (CL 27434)
crypto/tls: add VerifyPeerCertificate to tls.Config (CL 26654)
crypto/tls: add a SignatureScheme type. (CL 32119)
crypto/tls: don't generate random ticket keys if already set (CL 27317)
crypto/tls: enable ChaCha20-Poly1305 cipher suites by default. (CL 30958)
crypto/tls: expand ClientHelloInfo (CL 31391)
crypto/tls: fix deadlock when racing to complete handshake (CL 29164)
crypto/tls: flush the buffer on handshake errors (CL 28818)
crypto/tls: implement countermeasures against CBC padding oracles (CL 18130)
crypto/tls: set Conn.ConnectionState.ServerName unconditionally (CL 22862)
crypto/tls: support AES-128-CBC cipher suites with SHA-256 (CL 27315)
crypto/tls: support ChaCha20-Poly1305. (CL 30957)
crypto/tls: support X25519 (CL 30824, CL 30825)
crypto/x509: Fix bug in UnknownAuthorityError.Error (CL 27992)
crypto/x509: allow a leaf certificate to be specified directly as root (CL 27393)
crypto/x509: check that the issuer name matches the issuer's subject name (CL 23571)
crypto/x509: don't accept a root that already appears in a chain. (CL 32121)
crypto/x509: fix name constraints handling (CL 30155)
crypto/x509: implement SystemCertPool on Windows (CL 30578)
crypto/x509: parse all names in an RDN (CL 30810)
crypto/x509: recognise ISO OID for RSA+SHA1 (CL 27394)
crypto/x509: require a NULL parameters for RSA public keys (CL 16166)
crypto/x509: require a NULL parameters for RSA public keys (CL 27312)
crypto/x509: return error for missing SerialNumber (CL 27238)
crypto/x509: support PSS signatures (CL 24743)
crypto/x509: support RHEL 7 cert bundle (CL 30375)
database/sql: accept nil pointers to Valuers implemented on value receivers (CL 31259)
database/sql: add Pinger interface to driver Conn (CL 32136)
database/sql: add context helper methods and transaction types (CL 31258)
database/sql: add context methods (CL 29381)
database/sql: add option to use named parameter in query arguments (CL 30166)
database/sql: add support for multiple result sets (CL 30592)
database/sql: don't hang if the driver Exec method panics (CL 23576)
database/sql: support returning query database types (CL 29961)
debug/elf: add sparc64 relocations (CL 30870)
debug/pe: revert CL 22720 (CL 27212)
doc: document minimum OS X version as 10.8 (CL 28870)
encoding/base64: add Encoding.Strict (CL 24964)
encoding/binary: add bool support (CL 28514)
encoding/json: add struct and field name to UnmarshalTypeError message (CL 18692)
encoding/json: fix decoding of null into Unmarshaler, TextUnmarshaler (CL 30944)
encoding/json: marshal the RawMessage value type the same as its pointer type (CL 21811)
encoding/json: use standard ES6 formatting for numbers during marshal (CL 30371)
encoding/pem: be stricter about the ending line (CL 27391)
encoding/xml: add wildcard support for collecting all attributes (CL 30946)
encoding/xml: prevent omitempty from omitting non-nil pointers to empty values (CL 15684)
expvar: add Value methods (CL 30917)
expvar: export http.Handler (CL 24722)
flag: arrange for FlagSet.Usage to be non-nil by default (CL 31576)
fmt: document and adjust Scanf space handling to eliminate a few paradoxes (CL 30611)
go/ast, go/parser: parse alias declarations (CL 30211)
go/build: allow % in ${SRCDIR} expansion for Jenkins (CL 31611)
go/build: do not record go:binary-only-package if build tags not satisfied (CL 31577)
go/doc: add IsPredeclared function (CL 29870)
go/doc: allow ToHTML to properly handle URLs containing semicolons (CL 25385)
go/internal/gcimporter: fail gracefully on export format skew (CL 27816)
go/token: fix race in FileSet.PositionFor. (CL 25345)
go/types: expose Default function, which converts untyped T to T (CL 30715)
go/types: handle imported aliases (CL 32534)
go/types: match cmd/compile's alignment for complex64 (CL 31939)
go/types: minimal support for alias declarations: don't crash (CL 30213)
html/template: check "type" attribute in <script> (CL 14336)
image/color: tweak the formula for converting to gray. (CL 31538)
image/png: implement grayscale transparency. (CL 32143)
image/png: implement truecolor transparency. (CL 32140)
image/png: improve compression by skipping filter for paletted images (CL 29872)
internal/trace: fix analysis of EvGoWaiting/EvGoInSyscall events (CL 25572)
io: fix infinite loop bug in MultiReader (CL 27397)
io: make MultiReader nil exhausted Readers for earlier GC (CL 28533)
math/big: Rat.SetString to report error if input is not consumed entirely (CL 30472)
math/big: add (*Int).Sqrt (CL 30706)
math/big: implement Float.Scan, type assert fmt interfaces to enforce docs (CL 30723)
math/big: support negative numbers in ModInverse (CL 29299)
math/big: test and optimize Exp(2, y, n) for large y, odd n (CL 30708)
math/cmplx: prevent infinite loop in tanSeries (CL 31952)
math/rand: add Rand.Uint64 (CL 27253)
math: fix Gamma(-171.5) on all platforms (CL 30540)
mime/quotedprintable: accept = not followed by 2 hex digits as literal equals (CL 32174)
mime/quotedprintable: accept trailing soft line-break at the end of message (CL 27530)
mime: preserve unnecessary backslash escapes as literals (CL 32175)
net/http, net/http/httptest: make http2's TrailerPrefix work for http1 (CL 32479)
net/http/httptest: fill ContentLength in recorded Response (CL 28302)
net/http/httptrace: add ClientTrace.TLSHandshakeStart & TLSHandshakeDone (CL 30359)
net/http/httputil: add ModifyResponse to reverseProxy (CL 32356)
net/http/httputil: copy header map if necessary in ReverseProxy (CL 28493)
net/http/httputil: log err encountered during reverseproxy body copying (CL 30692)
net/http/httputil: make ReverseProxy send nil Body requests when possible (CL 28412)
net/http/httputil: remove custom hop-by-hop headers from response in ReverseProxy (CL 28810)
net/http/httputil: remove proxied headers mentioned in connection-tokens (CL 27970)
net/http/internal: don't block unnecessarily in ChunkedReader (CL 31329)
net/http: add NoBody, don't return nil from NewRequest on zero bodies (CL 31726)
net/http: add Request.GetBody func for 307/308 redirects (CL 31733)
net/http: add Server.Close & Server.Shutdown for forced & graceful shutdown (CL 32329)
net/http: add Server.ReadHeaderTimeout, IdleTimeout, document WriteTimeout (CL 32024)
net/http: add Transport.ProxyConnectHeader to control headers to proxies (CL 32481)
net/http: add an interface for HTTP/2 server push (CL 32012)
net/http: allow Handlers to test Hijacked conn without spamming error log (CL 30812)
net/http: don't sniff Request.Body on 100-continue requests in Transport (CL 30151)
net/http: handle 3xx redirects properly (CL 29852)
net/http: make Client copy headers on redirect (CL 28930)
net/http: make DefaultTransport's Dialer enable DualStack ("Happy Eyeballs") (CL 28077)
net/http: make NewRequest set empty Body nil, don't peek Read Body in Transport (CL 31445)
net/http: make Redirect escape non-ASCII in Location header (CL 31732)
net/http: make Server Handler's Request.Context be done on conn errors (CL 31173)
net/http: make Transport reject URLs with bogus ports with non-digits (CL 32482)
net/http: make Transport retry non-idempotent requests if no bytes written (CL 27117)
net/http: make Transport support international domain names (CL 29072)
net/http: omit Content-Length in Response.Write for 1xx or 204 status (CL 28351)
net/http: returned typed error on Transport proxy dial (CL 30750)
net/http: send Content-Range if no byte range overlaps (CL 24212)
net/http: skip test needing good DNS in short mode, except on builders (CL 28782)
net/http: support multiple identical Content-Length headers (CL 31252)
net/http: update bundled http2, add h2 Transport.IdleConnTimeout tests (CL 30078)
net/mail: allow empty quoted string name in address again (CL 32176)
net/mail: expose ParseDate, for use parsing Resent-Date headers (CL 31581)
net/url: add PathEscape, PathUnescape (CL 31322)
net/url: add URL.Hostname and URL.Port accessors (CL 28933)
net/url: handle escaped paths in ResolveReference (CL 28343)
net/url: make URL implement encoding.BinaryMarshaler, BinaryUnmarshaler (CL 31467)
net/url: prefix relative paths containing ":" in the first segment with "./" (CL 29610)
net/url: reject colon in first segment of relative path in Parse (CL 31582)
net: add (*UnixListener).SetUnlinkOnClose (CL 32099)
net: add Buffers type, do writev on unix (CL 29951)
net: add Resolver type, Dialer.Resolver, and DefaultResolver (CL 29440)
net: always wake up the readers on close on Plan 9 (CL 31390)
net: break up >1GB reads and writes on stream connections (CL 31584)
net: close the connection gracefully on Plan 9 (CL 31271)
net: implement network interface API for Plan 9 (CL 29963)
net: implement network interface API for Solaris (CL 29892)
net: make LookupPort and lookupProtocol work on nacl (CL 28951)
net: make lookupPort case-insensitive on Plan 9 (CL 29051)
net: only remove Unix domain socket file on the first call to Close (CL 32098)
net: remove parsing of negative decimals in IPv4 literal (CL 28414)
net: respect resolv.conf rotate option (CL 29233)
net: support "option ndots:0" in resolv.conf (CL 24901)
net: there are no invalid domain names anymore (CL 31468)
net: use libresolv rules for ndots range and validation (CL 24901)
os, syscall: fix incorrect offset calculation in Readlink on windows (CL 31118)
os: add ErrClosed, return for use of closed File (CL 30614)
os: add Executable() (CL 16551)
os: consider only files from #M as regular on Plan 9 (CL 32152)
os: don't let File.Readdir return an empty slice and nil error (CL 28056)
os: make IsExist report true on ERROR_DIR_NOT_EMPTY on Windows (CL 29753)
os: make Windows readConsole handle input and output correctly (CL 29493)
os: prevent infinite symlink loop of Stat on Windows (CL 27580)
os: reject Rename("old", "new") where new is a directory (CL 31358)
os: use GetConsoleCP() instead of GetACP() (CL 27575)
path/filepath: don't return SkipDir at top (CL 24780)
path/filepath: fix Abs on Windows (CL 32292)
path/filepath: fix match of \\?\c:\* on Windows (CL 31460)
path/filepath: handle ".." in normalizing a path on Windows (CL 27410)
path/filepath: handle "C:." correctly in EvalSymlinks on Windows (CL 28214)
plugin: darwin support (CL 29392)
plugin: mention OS X support and concurrency (CL 31463)
plugin: new package for loading plugins (CL 27823)
reflect: add Swapper func (CL 30088)
reflect: fix DeepEqual for some cyclic corner cases (CL 31588)
reflect: ignore struct tags when converting structs (CL 30191)
runtime, cmd/trace: annotate different mark worker types (CL 30702)
runtime, runtime/cgo: revert CL 18814; don't drop signal stack in new thread on dragonfly (CL 29971)
runtime/pprof: write profiles in protobuf format. (CL 32257)
runtime/race: don't crash on invalid PCs (CL 29714)
runtime/race: update race runtime (CL 32160)
runtime: Profile goroutines holding contended mutexes. (CL 29650)
runtime: assume 64kB physical pages on ARM (CL 25021)
runtime: disable stack rescanning by default (CL 31766)
runtime: don't call cgocallback from signal handler (CL 30218)
runtime: fetch physical page size from the OS (CL 25050)
runtime: fix check for vacuous page boundary rounding (CL 27230)
runtime: fix map iterator concurrent map check (CL 24749)
runtime: fix newextram PC passed to race detector (CL 29712)
runtime: implement unconditional hybrid barrier (CL 31765)
runtime: limit the number of map overflow buckets (CL 25049)
runtime: pass windows float syscall args via XMM (CL 32173)
runtime: print sigcode on signal crash (CL 32183)
runtime: record current PC for SIGPROF on non-Go thread (CL 30252)
runtime: report GCSys and OtherSys in heap profile (CL 29276)
runtime: sleep on CLOCK_MONOTONIC in futexsleep1 on freebsd (CL 30154)
runtime: use RtlGenRandom instead of CryptGenRandom (CL 29700)
runtime: use clock_gettime(CLOCK_REALTIME) for nanosecond-precision time.now on arm64, mips64x (CL 32177)
runtime: use correct system page size on all arches (CL 25022)
sort: add Slice, SliceStable, and SliceIsSorted (CL 27321)
spec: add new language for alias declarations (CL 30601)
spec: ignore struct tags when converting structs (CL 24190)
spec: require 16 bit minimum exponent in constants rather than 32 (CL 17711)
spec: update language on type switches to match implementations (CL 27356)
strconv: strip \r in raw strings passed to Unquote (CL 31210)
strings, bytes: panic if Repeat overflows or if given a negative count (CL 29954)
sync: enable Pool when using race detector (CL 31589)
sync: throw, not panic, for unlock of unlocked mutex (CL 31359)
syscall: add bounds checking and error returns to ParseNetlinkMessage (CL 26990)
syscall: fix Send{msg,msgN}, Recvmsg and control message handling on solaris (CL 30171)
syscall: make Getpagesize return system-reported page size (CL 25051)
syscall: make Utimes on Solaris match all the other geese (CL 31446)
syscall: remove X__cmsg_data from Cmsghdr (CL 32319)
syscall: unify NsecToTime{spec,val}, fix for times < 1970 (CL 30826)
syscall: validate ParseDirent inputs (CL 23780)
testing/quick, text/tabwriter: freeze packages (CL 31910)
testing: add Name method to *T and *B (CL 29970)
testing: add a method testing.CoverMode (CL 32483)
testing: respect benchtime on very fast benchmarks (CL 26664)
text/template: add support for reflect.Value args, results in funcs (CL 31462)
time: add Until helper function (CL 20118)
time: allow long fractions in ParseDuration (CL 29338)
time: be consistent about representation of UTC location in Time struct (CL 31144)
unicode: change SimpleFold to handle invalid runes (CL 30935)
website: recreate 16px and 32px favicon (CL 26850)

Optimizations:

bytes, strings: optimize for ASCII sets (CL 31593)
bytes, strings: optimize multi-byte index operations on s390x (CL 32447)
bytes,strings: use IndexByte more often in Index on AMD64 (CL 31690)
bytes: Use the same algorithm as strings for Index (CL 22550)
bytes: improve WriteRune performance (CL 28816)
bytes: improve performance for bytes.Compare on ppc64x (CL 30949)
bytes: make IndexRune faster (CL 28537)
cmd/asm, go/build: invoke cmd/asm only once per package (CL 27636)
cmd/compile, cmd/link: more efficient typelink generation (CL 31772)
cmd/compile, cmd/link: stop generating unused go.string.hdr symbols. (CL 31030)
cmd/compile,runtime: redo how map assignments work (CL 30815)
cmd/compile/internal/obj/x86: eliminate some function prologues (CL 24814)
cmd/compile: accept literals in samesafeexpr (CL 26666)
cmd/compile: add more non-returning runtime calls (CL 28965)
cmd/compile: add size hint to map literal allocations (CL 23558)
cmd/compile: be more aggressive in tighten pass for booleans (CL 28390)
cmd/compile: directly construct Fields instead of ODCLFIELD nodes (CL 31670)
cmd/compile: don't reserve X15 for float sub/div any more (CL 28272)
cmd/compile: don’t generate pointless gotos during inlining (CL 27461)
cmd/compile: fold negation into comparison operators (CL 28232)
cmd/compile: generate makeslice calls with int arguments (CL 27851)
cmd/compile: handle e == T comparison more efficiently (CL 26660)
cmd/compile: improve s390x SSA rules for logical ops (CL 31754)
cmd/compile: improve s390x rules for folding ADDconst into loads/stores (CL 30616)
cmd/compile: improve string iteration performance (CL 27853)
cmd/compile: improve tighten pass (CL 28712)
cmd/compile: inline _, ok = i.(T) (CL 26658)
cmd/compile: inline atomics from runtime/internal/atomic on amd64 (CL 27641, CL 27813)
cmd/compile: inline convT2{I,E} when result doesn't escape (CL 29373)
cmd/compile: inline x, ok := y.(T) where T is a scalar (CL 26659)
cmd/compile: intrinsify atomic operations on s390x (CL 31614)
cmd/compile: intrinsify math/big.mulWW, divWW on AMD64 (CL 30542)
cmd/compile: intrinsify runtime/internal/atomic.Xaddint64 (CL 29274)
cmd/compile: intrinsify slicebytetostringtmp when not instrumenting (CL 29017)
cmd/compile: intrinsify sync/atomic for amd64 (CL 28076)
cmd/compile: make [0]T and [1]T SSAable types (CL 32416)
cmd/compile: make link register allocatable in non-leaf functions (CL 30597)
cmd/compile: missing float indexed loads/stores on amd64 (CL 28273)
cmd/compile: move stringtoslicebytetmp to the backend (CL 32158)
cmd/compile: only generate ·f symbols when necessary (CL 31031)
cmd/compile: optimize bool to int conversion (CL 22711)
cmd/compile: optimize integer "in range" expressions (CL 27652)
cmd/compile: remove Zero and NilCheck for newobject (CL 27930)
cmd/compile: remove duplicate nilchecks (CL 29952)
cmd/compile: remove some write barriers for stack writes (CL 30290)
cmd/compile: simplify div/mod on ARM (CL 29390)
cmd/compile: statically initialize some interface values (CL 26668)
cmd/compile: unroll comparisons to short constant strings (CL 26758)
cmd/compile: use 2-result divide op (CL 25004)
cmd/compile: use masks instead of branches for slicing (CL 32022)
cmd/compile: when inlining ==, don’t take the address of the values (CL 22277)
container/heap: remove one unnecessary comparison in Fix (CL 24273)
crypto/sha256: improve performance for sha256.block on ppc64le (CL 32318)
crypto/sha512: improve performance for sha512.block on ppc64le (CL 32320)
crypto/{aes,cipher}: add optimized implementation of AES-GCM for s390x (CL 30361)
encoding/asn1: reduce allocations in Marshal (CL 27030)
encoding/csv: avoid allocations when reading records (CL 24723)
encoding/hex: change lookup table from string to array (CL 27254)
encoding/json: Use a lookup table for safe characters (CL 24466)
hash/crc32: improve the AMD64 implementation using SSE4.2 (CL 24471)
hash/crc32: improve the AMD64 implementation using SSE4.2 (CL 27931)
hash/crc32: improve the processing of the last bytes in the SSE4.2 code for AMD64 (CL 24470)
image/color: improve speed of RGBA methods (CL 31773)
image/draw: optimize drawFillOver as drawFillSrc for opaque fills (CL 28790)
math/big: avoid allocation in float.{Add, Sub} when there's no aliasing (CL 23568)
math/big: make division faster (CL 30613)
math/big: 10%-20% faster float->decimal conversion (CL 31250, CL 31275)
math/big: use array instead of slice for deBruijn lookups (CL 26663)
math/big: uses SIMD for some math big functions on s390x (CL 32211)
math: speed up Gamma(+Inf) (CL 31370)
math: speed up bessel functions on AMD64 (CL 28086)
reflect: avoid zeroing memory that will be overwritten (CL 28011)
regexp: avoid alloc in QuoteMeta when not quoting (CL 31395)
regexp: reduce mallocs in Regexp.Find* and Regexp.ReplaceAll* (CL 23030)
runtime: cgo calls are about 100ns faster (CL 29656, CL 30080)
runtime: defer is now 2X faster (CL 29656)
runtime: implement getcallersp in Go (CL 29655)
runtime: improve memmove for amd64 (CL 22515, CL 29590)
runtime: increase malloc size classes (CL 24493)
runtime: large objects no longer cause significant goroutine pauses (CL 23540)
runtime: make append only clear uncopied memory (CL 30192)
runtime: make assists perform root jobs (CL 32432)
runtime: memclr perf improvements on ppc64x (CL 30373)
runtime: minor string/rune optimizations (CL 27460)
runtime: optimize defer code (CL 29656)
runtime: remove a load and shift from scanobject (CL 22712)
runtime: remove defer from standard cgo call (CL 30080)
runtime: speed up StartTrace with lots of blocked goroutines (CL 25573)
runtime: speed up non-ASCII rune decoding (CL 28490)
strconv: make FormatFloat slowpath a little faster (CL 30099)
strings: add special cases for Join of 2 and 3 strings (CL 25005)
strings: make IndexRune faster (CL 28546)
strings: use AVX2 for Index if available (CL 22551)
strings: use Index in Count (CL 28586)
syscall: avoid convT2I allocs for common Windows error values (CL 28484, CL 28990)
text/template: improve lexer performance in finding left delimiters (CL 24863)
unicode/utf8: optimize ValidRune (CL 32122)
unicode/utf8: reduce bounds checks in EncodeRune (CL 28492)

Documentation:

all: many more examples in documentations (many CLs)
runtime: runtime.MemStats has much more detailed documentation (CL 28972)

Binary Size:

cmd/link: more efficient encoding of DWARF line number information (CL 30577)
cmd/compile: recognize integer ranges in switch statements (CL 26770)
cmd/compile: use two tables for table-driven map inserts (CL 26669)
cmd/link: when dynlinking, do not mangle short symbol names (CL 26890)
cmd/compile, runtime: stop padding stackmaps to 4 bytes (CL 30817)