Go 1.4

Most of the runtime converted from C to Go (scheduler, channels, maps, panics, signals). Stack copying is the only mechanism, with 2 KB minimum stacks. The compiler emits write barriers. atomic.Value. Android.

Each area lists the stage every thread reached in this release (with what was left open afterwards), then changes that are not part of a thread. Thread names link to the full thread on its topic page.

Memory management

From Memory management: GC and allocator (Go 1.0–1.17)

Allocator and collector prepared for Go: free removed, stack allocator split out, byte-array bitmap, more parallelism; GC still stop-the-world.

• Stop-the-world mark-sweep, then the parallel collector — Done: parallelism pass (44106a0880, 192bccbf33, f6f2f77142, 0c32bd6262, 98bebcc90a parfor in Go, aac7f1a0d6 markallocated in Go, c46bcd4d13 finalizer goroutine in Go); stack shrinking delayed until GC is done to avoid the GC seeing freed stacks through SudoG.elem (91e8554b8b); invalid pointers into the GC arena crash (11e53e46a6); MemStats.PauseEnd (46af78915a); go1.4 gctrace shows goroutine count (ed7db89b90). Left open: all of it still stop-the-world, with mark termination doing all marking; the power64 port disabled GC (9b88857f75^1.5, in the dev.power64 branch landed in 1.5).
• Concurrent sweep and proportional sweep — Done: sweepgen set before span state (3590d9ce69); transfer cache so a swept span does not bounce between mcentral/mheap locks (e0df11d57e: the previous dance was lock mcentral, remove, unlock, unmark, lock mheap, insert, unlock, lock mcentral). Left open: nothing noted.
• Concurrent mark: write barriers and the dev.garbage collector — Done: compiler-inserted write-barrier call sites (a no-op barrier; b035e97315^1.5’s message refers to barriers inserted “for Go 1.4”). Left open: collection still STW.
• Stack scanning: conservative, precise by frames, stack barriers, hybrid barrier, async safe points — Done: conservative scanning of stacks removed for Go frames (d208361cde), shrunk stacks freed only after GC (91e8554b8b, d57056ba26^1.5 later), parallel shrink (192bccbf33). Left open: stack rescan in STW.
• Precise heap scanning: type information, the heap bitmap and GC programs — Done: byte-array bitmap (ff3fa1b32d), unrolled mask cache (b91223edd1), backward scan removal (03f2189a1b), bitmap corruption fix (5bfe8adee5), type mandatory for scannable allocation (fb44fb6cb7). Left open: 4 bits per word and boundary bits.
• Size classes, tiny allocator and mcache/mcentral — Done: free removed (cecca43804), transfer cache (e0df11d57e), alloc counted for tiny allocs for testing.AllocsPerRun (e19d8a47d1). Left open: nothing noted.
• Span lifecycle in mheap: free lists, treaps, first-fit and the page reclaimer — Done: mheap not locked on user goroutine (e91704af27: the code under lock could grow the stack), allspans races (7f223e3b3b). Left open: nothing noted.
• Heap address space: contiguous arena to sparse arenas — Done: heap growth by 64K (0622e13b4d); mincore in addrspace_free (0e1b6bb547^1.3). Left open: nothing noted.
• Finalizers and span specials — Done: finalizer thread in Go (c46bcd4d13). Left open: nothing noted.
• Mark work distribution: parfor, work buffers, gcWork and root jobs — Done: parfor converted to Go (98bebcc90a), workbuf cache (f6f2f77142, ac9218f5f0), parfor untyped allocation removed (fc46931442). Left open: nothing noted.
• Runtime allocators for runtime metadata and the port to Go — Done: stack allocator (7c13860cd0), stack orders raised to 4 in 1.5 (5aae246f1e^1.5), sysAlloc nosplit (99a08262af). Left open: C-written malloc.
• Memory statistics and accounting — Done: PauseEnd (46af78915a), stats fixes (30ef2c7deb, 266d350f5e, 01a7d39df1), tiny allocs counted (e19d8a47d1), gctrace goroutine count (ed7db89b90). Left open: nothing noted.

Other changes

• GC cleanups before the Go port internal — gobuf.ctxt handling removed because it was wrong (d3be3daafe), getgcmask on the M stack (005806cab1), gctrace deadlock via ReadMemStats on m0 (a0dbbeae67), UncacheSpan simplification after free removal (f3dd6df6b1), FlagNoProfile removed (1837419f30), Plan 9 and Windows accounting (846db08936, 048692e5de), gctrace fix (2425a2e32f), Go/C mallocgc signatures (489ff75ab8, 58241bfdf7).
• Scan and bitmap micro-optimisations internal — markspan 2x on NUMA (acb03b8028^1.3), scan-loop optimisations (b8fdaaf028, 9dc6764d3c), memmove in mgc0 (ab5d105ba9).
• Convert GC helpers to Go internal — Removed the C version of the GC, converted freeOSMemory and clearpools/registerPoolCleanup to Go, and restored the g0 check in GC. (9f38b6c9e5, 60447c2d95)

Scheduler and concurrency

From Scheduler and concurrency runtime (Go 1.0–1.17)

Conversion of the scheduler, channels, select, semaphores, timers and netpoll from C to Go, plus atomic.Value; threads: C→Go conversion, channels.

• The G-M-P scheduler: from global-lock M:N to per-P run queues, spinning Ms and work stealing — Done: scheduler functions converted to Go 684de04118, 5d40742728, 6ed58c2962, dropg/schedule rework to handle locked goroutines in one place 64c2083ebc; scheduler trace now prints spinning Ms a7186dc303; goroutine ids start at 1 aa76377423; allp static array 858c57f5bd; NumGoroutines O(1) 92c1e72040.
• Network poller: from the netFD select loop to the runtime-integrated epoll/kqueue/IOCP poller — Done: netpoll converted to Go (epoll/kqueue) 91a670d179, Solaris 97fdfdb52c; shrinkstack vs netpoll race 2b62e1eaec^1.5 (Go 1.5 list).
• Timers: timerproc goroutine → per-bucket heaps → timers on Ps — Done: timers converted to Go 9601abaf8b; fake time support revived 2fe9482343.
• Channels and select — Done: chansend/chanrecv/closechan/select converted to Go 9a1e142bbc, 47d6af2f68, 6a76bca33f, 1d8fa7fa5d; non-blocking fast paths (BenchmarkChanNonblocking 27.8 → 7.8ns) f6ceefa2bf; chan type info dfa5a99ebb; sudog stale-pointer leaks 0120f8378d, 13da360845, e330cc16f4, b3932baba4, 2ad99f0960, b3932baba4.
• Semaphores, runtime locks and Notes — Done: sync and async semaphores converted to Go a6950fe0f9, ebac0e6f30; notes afb2260491, futex notes fix d2165672ca; block-profile fix 7b3677bf3c; semacquire always on the G stack da8cf5438a and 71de7e7539.
• sync.Mutex, RWMutex, WaitGroup, Cond, Once — Done: RWMutex misuse detection 22d46d53ea; panicking functions still mark Once complete b22dc6385d.
• sync.Pool — Done: Pool memory released across second and later GCs af3868f187.
• sync.Map, atomic.Value and sync/atomic — Done: user-visible atomic.Value 98a1e207e2; nacl/arm 62af04c0bc; missing prototypes 735289ff76.
• Runtime from C to Go: scheduler, channels, semaphores, timers, netpoll — Done: common scheduler 684de04118, notes afb2260491, chan 9a1e142bbc, 47d6af2f68, 6a76bca33f, semaphores a6950fe0f9, ebac0e6f30, timers 9601abaf8b, select 1d8fa7fa5d, netpoll 91a670d179, cgocall c08d8834dd, forcegc helper 42486ffc5d, cpuprof ac49e6735b, mprof 548d0805f7, mallocgc bffb0590c1, funcPC 0e07f1c99f, getgcmask, Gosched 5d40742728, newproc1 on M stack 6ed58c2962, runtime.init run 1d0c89a454, goroutine start/stop at safepoints 56bd176e1d, entersyscall safe for stack splits 5ea69978fd.
• Goroutine and M lifecycle: caches, ids, LockOSThread, Goexit, cgo extra Ms, deadlock detection — Done: ids start at 1 aa76377423; goroutine locked marker in crash report 07f6f313a9; per-P defer pool 1ba04c171a^1.3 (1.3).
• Stop-the-world, safe points and GC–scheduler interaction — Done: start/stop individual goroutines at GC safepoints 56bd176e1d.

Other changes

• Runtime-level pprof/cpuprof bug fixes internal — e0f08b938a, f595f834be, 7ed8723d49.
• Misc internal — 8fcdc70c5e (GODEBUG invalidptr), 99080c4b6f, 1d2955a2af (chan size rounding), 6c934238c9 (minimum stack 2K), 45143aeca4, 70b2da98ca.
• C-to-Go conversion mop-up internal — aac7f1a0d6, e03bce158f, 8bca148a3e, 30940cfad6 (no acquirem on malloc fast path), d21638b5ec, 6179aca548, 2c1fde07ac, e77c2fe313, 649c83530a, 503bcd464e, 005806cab1, 8620e2b04e, a09e61395e, c01c2c8895, 15a5c35cec, 91baf5c65d (Gosched to Go), 44753479c6, c3b5db895b, cd2f8356ce, 6c007bb065, b83d8bd0b8 (dedicated scavenger thread removed), 21a4bdef2f.
• Forcegc and scheduler robustness internal — 9aa7d136f5, 176c44699b, 93805d711c, 7283e08cbf, 6ad16c4a48, 1d550b87db, 99e9bac8c4, b02450da02, 8422d1ea65, d3be3daafe, 0603fbb01c, 4534fdb144, 0f4b53c1c2, 97c8b24d01, 76f1b901db, 101c00a44f, 16c59acb97, 9a5654abef, 8c2484ec11.

Data structures and type metadata

From Runtime data structures and type metadata (Go 1.0–1.17)

The C-to-Go conversion of maps, slices, hashing, interfaces and printing; the 2-bit GC type info; direct-interface policy moved into the compiler; random start bucket for iteration; 3-word Value; reflect call-frame cache.

• Hash map core: from the first hashmap.c to the 8-entry bucket design — Done: map implementation converted to Go (0c6b55e76b), constants moved from header to map type (668a55a882), hmap type size verified (fe3ee5741d), pass correct size to malloc for the new GC (7bcbdbd904). Left open: “room for improvement (saving space so we can use nosplit, and removing the requirement for hash/eq stubs)”.
• Map growth, iteration order, overflow buckets and GC interaction — Done: random starting bucket for bigger maps (55c458e05f, 251daf8650).
• Map fast paths and compiler/runtime specialization — Done: fast routines in Go (0c6b55e76b).
• Hash functions and algorithm tables: memhash, AES hash, fallback hash — Done: hash in Go (a2a9768414, ea3ac6ba75), better interface/float hash (f098a29630, 5fbcdb2661), equal in Go (7aa4e5ac5f), NaCl aeshash off (18ab35f7ba).
• Compiler-generated equality and hash functions — Done: alg generated after dowidth (8d47b08255).
• Runtime type descriptors: layout, shrinking and name encoding — Done: sparse 2-bit GC type info (cd17a717f9), direct-iface flag in kind (1806a5732b), unrolled GC bitmask in reflect (3cf9acccae), Type.Comparable (a325f4f2b3), type.go duplicate removed (81674f3135).
• Interface values, itabs and type assertions — Done: direct-iface decision in compiler (1806a5732b), iface in Go (483cb61921, b53b47f5ac), reflect interface allocation type (7b9c5ec24b: GC saw empty-interface layout for non-empty interface), x.(T) for 0-byte T (d646040fd1).
• reflect redesign: from string parsing to Type/Value structs — Done: 3-word Value (a1616d4a32), Type.Comparable (a325f4f2b3), fast FieldByIndex (94950afdf8), struct size includes trailing padding (4e1d196543), memmove shared with runtime (b78d7b75c7), a few microoptimizations (0d81b72e1b).
• reflect.Call, MakeFunc, method values and argument-frame GC precision — Done: sync.Pool frame cache (67f8a81316^1.5), stub arg maps in traceback (f0d44dbeaf), assignTo/cvtT2I allocate correct type (7b9c5ec24b).
• reflect performance, caches and API additions — Done: three-word Value, FieldByIndex fast path, microoptimizations (a1616d4a32, 94950afdf8, 0d81b72e1b).
• memmove, memclr, duff routines and pointer-write atomicity — Done: amd64 memmove (a712e20a1d), no pointless jmp (bc9e160443), memclrBytes in Go (68f91aea57), reflect uses runtime memmove (b78d7b75c7).
• internal/bytealg and string/byte comparison primitives — Done: compare only to min length (5ea131f442).
• Slices and append: growslice, makeslice and string/slice conversions — Done: Go port (cc9ec52d73), correct malloc size (7bcbdbd904).
• Strings: concatenation, conversion and printing helpers — Done: print in Go (721c8735df, 597b266eaf, ef64d9ffcc, d8cbbe6802), gostringnocopy updates maxstring (bcd36e8857), concatstring panic uses gothrow (fa5f86281e).
• Soft-float, 64-bit division and complex arithmetic helpers — Done: 64-bit division, complex division and conversions in Go (d11bb3b177, c403af83a6, 32b3a48ea8, 0eaea6010a), nil pointer in softfloat (4b3906fec3).
• C-to-Go conversion of runtime data-structure code — Done: conversions listed above (0c6b55e76b, cc9ec52d73, a2a9768414, 7aa4e5ac5f, 483cb61921, b53b47f5ac, 68f91aea57, d11bb3b177), errorCString adjusted to avoid allocation (48452a276d).

Other changes

• Reflect trampoline and funcPC internal — 6baf173b67, 0e07f1c99f.
• Reflect correctness internal — Value.String on methods (dd8f29e3fe), IsValid vs Kind after Elem of nil interface (62d3202aaa), gc[0]/gc[1] type-punning removed (18172c42ff), runetochar reconstituted for gostringw (0f4b53c1c2), NOPTR global (d514e2915c), build fixes of the C-to-Go conversion (53304558f9, 8ee2a6658b, 433d643732, 6f19fd438e, ee6c6d96b6, 8b7da4de48).

Diagnostics and knobs

From Diagnostics and knobs (Go 1.0–1.17)

Runtime converted from C to Go reaches profiling (cpuprof, MemProfile, traceback) and race code.

• Race detector integration — Done: runtime converted to Go-compatible race handling, ignoring accesses on g0/gsignal (467a6d28be); writebarrier dst argument instrumented (d78823168f); undefined behaviour in racewalk.c fixed (1f5800673b). Left open: nothing noted.
• CPU profiler and runtime/pprof writers (legacy format to compressed protobuf) — Done: MemProfile, BlockProfile, ThreadCreateProfile converted to Go (04487d5612); cpuprof converted from C to Go (ac49e6735b); data race in pprof double-checked locking fixed (fe7b29f5fd); profile Bucket sub-structs named (a9cef4952f); no tracing past jmpdefer on arm (597f87c997). Left open: nothing noted.
• GODEBUG, runtime/debug, debug log and traceback knobs — Done: functions of runtime/debug converted to Go (ef50462378); exported runtime functions shown in stack traces (54245cba1f); gentraceback of self on the user stack forbidden because it may grow the stack (39bcbb353c); Stack fixes (a8c5e87b1e, 9a5654abef). Left open: nothing noted.
• Traceback correctness and inlining (diagnostic output) — Done: traceback converted from C to Go (fa2af441f1); arm trap and unexpected-pc fixes (d889f5f01e, e5e547c71f); newproc1 on M stack (6ed58c2962). Left open: nothing noted.

Other changes

• Windows fixes internal — sigtrampPC and build (996835887c, 60be96217d).
• C sources prohibited user-visible — cmd/go rejects C files unless cgo is used (a0785a53ad); static-marking, $sym(SB), and nacl flakiness (28cf62ed85, d89cd24857, 84a36434d9); type kind mask (1e0b378905); Stack deadlock (50bc3d5bbc^1.5, 1.5).
• mprof.goc pasted as comments internal — Pasted mprof.goc into mprof.go as comments during conversion to Go. (4dba769b73)

OS layer, stacks and panics

From OS interface, stacks and panics (Go 1.0–1.4)

Stack copying becomes the only mechanism with a 2 KB minimum; panic/defer, symtab, signal queue and locks converted to Go under the new C calling convention; Android and NaCl/ARM; PC/traceback semantics for Callers.

• Segmented stacks to contiguous (copied) stacks — Done: single contiguous stack with (lo, hi) bounds 15b76ad94b; 2 KB minimum 6c934238c9; StackCopyAlways stress mode toggled on/off several times during the conversion (277ef8fa07 off, 318294286a on, 176020e1b1 off after a windows/amd64 failure in copystack, 815a843b6a on, finally assumed by 15b76ad94b); f8f630f5ec uses reflect.call in panics instead of newstackcall; 0f99a91bb5 lets the copier update Panic structs; 47f251c1ce/1b6807bb06 make cgo cope with a moved G stack; 59dd20f4d3 fixes Windows syscalls for copying stacks; Gdead stack freeing 92eb1e1600. Left open: nothing noted beyond later fixes (a shrink/netpoll race was still fixed on the release branch).
• Stack-split prologue, nosplit budget and C-on-Go-stack detection — Done: fe91006a02 and 397bdb216f enlarge the nosplit area, c81a0ed3c5 C-on-Go-stack detection, 32ecf57d22, d16a2ad09b, 12308d5a0b, 99f7df0598, 653fb6d872, 40dd6bf38e; 9198ed4bd6. Left open: the dynamic check only catches code that executes.
• Panic, defer, recover and Goexit — Done: full conversion to Go (f44073785a, 8217b4a203, 3a3d47db37, 523aa93288, 7006aafdcd, f8f630f5ec); 8473695797; f95beae61d; 15274e5c9b; 0306478fe5; 36207a91d3, 060a988011; c4efaac15d fixes unrecovered panic on an external (cgo) thread; 7bcbdbd904 fixes the size passed to malloc for Panic. Left open: recover still depends on argp arithmetic.
• Tracebacks, crash output and GOTRACEBACK — Done: a22c11b995, a5a0733144, 3de7ba1873, 7ba41e9972, d16a2ad09b, 597f87c997 (no trace past jmpdefer on ARM), 6fb9d50d15 more detail on adjustframe crash, b3d5a695a6 diagnostics for non-copyable frames. Left open: nothing noted.
• Symbol tables, pclntab and runtime.Caller/FuncForPC — Done: Go symtab 0be59730fd, 97f8386af7; FUNCDATA holes 3d128dbf96; ftab endianness 3e62d2184a; Left open: nothing noted.
• Signals: handling, os/signal, foreign threads — Done: sigqueue in Go 651d0cf204, 81ed684a71; 201cfe4afb runs the Windows sighandler on g0; c548cc2ec8 fixes Windows handlers; de14137b4f drops SA_RESTORER on ARM; d7b678b2ca Solaris sigtramp register restore. Left open: nothing noted.
• Threads, locks and the OS scheduler interface — Done: 3a7f6646cf lock.c converted to Go; the Lock to Mutex rename (fee7c69c6c); df75f082d3 makes usleep/osyield callable from a cgo callback; 88d53ddb17 releases Windows thread handle in unminit; 9f012e1002 calls rfork on the scheduler stack on Plan 9; b143feb143 int64 reconstruction in semasleep. Left open:* nothing noted.
• cgo runtime support and non-Go threads — Done: 54138e1ac3, cb767247ca, 47f251c1ce, 1b6807bb06, 1aa65fe8d4, b4bfa6c964 (save g to TLS more aggressively: callback thread with TLS holding g0 instead of curg faulted into sigpanic with wrong g). Left open: nothing noted.
• TLS, g/m registers and shared-library linking — Done: a36348008c, 12b990ba7d, c1c8c3c8c4 export _rt0 for android, 72faffbc70; 89f185fe8a removes extern register m; 4769f87e0d; 0b36211cfb. Left open: nothing noted.
• Clocks, vDSO and timers — Done: 74b62b4864, 13d0b82bc8, 1db4c8dc41, 2fe9482343, 138b5ccd12, b60d5e12e9 warns that cputicks may not be monotonic. Left open: nothing noted.
• Windows runtime port — Done: 74b62b4864, a1778ec146, 17a108ba07, e9ecd4aec5, 38ce599494, 2eccf0d18f, 73f5010dc6, 59dd20f4d3, 201cfe4afb, 2c780a35b9, f8474fa01d, 2ed209eaf5. Left open: nothing noted.
• Platform ports: OS and architecture matrix — Done: user-visible Android a36348008c, 12b990ba7d, c1c8c3c8c4; NaCl/ARM d1177ed40d; Plan 9/amd64 decd810945; a84e3ad198 (nsec syscall on Plan 9). Left open: nothing noted.
• Integrated network poller: OS back-ends — Done: 91a670d179. Left open: Windows and Solaris code remained C.
• Runtime C-to-Go conversion and the Go calling convention in C (1.4) — Done: 25f6b02ab0, 012ceed914, 4aa50434e1, d4df63c3e8, 3a7f6646cf, 50199d7b35, 47d6af2f68, 39ffa8be78, 38ce599494, b4c28d9180, 0a7c7ac80e, 9a75c74836, f611ae1c75, d2574e2adb, ddce7c35f4; c007ce824d moves package sources from src/pkg to src. Left open: Windows/Solaris netpoll still C; onM bridge between Go and C.

Other changes

• Port build fixes during the C-to-Go conversion internal — Plan 9 (a6999c8845, c5b2c370c6, 9e36092697, b3de7f28a8, b1d0152997, f9829e92e1, 2302b21bbe), NaCl (3a3f8993ce, f9b9ecc5ee, add7b22010, dae8038639, 8a7597fd7a), Solaris (997809c809, 6c59cdcf34, e8a74dcad9), OpenBSD/NetBSD/FreeBSD/Linux (4dbd0dbf15, 2758cb75f0, b70bc22cd0, 29225211e1, d703ac338e, a287567d3c), ARM (22af2b8ee0, 45c819b2da, c486d4130d), windows/amd64 (3e9c7a8a1d, f950a14bb5, 2b1659b57d, 418b39d436, bf13b711bd), cgo (b2c75ae2be, f7a8adbd51).
• Conversion adjustments and pointer hygiene internal — gogetcallerpc (14c8143c31), alignment (5035750f23, 34655223ef, 9aa1e9afda), global variables marked NOPTR (5dab2da954, 75cca0526d, 3c94b1d305), aff7883d9a (assembler macros), 5a008acec1, 61b1d3a719, e4f3db3852, 6c67dd90f7, e5a06ccd37, 3306d119b0 (unify fastrand1/2), e3edfea07f, f545b05aae, db58ab96fa, 9e7c22938c, 857d55a3f9 and 5103500d13 (nosplit for freedefer/deferclass/endcgo), b78d7b75c7 (reflect uses runtime memmove), a7c6d89166, 5d5312c5dd (NewCallback parameter checking), dcc4a674d8, b02450da02 (zero dead or pointer-looking values), cb6f5ac0b0 (remove hand-written reflectcall bitmaps).
• Go source layout internal — packages moved from src/pkg to src (c007ce824d, de4964a78c); golang.org/x/... imports (7f0be1f781).
• os.Unsetenv user-visible — 85cdc49e8a.
• Misc internal — fake time (2fe9482343), eqstring in assembly (b36ed9056f), select descriptor on stack (40d7d5a656), GC bitmap byte array (ff3fa1b32d), heap dump bitmap 5b110c7b08, d1b2913710, 9d06cfc810, b3f224b280, 20d9cc4bb0.
• Cleanups and heap dump format internal — A few runtime cleanups and an updated heap dump format for 1.4. (526319830b, 6ea3746adf)

Compiler frontend

From Compiler frontend (Go 1.1–1.9)

Write barriers emitted (fcb4cabba4), pointer-only interface data word (950ad4fa2b), for range x {}, escape-analysis soundness fix for stack copying, go:nosplit.

• Parser: from yacc to a hand-written recursive-descent parser — Done: user-visible 8d504c4e97 for range x {; 2565b5c060 drops the parenthesization restriction for receiver types.
• Escape analysis and stack allocation — Done: fe3c913443, 00d2f916ad, a3416cf5cd-adjacent write-barrier work lives in the GC thread. Left open: result mapping is not recorded; imprecise.
• Closures, method values and variable capture — Done: 6c0bcb1863^1.3 (method value closures on nacl, 1.3).
• Language changes and rules as implemented in the compiler — Done: user-visible 8d504c4e97, 7f40e5e6e5, 55df81d37f, db4dad7fd7, 93fcb92257, fe8f799ef7, 870f4e190c, 2565b5c060.
• Static initialization, composite literals and init — Done: cfafa9f4cb, 3c40ee0fe0 (simplify explicit zeroing).
• Walk-level lowering and runtime-call optimisations — Done: 61dca94e10, 4af796fb6e (runtime.hex printing type).
• Write barriers, precise stacks and liveness (compiler side) — Done: fcb4cabba4, a3416cf5cd, 3c40ee0fe0, 1552e62d70, 950ad4fa2b, 75b72b1b27, 7aa3031eba. Left open: elision of x = x[0:y] and append is a 1.4-only simplification; “for Go 1.5, will need to change the compilation” (1552e62d70).
• Pragmas, directives and compiler flags — Done: 516d9ef53b.

Other changes

• Misc compiler fixes internal — 9e04ff7953, ae027f52fe, 689995a73e, 9c504696f4, 6a2e844f51, 8d61334dd5, 43c4287b25, 53c66543e0, 52e9bcafe1, ff6d0a4df4, 5e56854599, 516d9ef53b.

Middle end and SSA optimizer

From Middle end and SSA optimizer (Go 1.0–1.9)

Escape-analysis soundness fixes motivated by stack copying (indirect-of-param), write barrier prep (threads: escape analysis).

• Escape analysis (esc.c → esc.go) — Done: fe3c913443 (the indirect-of-param fix), 775ab8eeaa, f20e4d5ecb, 0f2cde8bdc, d2204e6c0e, 337fe4134f. Left open: per-result mapping and indirection counts (message).
• Inlining (inl.c → inl.go) — Done: eb54079264 (liveness for address-taken variables in inlined functions). Left open: nothing noted.
• Order, walk and temporary lifetimes (order.c, walk.c) — Done: 9aefdc8028, 5225854b74, e024ed5ca4, 454d1b0e8b. Left open: nothing noted.

Other changes

• Fixes internal — eb54079264, 88b78b41c5, 897f7a31fa, 20e97677fd, 8e89f87158, 6b54cc93d0.

Backends and assemblers

From Backends and assemblers (Go 1.0–1.6)

Preparation for translation (c2go annotations), plan9/amd64 and nacl/arm in liblink, assembly-function stack maps, small-struct registerization. Threads: liblink, C compilers, stack maps.

• Per-architecture compilers 6g/8g/5g/9g and the shared gc code generator — Done: registerize small structs/arrays in 5g and 8g (527ae57e65); explicit zeroing simplified so *x = T{} needs no write barrier (3c40ee0fe0); fatal “out of registers” (c1c5d479bd); 5g does not make register variables for directly called functions (bb4a358af3).
• Register allocation and the peephole optimizer (reg.c, peep.c) — Done: register variables for small structs/arrays on 5g/8g (527ae57e65); registerized addr nodes cleared so full registerized temporaries stop reserving stack (be2ad1d7f5); optimizer failure fatal in the C compilers (3147d2c4ee).
• Expression and statement code quality in 6g/8g/5g (division, bounds checks, loops, slices, interfaces) — Done: explicit zeroing without write barrier, MOVs instead of repeated STOSQ (3c40ee0fe0); extern = <N> code (0edafefc36); no address-as-constant in amd64 instructions (ce35994d4e).
• Stack frames, pointer maps and liveness analysis in the compiler — Done: local type information is emitted explicitly (see the 1.1 note on 1d5dc4fd48^1.1, 43c04ba1b8^1.1, aa3efb28f0^1.1); args_stackmap for assembly functions from Go prototypes (99f7df0598), slices/strings scanned like pointers (613383c765), all G frames copyable (00365b13b4), argsize PCDATA dropped (68c1c6afa0), auxiliary symbols marked pointer-free (8b20e7bb7e), runtime package decls never heap-promoted (064acace5b), liveness ~10x faster (7aa3031eba), invalid GC pointer crashes (11e53e46a6), emit code for extern init (0edafefc36).
• Stack frame layout, prologues, stack split and frame pointers — Done: ARM wrapper prologue (fb818eab7f).
• Zeroing and copying: Duff’s device, REP, unaligned moves and AVX2 runtime assembly — Done: 3c40ee0fe0;
• liblink: a shared assembler/linker library — Done: preliminary plan9/amd64 (decd810945), nacl/arm (783bcba84d), LinkArch.textflag() instead of thechar switches (3c24b60fd3), big-endian support (08ee2661f2), shorter zeroing-register encoding (24db881689), MOVBQZX as MOVZBL (bbc6bb9a99), literal-word comparison on ARM (b916dc1992), way to avoid pc-relative addressing for Solaris (4516a60062), DATA must be offset-ordered with no overlap (5e6bd29c2c), %^ verb and C_* constants moved (d69d0fe92b), arm MRC replacement generated in liblink (0b36211cfb), gotos rewritten for translation (8e0e09ae7d), fb818eab7f, 20a5de9eb6, a6feaf3aff, ae027f52fe.
• The Plan 9 C compilers (cc, 5c/6c/8c) in the Go toolchain — Done: Eface → interface{} (948bb9150e), no tag-less structs (3ffd29fb2c), make optimizer failure fatal (3147d2c4ee), diagnose Go calling C (0bb14d74f1), stop emitting argsize PCDATA (68c1c6afa0), #pragma pack off error (86c4c4f00c). Left open: the runtime still contained C (c2go translation was the plan).
• Assemblers: 5a/6a/8a/9a and the Go cmd/asm — Done: AJxx condition-code docs (c6442c994a), SETPC encoding (a6feaf3aff).
• C→Go translation of the toolchain (liblink, assemblers, compilers; dev.cc) — Done: c2go annotations (ebce79446d). Left open: the actual conversion.
• Native Client (nacl/386, nacl/amd64p32, nacl/arm) and amd64p32 in the toolchain — Done: nacl/arm (783bcba84d), ac0e12d158, 8a7597fd7a.
• Position-independent code, dynamic linking and TLS in the assemblers — Done: 4516a60062.

Other changes

• Source tree move internal — build adjustments for the move from src/pkg to src (220a6de47e, 3511454e13).
• Runtime escape is an error internal — 337fe4134f.
• -X flag, big endian, Solaris internal — df781cc4ab, 08ee2661f2, 4516a60062.
• Heap-bit GC prerequisites internal — 613383c765, 8b20e7bb7e, 064acace5b.
• ARM div/mod internal — avoid clobbering R12 in div/mod routines (f666167572).
• Remaining small code-generation, optimizer and tooling fixes (4 commits) internal — per-operator and per-back-end bug fixes and cleanups that do not carry design of their own: liblink and arm fixes, cap(chan) register, undefined-behaviour fixes in reg.c and bv.c, heap buffer overflow (1ec56062ef, 055dfc204c, a57dda74d9, 53056c37c2)
• Build, portability and warning fixes (5 commits) internal — Plan 9/gcc/clang warnings, yacc/bison, format verbs, buffer sizes, output-file handling and Windows paths in the compilers/assemblers/liblink (90c146f390, afb6221bf7, e8d65b92d7, 4a40fb1979, cbf97d9103)

Linker and object files

From Linker and object files (Go 1.0–1.9)

Go-specific DWARF type info and fixed frame tables, linker-defined symbols moved into package runtime, Android TLS, and a quiet cycle in the linker core.

• Go symbol table, pc/line table and function metadata (gosymtab, pclntab, findfunc) — Done: linker-defined symbols (runtime.pclntab, runtime.etext etc.) moved into package runtime (2c110a11e0); PC deltas in DWARF line table fixed (507afa68c5).
• Dead code and data elimination — Done: symbols created by -X no longer automatically marked reachable (f6fc14094a).
• DWARF generation in the linker — Done: Go-specific type info (e1821692ca), array encoding (cddad8affe, 74c9cc8394, 79b106ec62), frame table fixes (7b0ee53429), struct output change (125d1e9269).
• External (host) linking and cgo — Done: hostobj sections marked noptr (65e2b6f847), diagnostics for Go calling C (0bb14d74f1), clang integrated assembler disabled in cgo (cf9558c8ab), ignore .Linfo_string (82a5e95ccc).
• liblink, the object file format and the move into the compilers — Done: %^ formatting and C_* constants moved (d69d0fe92b), pc-relative amd64 addressing (ca85d572d6).
• From C to Go: cmd/link — Done: eae9fee3bf fixes zig-zag decoding in the Go skeleton; nothing else notable. Left open: nothing noted.
• Architecture and OS ports in the linker (arm, power64, arm64, mips, s390x, nacl, BSDs, Solaris) and trampolines — Done: Android TLS emulation (12b990ba7d), NaCl fix (a9b2651ade), big-endian addstrdata (f29bd6c4a4), large link base addresses (9abf0b6e9f).
• Build IDs, ABI hashes, flags and determinism — Done: flags documented (6012ac9b79, c3dbf56a14).

Other changes

• Operator precedence and UB fixes internal — 2c181f0355, 41d75933d7, 78cc89ce67, f129370b3e, faa223459a, 595dcef80a; diagnostics on unaligned symbols (9333fe8e92); cross-linking on Windows hosts (5a40b568d0); ELF build fixes (117a6973cb); go shows program name on crash (13a2c1ca78); fix off-by-one when emitting symbol names (8fe5ef4052).
• 386 GOT32 in push internal — 609d996fac accepts R_386_GOT32 in push instructions.