Go 1.12

Mark termination simplified, page reclaimer, more aggressive scavenger. Stack objects. ABI0/ABIInternal symbol split. Binary export removed; -lang. AIX port. MADV_FREE. macOS syscall via libSystem.

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)

Mark termination simplification (mark 2, gchelper, gctrace=2 removed), page reclaimer, treap-only span tracking, aggressive scavenger with fixes.

• Concurrent sweep and proportional sweep — Done: sweepone simplified and gosweepone removed (06afc8b152, f3bb4cbfd5), span mark bit (ba1698e963), arena slice and in-use page bitmap (e500ffd88c, 69e666e4f7), efficient page reclaimer (5333550bdc), large-allocation sampling fix (dc889025c7). Left open: nothing noted.
• Decentralized GC state machine and mark termination simplification — Done: mark-termination cleanup listed above (9c634ea889, a2a2901b25, 9108ae7751, d398dbdfc3, 918ed88e47, 1678b2c580, e25ef35254, ecc365960b, edc2d17086, 198440cc3d, 457c8f4fe9, 550dfc8ae1, 873bd47dfb, 0906d648aa, 578667f4b5 preemptible mark termination goroutine); gList types for G queues (3578918b66, d02169d380, 083938df14). Left open: “P has cached GC work” cause not found, only worked around (95a6f112c6).
• Stack scanning: conservative, precise by frames, stack barriers, hybrid barrier, async safe points — Done: gcrescanstacks removed (198440cc3d). Left open: nothing noted.
• Hybrid write barrier and buffered write barrier — Done: barrier buffer flush creates GC work (9c634ea889), poisoning (fe2feb978e), growslice bulk barrier (96dcc4457b, 4363c98f62). Left open: nothing noted.
• Allocating from mark bits: allocBits, freeindex and ctz — Done: span mark bit set whenever any object on the span is marked (ba1698e963). Left open: gcmarknewobject path missed it, fixed in 1.15 (886caba73c^1.15).
• Size classes, tiny allocator and mcache/mcentral — Done: mcache refill simplified (2d23ece135, 01e6cfc2a0), unneeded span tracking in mcentral dropped (70d7e96c78), newarray uses multiplication with overflow check (1e50dd02a9). Left open: nothing noted.
• Span lifecycle in mheap: free lists, treaps, first-fit and the page reclaimer — Done: treap-only heap, separated scavenged spans, iterator, coalescing refactor (07e738ec32, b00a6d8bfe, b46bf0240c, e508a5f072, 3651476075, 79ac638e41, 2f99e889f0, 6e9f664b9a, 689fae2d78, 011b8eb6bb). Left open: best-fit by size led to fragmentation; first-fit adopted in 1.13.
• Scavenger: returning memory to the OS — Done: scavenged/unscavenged separation and credit (b46bf0240c, e508a5f072, c803ffc67d, 06be7cbf3c, 064842450b, 6e9f664b9a, 8e093e7a1c, faf187fb8e). Left open: scavenging still inline with allocation.
• Heap address space: contiguous arena to sparse arenas — Done: arenas slice (e500ffd88c), race-mode MAP_FIXED (7ef718f16f, from Dec 2018). Left open: nothing noted.
• Mark work distribution: parfor, work buffers, gcWork and root jobs — Done: work-flush debugging (9098d1d854, 438b9544a0, bae1e70ac4, 8e6396115e). Left open: nothing noted.

Other changes

• Misc internal — treap nodes not zeroed twice (011b8eb6bb), table of arena sizes (4c1c839a3d), sysUsed fixes (213845f7b9, db82a1bc12), TestArenaCollision (6fcab648af).
• Misc internal — sysStat alignment for arenas (c823155828^1.11), mheap.freeSpan and free-count tidy-ups (3f86d7cc67, 416804f3e2), mbits.setMarked inlining undone (1d09433ec0), npreleased as boolean (78bb91cbd3), non-in-use span check (7d2f46dacd), os.File.Fd doc (7bb6fed9b5^1.16).
• Skip persistent memory writes in cgo checker internal — The cgo pointer checker now skips writes to persistent memory. (0d6a2d5f9a)

Scheduler and concurrency

From Scheduler and concurrency runtime (Go 1.0–1.17)

gList, gchelper removed, netpoll timer merging, scheduling by class; threads: scheduler, netpoll.

• The G-M-P scheduler: from global-lock M:N to per-P run queues, spinning Ms and work stealing — Done: manually managed G dequeues replaced by gList 3578918b66 (used in netpoll de990545c3, gfree 8e8cc9db0f, closechan a034f310b0); gchelper eliminated 0906d648aa; scheduling disabled by class 6e9fb11b3a; m.p never stale 8e0ec5ec09.
• Network poller: from the netFD select loop to the runtime-integrated epoll/kqueue/IOCP poller — Done: deadline timers merged: modtimer used by netpoll a86f549703, no re-creation of unchanged timers 86d375498f, memory barrier only if a timer fired 31e7842f3d, StorepNoWB 56421f26ef, no runtimeNano on the common path (negative duration = expired) 21f7f01289; nanotime wrappers moved to time/poll ff51353c38.
• Timers: timerproc goroutine → per-bucket heaps → timers on Ps — Done: timerproc not woken needlessly a9280fa2de; startNano refactor a1ee0a21cf.
• Channels and select — Done: races between close and len/cap ignored 83dfc3b001; makechan overflow multiplication check 286c7ae10c.
• sync.Map, atomic.Value and sync/atomic — Done: 32-bit MIPS alignment ca7c12d4c9; Map simplification 756c352963.
• Goroutine and M lifecycle: caches, ids, LockOSThread, Goexit, cgo extra Ms, deadlock detection — Done: lockedExt stays when G exits d0f8a7517a.
• Stop-the-world, safe points and GC–scheduler interaction — Done: gchelper eliminated 0906d648aa; scheduling disabled by class 6e9fb11b3a.

Other changes

• js/wasm sync callbacks internal — 6dd70fc5e3, f4f6594124, 3879ea54ed, eae5fc88c1, 0f0b10818b, 688667716e, a361ef36af, 2de53906e1 (GODEBUGCPU moved into GODEBUG=cpu.*), 5ee06f5471.
• timediv bitsets internal — 178a609fed.

Data structures and type metadata

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

emptyOne/emptyRest early exit in map scans, overflow-checked multiplication in make/growslice/makemap, growslice bulk barrier, reflect return-value scanning fix, MapRange.

• Hash map core: from the first hashmap.c to the 8-entry bucket design — Done: emptyOne/emptyRest markers let bucket scans stop early (4b05c01f9c, MegOneMap 8.91→5.53 ns), delete updates entries after the new last element (df2bb9817b), multiplication-with-overflow-check in makemap (e85b8db604), panic on uncomparable key type even for empty maps without growing the header (ed15e82413).
• Map growth, iteration order, overflow buckets and GC interaction — Done: early exit on emptyRest (4b05c01f9c), delete re-marks trailing empties (df2bb9817b), bucketCnt bounded scanning. Left open: delete used the “safe but non-optimal” choice of emptyOne in some cases (message of 4b05c01f9c).
• reflect.Call, MakeFunc, method values and argument-frame GC precision — Done: results scanning fix (ef50373983), method-func write barriers (e35a41261b), s390x method calls (0b994a9037), no write barrier copying results (7e987b7b33).
• reflect performance, caches and API additions — Done: MapRange (ede5958385), UnsafePointer IsNil fix (3b66c00857).
• memmove, memclr, duff routines and pointer-write atomicity — Done: ppc64x VSX memclr/memmove (aa9bcea390).
• internal/bytealg and string/byte comparison primitives — Done: arm64 Equal (de28555c0b), ppc64x asm (a0fad982b1, 6994731ec2, 23f7554194), linknames and trampolines (ef7ce57ac2, ad4a58e315).
• Slices and append: growslice, makeslice and string/slice conversions — Done: bulk barrier in growslice, no barrier on new slice, overflow-checked multiplication (96dcc4457b, 4363c98f62, 05166bf54d, e85b8db604, 3b091bf6cc).

Other changes

• Internal/cpu, panic and wrappers internal — internal/cpu variables in assembly (c15c04d9e8, 05c02444eb), concurrent stack detection (37ea182660), compiling_wrappers removed (41c0b9eb88), preallocated in/out arrays in methodfunc (72f099c36b), no write barrier in startpanic_m (9ed9df6ca2).

Diagnostics and knobs

From Diagnostics and knobs (Go 1.0–1.17)

Race on arm64, debug.ReadBuildInfo, GODEBUG=madvdontneed, mid-stack inlining traceback work, gctrace=2 removed.

• Execution tracer (trace v1): events, per-goroutine sequencing, annotations — Done: only maintenance: internal/traceparser reverted in cmd/trace (6d5caf38e3, Go 1.12). Left open: no new tracer features; the v1 design stays through 1.17.
• Race detector integration — Done: user-visible user-visible arm64 (978cfa8e46, 1.12) with arg maps for sync/atomic functions (c6e698d5dd). Left open: nothing noted.
• CPU profiler and runtime/pprof writers (legacy format to compressed protobuf) — Done: memory profile block size computed from sampled values (f9a4ae018d); “deleted” suffix stripped from maps (73b8e5f81b).
• GODEBUG, runtime/debug, debug log and traceback knobs — Done: user-visible debug.ReadBuildInfo returns module information (45e9c5538b); GODEBUG=madvdontneed=1 (22738f07c8); gctrace=2 removed (edc2d17086); proper panic tracebacks with mid-stack inlining and FuncForPC returning the innermost frame (af134b17da, 956879dd0b, 232c979309). Left open: nothing noted.
• Traceback correctness and inlining (diagnostic output) — Done: getArgInfo fixes (d5bd797ee5^1.8 1.8; fast path 13cd006139^1.11, 1.11), defers on LR machines (e391faded7^1.11), isSystemGoroutine stable mode (29b21ec4c3), gentraceback wrong g and morestack transition (c9986d1452, ae6361e4bd), inline-aware panic tracebacks (af134b17da) and encouragement of single-call-body inlining (13baf4b2cd). Left open: systemstack frame not included in the traceback (ae6361e4bd).

Other changes

• Runtime math helper internal — MulUintptr with overflow check (c9130cae9a); misc cleanups (fd7d3259c9, fa6639d626, 68527ff4fb, da0d1a44ba, e47c11d8b1, 1ba74448f2, 084f2eafcd, 8962b71c49).

OS layer, stacks and panics

From OS interface, stacks and panics (Go 1.5–1.17)

stack objects, windows/arm and AIX ports, GODEBUG=cpu., libSystem-backed syscall on macOS, MADV_FREE, ABI hygiene for runtime symbols.

• New and ported OS/arch targets, 1.5–1.17 — Done: windows/arm (d24ec86e4f, QPC time e3b4b7baad, 84066f1b0b, traceback/profile fixes 9ab2ffe8e9, 6764d7aeac, 1ca84deeb0), AIX (bf8e6b7027, 9f78aa7744, ff99a61e5e, 8f9902da26, 49be65eeba, 18b84cbd42, 3855fe7254, 976bab6003), openbsd/arm cgo (c52beb1087, 47a71d9d77, f95578cd5f), initial cgo for ppc64 (1135071b47), FreeBSD 12 ino64 syscall types (dc6eb200dd).
• Goroutine stack growth, shrinking, GC stack barriers and stack objects — Done: stack objects (cbafcc55e8), reduced pcvalue linear search with a 2x8 associative cache (7d6b5e340c).
• Tracebacks, symbol tables and runtime.Callers/CallersFrames — Done: traceback marks freshly allocated _defer (db1e8a9e1f), FuncForPC no longer crashes between functions (462e90259a), refined pcvalue cache (7d6b5e340c), windows/arm sigpanic tracebacks (9ab2ffe8e9).
• Defer, panic, recover and Goexit (runtime side) — Done: traceback shows whether a _defer was just allocated (db1e8a9e1f), no write barrier in startpanic_m (9ed9df6ca2).
• Signals: masks, forwarding, sigaltstack and the unified Unix signal layer — Done: sigInitIgnored nosplit (97f1535285), tgkill for raise (43f54c8d2e), abort check on Windows (9be01c2eab).
• vDSO, time sources and process-wide randomness — Done: ppc64x vDSO (dbd8af7472), refactored startNano (a1ee0a21cf).
• Darwin and OpenBSD move to libc; Solaris and AIX libcall; syscall wrapper layer — Done: libSystem for package syscall (a3b01440fe, be5f646dab, 9eb383e8f0), Solaris syscall to libc files (49be65eeba).
• Windows runtime — Done: windows/arm (d24ec86e4f), Syscall18 (e8df7df68f), case-insensitive env (f08352bd16), unminit/profile race (c216c3aa9f).
• CPU feature detection (internal/cpu), auxv parsing and GODEBUG=cpu.* — Done: GODEBUG cpu options (2de53906e1, 4fb8b1de3c, 3e0227f6a0, 980340ade7), ARM hw divide (2e8c31b3d2), cache-line padding (7b9c2c1950, 961eb13b67, 60f83621fc), AIX detection (cb07f492db), z14 (897e0807c3), constants typed (2556df0ac0, 21ac811924, bb3bf5bb53).
• Assembly-level runtime entry points: memequal/cmp/IndexByte, hashing, atomics and ABI wrappers — Done: internal/math.MulUintptr (c9130cae9a), whitespace in asm (b8ac64a581), Go prototypes in amd64 asm (3879ea54ed), ppc64x lightweight atomics (5c472132bf), CALLFN 8-byte copies (e945623930), ABI information (af1bfe0aa3, 4f3604d3f2), MADV_FREE (77f9b2728e), runtime.cputicks ppc64x (cfbe3cfbeb), arm64 8.1 atomics off on Android (efd229238a), iscgo unsigned load (e41fbc79cc), explicit argmap arglen (0098f8aeac), REFLECTMETHOD (204a8f55dc), no TLS before setup on iOS (a889aaf8bf), race with retaken P (e496e612b7), cgo panic alias (6096b85b13).
• Thread lifecycle, physical page size and scheduler-facing OS hooks — Done: MADV_FREE (77f9b2728e), semasleep timeouts (42257a262c).

Other changes

• other runtime/OS plumbing internal — all: use consistent shebang line across all shell scripts (c92354f46e)
• Linux, vDSO, time and auxv internal — user-visible runtime: replace calls to hasprefix with hasPrefix (b0dc54697b); user-visible runtime: don’t use linkname to refer to internal/cpu (cd7cb86d8e); user-visible runtime: fix heap pointer invariant rules in HACKING.md (d029058b59)
• cgo and C interop internal — runtime/cgo: added missing includes for errno.h to the windows gcc stubs (595bc63e8f)

Compiler frontend

From Compiler frontend (Go 1.10–1.17)

Binary export removed, -lang introduced, constant folding restricted to Go constants, typechecker tracing and new node dumper.

• dev.regabi: from *Node struct to the ir.Node interface and concrete node types — Done: OCMPIFACE/OCMPSTR ops removed (28fbbf4111, a0d6420d8b); alternative node dumper for debugging (5d444e36a6); labels represented as bare Syms (2dda040f19); TPTR32/TPTR64 merged into TPTR (62e5215a2a). Left open: nothing noted.
• Indexed export format and the export-data lifecycle — Done: the old binary export is disabled then removed (d546bebe34, 433496615f), the -iexport-style flags -i (b4150f7614) and -dolinkobj (965fa3b191) go; export of Func.Endlineno (c374984e99); inlining of (*T).M wrappers re-enabled (fa913a36a2). Left open: nothing noted.
• Constants: Go 2 number literals, evconst, untyped conversion and go/constant — Done: index-bounds error (a37d95c74a); non-Go constants not folded (1602e49701, eb6c433eb3). Left open: nothing noted.
• Language version gating (-lang) and language changes implemented in the frontend — Done: user-visible -lang flag 2e9f0817f0, validity check 7ebe35093d, default accept-all 69397422c0; //go:linkname allows bodyless functions (ca3749230b). Left open: “no consistent support for changes made before 1.12” (2e9f0817f0).
• Package initialization order, static initialisation and init functions — Done: sparse slice literals (6fff980cf1), static copy fix (4a1a783dda), hidden init in tracebacks (eafe9a186c), early init symbol (b52db19b98). Left open: nothing noted.
• Inlining-related frontend work: export of bodies, type switches, closures, devirtualization — Done: fa913a36a2. Left open: nothing noted.
• The legacy typechecker: error quality, alias/recursive-type handling and type checking order — Done: e6305380a0, 62c52a5ee1, a37d95c74a, 5538ecadca, 6761b1eb1b, e25823edce (typecheck tracing). Left open: “the more general problem remains” for alias cycles (e6305380a0).
• Lowering in order/walk and the shape of runtime calls emitted by the frontend — Done: 0e9f8a21f8, 5848b6c9b8, 389e942745, 020a18c545. Left open: nothing noted.
• checkptr instrumentation and compiler debugging flags — Done: e25823edce, e34f660a52, c68e3bcb03, 5185744962. Left open: nothing noted.
• Types package internals and type printing — Done: 62e5215a2a, 2d58fbac2f, 9e619739fd, 99e4ddd053, 16e6cd9a4d. Left open: nothing noted.
• Register-ABI plumbing in the frontend — Done: 16e6cd9a4d. Left open: ABI info not yet used.

Other changes

• Compiler flags cleanup user-visible — b4150f7614, 965fa3b191, 7e64377903 (-race/-msan only where supported).
• Intrinsify math/bits.Div on amd64 internal — 319787a528.
• Runtime capability variables internal — 75798e8ada.
• Soft-float OMUL internal — c92e73b702.
• Walk/typecheck overflow and ICE fixes internal — 42cc4ca30a (walkinrange called Int64() on constants over 2^63 producing bad rewrites), d397d4bffc, 706b54bb85, c03d0e4fec (samesafeexpr handles arithmetic), e3e043bea4 (OSLICEHEADER), 95a4f793c0 (labels not removed by deadcode), b2c397e537 (string to notinheap slice rejected), f2cd0fa7b7.
• Wrapper line numbers and -dynlink internal — f64385b720, debca77971, a1aafd8b28 (wrapper for error.Error method expression), 1ac3b06181.
• Housekeeping internal — 02b444bc1d, c5d38b896d, 34c58fe184, ef7212e2cf, 5ddb209120, e7f59f0284, 7b88b22acf, 9a8372f8bd (ambiguously-live logic removed), 5b2030cbca, 41c0b9eb88, 3f485e14b2, cc36b835e4 (expanded stack-frame errors), bc4a10d16c, e4c1feef74, 57c8eb92b7 (CLOBBERDEAD experiment removed, later resurrected as a flag by 8628bf9a97^1.17), 8b7cf898af.
• gc cleanups: fconv, evconst, noder internal — Minor cleanups in gc, removal of the flag argument from fconv, better names for conf functions, major evconst cleanup and a more direct noder.nod. (3b7b9dce43, 919d5aee22, 9c2e5f2971, 48dc42b6af, f6f27bfb97)
• AIX cgo_import_dynamic internal — Updated cgo_import_dynamic handling for AIX. (e1978a2d7a)
• Bulk rename internal — A bulk rename across the compiler. (bc43889566)

Middle end and SSA optimizer

From Middle end and SSA optimizer (Go 1.10–1.17)

Argument stack construction moved from walk to SSA, write barriers eliminated for non-heap stores, inlining cost tuned (57, single-call bodies, wrappers), ssa.html gained sources and CFGs, and bits intrinsics expanded (threads: Late call expansion, Write barriers, Inlining, Diagnostics, Arithmetic).

• Prove pass: unsatisfiability, partial-order facts, loop bounds-check elimination — Done: fix fence-post implications for the unsigned domain (09ea3c08e8); negative upper bound check for IsSliceInBounds (ea6259d5e9); overflow fix when deriving from x+d >= w (2e217fa726); avoid implicit bounds checks after explicit append checks (9f66b41bee). Left open: nothing noted.
• Escape analysis: the esc.go fixes, the escape.go rewrite, and the move to package escape — Done: self-assignment handling unified in esc.go (ff468a43be, 859cf7fc0f, 499fbb1a8a), mayAffectMemory fixes (4cf33e361a, 2d82465d18), sink-node positions (67ac554d79), unnamed parameters (be09bdf589). Left open: esc.go’s encoding limits, fixed by the rewrite.
• Inlining: budget, mid-stack inlining, closures, and what became inlinable — Done: single-call bodies encouraged (13baf4b2cd), call cost 57 (624e197c71), budget hacks removed (555d8c455a), autogenerated wrappers inlined (fa913a36a2), mid-stack tracebacks (69c2c56453). Left open: the mid-stack-inlining flag and its default are outside this unit.
• Late call expansion and the SSA side of the register ABI — Done: argument construction moved to SSA (2578ac54eb). Left open: calls still fully expanded at SSA build.
• DWARF location lists from SSA — Done: params get slots (fa31093ec4). Left open: nothing noted.
• Range loops, append and map idioms in walk — Done: []byte("...") (ceb0c371d9), struct/array key literals (a0f57c3fd0), copyRet allocs (5dbc67a99a). Left open: nothing noted.
• Rewrite-rule generator, typed Aux/AuxInt, and rule syntax — Done: randomized value order for testing (2b4f24a2d2), v.Pos.line warnRule (25b84c0155). Left open: nothing noted.
• Write-barrier elision and the writebarrier pass — Done: non-heap pointer elision (2140975ebd), memclrHasPointers (c8ca793176), slice-clear notinheap (6454a09a97). Left open: only freshly-allocated objects.
• Memory-op optimizations: memmove, Move/Zero, dead stores, nil checks — Done: amd64 disjoint memmove (c292b32f33), Move chain with VarDef (8607b2e825, a98bb7e244), nil-check use in dead-auto (54f9c0416a), AIX nilcheck (9fe9853ae5). Left open: nothing noted.
• Arithmetic strength reduction, divisibility and intrinsics — Done: bits.Mul, bits.Div, RotateLeft, c6118af558, 379d2dea72. Left open: Div intrinsic amd64-only.
• CFG and control-flow passes: branchelim, fuse, shortcircuit, phiopt — Done: fuse before branchelim (a55f3ee46d), CMOV load addresses (0b79dde112). Left open: nothing noted.
• Compiler front of walk/order: ordering fixes and the dev.regabi IR refactor (package walk) — Done: arg stack in SSA (2578ac54eb), order temporaries reuse (389e942745, 63e964e174), fe2c588b1c. Left open: nothing noted.
• Diagnostics for the optimizer: ssa.html, GOSSAFUNC and optimizer logging — Done: sources, CFGs, AST. Left open: nothing noted.

Other changes

• Frontend/race fixes internal — racy Config.Race (c180798956), symFunc init race (5cf2b4c2d3), constant string symbols emitted before parallel phase (df459d5e6c), racefuncentry/exit omitted when unneeded (4201c2077e), racewalk removal (14bdcc76fd), Deferproc/Newproc unexported (e7f59f0284).
• Rule and codegen fixes internal — OffPtr rule types (c96e3bcc97), a == a typo (9850ad045f), sNaN store-to-load forwarding (48af3a8be5), softfloat store types (63a3993a33), load+op with SymAddr (05bbec7357), OpArg decomposition order (04105ef1da), nil-check removal (669fa8f36a), walkinrange overflow (42cc4ca30a), append length overflow (38e7177c94), 0-size comparisons (f14067f3c1), memmove with wrong arg types (8f854244ad), convnop/appendslice refactors (c5d38b896d, c907a75494, d6e80069f3), VARDEF at top level (6933d76a7e), append(f()) conversion (dca769dca9), 15c4575293, 7a634034c8, 5e8beed149 (remove pointer arithmetic), source cleanups (0a87205809, 713edf8b31, 88c1fd642e, 85066acca1, 78c0e1f81d, 3813edf26e, 8c5c2b71f4, c35069d642, de31f637a9, c8b2ac6890, 0c706fddce, d924c3336c).

Backends and assemblers

From Backends and assemblers (Go 1.12–1.17)

Dominated by incremental lowering work (amd64/386/ARM/arm64/ppc64/s390x peepholes), arm64 constants without the literal pool, arm64 frame pointers and the first symabis plumbing for the future register ABI.

• Register-based ABI (ABIInternal) and ABI wrappers — Done: -symabis collection mode in cmd/asm (ba2e8a629b), compiler parsing of symabis (97e4010fd4), separation of data and function LSyms (a2e79571a9). Left open: the information is parsed but “doesn’t yet do anything” (97e4010fd4).
• amd64 lowering: read-modify-write, load-op, addressing modes pass, intrinsic-friendly rules — Done: RMW/loadop work above (705f3c74e6, b75c5c5992, 3bc34385fa, c6bf9a8109, 5f5ea3fd4d, b40db51438, 24e51bbe64, b1f656b1ce, 623c772814), MULQ overflow intrinsics (a1ca4893ff), RotateLeft (5ac2476748), simplify asm generators (4545fea4fc, d17ac29158, 2294e3ebd3, ccc337d8ee), correction of load-compare combination (9f291d1fc3). Left open: address mode rules are order-sensitive.
• arm64 backend and assembler — Done: constant synthesis (644ddaa842, 86ce1cb060, c430adf136, 808186203b), indexed FP and atomics (84feb4bbb7, 1018a80fe8, 26d62b4ca9), FRINTND/Abs/Copysign/Float bits (8149db4f64, 2e5c32518c, a19a83c8ef), madd (b444215116), frame pointer (8f4fd3f34e). Left open: nothing noted.
• PPC64 / POWER backend and assembler — Done: rule improvements, indexed addressing, record-form compare avoidance, Mul/TrailingZeros/OnesCount intrinsics (see hashes above), float zero (f776d51bf7), PCALIGN (bdba55653f), AIX 64-bit addressing (041526c6ef, 4295ed9bef, 503091a77c, 20ac64a2dd). Left open: nothing noted.
• s390x backend: compare-and-branch, intrinsics, assembler — Done: OnesCount, RotateLeft, 6f9b94ab66, f94de9c9fb, 4f15b54780 (int32 overflow in moves), abd1dde1f7 (no-op), VMSLG (3f3142ad99). Left open: nothing noted.
• 386, ARM (32-bit), MIPS/MIPS64 and the 387 removal — Done: the 386 and ARM items listed through a0a7e9fc0c, 3933302550, 2b69ad0b3c, MIPS fix 6a64efc250. Left open: nothing noted.
• WebAssembly backend — Done: 6c631ae227, 52cae2763e. Left open: nothing noted.
• math/bits, atomic and runtime intrinsics (cross-architecture) — Done: a1ca4893ff, 899f3a2892, dd789550a7, 5ac2476748, 6f9b94ab66, f94de9c9fb, 9aed4cc395, 23578f9d00, 8149db4f64. Left open: nothing noted.
• SSA infrastructure passes: layout, regalloc, scheduling, flagalloc, block shape — Done: bce1f12225, 13d5cd7847, 3068fcfa0d, ff9481ec0d, 5403b8eceb, f493e55723, a3593685cf. Left open: nothing noted.
• Safepoints, unsafe points and stack maps for asynchronous preemption — Done: only call-site clobbering experiment (c8545722a1, 360771e422). Left open: “stack maps at non-call safepoints are still imprecise” (c8545722a1).
• Debug info generated by the backend: statements, location lists, line tables — Done: 7b88b22acf, 2b58ca6e3d, b3294d9491, 321a3d6e85, 72496e35ce, 01a1eaa10c, 9a7e70e34f (OpArg scheduled earlier for debugging). Left open: nothing noted.
• Assembler directives and tooling: PCALIGN/ALIGN, FuncInfo flags, prologue handling — Done: PCALIGN on ppc64 (bdba55653f), parse refactor (52b2220559). Left open: nothing noted.

Other changes

• Cleanups and fixes folded from the uncited list internal — ppc64 VPERMXOR in the assembler (048580d341); regalloc-neutral OpArg scheduling for debugging (9a7e70e34f).
• amd64/386/ARM micro-optimizations internal — many Ben Shi and others peepholes: b40db51438, 24e51bbe64, 0a382e0b7f, d17ac29158.
• -race/-msan restriction user-visible — only supported where they work (7e64377903).
• AIX/ppc64 addressing internal — 041526c6ef, 4295ed9bef, 503091a77c, 20ac64a2dd.
• Compiler internal — 8aee193fb8, 9e277f7d55, c3304edf10, ed2f84a94e, e7f5f3eca4, 7ab4b5586d, 441cb988b4, 84374d4de5, 477b7e5f4d, c0281afd87, 15265ec421, 0ad332d80c, 69c2c56453 (mid-stack inlining tracebacks), 69c5830c2b, 3a3b98fdf9, c5414457c6, abd1dde1f7, 05bbec7357, 1fb596143c, 5403b8eceb, 3bab4373c7, 653a4bd8d4, 95dda75bde, 4b78fe57a8, 9774fa6f40, 096229b2ec, 2db1a7f929, 891f99eb43, e546ef123e, bd483592a2, 1fb596143c, 7b88b22acf, 4545fea4fc, a2e79571a9, d0cbf9bf53^1.13.

Linker and object files

From Linker and object files (Go 1.10–1.17)

AIX/XCOFF port, stable ABI0 vs ABIInternal separation and ABI aliases in the object file, linker memory slimming (cold Symbol fields), deadcode-before-mangling.

• Linker performance and memory engineering — Done: fewer allocs in Archreloc by returning the value instead of an out pointer (328adf9d62: 1.8%), avoiding Reloc copies in range loops (bc276c585b, 48-byte struct), cold-field splitting (above), 3d72ca9908 direct max-pc in findfunctab. Left open: nothing noted.
• pclntab, funcdata and pc tables — Done: 3d72ca9908 simplifies findfunctab max-pc; af134b17da proper tracebacks with mid-stack inlining (runtime reads inline tree funcdata that the linker lays out); 9dac0a8132 sets the traceback address to a deferreturn call on signals, eafe9a186c hides compiler-generated init functions from tracebacks via a funcID wrapper class. Left open: nothing noted.
• Dead-code elimination and method pruning — Done: type-name mangling moved after deadcode (618bfb28dc, 9c833831b2) so fewer symbols get renamed, ffbf479ae1 removes statictmp variables from the symbol table. Left open: nothing noted.
• DWARF generation in the linker — Done: a0f5d5f883 refs point at the typedef entry, global variable DIEs moved to their compile unit (1c8943bd59), ec4ae29f52 abstracts DWARF metadata symbol lookup, 75a0b9dbf3 DWARF64 for AIX. Left open: nothing noted.
• Symbol ABIs: stable ABI0 vs ABIInternal in the linker and object files — Done: c5718b6b26, 685aca45dc, 1794ee6829, c0281afd87 (obj writer stops de-duplicating symbols). Left open: the ABIs are identical; wrappers are aliases “until the ABIs diverge”.
• Mach-O and Darwin support — Done: 66bb8ddb95 silences a bogus Xcode .tbd warning, cfac65bf2f omits deprecated linker arg for iOS. Left open: nothing noted.
• PE / Windows — Done: aa311fecda windows/arm, 8256bcdae0 moves .rel into .text, 41fd4c88ad no _GLOBAL_OFFSET_TABLE_ on windows/386. Left open: nothing noted.
• AIX / XCOFF — Done: initial port (a3a69afff8, 269e531917), XCOFF fixes (63ac89bfb1, 3f9efe7500, b41cdc4a59, 4295ed9bef, 9a3c1a1bc8), cebf9d47cf. Left open: only internal linking (external linking disabled).
• WebAssembly — Done: 48e22da1d2 fixes the deferreturn location on wasm. Left open: nothing noted.
• Host object loading and external linking — Done: 484fc06849 doesn’t link sections not named .o, 281ce28c50 in-package syso linking, 35435b27c4 closes input files, 1135071b47 initial cgo support for ppc64. Left open: nothing noted.
• Linker restructuring (1.10 code health and error reporting) — Done: 66065c3115 clearer unresolved-symbol error, 14560da7e4 file-local symbols start at version 10, 9555769aa5. Left open: nothing noted.

Other changes

• Small items internal — aa4fc0e736, da0d1a44ba (library idiom sweeps), 94f7795d05 (experiment isolation in cache key), bed88f4e81 (error messages for external linking on ppc64).
• GODEBUGCPU user-visible — a5248acd91 enables GODEBUGCPU in non-experimental builds.
• Statictmp symbols internal — ffbf479ae1 removes statictmp variables from the symbol table.
• Mid-stack inlining tracebacks internal — af134b17da; eafe9a186c hide init functions.
• Silence Xcode warning user-visible — 66bb8ddb95.
• Flag docs user-visible — 8b7cf898af documents more compiler/linker flags.
• .init_array internal — a11aa2aaec only when non-empty.
• Dedup pctab, mid-stack — see threads.
• relocsym comments internal — Improved relocsym comments. (c7271c0c25)