Go 1.17

Register-based ABI on amd64. The dev.regabi split of the compiler into packages. dev.typeparams: types2, -G, irgen and first stenciling, all off by default. Pacer extracted into gcControllerState. unsafe.Add/unsafe.Slice. Slice-to-array-pointer conversion. windows/arm64. go/defer wrapped into closures.

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)

Pacer extracted into mgcpacer.go as gcControllerState, sweep completion unified, incremental arena preparation, stack-object GC data only.

• Concurrent sweep and proportional sweep — Done: sweep completion unified: runtime.GC now blocks on all sweep paths (a25a77aed2, 1b736b3c19). Left open: nothing noted.
• GC pacer: trigger controller, assists and background utilisation — Done: pacer extracted into mgcpacer.go with gcControllerState methods (f5f7647107, f2d5bd1ad3, 728e3dc6f9, 2d4ba2601b, 9bce7b70fd, e7ab1a5ba8, 7ec7a3cf33, e9cc31e736), minimum scavenge fraction constant fixed (14ade57ab8). Left open: the trigger-ratio model itself; this refactor is the preparation for the 1.18 pacer redesign.
• Stack scanning: conservative, precise by frames, stack barriers, hybrid barrier, async safe points — Done: stack-object metadata emits only GC data instead of the full type descriptor, avoiding keeping the descriptor and everything it references alive (02ab8d1a1d); GC testing helpers for moving stacks (4e1bf8ed38, 97b3ce430b, 41e8a9f1cf). Left open: nothing noted.
• Precise heap scanning: type information, the heap bitmap and GC programs — Done: scanobject hbits advance folded into the loop (72483de87a). Left open: nothing noted.
• Size classes, tiny allocator and mcache/mcentral — Done: simplified divmagic (4662029264), alignment doc fix (a8a85281ca), tiny allocs top-aligned in race mode (2c05ba4ae0), large clears broken into chunks so preemption can occur (0bbfc5c31e). Left open: “huge” clears remain non-preemptible while a single clear runs (explicit in the commit message: zeroed by chunks “so that preemption can occur”).
• The bitmap page allocator — Done: arenas prepared incrementally via sysMap in grow for strict-overcommit systems (bd6aeca968), pageAlloc handles sysAlloc failures (0e8a72b62e). Left open: nothing noted.
• Scavenger: returning memory to the OS — Done: scavengePercent min fraction constant fix (14ade57ab8). Left open: the 1.18 redesign (controller-paced) follows.
• Heap address space: contiguous arena to sparse arenas — Done: incremental arena preparation, 4 MiB arenas on iOS (bd6aeca968, e03cca6407). Left open: nothing noted.
• Finalizers and span specials — Done: register-ABI finalizers (f009b5b226), abstracted specials list iteration (1ef114d12c). Left open: nothing noted.
• Mark work distribution: parfor, work buffers, gcWork and root jobs — Done: root bases computed in gcMarkRootPrepare (82e4a6310b), nFlushCacheRoots removed (94817890c2). Left open: nothing noted.
• Memory statistics and accounting — Done: internal pacing stats moved into gcController (f2d5bd1ad3). Left open: nothing noted.
• Allocation-site profiling and GC debugging modes — Done: clobberdead check in GC (0ccdcb2102), GC testing helpers (4e1bf8ed38). Left open: nothing noted.

Other changes

• Misc internal — regabi finalizers, clobberdead, KeepAlive doc warning that it is not an unsafe.Pointer workaround (fd45e267c2), formatting (e224787fef, d434c2338b, 8a4b7294af).
• Alignment info in sizeclasses comments internal — Added alignment information to the sizeclasses.go comments. (735647d92e)

Scheduler and concurrency

From Scheduler and concurrency runtime (Go 1.0–1.17)

Value.Swap/CompareAndSwap, findrunnable refactors and spinning documentation ahead of 1.18, runqdrain, Pool random stealing; threads: scheduler core, atomics, Pool.

• The G-M-P scheduler: from global-lock M:N to per-P run queues, spinning Ms and work stealing — Done: findrunnable refactoring in preparation for the 1.18 spinning rework: work stealing in its own function 60ab197bc2, spinning coordination documented 13368ab56a, timer and spinning rechecks reordered f6e7fe2711, dbade774c3, 4d56576ec0, tryWakeP removed 800fb11efb; runqdrain for GC workers fbb600b283/3b304ce7fe; gFree lists moved in batches between P and global 1f7a01459b; pidleget/pidleput under sched.lock 2520e72d3b; exitsyscall0 race e0d029f758; p struct padding 55d7dcc3cd. Left open: the findrunnable commit messages cite #43997 and #44313 (spinning M races) as unresolved.
• Preemption: cooperative stack-check preemption (1.2) to signal-based asynchronous preemption (1.14) — Done: R15 saved before checking AVX state c49c7a675a; SPWRITE functions in traceback accounted for (not async-preempted since assembly functions never are) 03886707f9; preemption disabled in addtimer aa26687e45.
• Network poller: from the netFD select loop to the runtime-integrated epoll/kqueue/IOCP poller — Done: netpollopen error handled in poll_runtime_pollOpen ebb92dfed9, netpollclose documented 437d229e2a, pollDesc lock partial edges e8e425cb23, 0e0a872a76^1.16.
• Timers: timerproc goroutine → per-bucket heaps → timers on Ps — Done: findrunnable timer computation moved f6e7fe2711; adjustTimers counter removed bfbb288574, 798ec73519; addtimer without preemption aa26687e45; time.now in assembly on linux/amd64 d09947522d with walltime removed 42953bc9f5, b15372f39b, c96fec9036.
• sync.Pool — Done: random victim selection when stealing d5d24dbe41.
• sync.Map, atomic.Value and sync/atomic — Done: user-visible Value.Swap and CompareAndSwap 2422c5eae5.
• Runtime lock ranking (static lock order checking) — Done: partial order self-check c41bf9ee81; pollDesc edges e8e425cb23; forceGC to traceStackTab edge d75fbac54d.
• Goroutine and M lifecycle: caches, ids, LockOSThread, Goexit, cgo extra Ms, deadlock detection — Done: zero-sized frame check moved to newproc1 352d329c44; ncgocall made a global counter d01bc571f7.
• Stop-the-world, safe points and GC–scheduler interaction — Done: runqdrain for GC mark workers fbb600b283/3b304ce7fe.

Other changes

• Misc internal — f009b5b226 (register ABI for finalizers), 9c54f878d2, b110a43628, 095ba22597, 31d2556273, b36596b14f, d09947522d.
• reflectcall signature and idle M recheck internal — Updated the reflectcall function signatures and skipped the work recheck for non-spinning Ms. (bc489dd6d5, ecfce58965)

Data structures and type metadata

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

Register ABI support in reflect and runtime assembly (internal/abi, makeFuncStub/methodValueCall), wyhash 32-bit fallback, varint type names, VisibleFields, slice-to-array-pointer conversion, CanConvert.

• Hash map core: from the first hashmap.c to the 8-entry bucket design — Done: bucket type descriptor loosened (15085f8974), mapassign_faststr overwrites existing keys (23ffb5b9ae), pointer arithmetic syntax simplified in mapaccess (0da9eff503). Left open: nothing noted; the 8-slot bucket stays until Swiss tables.
• Map fast paths and compiler/runtime specialization — Done: mapassign_faststr fixed to overwrite existing keys (23ffb5b9ae).
• Hash functions and algorithm tables: memhash, AES hash, fallback hash — Done: wyhash fallback for 32-bit (78f9015236). Left open: nothing noted.
• Compiler-generated equality and hash functions — Done: hash loop reorganized, unaligned-load guard (617383377f, 873401df5b), memequal_varlen referenced as ABIInternal (411860251e).
• Runtime type descriptors: layout, shrinking and name encoding — Done: varint name lengths (287025925f), GC prog symbols content-addressable (e99dfb0e5c), no reflect data for method types (1d9a1f67d5), typesByString uses all methods (2169deb352), unsafe.Pointer package path fix (40254ec0db), reflectdata.WriteType unexported and LinksymOffsetExpr for TypePtr/ItabAddr (03a875137f, 4c835f9169), bucket type tweak (15085f8974), internal/abi created (baa6c75dce).
• Interface values, itabs and type assertions — Done: register-ABI-aware paths (849dba07a5). Left open: type switches and assertions had no per-site cache yet (appears in 1.19+).
• reflect dynamic types: ArrayOf, ChanOf, MapOf, SliceOf, FuncOf, StructOf — Done: user-visible ArrayOf panics on negative length (d7cc2f1d7c), ArrayOf/StructOf regressions 7473a6a0eb (stack overflow in haveIdenticalUnderlyingType).
• reflect.Call, MakeFunc, method values and argument-frame GC precision — Done: register-ABI reflect.Call (see next thread).
• Register ABI support in reflect and runtime assembly (Go 1.17) — Done: internal/abi (baa6c75dce), reflect register algorithm (28c5fed557, a2f7067233, 34b87b4a1a, cda8ee095e, c5a1c2276e, 51cd074c59, ef36e4fd0e, 9d46ee5ac4, 4fb74e0555, 41cf18eda7, d446cb7cff), regabiargs assumption (27d306281c, 8cfbf34dd9), wrapper avoidance (849dba07a5, 8f4c5068e0, 411860251e, 45e87cd3ec). Left open: register ABI stays an experiment; reflect register count variables must be flipped when it becomes default (message of c5a1c2276e).
• reflect performance, caches and API additions — Done: user-visible VisibleFields (009bfeae86), IsExported (b83d073e9e), slice→array pointer conversion (760d3b2a16), CanConvert (48c88f1b1b), IsVariadic cache (6cadfe2fee), New of a go:notinheap type panics (554d2c4f06); shared conversion panic (0fd20ed5b6), documentation of convertibility (cf4e3e3d3b). Left open: Value still escapes in many paths (addressed in 1.18+ per the later threads).
• memmove, memclr, duff routines and pointer-write atomicity — Done: ABIInternal ports (849dba07a5).
• internal/bytealg and string/byte comparison primitives — Done: ppc64x Index (8009a81f7a, 54af9fd9e6), ABIInternal ports (8f4c5068e0).
• Slices and append: growslice, makeslice and string/slice conversions — Done: slice→array pointer conversion in reflect (760d3b2a16).
• Strings: concatenation, conversion and printing helpers — Done: consistent concatstring entry points (35a8bbc9ea).
• internal/reflectlite and checkptr — Done: nil pointers in checkptrAlignment (b39e0f461c).

Other changes

• Misc internal — types constructors preferred over typecheck (addade2cce), duplicate go:build line (abc56fd1a0), InterfaceData documented as low-entropy (c309c89db5), faster binary-search midpoint (7af821a661, 20.3→16.6 ns), hex prefixes in traceback debug (a1e9148e3d), fa3a121a79^1.14 version parser (Go 1.14).
• Outdated comment update internal — Updated an outdated comment. (ce76298ee7)

Diagnostics and knobs

From Diagnostics and knobs (Go 1.0–1.17)

More metrics (scheduling latency, allocs/frees); block profile bias fix; mem profiling disabled when unreachable; race on openbsd/amd64 and register ABI for race calls; GOEXPERIMENT refactor with regabi sub-experiments on by default and experiments in runtime.Version().

• Race detector integration — Done: user-visible openbsd/amd64 (b3b65f2176); register ABI: racecallbackthunk ABIInternal, X15 zeroed in racecall, BX instead of R15, and raceread/racewrite/racewriterange use the actual internal ABI (e79c2fd428, 946351d5a2, a4dac8bd22, 0a510478b0); racefuncenterfp removed (87d29939c8). Left open: nothing noted.
• CPU profiler and runtime/pprof writers (legacy format to compressed protobuf) — Done: user-visible block profile bias corrected by aggregating short events as longer, less frequent events (0ae9c3b98b, 1.17); memory profiling is disabled when runtime.MemProfile is unreachable in the linked binary (18510ae88f, 1.17); cpuprof handles nil gp (c80da0a33a); writeProfileInternal common code (79d03ad739). Left open: nothing noted.
• Heap profile accounting and MemStats — Done: next_gc/last_next_gc moved to gcControllerState as heapGoal/lastHeapGoal (3eaf75c13a). Left open: nothing noted.
• runtime/metrics — Done: user-visible scheduling latency distribution (bedfeed54a, approximation by sampling); additional allocation metrics /gc/heap/allocs:bytes|objects and frees, filling TotalAlloc (897baae953); tiny allocs metric (0b9ca4d907). Left open: nothing noted.
• GODEBUG, runtime/debug, debug log and traceback knobs — Done: GODEBUG=scavenge mode removed (9c54f878d2); mcall, morestack, asmcgocall no longer treated as top of stack (5ecd9e34df, 776ee4079a, a54f7fc0fd), SPWRITE ignored in syscall functions (02e5a8fdfc). Left open: nothing noted.
• GOEXPERIMENT handling (objabi, buildcfg, goexperiment) — Done: user-visible constants consolidated (b675e52e95); baseline moved to objabi (cf2396c70e); regabi sub-experiments enabled by default in turn: regabiwrappers (fd3612e433), regabig (bbb510ccc9), regabireflect (88655480f3), regabidefer (af8a176e91), regabiargs (9dd71ba913); regabi an alias (14dbd6e776) and enabling regabiargs (43466399cb); Android baseline included (9c12f1b433); bad GOEXPERIMENT sets Error instead of panicking (e15d1f4e64); ParseGOEXPERIMENT helper for go env validation (c95464f0ea); experiments reflected in runtime.Version() (5159c83641). Left open: go env GOEXPERIMENT support was the next step (c95464f0ea).
• Traceback correctness and inlining (diagnostic output) — Done: arg maps for unstarted goroutines (38c129b4f0^1.13), multiple frames per PC for tsan (a14efb1be3^1.14), faulting-line fix (9ee6ba089d^1.14), top-of-stack handling (5ecd9e34df, 776ee4079a, a54f7fc0fd). Left open: nothing noted.

Other changes

• allgs encapsulated internal — d85083911d.

OS layer, stacks and panics

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

register-ABI preparations in assembly, windows/arm64 port, cgo.Handle, openbsd/386 and arm on libc, SPWRITE/TOPFRAME-driven traceback, regabidefer prerequisites.

• New and ported OS/arch targets, 1.5–1.17 — Done: windows/arm64 (3527caa7d6, 427bd7599d, c7c6c113be, 16330817aa, a25d1d45d9, 78afca22c9), cgo for openbsd/mips64 (f68878f0fc), GOARCH=loong64 reserved (2b00a54baf). Left open: windows/arm64 is “intended to land in the Go 1.17 cycle” as a stack of CLs (3527caa7d6).
• Goroutine stack growth, shrinking, GC stack barriers and stack objects — Done: stack growth loop fix (287c5e8066); 49add6ad90 fixes spurious stack overflow detection, fbed561f8a resets an accidentally set stack poison flag, 97b3ce430b stops gcTestMoveStackOnNextCall from doubling. Left open: nothing noted.
• Tracebacks, symbol tables and runtime.Callers/CallersFrames — Done: SPWRITE and TOPFRAME driven traceback (fbe74dbf42, 54da3ab385, 5ecd9e34df), unified asmcgocall/systemstack traceback setup (01f05d8ff1), non-strict InlTreeIndex lookup in Frames.Next and expandFinalInlineFrame (e4a4161f1f, aad13cbb74), funcID-based abort detection (298975c634, ff614b13d9). Left open: the unwinder was still the monolithic gentraceback; the iterator-based replacement came later (see status link).
• Defer, panic, recover and Goexit (runtime side) — Done: regabidefer prerequisites (c847932804, e0ce0af6ef, 585b52261c), deferreturn frames checks, reflectcall ABI0 on amd64 (d8306ee1f9), gosave deleted (8fa84772ba, b110a43628), jmpdefer handled by SPWRITE (fbe74dbf42), direct unlockOSThread instead of a defer in Windows syscalls to avoid nosplit overflow (4dbad79510).
• Signals: masks, forwarding, sigaltstack and the unified Unix signal layer — Done: sigpanic0 on all OSes (2698be4905), ppc64 signals with cgo and callCgoSigaction (d9e068d289), CPU profiling disabled before removing SIGPROF handler (57aaa19aae), Windows non-Go thread signal aborts (cd28ca3a4e), Windows SEH on arm64 illegal instruction (70546f6404), macOS sigNoteSleep EINTR loop (77aa209b38).
• Asynchronous preemption: signal plumbing, injected calls and per-arch support — Done: save R15 before checking AVX state (c49c7a675a), gp==nil check before preemption state (98dd205fa4), SIGPROF handler ordering (57aaa19aae), avoid preemption when returning from Go to C (70fd4e47d7).
• cgo runtime support: pointer checks, callbacks, extra Ms, C-to-Go call path — Done: runtime/cgo.Handle for managing Go values across C (972e883925), unified C→Go ABI transitions (7ad496b6f5), cgocallbackg called indirectly (d3853fb4e6), setg_gcc in crosscall_amd64 (63de211014), msan unpoisoning of cgoCallers (7aeaad5c86), ppc64x crosscall2 (bade680867), needm bypasses ABI wrapper on Windows (fef5a15396). Left open: nothing noted.
• Shared-library and buildmode entry points (c-archive, c-shared, plugin, shared) — Done: Windows amd64 lib entry stack alignment and refactor (e0fae78e1d, 3e0b1cdb5d), arm64 Windows lib entry in 16330817aa.
• vDSO, time sources and process-wide randomness — Done: PPC vDSO g clobbering (16e82be454), Windows time constants and files consolidated (e51246c881, b36596b14f), removal of linux-amd64 walltime function (b15372f39b), nanotimeQPC called normally (6639bb894d, 4deaa6a178), Plan 9 hashkey init (a95454b6f3).
• Darwin and OpenBSD move to libc; Solaris and AIX libcall; syscall wrapper layer — Done: openbsd/386 and arm libc (listed above), Darwin entersyscall (700b73975e), ABIInternal marking (bfc7418e6d, c430313992), osyield nosplit on OpenBSD (02699f810a), raise nosplit ( is 1.15).
• Windows runtime — Done: windows/arm64 (3527caa7d6, 427bd7599d, c7c6c113be, 16330817aa, 76ab626bfc), long paths without fixup on Windows 10 1607+ (b8371d495b), Windows callback improvements for the register ABI (44dd06670f, 4356e7e85f, 836dbdb15b, 639cb1b629, ab02cbd29f), windows/arm fixes (75e273fc2c, 91cc484ea9, 5421c37a1d, c4b771348c, 080119799b, fbe74dbf42), profiler finds g by SP (ece954d8b8), abort crashes earlier (38672d3dcf), setlasterror removed (678568a5cf), non-Go-thread signal abort (cd28ca3a4e).
• CPU feature detection (internal/cpu), auxv parsing and GODEBUG=cpu.* — Done: LSE atomics on arm64 (07ff596404), internal/atomic extended to match sync/atomic (af1789a61c).
• Assembly-level runtime entry points: memequal/cmp/IndexByte, hashing, atomics and ABI wrappers — Done: the ABI list above, runtime.mcall regabi (f8892147bd), atomics extended (af1789a61c), 07ff596404, 4c9791299d, aa0388f2ed, 7764ee5614 (mips64x nil-g check fix), f0be3cc547 riscv64 unbreak, ab331c0254, 07ef313525, d4b2638234 (gofmt).

Other changes

• other runtime/OS plumbing internal — cmd/compile: process //go:linknames after declarations (2d6ff998ed); cmd/compile: allow conversion from slice to array ptr (faa4fa1a6e)
• BSD, Solaris, AIX, Plan 9, NaCl internal — user-visible runtime: use pipe2 for nonblockingPipe on dragonfly (ee2a45e5fb)
• Linux, vDSO, time and auxv internal — user-visible runtime: fix formatting (cae68700cc)
• Document internal/sys internal — Documented and cleaned up internal/sys. (8ac23a1f15)
• Debug call protocol for register ABI internal — Updated the debug call protocol for the register ABI. (a89ace106f)

Compiler frontend

From Compiler frontend (Go 1.10–1.17)

The largest frontend restructure: dev.regabi (Node interface, base/ir/typecheck/noder/inline/staticdata/reflectdata/pkginit split, go/constant), dev.typeparams (syntax type parameters, types2, -G, irgen, first stenciling), unsafe.Add/Slice, and typecheck info in export data.

• dev.regabi: from *Node struct to the ir.Node interface and concrete node types — Done: the entire dev.regabi sequence above, Nov 2020 to Jan 2021: getters/setters d166ef6876→acb4d1cef1; interface 41f3af9d04; concrete node types 862f638a89, c4bd0b7474, ffa68716a0, 9a5a11adfa; visitors and generated methods 0d1b44c645, 2cec6c4a8c; removal of Left/Right 14d667341f, f9d373720e; Nodes as slice 114af2a044; ir.Ident/BasicLit/ConstExpr (63bc23b545, c8610e4700, a2058bac21); Name.Opt moved to Name (289da2b33e); OSTMTEXPR added (45f3b646d4) then removed in April (7735ec96c1); OSELRECV removed (aeedc9f804); OBLOCK/OEMPTY merged (ec5f349b22, ecc8d15bc5); ONEWOBJ removed (ab3b67abfd); TailCallStmt added (87845d14f9); ir.StaticValue/OuterValue made safer (e09783cbc0, 9aa950c407). Left open: IR still carries both syntax-derived nodes and typechecker-created nodes; ir.CurFunc and the Ntype mechanism survive (33801cdc62, 3512cde10a only reduce their use); the old typechecker still runs after noding.
• dev.regabi: breaking up package gc into base, ir, types, typecheck, noder, inline, staticdata, reflectdata, pkginit — Done: all of the above (see hashes), plus linksym helpers so ir/staticdata/reflectdata do not need *ir.Name for symbols (25c613c02d, ec59b197d5, 0ffa1ead6e, 4a4212c0e5, 82b9cae700), ir.Pkgs trimmed (7e0fa38aad), go.map/go.track symbols created directly (a2f825c542), NewNamed and setUnderlying moved into types (f37aa5e4e2, 63a6f08b39). Left open: noder was still the legacy syntax-to-IR walker alongside the new types2 irgen (see generics thread); gc still hosts Main, ssagen glue and many leftovers.
• Indexed export format and the export-data lifecycle — Done: type information on exported bodies (1129a60f1c), described as an enabling change for generics: “the current typechecker can mostly go away in favor of the types2 typechecker”; closures exportable (1760d736f6, 5f3dabbb79), inlining of closure-containing functions disabled for now (8027343b63); ABI export (67d565d281); struct-field note info and separate param/field encoding (c7d708e42e, e12b0afa54); nil exported simply (c6de5d8d1f), iexport avoids map[ir.Node] (e885df2731), export debug mode (b60a3a8cfb), OSLICE2ARRPTR exportable (5f1df260a9), method-expression import (6d8ba77896), duplicate-import detection (b6df58bd1f), width fix for imported types (fee3cd4250), re-export of parameters (d89705e087), exportWriter.qualifiedIdent tightened (cb34026a95). Left open: the format still serializes the old ir node tree; generic bodies and shapes need a different carrier.
• Generics bring-up in the compiler (dev.typeparams): parser, -G, types2, irgen, first stenciling — Done: parser/syntax/-G 617b633917, b627988b0c, 48755e06aa, 73f529845c; types2 + importer ca36ba83ab, type-check generic code 87eab74628; scaffolding 6b4da14dd3, 5aff757efc; irgen ef5285fbd0; types2 Sizes matching the compiler’s struct padding (2e8f29b79d); OLIST for multiple type args (3d5c715bf2), generic type arg in call parse (13a7412983); first stencils dcb5e0392e onwards; type info threaded into types and ir (2440dd457a, 0aafd69124); allMethods replaces types.Interface.Fields (a4b8241d97); RParams overhead reduced (519f223aa2); comparable in constraint (832a01aad4); types2.Instantiate for imports, “experimental … not executed unless we enable generics” (9e0facd26e). Left open: generic code not accepted without -G; type lists vs. ~ unions only reached the parser late (4bbe046aad); “inlining functions with closures disabled for now” (8027343b63); generic export/import and dictionary-based sharing do not exist yet — every instantiation is a separate full stencil.
• types2 port of go/types: reviews, error-message parity and language-version support — Done: initial check-in ca36ba83ab; review series above; compiler-message mode 87bc85a846; language-version support 1ff2fdaaf1; -lang passed in 721488498a; sorted-methods criteria shared with the compiler (6923019a71, 5347241b5e); constant overflow 8fbdacf64c, 0123c9b321; types2.Instantiate 9e0facd26e; fixes from all.bash, e.g. tag-less fields copying the last tag and switch case-scope end (44d1a8523a); decl-cycle resolution aligned with go/types (6521c7b378); delayed recording of untyped operands against type parameters (51e4bb236c, 8f19394b62); type-switch with type parameter case (2c25cd5ba7); removal of pointer designation / implicit type arguments / disabled type-list code (fbc4c6a3ae, c4f0da5750, 9546596d77). Left open: CompilerErrorMessages explicitly “needs to be removed” later by adjusting either typechecker or tests (87bc85a846); types2 is not used outside -G.
• The syntax package: parser, scanner, source reader, positions and error recovery — Done: generics parsing and tree changes (617b633917, b627988b0c, 73f529845c), printing of channel types and of type parameters/lists (e9e58a4d49, a99ff24a26), Pos methods and testing helpers (5e46c6a10f, 6ff16fe3ee), syntax.Walk visitor moved from types2 (d017a1b649), ShortString removal (822aeacd9e), exported NewName (3a912f279f), ~ operator and union elements (4bbe046aad, 4638545d85), ...-without-type message (a63ff398d5). Left open: generics still gated by AllowGenerics (set when -G).
• Constants: Go 2 number literals, evconst, untyped conversion and go/constant — Done: the go/constant switch (742c05e3bc, 7d72951229, 259fd8adbb, 6a4739ccc5); types2 limits integer precision to 512 bits then 2048-bit overflow error (370e9f5843, a59cb5109d) and compiler refuses excessively long constants (c910fd7b77). Left open: old typechecker still folds via ir.ConstExpr nodes.
• Language version gating (-lang) and language changes implemented in the frontend — Done: user-visible unsafe.Add/Slice fadad851a3, 14056d0d00, 962d5c997a, 4bb0847b08; array-pointer slice conversion 5f1df260a9, a9705e157b; types2 language-version support 1ff2fdaaf1, 721488498a, f37b0c6c12, ddec18cf82. Left open: version checks are per compilation, not per file (the go:build-based per-file model arrives in 1.21).
• Package initialization order, static initialisation and init functions — Done: initorder state off Nodes (7fde0d2b50), 68e6fa4f68, pkginit package (3d8a3cb06b), blank var ICE (983ac4b086), ONAMEOFFSET for static addresses (c76be2a24e), LinksymOffsetExpr use (99a5db11ac, 4c835f9169), dynamic export of writable static temps (7a1e963058), lookup of redeclared dot-import symbol (c1cc9f9c3d). Left open: nothing noted.
• Concurrent compilation and frontend performance — Done: cc90e7a51e, c274a7c03b, b003a8b1ae. Left open: nothing noted.
• Directives and pragmas in the frontend (//go: handling) — Done: 861707a8c8, 083a26c7d2. Left open: registerparams is limited to development.
• Inlining-related frontend work: export of bodies, type switches, closures, devirtualization — Done: 06b86e9803, 8027343b63, 6d2a557a4d, 5b0ec1a6ac^1.16. Left open: inlining functions with closures disabled “for now” (8027343b63).
• The legacy typechecker: error quality, alias/recursive-type handling and type checking order — Done: 12a405b96a, 4b8b2c5864, 51d8d351c1, c082f9fee0, 0c1a899a6c, 785a8f677f, fd4b587da3, dadfc80bc1. Left open: checker remains legacy for non-generic code.
• Lowering in order/walk and the shape of runtime calls emitted by the frontend — Done: 4048491234, e52149822b, cf148f3d46, 49e933fc57, 3249b645c9, 326ea438bb. Left open: nothing noted.
• checkptr instrumentation and compiler debugging flags — Done: 87a3ac5f53, e617b2b0dd, 8628bf9a97, feb844f1ea, b60a3a8cfb. Left open: clobberdead TODO.
• Types package internals and type printing — Done: dac0de3748 (size calculation into types), a4b8241d97, 519f223aa2, 7e17b46c58, 5cd8a34495. Left open: nothing noted.
• Register-ABI plumbing in the frontend — Done: cabffc199d, 89f38323fa, 77973863c3, 67d565d281, 1e8fff0f7b, 33b4ffc357, 0d1423583b, 861707a8c8. Left open: nothing noted.

Other changes

• dev.regabi tree-traversal simplification internal — fbc4458c06 simplified some IR tree-traversal code during the dev.regabi node refactor.
• Diagnostic text internal — 2d4c95565a (nowritebarrierrec keyed by *ir.Func), f24e40c14a (Name.Class_ accessors removed); — 7b47f9a5f2 (-m can be repeated), 9423d50d53, a22bd3dc73.
• Noder refactors for types2 reuse internal — 3e1a87ac2a (posMap), 9e746e4255 (varEmbed), 106aa941df (DWARF scope marking), 099599662d (import logic), 6877ee1e07 (findpkg), bb53a5ad43 (importer matches compiler’s constant export), b7f4307761, 868a110c56.
• IR representation cleanups inside dev.regabi internal — addrtaken computed by a separate pass instead of the typechecker (fea898a4b0, 0523d525ae, 0620c674dd, b3e1ec97fd); Name.Canonical/Byval (77365c5ed7, 81f4f0e912); DeepCopy moved to ir (d40869fced, 989a3f5041, 5dbd2e8e44, 4da41fb3f8, ecff7628ea); removal of ODCLFIELD/ODDD, Orig (ae1a337809, 171787efcd, 84cb51d7d7), Walkdef, Vargen, Typegen, Rargs, Name.orig, Name.IsDDD, Sym.Importdef (bb1b6c95c2, 12ee55ba7b, 95acd8121b, fd9a391cdd, 8fe1197654, fda7ec3a3f, e563715b30); types.Field cached on selector nodes (351bc2f38c); ir.NewDeclNameAt, single Name typ (c769d393de, 5a3b6796cd); names for keep-alive and *ir.Name in Order/CaseClause.Var/Decl.X (77fd81a3e6, 46b6e70e3b, 850aa7c60c, 82ab3d1448); NameSet/NameQueue (6c5967e528, 1b5eed8982); ir.Dump/fmt untangling (158c9dd131, 8ce2605c5b, 3b25f3c150, 724374f859, 4dfc7333f4, a79742f39a, 9958b7ed3e, f0d99def5b, c28ca67a96, 4be7af23f9, bb31c75343 — ir.Node is no longer an ssa.Aux); closure setup (eb626409d1, c9c26d7ffb, b4d2a0445b, 098a6490b9); and typecheck prep (ef5964dd6b, e34c44a7c4, 31267f82e1, 451693af71, 57c426c9a5, 305d93ef84, cb4898a77d, 2755361e6a, 9ab3d854ad). Misc: 6ca23a45fe, 0f9f27287b, 2b76429eb0, 9f16620f46, 76136be027, 88e33f6ecb (break/continue export), c22bc745c3, d90b199e9c, e6c973198d/0de8eafd98 (ODOTMETH keeps original Sel), 082cc8b7d9 (IsAssignable→IsAddressable), 69cf39089f, 7b144ed4f7, 228b732ad9, 5fd949e4bd, 6dae48fb0b, 79a3d5ce15, 0c65a2f317, b09dbc6913, 420809ab08, 65ae15ac5d, 1b84aabb01, 9262909764, 6e583d65ab, 41ab6689ed, 9e0e43d84d, 837b35cc55, 9c5241e520, 578fbbe3aa, e2d278bfeb, eae8fd519b, ed9772e130, 6acbae4fcc, 6f30c95048, 9ea272e5ec, f9b67f76a5, b241938e04, 37babc97bb, f5816624cd, 477b049060, fd22df9905, 3a4474cdfd, 1544a03198, 2f2d4b4e68, f2538033c0, a30fd52884, 4a9d9adea4, 5a5ab24689, cd5b74d2df, 4476300425, 88956fc4b1, 280e7fd1ee, 06915ac14d, c45313bf45, 5f3bd59a0d, 137f0d2e06, 6c67677541, 3bdafb0d82, 40818038bf, e24d2f3d05, 82ad3083f8, 41ad4dec99, b30c7a8044, d5928847de, beb5e05404, b9df26d7a8, f6d2834f8f, f6efa3d4a4, 063c72f06d (backport from dev.typeparams), b29b123e07, f93b951f33, 094048b938.
• types2 error-checking fidelity and review CLs internal — ab18125567, cd15a48036, c32566c336 (endless recursion in Comparable), dbce27d29c, a20021227e (subst.go from go/types), df58f3368e, f8930a2413, 8fe8e29c9f, 8ec9e89000, 14e4267c34, 6b18081d01, 41e7901ca4, 0aede1205b (use syntax printer for expressions), 82c3f0a358, 502198c8dc, d8796b5670, 455c29af83, f8654579cd, f7d1c5990b, c0bf904ddf, a360eeb528, a324aebb7d (string(int) conversion regression in go/types and types2), 2140049172, ff6ab114c9, c32ac6c15f, 9392b82919, f1777cf84c, 20746b2f37, b20f9e2da1, 3aee461d5c, 0abd7b768b, 8960ce7735, 6a40dd05d8, a2e150c7cd, 6db80d7420, 96a96a9058, 2abf280a28, 3a30381b21, d6a90d06d2, 36c5f902f9, 48b368b01f, b8a359d984, be28caf0aa, ea65a12f89, 40d5e6d4e2.
• irgen / stenciling bug fixes internal — 90bfc73071 (cache mapped types), 89ec17be9a (qualified idents), 2427f6e6c0, 18bd7aa625, e4ef30a667, 2b95c28b18, 493eb6e6ec, 08a598f8c1, c97af0036b (force untyped constants to expected kind), 9a555fc24c, 1811aeae66, 71a6c13164, e87c4bb3ef, 032ef4bbfc, 96aecdcb36, f47fab938e, 1a7d921aa5, f2717b31b5, 281d168e2d, bf634c76b2, 55c517a8b3.
• dev.regabi cleanups internal — Finished Flag and Debug initialization cleanup, added NewBasic, cleaned up Linksym, removed unused code and fixed comments after renames. (756661c82a, eb3086e5a8, a17c5e2fce, a5ec920160, e40cb4d4ae, a956a0e909)
• Report unused variables in typecheck user-visible — Unused variable errors are now reported during typecheck. (b8fd3440cd)
• Typecheck and types2 cleanups internal — Decluttered generated builtin.go, simplified types2 error reporting, combined two loops and updated ir.Node op comments. (507e641963, 16ad1ea841, b3064b66d0, acf1b46de5)
• Export implicit operations internal — Removed skipping of implicit operations during export. (48895d021b)

Middle end and SSA optimizer

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

dev.regabi refactors reshaped the middle end into escape, walk and devirtualize packages over ir, capture analysis moved into escape analysis, go/defer were wrapped into argument-less closures, expand_calls grew to handle register arguments, and stack-slot alignment/branch-known-from-predecessor/phiopt improvements landed (threads: walk/order IR refactor, Escape, Late call expansion and regabi, Defers, CFG passes).

• Prove pass: unsatisfiability, partial-order facts, loop bounds-check elimination — Done: transitive slice len/cap relations in poset (5e804ba17d); strengthened branch-known-from-predecessor handling lives in the CFG thread (92d1afe989). Left open: poset remains the only relation store; the later per-value limit table is the 1.18+ redesign.
• Escape analysis: the esc.go fixes, the escape.go rewrite, and the move to package escape — Done: package escape split out (de454eef5f), escape state split (67ad695416), reorganized to walk closures in place (b1747756e3), capture analysis reimplemented (fd43831f44, ab523fc510), decoupled from Name.Vargen (f57f484053), stopped analysing NameOffsetExpr.Name_ (88956fc4b1), heap-allocated results fix (a429926159), closure escape inside tooHairy scan (51e1819a8d, 48badc5fa8), go wrapper closures always escape (1b0a031680). Left open: closures with captures are not yet inlinable by default (see inlining thread).
• Inlining: budget, mid-stack inlining, closures, and what became inlinable — Done: closure inlining simplified (fad9a8b528), inline results declared early for empty returns (6c3bcda866), OCONVOP cost reduced (adb467ffd2), tooHairy scans closure bodies (51e1819a8d), do not substitute OGOTO in closures (95dde3f029), no inltree for closure inside inlined body (6d2ef2ef2a), imported closure types fix (eb433ed5a2), workarounds for closures with type switches (9f601690da), functions with closures not inlined by default (8027343b63). Left open: bug #44370 behind the disabled default.
• Early devirtualization and static value tracing — Done: new devirtualization package (4b1d0fe66f). Left open: nothing noted.
• Open-coded defers and defer lowering — Done: argument-less wrapping for go/defer (769d4b68ef) and its follow-up fixes above, debug flag (e617b2b0dd), register results on return path (f5efa5a313). Left open: the go wrapper must not escape in the runtime (1b0a031680).
• Late call expansion and the SSA side of the register ABI — Done: register-ABI plumbing listed in the Design paragraph, plus GOEXPERIMENT=regabiargs incoming/outgoing fixes (3304b2235a, 1f29e69bad), expandCalls name preservation and deduplication (33d99905da, 0921211403, daee726a0b, e5bc4f2a77), OpArg dedup (5d6581d747, 64ca7e2cb3). Left open: regabi not default for all arches (experiment-gated); fast map functions for aggregates (TODO in 6c98ecda10).
• Statement boundaries (is_stmt) and source positions through the optimizer — Done: register-ABI ops (4df3d0e4df), prologue (00d42ffc89), -N entry block (5e4f9b077f). Left open: nothing noted.
• DWARF location lists from SSA — Done: debug analysis block/function end sentinels (afa58ddf5a), regabi name mapping for small in-params (f62739b861, 0921211403). Left open: only single-register params mapped.
• Rewrite-rule generator, typed Aux/AuxInt, and rule syntax — Done: no-op rewrite funcs smaller (bd8b3fe5be). Left open: nothing noted.
• Write-barrier elision and the writebarrier pass — Done: newobject in register ABI (2fa7163b06), ABI-specific barriers (89b141c06e), pointer store types preserved in expandCalls (ca3aefc4a9, 5579ee169f). Left open: nothing noted.
• Arithmetic strength reduction, divisibility and intrinsics — Done: intrinsic fixes (402f177efc, 42c25e65f3), FuncPCABIxxx. Left open: nothing noted.
• CFG and control-flow passes: branchelim, fuse, shortcircuit, phiopt — Done: 051bf37833, 92d1afe989, ba6bd967d2, shortcircuit guards (771c57e68e, 04903476fe). Left open: nothing noted.
• Compiler front of walk/order: ordering fixes and the dev.regabi IR refactor (package walk) — Done: package split and refactors above. Left open: nothing noted.
• Diagnostics for the optimizer: ssa.html, GOSSAFUNC and optimizer logging — Done: package-suffix match (70deaa33eb). Left open: nothing noted.

Other changes

• dev.regabi IR migration inside the optimizer internal — evconst made non-mutating (6826287c6b), Node.HasOpt dropped (0c65a2f317), explicit block statements for init (64bc656aed), OCONVNOP in SSA (59b8916d48), inlining helpers on new IR (7fcf5b994c, 99ecfcae31, d855b30fe4, 9f036844db, 7958a23ea3, 970d8b6cb2), *ir.Name conversions (133b03e1c3, 82ab3d1448, 77fd81a3e6, dfbcff80c6, fd22df9905, 1544a03198), node printing and header modes (a79742f39a, 3b25f3c150), FwdRefAux (1c8943a6ad, 8ce37e4110), NameSet in SSA (5248f59a22, d05d6fab32), field splits of SliceHeaderExpr/SliceExpr/RangeStmt/TypeAssertExpr/CallExpr.Rargs (d19018e8f1, d1d64e4cea, e24d2f3d05, c9b1445ac8, fd9a391cdd), IsAddressable rename (082cc8b7d9), OCALLMETH desugaring (e4f293d853), ONEWOBJ removed (ab3b67abfd), Init methods removed (2f2d4b4e68, f2538033c0), Class_ accessors (f24e40c14a), toolstash scaffolding removed (cb05a0aa6a), OFUNCINST/OTYPEINST for dev.typeparams (e633f343ba), OSELRECV2 unified (0328c3b660), OPANIC argument converted in typecheck (6113db0bb4), noopt/regabi builder fixes (d6d4673728, e3027c6828, 7f9febd4a1), ir.OSLICE2ARRPTR support (67b1b6a2e3, cce621431a), other refactors (00e5727790, 0c49440664, 578fbbe3aa, a997543292, c45313bf45, c40934b33d, d1d1099c91, 6acbae4fcc, 432f9ffb11, 9b636feafe, 5834ce1dd7, 4bd4dfe96a, b9dfaf77f5, c4c68fb57f, 32dbaac572, 9abedf4827, cca23a7373).
• Closure capture and walk fixes internal — closure vars bound during SSA construction (950cf4d46c), double-walk guards via walked flags (9734fd482d, 213c3905e9, 5a5ab24689), tempAssigns (68a4664475), non-nil init for mkcall (19a6db6b63), LinksymOffsetExpr in convI (99a5db11ac), SSA’d values’ addresses disallowed (7eaaf28cae), ODOTPTR now always uses a real Field and SelectorExpr.Offset is gone (a4f335f420, 0de8eafd98), refersToCommonName removed (676d794b81), ascompatee improvements and fixes (a317067d65, 907a4bfdc7, 8c66669764, 691e1b84c1), large uint64 constants (290b4154b7), CloneName removal (8fc44cf0fa), Defn for inlined vars (d310b2a6b8), defer wrapping fix (cfac62a1cc), nongeneric closures in generic functions (f432d3fc41), mapKeyTemp zeroing and pointerness (8c2a8b1771, 3ff6ff7f84), no VarDef for initialised results (abbb82957d), leftover late-call code (f7dad5eae4, aca22bddf2), funcsym tracking and ABIInternal assertion (33b4ffc357, 1e8fff0f7b), ABI wrapper type (f448cb8ba8), recover adjustment for ABI wrappers (0723f062ff), traceback argument info (8327d2150f, 404127c30f), WriteFuncMap for new ABI (196c33e92d), regabi test names (b4ca1cec69).
• expandCalls bug fixes and ABI plumbing internal — scratch mem removed (2a18e37c4e), argument stack alignment and slot sizes (593f5bbad7, 84ca4949a7, 85f62b0941, c4e3f6c4c7, 618b66e16d, 68f3344fe9, 90ec257735, eb437ba92c), SelectN confusion/sanitization (9f5298ca6e, 283b02063b, 998fe70b68), unused OpArg invalidation (254948a50e, b56177a303, a9e475a15a), IData-of-Arg case (ee40bb666b), register arg decomposer (5eb9912084, 98dfdc82c8, 04a4dca2ac, d6504b8097, 3e524ee65a, d6f6ef6358, 052da5717e, 4b00eb7af4), argument area size for typedmemmove (b55d900529), 0-sized fields in conversion selection (ec367e5b05), unspilled results (865d2bc78e), a93849b9e2, 4357f71ca7, 1824667259, 9d3718e834, b38b1b2f9a, 77860ad280, 109d7580a5, c8fb0ec5a0 (ppc64 ANDI/SRWI), 4f5aec4603, 8e725f8452, d553c0144d, 7beb988a3b (runtime wyhash; cross-area).
• Walk and ssagen cleanups internal — Cleaned up shortcircuitBlock, walkExpr, stray comments and AuxCall.results. (0f732f8c91, d9691ffa37, 9b78c68a15)
• Default ABI for calls internal — Updated default ABI choices for calls and bodyless function stack maps. (33945869c1)

Backends and assemblers

From Backends and assemblers (Go 1.12–1.17)

Register-based ABI on amd64 (X15, R14, wrappers, expand_calls, spills) delivered with dev.regabi package split; depth-first block layout; arm64 conditional-select rules; memmove inlining; large clean-up of ppc64 assembler optab.

• Register-based ABI (ABIInternal) and ABI wrappers — Done: [dev.regabi] ABI wrappers as IR (cb28c96be8), morestack spill support (c1370e918f), AMD64 parameter register defs and Arg ops (74cac8d479), abiutils refactor and plumbing (c41b999ad4, 5a76c3d548, 7a2f3273c5, d0d21b7c4c), X15/R14 reservations (401d7e5a24, 5d7dc53888, 397a46a10a, 2e60c00f56), register args retrieved from registers (f2df1e3c34), passed to callees (4532467c18), simple register results for ints and strings (9d88a9e2bf), aggregate OpArg in registers (9f33dc3ca1), morestack handling (a2d92b5143, 3778f8e07d, b6e1c33603), results loaded into registers on the open-defer return path (f5efa5a313), output parameters passed in registers spilled as autos (8ed438c077, fixed 0ec2c4abba), partially-live argument spilling reworked to occur after liveness (23f8c203f0) and spills placed after OpArg{Int,Float}Reg (56af34f875, a690a5d75f), frame offsets checked against the ABI (5ff7ec98b7, 97b32a6724), redundant register moves reduced in call setup by allocating inputs in a better order (6b8e3e2d06), reflect.callReflect/callMethod wrappers not clobbering arguments (3711ea0b5d), struct field padding in register-passed structs (d19eece91f), several offset/trailing-empty-field fixes (998fe70b68, 98dfdc82c8, 5f646f0a98, 45ca9ef5c1, 052da5717e, 382851c1fd, 14ef2d8c01, d6f6ef6358), the five-way experiment split (eaa1ddee84). Cross-checked with git log: the five sub-experiments (and regabiargs) were switched on by default for amd64 in April 2021 (9dd71ba913, fd3612e433, bbb510ccc9, 88655480f3, af8a176e91; Android 9c12f1b433). Left open: only amd64 (regabiSupported); ABI0 vs ABIInternal still gated by experiment machinery; all non-amd64 ports remain stack-based.
• Late call expansion, AuxCall and the expand_calls pass — Done: Results-returning StaticCall (e25040d162), late return expansion (92cb157cf3), integration with abi info (d0d21b7c4c), AuxCall.args made redundant and removed (a93849b9e2), type-preserving stores (ca3aefc4a9), recursive invalidation (a9e475a15a), OpArg scheduling (cb42e3e979), Aux marker interface ssa.Aux (1a98ab0e2d) with ir.Node conversions rewritten to *ir.Name (6db970e20a, dcec658f6c). Left open: nothing noted beyond the architecture ports.
• dev.regabi package decomposition (ssagen, liveness, objw, types, abi) — Done: all of the above hashes. Left open: nothing noted.
• Rewrite-rule generator (rulegen): ellipses, commutativity loops, typed aux — Done: reserved-name check (5437b5a24b), resultInArg0 check automation (4ebb6f5110), ValAndOff int32 (b70a2bc9c6), explicit Aux match in store-combining rule (a829114b21, which notes a TODO to require Aux/AuxInt to be always specified on the LHS), smaller no-op rewrite funcs (bd8b3fe5be). Left open: the a829114b21 message flags the “unspecified aux is ignored in matching” behaviour as error-prone.
• amd64 lowering: read-modify-write, load-op, addressing modes pass, intrinsic-friendly rules — Done: memmove inlining (3b321a9d12), multi-register shifts (43d5f213e2), BT-modify removal (b211fe0058), RMW fix (359f44910f), store coalescing (bf48163e8f). Left open: b211fe0058 leaves “which fallback strategy is better” as TBD.
• arm64 backend and assembler — Done: conditional-select rules (f5e6d3e879), REV16 (b182ba7fab), float slices (3ee32439b5), inlined memmove (3b321a9d12), 128-bit FP pair loads (79beddc773), extended register ops with RSP (a607408403, 355c3a037e), shift-amount range checks (0636d88f6d, 9726c78539), R16/R17 and R12 clobber marks for special calls (11b4aee05b, 4a7effa418), encoding fixes (48b7432e3f, 5daefc5363, f439a76253, c925e1546e, e2e05af6e1, a6a853f94c, 27dbc4551a), small-stack NOSPLIT (d8394bfc7f), huge-frame prologue (4702dd67a7). Left open: nothing noted.
• riscv64 port: assembler and compiler — Done: constant materialization (6517844129, c2d625168f, 8fd0f83552), IsNonNil (125eca0f72), Eq32/Neq32 zero-extend before subtraction (c584f42dcf), huge-frame prologue (042f4cbb6f), atomics And/Or (497feff168). Left open: nothing noted.
• PPC64 / POWER backend and assembler — Done: optab consolidation and DS-form handling (hash list above), 5-operand RLWNM (48ddf70128). Left open: nothing noted.
• s390x backend: compare-and-branch, intrinsics, assembler — Done: shift-count type fix (a58be734ea^1.16). Left open: nothing noted.
• 386, ARM (32-bit), MIPS/MIPS64 and the 387 removal — Done: ARM: 4826abb6c2^1.16, c4190fc34d; MIPS: afe517590c, e31e84010e; scratch mem removal (2a18e37c4e). Left open: nothing noted.
• math/bits, atomic and runtime intrinsics (cross-architecture) — Done: riscv64 And/Or. Left open: nothing noted.
• SSA infrastructure passes: layout, regalloc, scheduling, flagalloc, block shape — Done: depth-first layout (600259b099), 6ae3b70ef2, 5b328c4a2f, 90ec257735, b38b1b2f9a, 4357f71ca7. Left open: 600259b099 accepts that some functions get larger or slower.
• Debug info generated by the backend: statements, location lists, line tables — Done: register param location work (listed above). Left open: nothing noted.
• Assembler directives and tooling: PCALIGN/ALIGN, FuncInfo flags, prologue handling — Done: FuncInfo (4dd77bdc91), prologue simplification. Left open: nothing noted.

Other changes

• dev.regabi leftovers internal — InvertFlags ordering stability (9a19481acb), arm64 addpool class check (775f11cda1), leftover late call lowering code (f7dad5eae4), atomic Attribute access (52d5cb2822), OpArgXXXX Aux passes ssa/check (3e524ee65a).
• Misc internal — bf48163e8f, 975ba6e2b2, 289d34a465, 95ed5c3800 (build configuration moves out of objabi), d4aa72002e, 5437b5a24b, 6ae3b70ef2, a61524d103, c870e86329, 873401df5b (equal functions must not do unaligned loads), b4881d930a, 196c33e92d, 6bbb0a9d4a (windows/arm64 c-shared), b345a306a0, cef3a442ea.
• Backend cleanups internal — Code cleanup and ppc64 MOV optab reorganization with unused classes removed. (939b561a6e)

Linker and object files

From Linker and object files (Go 1.10–1.17)

Register ABI plumbing (ABI-mangled shared/PE/Mach-O names, cgo export ABIs, argument-printing metadata, DWARF location expressions), weak itab references, two-pass trampolines, windows/arm64, centralised GOEXPERIMENT.

• New object file format and the loader (dev.link) — Done: f901ea701d stores relocation type as uint16, 414fa8c35e uses a separate bit to mark weak relocations, e8700f1ce6 uses a weak reference in itabs; 89ca1ce9a8/cef3a442ea abstract and use the full objabi header string; 3651eff74e deletes CompilationUnit.Pkg. Left open: nothing noted.
• Linker performance and memory engineering — Done: two-pass trampoline insertion makes small programs skip trampoline work (18852e8372); 9f7079c44e sorts pclntab relocations, 199575a119 counts relocations better, 48531da9e7 builds dynexp list directly, e03383a2e2 checks mmap errors. Left open: nothing noted.
• pclntab, funcdata and pc tables — Done: 9f7079c44e sorts pclntab relocations; 537cde0b4b adds argument-layout metadata funcdata so tracebacks print register-ABI arguments in syntax order (binary size +1.5%); bdb8044665 keeps arginfo symbols out of the symbol table. Left open: hot-spill liveness for arg printing not implemented in that CL (“just assumes all the slots are live”).
• Dead-code elimination and method pruning — Done: weak itab references (e8700f1ce6), 92c189f211/b4833f7c06 resolve and always mark runtime.unreachableMethod, a1222b7535 adds a debug print, a655208c9e handles types converted to interface under dynlink, 18510ae88f and runtime disable memory profiling when runtime.MemProfileRate data are unreachable, a22e317220/aa5540cd82/49402bee36 change map type and map.zero handling for linking. Left open: nothing noted.
• DWARF generation in the linker — Done: c819907754 relocates global-variable DWARF generation, 537cde0b4b/162d4f9c92/b83610699a regabi support (producer records regabi status), fd4631e24f/169155d61e/41afd3af42 parameter DIE ordering and abbrevs, fce2a94d84/e78e04ce39 panics in inlined/obfuscated code, dwarfgen package split in the compiler (01fd2d05c8), 6d98301114 correct PE DWARF alignment. Left open: nothing noted.
• Symbol ABIs: stable ABI0 vs ABIInternal in the linker and object files — Done: the commits above plus d28aae26b0 recognising internal/abi as a runtime package for trampoline ordering, bfc7418e6d marking Darwin syscall wrappers ABIInternal, 1f7ddf57d2 using abi.FuncPCABI0 for libc wrappers. Left open: “for functions without ABI wrapper generated, only one ABI exists but we don’t know what it is, so we still use alias” (a21de9ec73).
• Mach-O and Darwin support — Done: d5b2d809b0 LC_BUILD_VERSION, b6ff3c69d5 more load commands, dcf85b30ba ABI name mangling, f39997b2be splits large text sections on Darwin/ARM64 for external linking. Left open: nothing noted.
• PE / Windows — Done: windows/arm64 (985d087782, f41460145e, c0e1301b8c, 8e368708c5 external linking, e5a6c5243c force external for cgo), a51daac840/91cfbf39e4/811167e2c9 COFF section fixes, a0248a99a8, c432917061 links libgcc after mingw, fd5e0bd385. Left open: windows/arm64 cgo requires external linking (e5a6c5243c).
• Build modes: PIE, plugin, c-shared, c-archive, shared libraries — Done: 983dea90c1 disables plugin support when cgo is disabled, 723f199edd correct flags in .dynamic for PIE. Left open: nothing noted.
• Host object loading and external linking — Done: 7252e1e5b6 converts -I to -Wl,--dynamic-linker for external linking, 24ea547a21 not with -static, 3bf645a633 force external for DragonFly cgo, 24e9707cbf support -flto in CFLAGS, bd0fc0b9c3 preserve ELF phdr flags from external objects, e4253cd023/975b097307 reloc-variant plumbing, 6208b10d1e/007e247af1 setCgoAttr refactor. Left open: nothing noted.
• Architecture ports and trampoline insertion — Done: two-pass trampolines and per-arch support (above), f68878f0fc openbsd/mips64 cgo, 31df4e3fcd mips64x relocs, ff5cf4ced3 mips32 .gnu.attributes/.MIPS.abiflags, 3e5bba0a44 32-bit TLS_LE offsets on PPC64 (for thread sanitizer), 0a655598e1 ppc64le glink resolver, 82a1e0f9d3, 9ed736ac2a. Left open: nothing noted.
• GOEXPERIMENT plumbing and tool configuration — Done: the commits above. Left open: nothing noted.
• Build identity, buildinfo and reproducibility — Done: a78879ac67 moves sys.DefaultGoroot to runtime.defaultGOROOT, b05903a9f6 fixes the linker’s setter. Left open: nothing noted.

Other changes

• GOEXPERIMENT initialization clarity internal — 8752454ece.
• runtime/cgo.Handle user-visible — 972e883925.
• Runtime framepointer internal — 09e059afb1 on all arm64.
• Default GOROOT internal — a78879ac67.
• StackPreempt internal — 9e3328e740.
• Debug output internal — 6c3f8a2f47 uses ctxt.Logf, f82ce7fb23 better nonexistent-package error, db4adb1a9b symbol versions in stack-bound check, 053fe2f485 better duplicate definition error, 59ceb985c7, 41e5ae4883, af0f8c149e.
• Elf checks internal — 31e12b953a error if ELF header overruns, 60abe01321 XCOFF file-local checks, be1da9cdee unifies text segment write.
• Misc dev.regabi/dev.typeparams internal — 35b9c66601, d7e71c01ad, 7d55669847, 106aa941df, d6d4673728.