Go 1.18

Generics land: types2 plus GC-shape stenciling on the old typechecker. The register ABI spreads to arm64 and ppc64. The pacer is redesigned to count stacks and globals. GOAMD64 levels appear. Defers become argless closures. pclntab starts losing relocations.

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 Runtime: memory allocator and garbage collector (Go 1.18–1.28)

• GC pacer redesign — Done: user-visible Pacer state was untangled from global state so it could be unit-tested: atomic gcPercent (6508fdad9d), scavenger pacing (f99e40aac0), sweeper pacing (413672fc84), startCycle/endCycle/heapLive methods (4a5d78ff8b, 8e112a7c2a, 5ec2427357), atomic types (75b73d68b3, 2f71c86370, 09e8de70c2), and a simulation test framework driven by the real pacer (994049a9ad, b5a5b7bfb1). The redesign landed behind GOEXPERIMENT=pacerredesign. Its message says “on by default”, but the commit does not touch internal/buildcfg (a108b280bc); a separate commit turned it on (961aab26bf). The minimum heap was cut to 512 KiB on the basis of ~200 KiB of runtime globals. That was pulled back into its own off-by-default heapminimum512kib experiment after ~1% build slowdowns and “up to 8x” more GCs for <4 MiB heaps (c5c1955077). Fixes: hard-goal computation (156abe5122); the PI controller made robust to overflow/NaN (e4a173adf6); exact float arithmetic for GOGC=25 (8f374aa27f). Left open: the hard-goal case “is impossible [to test] in the idealized model … leave a TODO” (156abe5122). The heap-minimum question was deferred to “next cycle” (c5c1955077). biogo-igor regressed because the write barrier stays on longer (a108b280bc).
• Scavenger redesign — Done: PI controller (e48e4b4cbb), atomic scavengeGoal (fc5e8cd6c9), lock-free scavenging (4f543b59c5, 6d1fffac63), the 1% total-CPU target (6f32d2050d), a released-bytes accumulation fix (f986191325), and a conservative fallback when the controller overflows (e4a173adf6). Left open: the scavenger “is not really in a testable state” (e4a173adf6).
• Allocation publication, zeroing and preemptibility — Done: zeroing unified in mallocgc. Small-object spans from mheap are never zeroed eagerly, and the flag became delayZeroing, used only for pointer-free large objects (d8fc7f785e). Left open: nothing noted.
• Sweeper termination and pacing — Done: atomic sweep termination (3aecb3a8f7); GCSweepStart trace event fix (903f313d8b). Left open: nothing noted.
• Stack and register root scanning — Done: markroot read allgs concurrently with allgadd and could see nil on weak memory; gcMarkRootPrepare now snapshots the slice header during STW (08ecdf7c2e). Also clobberdead pointer crash support on ARM64 (55b4310acd). Left open: nothing noted.
• Address-space layout, tagged pointers and the mem.go layer — Done: ios/arm64 moved to 40 address bits with the 64-bit incremental page allocator (c27a3592ae); mmap failure printed (bb7fb8a5fa). Left open: the exception for iOS <14 stays “Once iOS <14 is deprecated” (c27a3592ae).

Other changes

• mheap sweep/reclaim counters to typed atomics internal — pagesInUse, pagesSwept, pagesSweptBasis, reclaimIndex, reclaimCredit converted with rf scripts (d419a80bc7, e90492882a, 1dff8f0a05, a91e976fd2, 016d5eea11).
• fixalloc hardening internal — object size bounded to [sizeof(mlink), _FixAllocChunk] (90ed541149); chunk tail waste eliminated (4591f49938). getMCache takes an mp (84ba117fd7).
• reflect.Value.Elem on notinheap pointers user-visible — panics instead of creating a GC-visible bad pointer (8331f25e96).
• faketime vs GC internal — the scavenger runs one loop under faketime, and the write path has no write barriers (0440fb8334). gcParkAssist dropped nowritebarrier (aeb4fbabc0).
• GC background goroutines use real closures internal — once the compiler allowed escaping closures in the runtime (dev.typeparams defer/go wrapping), the argumentless-closure workaround for go’d GC, sweep and scavenge goroutines was undone (3298c749ac).

Scheduler and concurrency

From Runtime: scheduler, timers, channels, locks and synchronization (Go 1.18–1.28)

• Timer rewrite: per-P timer heap, timer.lock, and GC-able synchronous timer channels — Done: fixes in the old CAS-state machine: adjustTimers backs up as far as needed (2da3375e9b). Left open: nothing noted.
• Scheduler core: spinning Ms, work conservation, stealing, STW interaction — Done: redundant loop removed in runqget (3920d6f208); tracking time for scheduler latency only when needed (29ec902efc); sysmon NetBSD workaround skipped on >=9.2 (6406227d71). Left open: nothing noted.
• Asynchronous preemption: extended register state — Done: restartable-sequence pcdata accepted in isAsyncSafePoint (8ff16c1990); maymorestack always-preempt and stack-moving hooks for testing (35c7234601, bd580a0d10). Left open: nothing noted.
• sync package API evolution — Done: user-visible Mutex.TryLock, RWMutex.TryLock/TryRLock (645d07819b), TryLock fix to acquire even when state != 0 (fdd67930a0); WaitGroup avoids a dynamic alignment check on 64-bit (ad7db1f90f); Map.Range re-entrancy doc (d5a5a13ad9). Left open: nothing noted.
• Runtime lock ranking — Done: rank ordering fixes (62c6ff4296). Left open: manual order.
• Netpoller — Done: atomic accessors for pollDesc (1b072b3ed5); net poll race fixes (17b2fb1b65). Left open: stale events.
• Fast random numbers for the scheduler — Done: fastrand switched to wyrand (483533df9e); fastrandn instead of modulo (ecb2f231fa). Left open: nothing noted.

Other changes

• Closed-channel receive and time.now internal — time.now becomes ABIInternal, dropping a wrapper (71adc658de); pollNoError constant in netpollblock (69107e73ce); redirectable builtin write (901bf291bc).
• Defer/newproc plumbing for regabi internal — newproc may split the stack (4468e1cfb9), defer-record simplification (e0e9fb8aff), d.link freeing subtlety (e590cb64f9); deferproc(func()) attempt reverted (83da32749c, a4121d7dd6).
• pprof labels / sigprof internal — missing pprof labels fix and revert (9b0de0854d, c6a0b6f2de); sigprof flag normalisation reverted (2bc8ed8e9c, 822dbcb7d4); sigprofNonGo moved (5b90958084); drop SIGPROF in ARM<7 helpers (20a620fd9f).
• Clocks/faketime internal — Windows nanotime read (cfd016df1f), nsec remainder constant (0e5f287fde), faketime GC robustness (0440fb8334).
• Misc 1.18 extras internal — funcPC misuse (6a81e063dd), pprof label fixes (da7173a2ed, 3e45eb3ce1), funcinl sentinel (6c163e5ac9).
• Misc internal — scannable stack tracking for the pacer (9ac1ee2d46); mp.fastrand init restored (5442f4d51b); doAllThreadsSyscall moved (7a132d6f4e); fork hooks without systemstack (2eb4d68833); cpu feature fix (03df68d3c3); atomic.Value first-store marker is a real pointer (3a0cd11214, 2278a51fa0^1.19 in 1.19).

Data structures and type metadata

From Runtime: maps, built-in data structures, hashing, randomness and type metadata (Go 1.18–1.28)

• Compiler-generated equality/hash functions and type descriptor emission (reflectdata) — Done: generics support in type metadata: always generate (*T).M wrappers for instantiated methods (4ed6317e73), crawl embeddable types so all methods are re-exported (132ea56d29, allows methodWrapper to always inline), Type.LinkString for map keys in typecheck/order (ed647b16d0), avoid redundant wrappers for anonymous types from imported packages in unified IR (7ab8754029, protobuf-heavy builds blew build-cache limits), shape types in their own package (b730a26729), no methods on shape types (48cf96c256), dictionaries reuse global node (8eeb1bff1d), type descriptors always dupok (79c5240799), prevent duplicate work in WriteRuntimeTypes (91e2e3b903), any definition emission when compiling runtime (3d7cb23e3d), unsatisfiable type assertions in instantiations (cf1ec17360). Left open: unified IR flagged as in-progress.
• reflect implementation: performance, allocation and escape behaviour — Done: user-visible MapIter.SetKey/SetValue→Value.SetIterKey/SetIterValue, MapIter.Reset, Value.UnsafePointer, Value.CanInt/CanUint/CanFloat/CanComplex, FieldByIndexErr, Pointer/PointerTo kind renames (54cdef1f10, 8dab959a8e, 4d550727f8, 04f7521b0a, 33c392f72d, 17910ed4ff); string-key map fast path (23832ba2e2, “over 80% of all Go map types use a string as the key”), DeepEqual fast paths (a0c409cbc8), hiter embedded in MapIter (1b2d794ca3, 89c527007f), Elem/Pointer panic on bad notinheap pointers (8331f25e96, 23e57e5955). Left open: nothing noted.
• Register ABI completion for reflect, memmove/memclr and bytealg across architectures — Done: amd64 always on (eeb7899137, bootstrapping hard-codes amd64), non-regabi fallback removed from amd64 runtime/bytealg (d7d4f28a06); arm64 reflect MakeFunc (0c123cdf8b), bytealg and runtime hot functions (5a40fab19f, 5a008a92e8), ppc64x bytealg/memmove/memclr/reflect (b8a601756a, 6c3cd5d2eb, daec057602, 9c43872bd8, 24c2ee7b65, adds duffcopy on ppc64x), internal/abi constants for ARM64/PPC64 (c3639918d1, 9cbdc1d48f), reflect big-endian fix (f1d8ea1da3, fb84d213a8), softfloat functions rewritten to avoid floats (aa3d54da07). Left open: arm64/ppc64 still switchable.
• Slice growth, string building and allocation-free bytes/strings helpers — Done: smoother growth (2dda92ff6f), unsafe.Slice bounds check and up-to-end-of-address-space (4efa216c9d, 40f82f8a09). Left open: nothing noted.

Other changes

• runtime/syscall asan hooks internal — calls to asan functions added (6f327f7b88).
• 386 SSE2 detection replaced by GO386 setting internal — (8157960d7f).
• reflect narrow-width float hooks and tests internal — (ea434450c2).
• reflect method-value and ABI correctness internal — methodValueCall code pointer mismatch fixes keeping Value.Pointer stable (f92a3589fa, d7149e502d, 07e5527249), keep pointers live for aggregate args in Call (23adc139bf), ABIInternal moveMakeFuncArgPtrs on ARM64 (20b177268f), reflect using internal/abi.FuncPCABI0 (f642742678), ABI0 spill functions on AMD64 (6633dc8b09), Pointer/UnsafeAddr/Ptr/PtrTo un-deprecated (2ff1074f5a, 056dfe6ff3).
• Generics type-metadata plumbing in dev.typeparams internal — about 12 commits fixing dictionaries, wrappers for imported generics and embedded fields, shapes, and comparable (ef6c5be160, ee4fc0c1bc, 3f1a517a45, e6a2cf233f, 40e561d933, 27283d208f, 5344dcae41, 52078fa477, 55e7f7e12d, 0ae0d5c62e).

Diagnostics and knobs

From Runtime: tracing, profiling, metrics and diagnostics (Go 1.18–1.28)

• The new execution tracer (trace v2): generations, per-M buffers, new parser — Done: v1 tracer maintenance: guard against negative/huge tick frequency on riscv64 (a78532a412), ensure at least one tick between events (ee92daae25). Left open: nothing noted (redesign had not started in this log).
• CPU profiling, goroutine profiling, pprof labels and the protobuf writer — Done: missing-label fixes (da7173a2ed, 9b0de0854d; one reverted c6a0b6f2de), profile dump includes labels (90f47dbba6), first CPU record tag consumed (a3ae45ebe1), goroutine-profile traceback bypasses the scheduler for cgo traceback to avoid deadlock at exitsyscall under STW (8c73f80400), histogram bucket off-by-one fix (2e9dcb5086). Left open: labels on racecall frames in tests.
• Race detector, ASan, MSan and Valgrind integration — Done: ASan runtime support, asanread/asanwrite, runtime/asan package (adfb85b315, NOSPLIT 2c58bb2e42, C declarations a0f373ca08, error location fix 91e782106e); race functions ABIInternal (40fce515f9, d93cc8cb96), arm64 stack space (d27248c52f). Left open: globals not yet checked.
• Crash output, runtime/debug, BuildInfo and debuglog — Done: user-visible runtime/debug.BuildInfo gains GoVersion (85a068fdf2), debug/buildinfo package (434cdd0337), VCS stamping (a37bebc042), Settings aligned with flags/env (931d80ec17), Parse/String replace Marshal (9cec77ac11). Left open: nothing noted.

Other changes

• GDB helper robustness internal — parametric type printing fixed (6d02ce8584); repeated timeouts and skips for gdb internal bugs in TestGdbBacktrace (8692bacb6a, 275aedccd4, 0a9d6a31b1).
• Stack-size feedback loop internal — GC measures average goroutine stack use and starts new goroutines with that size; Issue18138 −29% (016d755213^1.19, belongs to the stacks area but listed in this bucket).

OS layer, stacks and panics

From Runtime: OS and platform layer, stacks, panics and tracebacks (Go 1.18–1.28)

• Defer, panic and recover re-implementation — Done: argless-closure defers: variadic defer/go removed (12b37b713f), siz removed from newproc/deferproc (8e5304f729), tracebackdefers deleted (00d01b5786), open-defer metadata simplified (b20747334a), func() used for deferred functions (ea94e5d3c5). jmpdefer replaced by a loop (fd0011dca5, 1a0630aef4; first attempt reverted by e3e9f0bb2d because its parent was backed out). Fixed stack-copy hazard where a heap _defer.link points to a stack defer (e590cb64f9), and a new invariant for panics: never add an open-coded defer entry above one already started (8dfb447231, issue 48898). Left open: the freedefer call-site subtlety (unlink then clear d.link) is explicitly noted as unresolved; “popDefer” idea not done.
• Unwinder: gentraceback → unwinder iterator, inline unwinder, pcvalue cache — Done: unwinding through morestack on LR machines uses the saved LR, plus an infinite-loop detector (74f0009422^1.19); gentraceback prints goid on throw (cc9d3f548a^1.19, 1.19); ARM atomic kernel helper traceback starts in caller (3634594790); vdsoSP set consistently (217507eb03). Left open: 74f0009422^1.19 notes a missing test (low reproduction frequency).
• Symbol tables, runtime.Caller and CallersFrames — Done: funcInfo/entry-offset and findfunc work listed above; bad pcHeader/ftab output improved (13aa0d8f57, cd4d59232e); no_pointers_stackmap eliminated (c2483a5c03). Left open: nothing noted.
• Stack growth, stack bounds and the crash stack — Done: maymorestack always-preempt hook (35c7234601); stack-move race in stackForceMove fixed (71559a6ffd); debug-call tests keep GC off (7ee3f1427b). Left open: nothing noted.
• C-to-Go callbacks: extra-M reuse, system-stack bounds, init gating — Done: asmcgocall g0/gsignal checks made consistent (fcdc3c098c), mips64 signal-stack behaviour fixed (160d797260), sigprofNonGo moved (5b90958084), cgo traceback on linux/arm64 (81767e23c2^1.19, listed 1.19), runtime/cgo GCC/clang warnings (426ff3746f). Left open: nothing noted.
• Library entry points and runtime initialization — Done: sigPreempt handler for c-archive/c-shared (a4b2c579e9). Left open: nothing noted.
• Security hardening: AT_SECURE, std fds, AT_RANDOM, gated debug features — Done: Windows crash dumps added (353d5b6c53) then retracted (6dcf83d882). Left open: needs proposal process (per revert message).
• vDSO, vgetrandom and fast clocks — Done: riscv64 vDSO clock (1bd35fab05), async fatal signals in VDSO handled (86f6bf18b0), vdsoSP consistent (217507eb03), RDTSCP for cputicks ordering (22540abf76). Left open: nothing noted.
• Signals and async-preemption machinery — Done: TOPFRAME for sigtramp, handler for stray profile signals (8cfcee1fff), sigPreempt in c-archive (a4b2c579e9), AllThreadsSyscall rewritten on signals (see syscall thread), SIGPROF per-thread timers (8cfd8c3db8, 8d09f7c517), runtime: don't inspect the stack for delayed signals from TSAN (d29d0314c1^1.19, 1.19). Left open: nothing noted.
• Syscall layer: AllThreadsSyscall, internal/runtime/syscall, libc and Windows SyscallN — Done: AllThreadsSyscall via signals (0a5fae2a0e, 7a132d6f4e), runtime/internal/syscall (0b321c9a7c), SyscallN on Windows user-visible (0e598e7da4), android per-thread syscall (b5af5c0834). Left open: SyscallN only Windows (“existing API set already contain differences”).
• Windows runtime port — Done: crash dump added/reverted (353d5b6c53, 2622235a99, 6dcf83d882), nanotime barrier (cfd016df1f), non-cooperative preemption on windows/arm and arm64 (c58243aa8a, f7e34e705c), ConsoleControlHandler park fix (54b9cb8037), os.Interrupt handling added then reverted (345184496c^1.19, f86f9a3038^1.19, listed 1.19). Left open: nothing noted.
• New, ported and removed platforms — Done: ARM64 and PPC64 register-ABI runtime support (2e4b79949f, 0c123cdf8b, aa9cfdf775, 6e5dd0b59b), riscv64 GP freed (5b213178e7), goos/goarch constants moved to internal/goarch/internal/goos (122f5e16d6, 6d85891b29). Left open: nothing noted.
• CPU feature detection, GOAMD64 checks and cpu GODEBUG options — Done: GO386 replaces runtime SSE2 detection (8157960d7f); amd64 level check (8c8baad927); RDTSCP ordering (22540abf76). Left open: nothing noted.

Other changes

• ABI0/ABIInternal address hygiene (dev.typeparams) internal — ~12 commits replacing funcPC with internal/abi.FuncPCABI0/ABIInternal for syscall wrappers and sigtramp on OpenBSD, FreeBSD, DragonflyBSD, Solaris, Plan 9, Windows/ARM64 (140cd7c1d3, 077f03f4d8, 3f6f12972b, a5cd89b8c3, ed2001232a, fb42fb705d, 0e0a1f94f3, 7d928460a1, 6a81e063dd, 626e89c261), so the register ABI can be enabled without wrapper breakage; deferproc func() attempt reverted (83da32749c, a4121d7dd6), split-stack/defer cleanups (b80a4c56f0, 53fd5b1b77, 077925e2b0, 88bd92bb6d, cb14e673ec).
• Misc platform fixes internal — riscv64 GP save in crosscall1 (70493b3eb0) and sigaction mask offset (2c5d2083e4), cgo signal detection (091db6392d), cgo_unsafe_args args kept alive (f463b20789), darwin/arm64 syscall wrappers without cgo_unsafe_args (57e3809884), netbsd-arm64 setcontext crash (f300fc2d2c), ARM walltime fixes (577287728a, 15a54d627c), AES maphash on 386 (be0d049a42), pclntab micro-optimisations (113b52979f, 2a5d4ea97e, 88ea8a5fe0).
• Per-thread CPU-profile timers on Linux user-visible — timer_create per M, plus setitimer for non-Go threads, random initial offset; fixes under-reporting above ~2.5 parallel goroutines (3d795ea798, 8cfd8c3db8, 8d09f7c517).
• amd64 microarchitecture check internal — runtime throws if built with GOAMD64 > CPU capabilities (8c8baad927, TLS ordering 01b6cf09fc; darwin v4 6a40bdcbaf^1.19 in 1.19); SSE2 detection replaced by GO386 (8157960d7f).
• runtime/internal/sys explosion internal — goarch/goos packages (122f5e16d6, 6d85891b29, 46e1e74a86, 671954e72e, 33d1b82d16).
• Atomic types internal — runtime/internal/atomic typed API for all functions (3ec8d4b5ed); more in 1.19 (f1b5c048d7^1.19 Bool) and 1.20 (0581d69dc6^1.20 Pointer[T], 9fedc481ea^1.20 write-barrier pointer atomics).
• Misc ports internal — AIX syscall stack convention (002283eaca), NetBSD sysmon workaround skipped >= 9.2 (6406227d71), OpenBSD asmcgocall_no_g for sigprocmask (6416bde023), pthread.h in OpenBSD defs (6a760d6c36), Plan 9 X15 not zeroed (02117775d1), crypto/x509 spurious expiry fix on darwin (d17b65ff54), Linux kernel struct padding (reverted 7ee4c16654).

Compiler frontend · types2

From Compiler frontend: the types2 type checker (Go 1.18–1.28)

• Bringing up generics in types2 (type-parameter operands, core/structural types, tparam-as-interface) — Done: user-visible full generic support in the checker. Ops on type-parameter operands (listed above). Constant conversion to a type parameter (d39c873966, f9285818b6 string conversion). Field access through struct core types (61014f00f2); this was disabled again in 1.19 (b8248fab89^1.19). Method calls on pointers to type parameters are rejected (18135150b0). Embedding a type parameter or a pointer to one is rejected (4ff0e04c2e, 37d2219960). any is accepted anywhere (1e57748892). Local defined types in generic functions are supported (1ba2074440). The nomono check for infinite instantiation was ported (519c0a2323). The implements/Satisfies machinery was factored out (e08aae2ee4). Aliases to generic types were disallowed at first (68152359fd). About 45 further commits are error-message polish for type-parameter code, for example 89cc528e43, 283991bd7f, 2639f2f79b, 91edf2b7f2, 3d3f5d912b. Left open: field access via core types, and an interface-typed operand switch for type assertions on type-parameter values (f9dcda3fd8 makes it an error). Fixes in this period also report recurring infinite-recursion and “broken alias” gaps, tracked in the other threads.
• Type sets, union terms, interfaces and constraint satisfaction — Done: user-visible type-set based constraints as above. Strict comparable: “does not satisfy comparable” is delayed until needed (a2004de088), and a “dynamic” flag on the comparable predicate distinguishes Go-comparability from static comparability (163da6feb5: an interface does not implement comparable, because a component interface is only dynamically comparable). Further fixes: comparable must not be visible before 1.18 (1cd505c353), “all interfaces implement comparable” tests (38729cff96), 67dd9ee92c (empty type set for invalid ~T), c3561dd346 (comparable in union), union-cycle checks (13f3c57cef), delayed union element checks (c90ead97ad), 4fea5935f5 (real/imag/complex disallowed on type parameters). Left open: 848b58e473 notes the intersection “does not always compute the largest possible intersection”.
• Instantiation, Named types, Context deduplication and lazy expansion — Done: user-visible Instantiate API and Context (above). Methods are instantiated with the type (d1fd3eb40e), af80af22b5 forbids new methods on instantiated types, 73418bca34 records all instances in Info.Instances. Fixes for recursion: f2ed30c31e (recursive substitution must terminate), 93b5309f0a (rename type parameters in self-recursive instantiation), ad99d8840e (invalid recursively expanding generic types), 7520c080b4 (SetUnderlying sets fromRHS), 48ec6df16c (mutating an instance panics), 186f375ecf (constructed type parameters are immutable), 3c00a2839a (length mismatch is an error). 2175e2f573 added lazy import resolution for types2 (Scope.InsertLazy, NewTypeNameLazy, InstantiateLazy) for the unified-IR reader. Left open: 2175e2f573 says the sync.Once-based laziness is “fragile” and unification with the generic lazy-instance mechanism is possible.
• Type inference and unification — Done: user-visible function and constraint type inference with core-type unification (f03ab0e014, 5bd734839d); ~20 fixes: argument-order independence for named/unnamed (68b3d36ff4, disabled at first, enabled by b004c739b5^1.19 in 1.19), “do not run CTI before FTI” (3d3f5d912b), b00447038a shorter list for the 2nd FTI phase, bf0bc4122f perf (context string not re-evaluated per argument), 9133245be7 detect constraint-inference cycles, 73a062c3e7 recursive type-parameter constraints, 3a07ab70a2 inference of type instances (disabled again in 1.19 by 28fab5ef21^1.19), 5140ad104b update the recorded function type after inference, 9284279b44 use Identical rather than unification in missingMethod, eab9a77a60 defined-type unification fix. Left open: 68b3d36ff4 leaves order-independence disabled “pending decision”.
• Type declaration cycles, valid-type detection and the object path — Done: fe85c24431 and 671e1150c6 add a stop-gap “broken alias” side table so the compiler does not crash on aliases that depend on incomplete recursive types (#50259 and others); 2abfa30f9e, cc14fcac2b (disallow cycles through type-parameter lists), 9062a5298b, ad99d8840e. Left open: fe85c24431 says the correct fix “will likely require some form of forwarding type”; ad99d8840e leaves undetected cases (#48962).
• Per-file language versions and version gating — Done: user-visible d3070a767b^1.19 (“check go.mod” hint for type parameter requires go1.18), 242d02dd5e, 3e41b18a46, eb3ac1f5a4^1.19 hint for any; 1cd505c353 hides comparable before 1.18.
• Language features as seen by the type checker (by release) — Done: user-visible generics (other threads); 1e57748892 any anywhere; type-switch/assertion improvements (cf51fb5d68, 254c497e5c).
• Method receiver checking — Done: c0840a7c72 receiver tparam count must match, 7c694fbad1 delay receiver validation, a7d3a0e971 identifier map for receiver type params, 8cfbb58bc7 removes SetRecvTypeParams.
• Error reporting: codes, messages, and sub-errors — Done: ~60 message commits (e.g. c25bf0d959 types in mismatched call/return errors, cf5d73e8a2 restore “too many return values” with have/want, b14fd720a8, e052044d6b, 63e833154c, 2e2ef31778 append, 8070e70d64).
• Checker performance, memory and API ergonomics — Done: 054710ce46, 6b609110fd, bf0bc4122f, 0a39e4a89d structural-type fast path, b66bc0a9d5 lazy methods.
• Robustness: invariants, incomplete types and importers — Done: eff66248ea, 2175e2f573, 3db4888a05 (types2.Unsafe in gcimports), 1b193598b3 fail early on types2.Invalid.

Other changes

• File and API restructuring internal — struct, signature, interface and remaining type declarations moved into per-type files (211244e172, cfe0250497, 243076da64, 1aadb18f83, 0e0b80cb56, 9c1e7d9eff, 30e5f266ed); a typeWriter replaced ad-hoc type printing (5f0d821add, 3342aa5f51); TypeParams API renames (49c688e45c, 5ecbd811b5, f5f8a911d8, b1cdf860dd, 0ac64f6d70) — all internal except the exported ones below.
• Exported generic API user-visible — NewSignatureType (4a8995179e), TypeParam.Constraint/SetConstraint (d6753fd491, 5ecbd811b5), Interface.IsMethodSet/MarkImplicit (8cf0a087c0, 3beab0cd71), Named.Origin (7dfe686a91), TypeParam.Index (26b6833308), Structure→coreType exported helper (12dc48fd54), removal of deprecated entry points (8ac5cbe05d).
• Test-suite conversions internal — testdata converted to type-set syntax (9a99e728fe, c790964ae4, 8cdce85bdf), .go2 files parsed as generic code always (565f457e81), 29483b3dae re-enables compiler tests with types2.
• Compiler/types1 integration internal — de5d1aca5e, 1c947e4f31 (tilde in types2-to-types1 union conversion), 60cb2cab97 (Instantiate with interface type parameter), feec53c4e5 (skip GC test during bootstrap).
• Assorted Checker fixes internal — fc9e64cc98, ddb5a42b25, fa4df6597e, 50869f377f (string(1<<s)), ffb6c79828, 1efc5815dd, 9bdbed1d96, 0981724eae, 49030c87e0, c5bce7445e, 286e3e61aa (x.sel with built-in x), 0400d536e4, 61d789db3a (incomplete struct literal error); 8c99421f01 delayed-action debugging; debugging/tracing improvements (fef14fdd1d, a4b6fc7b1d, f2cdc6d167^1.19 in 1.19).
• Instantiation, Named-type, Union/TypeList and API plumbing during the dev.typeparams merge internal — 108 small commits not individually discussed above, e.g. lazy-expansion tidy-ups, Named.SetTArgs removal, TypeList use, Identical for instances/unions, verification of instances, impl/missingMethod simplifications: 03ed590e51, c92ae885d9, 6bdfff112f, 1608577e05, cc7ceea585, 3c1d502a19, 95c618e99a, b47cbc2ffe, 9cb1b0f50b, 1eb756689c, 69d945fc6e, 3a047326e8, c6d3d0b0ad, 80127a7dfe, 9f928f9318, b93f646125, c079b6baaa, 46cc686381, 880ab6209e, 0d7dc417ea, f5f79c47f9, 508624f359, e4cfa2f6da, 7308d747e7, 50f4ebbdd3, 2d250043b4, 456759b246, b2253c8041, 9d9e3291fa, 805d38a352, 5d0c2840da, 1ff0554b53, e6798795ff, 5fb177163b, 86fa510d24, b06cfe9b25, ded10d75a9, 605d1aaea2, 2872496ba5, ccc927b8f6, 47f3e1e02c, b61e1ed863, b26d325cb1, 738cebb174, 4847c47cb8, 2f87b9c942, 1367a60b06, 5efa8ff340, 41bb7446dc, dab16c1c90, 33576247e2, 662c5eed33, a73c6cf762, 99fad12e47, 3ff39c5eda, 8151b56c5d, 76dd01f457, 3cd28baffd, a91d0b649c, 278b9b3a4c, d2b512160e, e2e910ef30, 0ae4c7ff4a, f801da7855, 8f0ca7dc72, 2cf85b1fb8, f934b8326f, 34abc12b2a, 0aa194f758, 96c94c2c83, 23f653df96, 9150c16bce, bc0b98eeff, c2397905e0, 184ca3cf99, 6b3f4d388f, f384c707ac, 9c60a09689, 773f43b356, c402d64f37, 3ca57c7fb8, f8a8a73096, 07ed86c57b, 7a3a2b18ff, c5540e53b1, c295137ad8, deb45802a4, 46f138f288, 4284d45553, cdd9e939ef, 9dfd458e64, 84eefdc933, 1a2435c95f, f5fe5a4524, 8f7d96f5bc, b37c6e1547, 360e1b8197, 77eff30ec0, 727790a2fd, d9eba71a64, ef843ae49c, f1903fd4ec, aadbfc30af, 7db75b368d, 875a6d4010, e534907f65, 78e99761fc, c15527f0b0
• Error-message, printing and position polish internal — 39 commits: 0d1e293b23, 90b6e72605, 8c99e5db43, c23294d6b3, 0c40cb4a07, f0206e3df2, 47547d8508, 3d8453e00e, 717894cf80, 03db2c2413, 8250141c9a, 1a9807906d, 5a94a90d84, d90f0b9200, b091189762, 5d414d180b, 02e5913406, 599de4b2c3, 747e4afe07, cfb3dc7710, 23dd389ac6, ccd41cc05e, 3a4b95073a, 92655582d0, 42fa03a88c, fda9261504, 95e85e3108, 79d0013f53, 83bfed916b, 8cdfe408bb, b77f5f9667, 2e6e9df2c1, f009910625, 6019a52d4d, 4ceb5a94d8, efbecc7eff, ca6a5c0d51, 902dc38212, badba359da

Compiler frontend · syntax, IR, generics

From Compiler frontend: syntax, IR, unified IR and the generics implementation (Go 1.18–1.28)

• Generics via GC-shape stenciling and runtime dictionaries — Done: Generics were first brought up on the old typechecker (-G=3, types2 type-checks, noder/irgen + stencil.go build IR and substitute with a type substituter (*subster)). Export/import of generic types and function bodies (15ad61aff5, 8e6dfe1b31, new export version 7b3ee6102d, fd2f4b58b3, f90a42b410, kept the old format if no generics are exported c2c1b53b39/40ba119e3f). Initially every distinct type-argument tuple was fully stenciled, then dictionaries were added (7b876def6c, bad388744b), then GC shapes (8767b87ab5, a7a17f0ca8, 9b85985d36): same-underlying-type types share a shape (40e561d933), all pointers one shape (0b8a9ccb25), pointer-to-array and notinheap pointers separate shapes (d4e0e8e4a4, fcf6afb82d^1.19 in 1.19), shapes live in their own package (b730a26729). Method-on-shape handling went back and forth (48cf96c256 no methods on shapes, dfd875d015 allowed without bodies). Generic code transformed lazily (6acac8b685 “delay all transforms for generic funcs”), plus the generics/inlining interaction (931e84af40: only dictionaries and shape instantiations of types referenced by exported inline bodies need exporting, not the types) and de61465156/6fefb7f9f3 (missing inline bodies became a graceful fallback). -G=3 enabled by default c9912780ab; -lang=go1.18 gates generic syntax 2aea44204e. Left open: 6fefb7f9f3 says perfect identification of inlinable bodies is “much harder with generics”; the structure is duplicated in -G=3/unified IR paths.
  • Stabilization burst (about 250 commits, mostly by Dan Scales and Cuong Manh Le, grouped here): the -G=3 stenciler needed a long tail of mechanisms. (a) Delayed transforms: types2 results are used to build IR in noder/irgen.go, but operations whose semantics depend on the concrete type (calls, assignments, composite literals, ==) are transformed only after substitution, via delayTransform/transformCall/transformAssign/transformCompLit (07b30a4f77, 0d838ea5a2, c94543b85f, 4edefe9568, 6acac8b685, cfa233d76b). (b) gfInfo/getInstInfo caches per-generic-function information (derived types, subdictionaries, bound calls vs field access, itab-needing conversions) used to build dictionaries (ddb09af1b8, 4a7975e73a, f88c3b9f4d, f154f8b5bb); CONVIFACE nodes made explicit early in noder2 (12866bd8ea, e6d956e1c5, 3fff213ac2, ba7673069d). (c) Export/import: ODYNAMICTYPE/ODYNAMICDOTTYPE (2be5b84665, 394a1ad295), recursive constraints (d35ed09486), instantiated types referenced from inlined bodies (98ed916369, a80e53ec43, 899d19ac83), the crawler for generic types (c9e05fdcf7, cea7a71d40, f6b5ffb5e1, ca5f65d771), MarkUsedIfaceMethodIndex removed (0ae0d5c62e). (d) Naming: type-parameter subscripts replaced by func/type prefixes for uniqueness (0d65c272c9), blank type params kept unique (32636cd1ff), go.shape package-path escaping (1387b5e91d), instantiated type names (5b64381155, 6226020c2f). (e) Lazy/recursive loading of types in importers (d7e2e2ec2b, 2a4845257f, 13c912d192, e581ec07ee). (f) Misc: comparable as a real builtin/interface (b614c05a15, d7a43e8912), any identity (0e1d553b4d, bc0aba9717), structural typing for field access / append of string|[]byte (ef4be98abd, f4aa021985, c74be77e63), ONONAME/closure handling in dead code (5a40100141, 771b8ea4f4, ac78501b9c).
• Unified IR: one serialization for noding, stenciling, inlining and export — Done: 79cd1687e6 (construction), cf1ae5fc36 (-d=unified), GOEXPERIMENT knob 804ecc2581, documentation 6fa0437958, TestUnifiedCompare toolstash-style comparison test (3f7a3133da), incremental typecheck while reading (a18726a648), wrappers generated inside unified IR (f4198f85d5, d44ed5d144, delayed to walk 20a04f6041), unified export data written after the iexport data via “scaffolding for export data experiments” (2954f11ead) so go/internal/gcimporter and x/tools importers keep reading iexport. Avoids redundant method wrappers for imported anonymous types (7ab8754029, to stop large protobuf projects blowing build-cache limits), f118d145a5. Left open: not default; no dictionaries (stencils fully); a quirks mode existed only to keep toolstash -cmp clean.
• Old typechecker and IR node-model cleanup — Done: new IR ops for desugaring (OCONVIDATA 77e0bf294c, ORECOVERFP/OGETCALLER{PC,SP} 9be8303df9, OCALLPART->OMETHVALUE 1b995f91a5, RawOrigExpr ea522bc546), StructKeyExpr points at types.Field (a94e4f5a85), OINLCALL flattened in walk (c45d0eaadb), Func.ClosureCalled set in escape (899b158ee9), ~r0/~b0 result naming simplified (e99e9a6e01). Base helpers base.Assertf (6a931673f0). types.Type.Vargen, Extra, New, NewBasic unexported (eb6a07fcf9, 3836983779, a9377183d0) and Type.OrigSym getters (68ecdc2c70).
• Static initialization and package init — Done: pkginit “init” and “inittask” logic separated (6c5f028242); opendefer info symbol content-addressable (d9952ff511).
• Compiler debugging infrastructure: bisect/hash debugging, flags, dumps — Done: -d flag parser moved to objabi (1c4cfd8010), -asan (85b3b4ee03), -memprofilerate (6113dacf32), always print ICE message for panics (1abe9c1c73), dumps: -W=3, c2966ae272 position details.
• Frontend support for new language features and spec changes — Done: user-visible generics (see above), any as alias like byte (b31dda8a2a, 8ff254e30b), comparable builtin (b614c05a15), -lang gating (2aea44204e, 4068fb6c21 always accept 1.18 syntax but complain if not 1.18), //go:embed into any byte slice type (4f2ebfe34b), -lang check for embed moved to noder (8eeaf961c5), unsafe.Sizeof on type parameters (be1a693477).
• The syntax package (parser, scanner, tree) — Done: generics syntax: embedded type literals (81b22480cf), type-set syntax in tests (90096f445e), constraint literals with elided interfaces (5279e534b5, bb49eb3e6a, 0bef30d28a array/slice constraints), type parameter list validity (2c60a99f72, 33a1a93a92, da1aa65053), go/ast-style Walk/Inspect/Visitor (8165256bc2, used by CaptureVars badb98364b), PosBase.Trimmed (ab9aaf46ee), “assume generic code for std lib” (aa878ee49b), AllowTypeSets removed (276fb279d1).
• Types package internals: size, algorithm kind, TFlag, SIMD flags — Done: types.RecalcSize (62f88b6dc8), PtrDataSize simplified (c81fa001a7), types init code moved into types (967a3d985d^1.19), Type.Extra/widthCalculated unexported.
• Method wrappers and promoted-method sharing — Done: wrappers generated in unified IR; wrapper emission after inlining (50f38d0405); “always generate (*T).M wrappers for instantiated methods” (4ed6317e73); 132ea56d29 fixes crawling of embeddable types so inline bodies for promoted unexported methods are exported; ABI wrapper comments.

Other changes

• dev.boringcrypto / release-branch backports internal — a handful of old (2017-2018) commits tagged to this cycle by branch merge: 7b49445d0f^1.19, e8eec3fbdb^1.19, 0cbb11c720^1.19 and release-branch.go1.9 cherry-picks (fbc9b49790^1.19, 5c48811aec^1.19, 0b55d8dbfc^1.19, d80889341c^1.19): file-descriptor limiting, GOROOT replacement in //line directives, panic-merge fix.
• Export data reviews internal — importer files reviewed after import from go/internal/gcimporter (8c5c5a9e69, cc52fdd1f3, c7b9811581, d36b7d7bdd, 2fc7df93fe), position reading (fb79f6955e).
• ABI documents internal — abi-internal.md for ARM64 (ae26b45113) and ppc64 (9e60c37147), Plan 9 SSE note (b3e1fbff4d).
• Error messages like Go 1.17 user-visible — types2 errors rewritten for compiler use (c8d6ee12d5, ff8a7e513b, 0626ac064d), nil-conversion message (375a1fba0e).
• Interface cycle user-visible — anonymous interface cycles rejected (840b346c5d^1.20 in 1.20 with -d=interfacecycles; removed 6fe0d3758b^1.22 in 1.22).
• -asan and DWARF user-visible — -asan option (85b3b4ee03); DWARF for dictionary entries (72bb8185b5).
• Concurrent compile on darwin/arm64 internal — re-enabled (579ff8b131).
• go_asm.h internal — exact constants for big ints (8b9b365493, f582778ee9).
• Unique LinkString internal — struct{ Name = Type } notation for alias-renamed embedded fields (1a8b4e05b1, first attempt 933f6685f7 reverted 55d10acb72 due to racy LocalPkg.Lookup).
• Generics via GC-shape stenciling: Generics dictionaries: layout, sub-dictionaries and hidden parameters internal — Dictionary design hardened during the dev.typeparams burst: a .dict hidden parameter is formalized (“hidden parameters” idea, constants for local/global dictionary prefixes), instantiations are separated from dictionary creation, .dict Params are created in the package of the instantiated function, global dictionaries reuse one node, the captured dictionary is copied to a local in closures, and sub-dictionary entries (including optional ones for typeparam-bound method calls, method references and shape sub-instantiation indexes) are written out. Fixes cover dictionary assignment being a defining statement, wrong dict param for dict types, and dictionaryCapture.go (201d55e637, ccfb0ce8df, ee4fc0c1bc, 6a5f7e8498, 9ba294e15b, b994cc69e0, 5dac279fbd, b4844c9f54, 1c783dc148, 5517053d17, 10c8b7c1d7, 4a97fe8c22, ee20dff27d, 5cb84f0604, 687f2acf6a, 8486ced8b0, 8eeb1bff1d, ee69b09424, 812c99f86a, be571a36c7, ad7eae21d5, a064a4f29a)
• Generics via GC-shape stenciling: Shape types: construction, identity and flags internal — Shape types (GC-shape stencil keys) were made robust: HasShape() becomes a type flag, Unshapify/concretify are removed so calls are transformed with the non-shape type, shapes get a proper package and size computation, any and shapes get correct identity, constructed types containing shapes are handled, and shape type parameters get proper indexes for sub-instantiation (3dc0a0a2c5, 5d8f90f904, 35dbdda2fe, 156eeb40a6, 5e33d11e10, 2dd7b770de, c2de759581, 7f2463cc36, 9bfe09d78b, b41185c5c3, a991d9dc27, 1ab8273718, eb8198d2f6)
• Generics via GC-shape stenciling: Method values, method expressions and closure instantiation under stenciling internal — Instantiated methods flip between being methods and functions several times before settling (keep as method, change back to functions, always strip the receiver type from instantiated method values). Method expressions on typeparams and (*T).M with dictionaries, method-value wrappers (moved to walk, sym.Def set, marked wrappers), OFUNCINST closures (missing ..., ddd, types), embedded-field receivers, imported instantiated types having their methods created, and methods of instantiated interfaces marked used are fixed (04f65d394c, 9daf3cca82, 468efd5e2f, ccbfbb1c33, 8d2b4cb6cc, 46beeed0ac, 0132b91127, f1b1c2f67f, 3f7f72a258, f99b3fe2ab, 4e6836e82c, e00a6ec084, 600b7b431b, fe73f28dc5, e61d1445ab, c2bd9ee2db, 3081f817da, 08d4cc20ca, 62ba72b353, 80783558b0, c981874a5a, 54079dfd7f, 6b4cf2be93, a45457df82, bee0c73900, 5344dcae41, 73a4bbb0df, 429d1e0155, 5b9207ff67, 042548b1fd, 1ee70da312)
• Generics via GC-shape stenciling: Conversions to interfaces and type switches in generic code internal — Conversions of generic values to interface types use dictionary entries (type parameter to interface, derived types converted to interfaces, ==/!= operands, only for conversions to type parameters), with fixes for interface-to-interface and interface-to-empty-interface CONVIFACE cases, stenciled conversions that become NOPs, early CONVIFACE otherwise created in order, interface type parameters in type switches, and slice-of-user-byte to string (498a48327f, cf4b6dc48e, 501725032c, bfcb7c4c8a, 3cdf8b429e, 2fbf6aafe7, b7b790a71a, c85695a117, 5d863f89fe, 4f0dedca71, 6a35e07512, 5670ff4ae5, 19457a58e5, 952df98158, bc0eb5789e, 7548327374, c1296af151)
• Generics via GC-shape stenciling: Export/import of generic function bodies (iexport) and inlining internal — Unified-IR-independent export data for generics: OFUNCINST, OSELRECV2, builtin calls, comm clauses/closures, range loops, Init/Def fields and constants of typeparam type are exported/imported; importers avoid re-typechecking and reading type parameters twice; instantiated functions and methods are loaded or not re-instantiated; inline crawling handles embeddable types; refactors split import reading and export writing (f3fc8b5779, b1a398cf0f, d48f6d9f6f, 22f5ece3b1, 97cb0113a3, 4c072c94dc, a5be3eaee2, 74d46381b2, 4a735ce068, 844c076359, d10a904712, 8ab59d812a, 56c3856d52, 08588e6036, ee91bb8319, e4dfd788e6, 50e4508269, a83a558733, 9fa85518ff, 229b909313, e8cda0a6c9, be18cd51de, 0103fd2b8b, 7f2314530e, e7d5857a5a)
• Generics via GC-shape stenciling: Type-parameter representation and the stenciling substituter (types1/-G=3) internal — Work in the old typechecker’s subster/Tsubster: typeparam bounds and union/constraint support in types1 (TypeParam.Constraint, Structure()), type-alias and generic-type handling, set type-parameter indices at bind time, Nname/Defn/Funarg/Embedded/note copying, delay-transform conditions, noder2 fixes (++/–, OFUNCINST types, transformDot/transformCall/transformAssign ordering, inferred targs), local-type instantiation scoping and many individual stenciling crashes (c3fa51c9a2, f208f1ac99, 701bd60646, b69347d24a, 5b1120fac7, 4c50721cda, fd54ae8b0c, 95748d1b74, b7f7d1cd7b, 417955d151, f32f4f58d9, 4b10e4c547, 2580e9a160, 026480d06b, bcb3927cb5, 18788245ea, 62e32dd386, 61888d47c4, 8f00eb0099, ee0420d3b5, 8f95eaddd3, dd95a4e3db, e9c01f9804, 493e177639, 107b1fce64, a8861b907d, 64e6c75924, 706c580ee1, ea5369bac0, cd00499c61, c65ca97a45, 85267f402c, 04acb8a7b9, e3e6cd3022, e6a2cf233f, dcc8350ad3, 8e9109e95a, 4cdc65d32a, 6992dcdad9, a2e2b0362b, 506fd520d5, 27552e9172, 9f4d6a8359, 677dfe5ad6, 099b819085, 3d667671ad, 82efc05403, 8f4c020660, 891470fbf7, ecfff58fb8, 6640171914, a9a01a3fbd, 2481f6e367, 1a708bcf1d, 8854368cb0, 4186db6155, 5d6d9f5610, 10d3b13551, b1b6d928bd, 1dc9af5cdc, 560dc9712d, e39ab9b01c, 0907d57abf, 06a43e4ab6)
• Unified IR: Unified IR: reader/writer refinements during dev.typeparams internal — Unified IR (-d=unified) was refined as it caught up: more incremental top-level typecheck, objStub handling, variable capture and closure construction simplification, implicit/explicit factoring, sync-point stack recording, //go:nointerface, blank-function skipping, $GOROOT extrapolation, importing-function optimization, inlining panics and removal of reader/writer ext fields (54fe57bc22, d24c90a153, e57da8e53c, 9bdbf73c98, b55cc6687d, 9fe7c38d3d, 1b60284c0a, 372b312735, 3c3c1d8d28, 0dcab98fd8, 82744bfbfc, 4a47e40a14, 1d35d8ffa5, 6dadee759c, 88859f3cd8, 9afbf82667, e30a09013b, 4c52eac49b, 42563f89d7, 376a079762, b8c802b116)
• Housekeeping, syntax-error messages and small fixes internal — Pure refactors, readme/TODO cleanups, and small bug fixes (syntax error messages and type-parameter positions in syntax, gcimporter tweaks, ir.Dump, ssa.html source view, uint64-to-float32 on 32-bit, checkptr alignment moved to SSA generation, Sym/Type API tidying) (692399fbaa, 6ed9463133, f457ecc7f0, d70c69d830, 4a9f0cec29, 4158e88f64, 1f8d4562de, 967a8017f7, c927599783, ef4cb2f776, 010817714e, b602daea1b, f27d6a23b0, faf9c7d8fe, 711e1c8224, 5e0f8edbdc, df4c625d88, d62866ef79, b9e1a24581, 73483df406, 96ab854ab0, 42057e9848, d09e09bc61, b6dddaccd7, cfd0868fc3, f375844342, 2043b3b47b, 4fb2e1cb86, 0c45ed0561, 22951fbc89, 4e565f7372, 73652af80d, 9ff91b9098, b2fe2ebab6, eb63cbd295, a419f2f5c3, 99699d14fe, d3aedb72c6, 5337e53dfa, 7f4a946fa2, 0f64c21d90, d34051bf16, bbe1be5c19, ece493eb83, 006d4e6278, c1f012a0d9, f1596d76f4, b850f3629f, edbe4742a2, bcee121ae4)

Middle end and SSA optimizer

From Compiler: middle end and SSA optimization (Go 1.18–1.28)

• Inliner: budget, closures, and the interleaved inline/devirtualize driver — Done:
  • dev.typeparams refactors simplified variadic calls and mkinlcall (6da1661371, 417955d151, 1ec056244e). Walk flattens OINLCALL (c45d0eaadb).
  • user-visible Functions containing ORANGE (a3bb28e5ff) and labeled for/switch (74acbaf94a) became inlinable, with fixes in b8da7e4c4c and c6e82e5808.
  • encoding/binary calls are treated as cheap (17c513e722).
  • Closure positions (08e2519ded, 465b402808), a TODO in inl.go (d92101f452).
  • Shape-typed generic bodies are not inlined when shape and non-shape arguments mismatch (6ba68a0581).
  Left open: the shape-mismatch restrictions were tightened in 1.19 and lifted for unified IR in 1.20.
• Escape analysis: call modelling, closures, func-variable callees, and solver speed — Done: dev.typeparams moved call handling out of order into escape:
  • Call logic was moved from order.go into escape (0a0e3a3dea), escape analysis of calls was refactored (99732b9070), and the package was split into multiple files (3e6219c6a9).
  • The special escape-analysis tags were removed (077100dfcd).
  • Method-expression calls are analyzed (eb691fdd62), and method calls are rewritten into method expressions (2493c72742, then during typecheck in 0cf71f7f92).
  • Constant go/defer arguments are wrapped without allocating (a72a499c24). Diagnostics are skipped for wrappers (df00abc61b). walkGoDefer was simplified (e59a19cceb).
  • CallExpr.PreserveClosure and the SetClosureCalled(false) hacks were removed (1a445dab66, 70f4ab6565). An outdated TODO was dropped (73162a54c2).
  • Defers lost variadic calls and _defer.siz, and open-coded defer metadata was simplified (5b350505da, 74b0b2772a, c0a86c10f1, b20747334a).
  • ORECOVER was desugared to ORECOVERFP (574ec1c645). “Hidden parameters” were formalized (5dac279fbd).
  • Method-value wrappers moved to walk (f99b3fe2ab, fe73f28dc5), and PartialCallType was renamed MethodValueType (4676c3675e).
  • OCALLMETH is caught in the backend (aee209c044, 180c338c68, 27e3b797bb).
  Left open: nothing noted.
• Lowering of builtins to memory ops: memmove/memclr/memequal inlining and generated equality — Done: memequal(x, const, sz) is inlined for 2/4/8 bytes, firing ~100 times in the compiler (810b08b8ec). Left open: nothing noted.
• Static devirtualization and shape-aware type-assertion pruning — Done: fixed AST generation in devirtualization on dev.typeparams (942bcc2d4f). Left open: nothing noted.
• Branch-free lowering: CondSelect-into-math and ARM64 CCMP — Done: branchelim enabled on ppc64 (259735f97a).

Other changes

• Fixes and small rules (~45 commits) internal — softfloat with register ABI (656f0888b7), checkptr false positive (de1c934b97), ODYNAMICDOTTYPE can panic (c2f96e686f), arm CMP->CMN fix (b7b44b3173), closures not compiled twice (85d2751d2e), tail calls keep LR (9012996a9a), int/float->complex (d107aa2cd1), map-init arrays not noalg (0a7f00ae23), unified IR selective method wrappers (f118d145a5).
• Register-ABI/dev.typeparams follow-ups internal — expandCalls fixes (bcdc61d830, 6e0adde1e9, bd49a998bf, f249fa27a9), regabi PPC64/riscv64 CALL ops (333f3de2a1), memmove ABI on ARM64 (e4003463ff), tail-call wrapper restoration and self-copy removal (c10b980220, f01721efb9), dictionary-argument handling (ccfb0ce8df, 315cec25bc).
• GOAMD64 v3 instructions internal — BMI1 (04572fa29b), TZCNT (060cd73ab9), MOVBE (3e5cc4d6f6), later LZCNT, SARX/SHLX/SHRX incl. load forms (a92ca51507^1.19, d6320f1a58^1.19, 66f03f79da^1.19, cb702a2a56^1.19) in 1.19.
• Intrinsics added internal — publicationBarrier (739328c694), prefetch (23f4f0db68, PPC64 6ae3afa7e7), Mul64 on riscv64 (efd206eb40), BitLen32 on PPC64 (33b3260c1e).
• Rewrite-rule infrastructure internal — automated rewrite cycle detection (bff39cf6cb), fuse CFG fix (8dbf3e9393), generic 2/3-operand arithmetic simplification (6cf1d5d0fa), eliminate successive swaps (e1c294a56d).
• Arch-specific rules (~35 commits) internal — arm64 bitfield/rotate/UBFX/SBFIZ merging (2091bd3f26, 43b05173a2, 7b69ddc171, 83b36ffb10, 6f35430faa), riscv64 FMA, branch-with-zero and NEG absorption (ea51e223c2, bcd146d398, 8fff20ffeb), amd64 MOVOstoreconst (144e0b1f6e), PPC64 inline memmove (b35c668072).
• Write barriers and misc internal — no write barrier for global-address offsets (6b9e3f883e), drop unnecessary amd64 extension checks (097a82f54d), SSA .this variable (4b654c0eec), checkptr moved to SSA generation (d62866ef79), better ssa.html line highlight and genssa dump (96ab854ab0, af72ddfcd7).

Backends and assemblers · architectures, ABI

From Compiler backend: architectures, register allocation, ABI and assemblers (Go 1.18–1.28)

• Register-based calling convention (ABIInternal) ports beyond amd64 — Done: ARM64 gets parameter registers 4bb927f82e, ABI-compatible prologue registers a4b2a04bc5, morestack arg spilling 4c68edd1fe, arg/result load/spill 06df0ee7fa, updated CALL ops 8e7abefdaa, memmove call matching e4003463ff, and is switched on by 963f33b03b; clobberdead on ARM64 6b1e4430bb. AMD64 regabi becomes unconditional and the regabig experiment is removed c93d5d1a52. Do not schedule in-register args late cf23daeda3. PPC64 gets ABI register info cceadf8527, initial spill 09d3df0183, new CALL ops 333f3de2a1, enabled with duffcopy support 24c2ee7b65, plus prologue 0edc6c4fa0. Argument stack-slot liveness for tracebacks 30a82efcf4. maymorestack debug hook (asm + compile) 3839b60014. Method-wrapper tail call restored by redefining OTAILCALL to carry an OCALL c10b980220. Tail-call fixes in leaf functions on PPC64 d198a36d8c, MIPS/S390X 67917c3d78. Loop jmpdefer replacement was landed and reverted in the same cycle (fd0011dca5, e3e9f0bb2d); see the defer note under Other. Left open: riscv64, loong64, s390x still on stack ABI; the bug “args not spilled into dedicated slots” is called out in 30a82efcf4.
• Register allocator, scheduler and block-level backend passes — Done: regalloc switch sorted by arch dcee007aad; eliminate successive swaps e1c294a56d; helper removal of phi args (7b554575e4, f686f6a963). Left open: nothing noted.
• amd64 code generation and GOAMD64 microarchitecture levels — Done: user-visible BMI1 instructions at GOAMD64≥v3 04572fa29b, TZCNT 060cd73ab9, MOVBE 3e5cc4d6f6 (reverted/relanded b0351bfd7d,fe7df4c4d0), POPCNT register break via shorter XOR b99abf3cce; TESTL for cpu-feature checks d2d21d98e4; ANDL for small immediates (4476→3024 ANDQ in the Go binary, 0.03% smaller) 732f6fa9d5; MOVOstoreconst with offset folding (16-byte stack zero as one MOVUPS) 144e0b1f6e; folding of 32-bit pointer offsets removed 46121306d3; prefetch and publicationBarrier intrinsics 23f4f0db68,739328c694; Plan 9 X15 not zeroed 02117775d1. Left open: more v3 instructions.
• arm64 code generation and assembler — Done: ZR/REGTMP encoding errors fixed (aef24d8f7d,9cbc76bdf9,8e18428e38; pseudo-register addressing and SXTB checks c92c2c9d62,e9e0d1ef70, move-constant checks 41f74079a9,6656269288); constant rotates 83b36ffb10, rotate merged with logical ops 6f35430faa, ext+shift → SBFIZ/UBFX 43b05173a2,7b69ddc171; double-negate fold 315dbd10c9; shift range checks for ARM/ARM64 ccfc41eee0.
• riscv64 compiler and assembler (RVA profiles, vector, compressed) — Done: FMA support ea51e223c2, Mul64/MulUintptr intrinsics efd206eb40,1951afc919, Abs/Copysign c69f5c0d76; branch-with-zero and NEG absorbed into branches bcd146d398,8fff20ffeb; immediate-operand constant folding (e.g. the 5-instruction arithmetic right shift becomes one srai) fe8347b61a; Prog-rewrite elimination series in obj/riscv (5ec298d7b0,9cb5716f00,ba66d62b68,8a01010c26,0b66310924,2d90df91a8,37e9c1d6fe,da790cccc5); c-archive/c-shared 6458b2e8db; stack-bounds prologue made nonpreemptible 59d04d104d; trampolines from large functions bde0463da3. Left open: register ABI (next cycle).
• PPC64 / Power10 backend (GOPPC64, prefixed instructions, PC-relative code) — Done: register ABI + duff (above), long conditional branch fixup 8f397bc118, prefixed-instruction alignment 46796703d7, operand classification rework (5a3d0f5a63, 1e2820a6d7,aa1c6f5639); memmove inlining b35c668072; prefetch 6ae3afa7e7; AtomicLoad rules ce72766a02; PowerPC rule fixes 94323206ae.
• Duff’s device replaced by generated loops; Zero/Move lowering — Done: duffcopy/duffzero initial use on ppc64x 24c2ee7b65; Plan9 duff. Left open: nothing noted.
• Multi-word arithmetic, intrinsics and carry-chain support — Done: Mul64 on riscv64 efd206eb40, MulUintptr 1951afc919.
• s390x, MIPS, 386 and 32-bit ARM backends — Done: MIPS64 extension elision fix d93ff73ae2; s390x/mips tail call fix 67917c3d78; Spectre assembler error on 386 c091767d87.

Other changes

• GOAMD64 guard test internal — test ensures >v1 instructions are only emitted at v≥v2/v3 (cbd7200167, 5d946f1892).
• obj: remove ABI aliases and funcdata offsets from object file internal — a630783ba0, cfd74f7727, e180e2c27c, 850a4ffb63; gcbits/stkobj symbols made content-addressable (c1a0aa300a,0e13da8fae,e5f6d8d00c, 534dfb2aeb); assembly routines flagged in FuncFlags 752cc07c77.
• Wrapper DWARF internal — DW_AT_trampoline for wrappers 5b48fca1fa; liveness diagnostics suppressed for wrappers 808dca3b2d.
• -buildmode=shared removal tried and reverted user-visible — 68bd5121ee, a88575d662.
• dump to file for genssa af72ddfcd7; LocResults formatting 48f431ee3c^1.22.
• fiat-crypto P-224/P-384 user-visible — 93bab8a2f9 (crypto, edge).
• 12 small ssa/regalloc/liveness/obj generic commits internal — e.g. cmd/go: remove double parallelism from “go fmt”; [dev.typeparams] runtime,cc,cmd/link: replace jmpdefer with ; cc: preserve statements better in expandCalls. (7bf7bbc241,1a0630aef4,bcdc61d830,d350a66532,48e2b1ea91,df63673d6a,a8d78fae95,e741e2fe0e,e9ef931e06,c49627e81b,f005df8b58,1ed30ca537)
• 2 small obj/ppc64 and PPC64 rules commits internal — e.g. obj/ppc64: allow VR register arguments to VS registers; cc: set PPC64’s MAXWIDTH as other architectures. (b3c6de9dcd,8da66a35ca)
• 10 small obj/riscv and riscv64 rules commits internal — e.g. obj/riscv: improve code generation for loading of constants; obj/riscv: simplify rewriteMOV; obj/riscv: simplify machine code output. (28dae3defb,f5bdbf311c,f030043e37,ab7c904bf2,c50d811c7a,50c69cc3a9,37d4532867,6602c86a38,e9eb66da30,f1935c5270)
• 1 small obj/loong64 and loong64 asm commits internal — e.g. cmd/internal/sys: fix placement of loong64 definition. (20a71c9a1d)
• 2 small obj/arm64 and arm64 rules commits internal — e.g. cc: fix simplification rules on arm/arm64; obj/arm64: adjust rule for VMOVQ instruction. (79159f2e83,897b3da2e0)
• 1 small obj/x86 and amd64/386 rules commits internal — e.g. obj/x86: modify the threshold of assert loop for span6. (14f2b2a4c5)

Linker and object files

From Linker, object files and debug info (Go 1.18–1.28)

• Relocation-free pclntab and funcdata (offsets instead of relocations) — Done: cmd/link,runtime: remove functab relocations uses an offset from runtime.text e31c9ab557; stkobjs relocations replaced by offsets from go.func.* 3100dc1a7f; _func.entry becomes an offset (about 10% fewer relocations on darwin/arm64) d3ad216f8e; FUNCDATA relocations converted to offsets (about 40% fewer relocations on darwin/arm64, smaller external-link binaries) 017ffcd10d; all FUNCDATA refs moved into go.func.* cfd74f7727; goobj loses the PCDATA block 850a4ffb63 and funcdataoff e180e2c27c; pcdata accessed via aux symbols 587b3c1192, 583eeaae50; symbol alignment logic moved to the object writer 17674e2f17; funcSize made constant 2d6d558417; textsectmap fields reshaped for the runtime 058fa255bc; holes in functab experimentally marked then reverted 1ceb72394e, bd41f2d3cd. Caching field size in debug/gosym.funcTab avoided a 20% PCToLine regression (message of e31c9ab557). Left open: pcHeader.textStart still needs a relocation.
• Type, itab and typelink layout (.go.type section, relro rework) — Done: type descriptor method arginfo placed in the correct section 52b23a50f8; gcprog symbols put with gcbits d480b5c790; type..importpath fix e5ad363fff. Left open: nothing noted.
• DWARF quality for debuggers (types, variables, trampolines) — Done: dictionary entries described in DWARF 72bb8185b5, types reachable only via dictionaries 6268468e02; wrappers marked DW_AT_trampoline 5b48fca1fa; register-resident output params 79e03a9281; gdb script section pinned daa55b21d1; column info dropped when line saturates 1de2344af1. Left open: nothing noted.
• Dead code elimination and reflection-aware pruning — Done: generic interface call relocations c26a32a500; dead reference link fix 58490972c0. Left open: nothing noted.
• Linker performance and memory — Done: output file not unmapped on error exit (race with concurrent writers) e9f0381a80. Left open: nothing noted.
• Reproducible build IDs, buildinfo and symbol tables — Done: version info made easier to extract b37a5391f9. Left open: nothing noted.
• ELF/relro/hardening and external-link policy — Done: note sections merged into one segment 1ea4d3b911; SHT_INIT_ARRAY cfb0cc3552; non-exec stacks on FreeBSD 782aa42255; -asan option ae4d67c89d; CC with spaces and quotes 742dcba7bb; start address 0 for external links c92f5ee170. Left open: nothing noted.
• Per-platform object formats and internal linking (Mach-O, PE, XCOFF, wasm, ppc64, riscv64, loong64) — Done: ppc64le TOC rework and internal linking of PIE 9295723079, 2c4f389c02, fa16efb835; riscv64 trampolines 3bbc82371e; Mach-O runtime.text.N 9112d296e8; AIX symbol mangling f1f626de53; wasm command-line args fix 77f2750f43. Left open: nothing noted.

Other changes

• Linker robustness and small platform fixes internal — ~30 small changes: CC --print-prog-name tool lookup (eb9f090d1b), GO_LDSO on cross compile (ddfcc02352), undefined func sym crash with external linking (014a9720f9), weak itab refs disabled with -linkshared (f687831e4c), funcdata alignment reductions (96d3ba868a, 77bd0da688, 8d494b0818), AIX go.buildid kept alive (415f0a3375), darwin libc-based fcntl in fallocate (d887d3be5f), forced eager binding for plugins on darwin (c5fee935bb), -d early exit on libc platforms (57aba325c8), wasm env space (252324e879), ppc64le glink PIC (732db407d3), ARM64 PE label symbols (988efd5819), fuzz coverage instrumentation (74f49f3366), Plan 9 ABI mangling (240d6d00ca).
• ABI aliases removed internal — ABIInternal normalized to ABI0 at link time, aliases deleted (98989f2a74, 55d22f7490).
• Generic-type symbols internal — instantiated types elided in tracebacks (a80cbc25bd).
• goobj version bump internal — 5e217284dc.