Go 1.19

Soft memory limit (GOMEMLIMIT) and GC CPU limiter. Scavenger index redesign. Jump tables for switches. riscv64 register ABI. linux/loong64 port. Unified IR gains full generics support.

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 the old pacer and the experiment were deleted (3334afd760). To support the memory limit, the goal and trigger are now computed on demand from current inputs, with a new triggered field recording where a cycle actually started (129dcb7226). The maximum-trigger computation was rewritten to match its intent (473c99643f), and trigger math moved to integer shifts (973dcbb87c). gctrace now prints the correct goal (a6c75aa5c3). A late regression came from making alloc counts truly monotonic (79db59ded9), which also made heapLive monotonic and caused small-heap memory growth; it was partially reverted to a “non-monotonic overestimate” (1ebc983000), and the pacer went back to the precomputed trigger (85a482fc24). Left open: “in the future we should consider moving away from such a history-sensitive smoothing function” (85a482fc24).
• Soft memory limit and GC CPU limiter — Done: user-visible the limiter was added and turned on unconditionally, along with a feature flag for memory-limit code (01359b4681). Then came, in order: limit plumbing (986a31053d), mappedReady (4649a43903), sys* wrappers (f990b0f1e8), alloc/free counts (85d466493d), heapFree (d36d5bd3c1), stats moved into gcController (375d696ddf), the dynamic goal (129dcb7226), the limit-derived goal (7e4bc74119), allocator and scavenger enforcement (b4d81147d8), the exported runtime/debug.SetMemoryLimit (f01c20bf2b), and the GOMEMLIMIT parser accepting B/KiB/MiB/GiB/TiB (0feebe6eb5). Limiter refinements: a private assist-time pool (2eb8b6eec6), idle-mark and total-idle accounting (08d6c4c2b9, 54bd44e573), cancelling assists (1f0ef6bec7), windowed accounting (d7941030c9), and a /gc/limiter/last-enabled metric (cfccb5cb7c). Left open: the 61-bit timestamp can produce “hiccups” when the top bits change (d7941030c9). Thrashing with idle mark workers disabled (periodic GC) is not handled (08d6c4c2b9). The fixed 1 MiB headroom later caused eager scavenging (#57069).
• Scavenger redesign — Done: scavenger refactored into a testable scavengerState (d29f5247b8); chunk-index redesign (91f863013e, ccb798741b); memory-limit goal and allocation-time scavenge assist (b4d81147d8); physical-page-aligned allocations restructured so scavenged-bit accounting stays exact (b58067013e). Left open: finding work can mean iterating “across the whole heap”, giving “worse overheads for memory limit scavenging” (91f863013e).
• Finalizers, runtime.AddCleanup and the cleanup queue — Done: the finalizer reflectcall frame did not include the register-ABI spill slot and could clobber the caller; fixed (58804ea67a). Left open: nothing noted.
• Mark worker scheduling and GC work queues — Done: periodic-GC idle-worker cap (e1b5f347e7); idle workers disabled when a dedicated worker exists (d8cf2243e0); merged wbuf checks in tryGetFast/putFast (86c8075675). Left open: idle workers are still “necessary for GC progress” when only fractional workers exist (e1b5f347e7).
• Address-space layout, tagged pointers and the mem.go layer — Done: sys* wrappers and consolidated docs (f990b0f1e8). Left open: nothing noted.

Other changes

• BoringCrypto GC-aware cache internal — boring.Cache, a fixed-size concurrent map from unsafe.Pointer to unsafe.Pointer cleared every GC, replacing a hidden struct field; later factored into crypto/internal/boring/bcache (a840bf871e, e845f572ec, 8f9bfa9b7b).
• 64-bit atomic field alignment test internal — (6b6813fdb7).

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: timerModifiedEarliest cleared when the last timer is deleted (c006b7ac27). Left open: nothing noted.
• Scheduler core: spinning Ms, work conservation, stealing, STW interaction — Done: work-stealing order randomness fixed: with GOMAXPROCS=12 only 4 coprime strides existed so position and stride were correlated; now chosen independently (510ad4561f). Scheduling decisions from schedule moved into findrunnable so any M in findrunnable can become a GC worker or trace reader and handoffp sees all work sources (fixes #44313, #39004) (13b18ec947). runqgrab yields instead of sleeping on OpenBSD/NetBSD (226346bb76, b93ceefa7b). Goroutine-profile STW reduced to fixed bookkeeping with a barrier in the scheduler (52bd1c4d6c). Left open: lost-wakeup race when a non-spinning M drops its P.
• Asynchronous preemption: extended register state — Done: loong64 asyncPreempt (740b0ebb76); arm64 uses stp/ldp (2e9facbdd4). Left open: nothing noted.
• sync package API evolution — Done: happens-before documented for sync, atomic, finalizers (a71ca3dfbd); Cond guidance (d42a48828f); semaphore-treap scalability tests (7bad61554e). Left open: nothing noted.
• sync/atomic and runtime atomics — Done: user-visible typed atomics (ffe48e00ad). Left open: runtime still uses old API.
• Runtime lock ranking — Done: partial order edge for trace/wbufSpans/mheap (482669db62). Left open: nothing noted.
• Fast random numbers for the scheduler — Done: fastrand64 (ebe1435fbb). Left open: nothing noted.

Other changes

• Regabi condition cleanup internal — d8bee94be2.
• Closed channel receive fast path internal — ca7c6ef33d.
• Goroutine profile with barrier internal — race annotations (209942fa88), STW reduction (52bd1c4d6c).
• Syscall via RawSyscall on Linux internal — landed and reverted (64e69d3925, bb004a179a, aac1d3a1b1).
• Misc internal — Pool.Put redundancy removed (507a44dc22); fastrand64 use in net (a4bbcd4b1f); faketime jump uses pidleget (13f6be2833); atomic alignment docs (0eb7051aad, 69bb7c6ef5); m.procid alignment on 32-bit (ea7e3e3c0f); execution-trace profile prefers curg (7b1f8b62be).

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: array-equal loop unrolling (1a955bcdb7), instantiating types excluded from type hash (d3672054fb), dupok adjustments for shape/non-generic types (884530b374, 909a7a3213), incomplete itab always writes fun[0] (6f5590edf6), struct comparison unification (3c29aca436), embedded bit moved from field offset to name bytes, leaving a full uintptr for offsets (e1e66a03a6), sort named types before unnamed for plugin signature (5b4fafd5db). Left open: nothing noted.
• Interface conversion: itabs, type switch and assertion caches — Done: incomplete itab always writes fun[0] (6f5590edf6). Left open: nothing noted.
• reflect implementation: performance, allocation and escape behaviour — Done: inlineable Value.Type, MapRange, Bool, String, Bytes, Len, Cap (e948c3394e, c5edd5f616, 67d6be139c, 01837ca7eb); Value.Bytes on addressable arrays (a5b8b56d1d); Len/Cap on pointer-to-array (892cd0b636); SliceHeader/StringHeader deprecation added then reverted (bc2e961cf4, e6d8b05a61); map key type check in MapIndex/SetMapIndex (11a650bb4a); StructOf overflow panics (c22a6c3b90). Left open: nothing noted.
• Register ABI completion for reflect, memmove/memclr and bytealg across architectures — Done: register ABI always on for ARM64 (8ff42d1bb1, fallback deleted 9f252a0462) and PPC64 (b810a74da3, 0a69c98214); RegabiArgs conditions dropped in reflect/runtime (d8bee94be2); riscv64 runtime/reflect/bytealg/memmove (8fefeabb35, b55a2fb3b0, 0652274c10, be1d7388b3; reflect support reverted once ad646b33c9, re-added 56400fc706/bb2b73635f^1.23, float32 93218ea1a7); loong64 support (2a5114f49a, 96a10b9c84, d28bf6c9a2). Left open: riscv64 still gated.
• memmove / memclr / memequal / internal/bytealg assembly optimisation — Done: amd64 memclr uses ERMS REP STOSB for 2KB..32MB (dcfe57b8c2, -8.43% geomean; 2KB threshold from Intel’s guide), AVX2-less memclr removed for GOAMD64>=3 (12acf9b0f0), pointer-size word stores in memclr (e0f99775f2), ppc64x memmove/memclr/equal/compare/index/indexbyte (9ccf5b8e86, 91b9915d3f, 8375b54d44, 78fb1d03d3, 7ca1e2aa56, 5c707f5f3a), riscv64 memequal/compare (3c42ebf3e2, 291bda80e5), dead code for GOAMD64 levels removed (330cffb869^1.20 in 1.20 cycle, -14.86%). Left open: nothing noted.
• Runtime randomness: fastrand, chacha8rand and math/rand/v2 — Done: fastrand64 in mapiterinit (01b8f5e882). Left open: nothing noted.
• Classic map maintenance and maps package helpers (pre-swiss) — Done: 29bbca5c2c. Left open: nothing noted.

Other changes

• GOMEMLIMIT byte count parser internal — 0feebe6eb5.
• Remove boringcrypto compiler kludge internal — cdcb4b6ef3.
• Skip exporting generic functions for plugin builds internal — b79c135f37.
• reflect and ppc64 fixes internal — Value panic messages (8b389eb2be), receiver stored in pointer slot for reflect call (74f0ccb68b), Kind.String negative kinds (0d71234ee4), ppc64x backward copy (d82c294da7).

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: user-visible CPU profile samples are emitted into the execution trace when both profilers are on, rendered as instant events in go tool trace; samples from threads known to the runtime, including g0 and no-P contexts (2c0a9884e0); internal/trace gets Go 1.19 test data (bd4753905d). Left open: samples are best-effort (see 1.22 fix).
• CPU profiling, goroutine profiling, pprof labels and the protobuf writer — Done: user-visible MaxRSS reported on all unix platforms (c1f22134f2); inlining correctness in the proto builder: PC reuse by inline NOPs (bd77d6e240), allFrames cache bug producing wrong C<-B<-A,A locations (ba8310cf29), pcDeck indexing (0d33a99675); finalizer G handling and race annotations in the concurrent goroutine profile (8fdd277fe6, 209942fa88); profBuf read-before-advance fix (1926fa5f84). Left open: nothing noted.
• runtime/metrics and MemStats — Done: user-visible /sched/gomaxprocs:threads (ece6ac4d4d), /cgo/go-to-c-calls:calls (9bd6e2776f), last GC cycle with limiter enabled (cfccb5cb7c); total allocation stats stored as uint64 (7c404d59db); user-visible debug.SetMemoryLimit exported (f01c20bf2b, GC area). Left open: nothing noted.
• Race detector, ASan, MSan and Valgrind integration — Done: user-visible new TSAN runtime v3: 2x smaller shadow memory, vectorized race detection, fixed 512-byte vector clocks, unlimited goroutines; e.g. encoding/json CodeDecoder −56%, net/http ClientServerParallel4 −92%, sync short tests −82% (d6a1ffd624, syso 995a604591); race on s390x (87cf92e7d5, syso 7c680974c6), PPC64LE C ABI (c8110c3df6); ASan on riscv64 (9956996f6e); ASan global checks attempted and reverted twice (1e5987635c, 507b70d1e8, 265b5fd2f1); amd64 syso avoids SSE4 (846490110a). Left open: ASan instrumentation of globals (reverted for breaking cmd/go tests).
• Crash output, runtime/debug, BuildInfo and debuglog — Done: debuglog avoids string allocation (73587b71a6). Left open: nothing noted.

Other changes

• Race/ASan loose ends internal — darwin syso rebuilt for macOS 12 (5f6552018d^1.18), PPC64LE v3 syso (6f1dce0fcb), racereadrange ABIInternal (f566fe3910), metricsSema race annotations (d6481d5b96), further ASan-globals attempts (f52b4ec63d, 1b0f9fbb67), RUSAGE_SELF (3c2e73c8c3); internal/trace ignores regions on system goroutines (123a6328b7).
• Heap goal and trigger computed dynamically internal — needed for the memory limit; triggered field added (129dcb7226, GC area).
• Scheduling decisions moved into findrunnable internal (13b18ec947, scheduler area).

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: don’t discard the value when panicking while panicking (5a4f0b6f1e); panic helpers marked go:yeswritebarrierrec (81d567146e, 568590b085); user throws simplified, runtime throws expanded (4289bd365c). Left open: nothing noted.
• C-to-Go callbacks: extra-M reuse, system-stack bounds, init gating — Done: cgo traceback on arm64 (81767e23c2), unified C→Go ABI transitions on arm64 (eee6f9f825, 2e9facbdd4); C-library sigaction racing: _cgo_sys_thread_start memset removed on linux/freebsd arm (7f71e1fc28, adfee1e1e7); g0 stack bound from frame address (3e97294663). Left open: nothing noted.
• Library entry points and runtime initialization — Done: musl static/dynamic start-up detection on ppc64le (946167906e). Left open: nothing noted.
• vDSO, vgetrandom and fast clocks — Done: s390x vDSO (636c5f0208), loong64 vDSO (8542bd8938, 3fa5ab0d83). Left open: nothing noted.
• Signals and async-preemption machinery — Done: preemption signal unblocked in new Ms (e3982660a7), sigtramp TOPFRAME on unix (4bb45f7549, cb8219a071^1.28), debug calls on arm64 (9717e8f80f), TSAN delayed-signal fix (d29d0314c1). Left open: nothing noted.
• Syscall layer: AllThreadsSyscall, internal/runtime/syscall, libc and Windows SyscallN — Done: RawSyscall6 in runtime (15602e8865), ppc64 r2 fixed (78070ec3d4), pipe2/accept4 on solaris (c3c74777bc, 3e00bd0ae4). Left open: nothing noted.
• Windows runtime port — Done: Breakpoint on windows/arm64 (9fcc8b2c1e), _beginthread retry (c7ccabf3fe), cgo thread-start bodies merged on Windows (91019cc13d). Left open: nothing noted.
• New, ported and removed platforms — Done: linux/loong64 port (2a5ceaaa78, c8de7628cb, 0084706528, 8542bd8938, a7cc865edb, 34507e879d), riscv64 regabi reflect reverted (ad646b33c9), Goarch loong64 constants (30b17b6f60). Left open: cgo-traceback, plugin, msan for loong64.
• CPU feature detection, GOAMD64 checks and cpu GODEBUG options — Done: required options can’t be disabled (5ccd8e5133); PPC64 IsPOWER8 and CPU report (d9d55724bd, 51859ec229); loong64 cache line (ec9258029e); AVX2-less memclr removed for GOAMD64>=3 (12acf9b0f0). Left open: nothing noted.

Other changes

• Sigtramp/ABI details internal — ABIInternal for most sigtrampgo calls (ba7f3d98d4), TOPFRAME on the rest of Unix (cb6fc99b32), loong64 flags (61fc5df689), PPC64 register save/restore stubs from the linker (9c9090eb1d), save_g not NOFRAME on ARM (aeaf4b0e5b), 64-bit atomic alignment (0f715f1ac9), pipe2 fallback removed (9d34fc5108), JS/Plan 9 write-barrier avoidance (364ced6255), Plan 9 exits string (3cf79d9610), stack split during fuzzing (386245b68e), nosplit guidance in HACKING (c29be2d41c).
• Boringcrypto/libFuzzer hooks internal — dev.boringcrypto merges (6e70f88f84, 3ed08db261), libFuzzer value profiling and string compare intercept (c1d197a96e, 2b0e457b42, 1821639b57).
• unix build tag internal — the new unix constraint used across std/runtime (a2baae6851).
• GOAMD64 internal/cpu internal — disallow disabling required options (5ccd8e5133), IsPOWER8 (d9d55724bd), loong64 HWCAP etc.

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: field access through type parameters disabled (b8248fab89), because it was not part of the accepted semantics. Inference disabled for type instances (28fab5ef21). Fixes for composite-literal key duplicates with a generic key type (2138124143: numeric key values are mapped to the smallest numeric type that represents them, so 0 and 0.0 collide). The comparable operand check, pointer base types and alias-to-constraint handling were adjusted (3a5e3d8173, 3ebb1720d9). Left open: nothing noted beyond the follow-on threads.
• Type sets, union terms, interfaces and constraint satisfaction — Done: 0807986fe6 and 7dc6c5ec34 (comparable in type-set intersection), 35fb79be6a (overlap test for term lists), 41fe746857 (underlying type used in union computation), d4fb93be87 (print | rather than a union symbol), 269bf7e855 and 3507805bcd (better type-not-in-type-set / constraint-misuse messages), 2ea9376266 (split the “term cannot be a type parameter” message), 86fa2551fb (parentheses around types in interfaces).
• Instantiation, Named types, Context deduplication and lazy expansion — Done: a type-lookup-by-identity fix for method sets (f088f4962e), Origin for Var/Func (1170771074), expansion no longer infinite (47e34ca533, 70668a4144), Named state simplified (846f971daa, 1323b0e8f0, 02e69cfa96, d5ae7a6487), 1a2ca95ad2 (instance context only set if packages match), 43b09c096a (record all instances even duplicates).
• Type inference and unification — Done: 0807986fe6 correct tilde handling in CTI (an imprecise ~ core type cannot determine an unknown type argument, but a known one must be unified against the underlying type; the whole loop is iterated until unknowns stops decreasing). b004c739b5 makes inference independent of parameter order.
• Type declaration cycles, valid-type detection and the object path — Done: 07eca49055, fc97075949 (simplify), 7751883379, 114d5deac2, 70668a4144.
• Method receiver checking — Done: 9b90838712 preserve parent scope when substituting receivers.
• Error reporting: codes, messages, and sub-errors — Done: d4fb93be87, 73475ef035 qualified names in cycle errors, f9747b7f73, test tweaks.

Other changes

• Test infrastructure internal — flag mechanism for test files (3395f74d86), .go2/.src → .go renames (82b810f79c, 4dc5553930), predeclared test functions separated (29866aa2b6), 6be52abfa1 removes unified-build exclusion.
• Platform sizes internal — 8140a605fe adds loong64 to gcArchSizes; 2aa473cc54 alignment of atomic.Int64.
• Misc fixes internal — d3fe4e193e scoping of range-clause iteration variables, 302f5ed21d overflow-check crash, 104742fdda iota value, b75e492b35 delayed field-name conflict check, 0a6ddcc4f0 (no unused-import error for unimported packages), 9038c24498, f71daa6fe6, 7cb1ae3e8e, 2da1e47fb0.
• Small fixes, unifier/assignment refactors, message and tracing tweaks internal — 10 commits: 20dd9a42fb, 914195c132, efbff6e43b, 5df3f491ac, 4a46e6e44c, 83327b4ae4, c05c0ca8cf, 0a6ddcc4f0, 3e58ef6cc7, c847a2c9f0

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: Unified IR gets full generic support with the same dictionary model (0e2f1abf5b DynamicType for derived types, ac3ba97907 itabs in dictionaries, 7fc38802e1/f326964824 method expression closures for bound calls, 64b6e44ad7, fcf6afb82d). d3672054fb stops including instantiating type args in type hashes. Left open: unified IR still generated static *runtime._types from shape types at some sites (see RTTI thread).
• Unified IR: one serialization for noding, stenciling, inlining and export — Done: quirks mode removed (4f04e1d99f); sync markers simplified (6d881da9c8); coding-level logic extracted to internal/pkgbits (7c151f3280); reader for types2 moved into importer (44e92e11c7), lazier import (258fc75505); -G flag and dead old-typechecker noder code removed (302af4be8e, ad52356536, 0fcb94895f, d6d2ebb7b8); pkgbits version number (d40e7bb174); fingerprints in the export format (42ca44494c) so iexport data is no longer needed for package fingerprints; 9a9bd10290 + e146d3eafa switch to the final unified export format and drop backwards-compatible iexport output (GOEXPERIMENT=unified go test on generic code works without -vet=off); union types for the backend (efbe17d6f1). Reentrancy fix for function body reading (7c292ddf1f); implicit interfaces (21998413ad). Left open: e146d3eafa: importer sets the receiver type to the underlying interface “until we make a decision on #49906”.
• Old typechecker and IR node-model cleanup — Done: removal of the old checker’s tail: typecheckdef/Name.Walkdef (1cfe1007cd), OIOTA (d661bdeabf), Broke/Diag/SetBroken machinery (da9649e6d9, 7ca6902c17, 515135f4c3, c10fb50894, 2792a414c6, 0eb2c77124), AllowsGoVersion checks (810868c9f6), typecheck.FuncBody (489e4882ef), NewClosureExpr (f25631b490). Then a sweep removing syntactic type nodes: Field.Ntype, Name.Ntype, Name.TypeDefn, CompLitExpr.Ntype, TypeAssertExpr.Ntype, ir.FuncType/OTFUNC (73fb829f59, 14fed2c8f1, a6a49d128b, e94fe09c33, 3ffc230a9f, 27b844f767, 025a9c3438, 983906fa6d), cf66a82b0b prunes remaining Ntype nodes. Type.OrigSym -> OrigType (adae6ec542: “first law of frontend development: thou shalt not rely on types.Sym”), Sym.Block/Lastlineno removed (79103faf2d).
• Compile-time performance, concurrency and the self-PGO’d compiler — Done: fixed a compiler deadlock on syntax errors from the open-file semaphore (5a90270d7f, 370cadd0e4), 128-bit hashes for content IDs (485a572243).
• Frontend support for new language features and spec changes — Done: user-visible //go:uintptrkeepalive (342b495301), sync/atomic typed values alignment (0f715f1ac9), unsafe.Slice open-coded (579902d0b1), constant-fold switch early (01b9ae22ed, better codegen 74b52d9519^1.21).
• The syntax package (parser, scanner, tree) — Done: generic-specific parse modes removed (bf408e741c), ~x as unary expression (09ada1af8f), CheckBranches checks fallthrough (6b309be7ab, one-time branch/label checks 666d736ecb), no parse of GOROOT/.git.
• Package paths, -p, and build-system contract — Done: user-visible -p required (a987aaf5f7), default -p=main for main (20ba3f5de5), LocalPkg.Path set (ab8d7dd75e) after removing "" assumptions in unified IR, iexport, staticdata embed symbols, ir.PkgFuncName and Ctxt.Pkgpath fallbacks (1973be519a, e3661d5f08, 499e334a28, 4170084ad1, 2540f4e49d), -importmap removed (1355ea3045), -installsuffix kept after revert, command-line flags parsed earlier (b6c5a5baa7), #ifdef-style ABI notes for riscv64 (1045faa38c).

Other changes

• Content hash width internal — 128-bit base64 hashes for content IDs (485a572243).
• -L/doc fixes internal — 9058080319.
• Asan checks user-visible — unsafe.Pointer conversions escaping under -asan (c379c3d58d), globals instrumented (1b0f9fbb67 after two reverts).
• Abort on stack-ful ABI internal — 128-bit values can be spilled (c2d373d5d1).
• Unified IR: noder/writer/reader refinements and pkgbits (1.19) internal — RType/implicit-conversion wiring, *At helpers, optional expression handling, UIR documentation and grammar, pkgbits.Index/SectionKind renames, synthetic closure positions, unsafe.Sizeof handling and related reader/writer fixes (82a6529905, 7900576bac, a1bf50eefe, 8c5917cd76, 6382c39e15, 4e4db1e257)
• Generics: dictionary/shape fixes in the stenciler (1.19) internal — fixes in dictionary passes for type assertions, comparisons, switches, nested instantiation packages, and recursive generic interface instantiation (8cf11694ab, 2e46a0a997, 8419ec295c, fa8efc1347, fd1b5904ae, c90a19a760, 920b9ab57d, e99275241c, dbf5220475, 085529bd5f, 7eeec1f6e4, 4045b1bc3f, ff17b7d0d4, 34f3ac5f16, 14abe8aa73, 923740a8cc, 27038b70f8)
• Old typechecker and IR node-model cleanup (1.19) internal — removal of unused typecheck/ir/types code (Ntype, CurFunc uses, vargen, Resolve dependencies), more typed IR node construction, simplified DeclFunc/NewMethodExpr and constant handling (dcb6547b76, 947bf333fc, b10164b292, f5a42cd4b4, 15381040fa, 96a1ad298a, 53647a1994, 115c3bfad5, 3abe8fe00b, 5073c1c740, a7ab208cbb, 72d1cb092e, 6399b24539, 1284cc2495, 80f3e3deba, 2a6e13843d, a8facc456f, a900a176bf, ccf84a9750)
• Syntax package: error messages and parser tolerance (1.19) internal — better syntax and go/parser error messages, accepted type-parameter lists, parser simplifications (a7e76b8e80, 0775730180, e49b80a754, ea6c828455)
• Housekeeping (1.19) internal — dead-code removal, ioutil/seek/slices/atomic-type replacements, README edits, debug-flag removal, assorted small bug fixes and doc comments (d81464e1eb, 9743e9b6d8, 5fd0ed7aaf, 1024503f84, e5e638e512, 129a2fcf6c, 63ea27e9e0, 7e0a1d340f, 3fd8b8627f, 3dac99ad4c, b1e83c0513, 3df9df8d6a, 1e5987635c, 12763d141d, c15d0a93c7, d4bfc87218, f52b4ec63d, ffe48e00ad, ac39dbdf58, 3391517c0e, 17dc7b487f, 7b314d27ce, b89a194889, fd17a4dc09, d602380f58, 1243ec9c17, 558785a0a9, 8e1e64c16a)

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:
  • user-visible select became inlinable (80a7504a13).
  • The shape-argument restrictions were refined (cb458c05a8, 19156a5474, f2b1cde544).
  Left open: nothing noted.
• Escape analysis: call modelling, closures, func-variable callees, and solver speed — Done: values with alignment greater than PtrSize are forced to the heap (162b88265e). Under -asan, making conversions to unsafe.Pointer escape (5fd0ed7aaf, c379c3d58d) was reverted in 599d5395eb. Left open: nothing noted.
• Prove pass and bounds-check elimination: from poset relations to a dense limit table, topo-sorted walk, and division-aware proofs — Done:
  • Results of math/bits operations are known nonnegative (3bd8c78575).
  • Constants discovered by prove are folded: about 70k hits building go, binary 0.04% smaller (e1e056fa6a).
  • And (1efe38750a). Upper bounds <= maxint fixed (31b8c23c57).
  • The induction variable detector was reworked for correct overflow handling (2acd3646fc, #53653, #53663).
  Left open: 2acd3646fc says induction variable detection “is still not quite right”.
• Lowering of builtins to memory ops: memmove/memclr/memequal inlining and generated equality — Done: memmove with a known size is inlined on loong64 (a6c95e75d9). Left open: nothing noted.
• Switch lowering: jump tables, type-switch caches, and switch lookup tables — Done:
  • Jump tables (1ba96d8c09); arm64 support (540f8c2b50).
  • String switches use a jump table on lengths (3d8cb26504), with prove changes so the length test is not repeated.
  • Jump tables are off under -N (78bea702cd). The table symbol is local (c5da4fb7ac).
  Left open: the go119UseJumpTables kill switch remained until 1.21.

Other changes

• Fixes and cleanups (~35 commits) internal — walk litas removal, appendWalkStmt (b922055572, ed462a66a5), static-init fixes (0bd7408f90, 1c77137d4f), intrinsify mulWW on mips64/riscv64 (4d350710a2), ORN on PPC64 (c570f0eda2), rewrite-loop detector off for deadcode-only changes (15728ce950), regabi magic names removed (3f8a694155).
• loong64 SSA bring-up internal — rules/ops and intrinsics (ec5bdefd0a, 900ae5b35a).
• Open-coded unsafe.Slice internal — avoids runtime call and lets bounds checks optimize (579902d0b1); arrayClear for array pointers (0668e3cb1a); BSRQ with nonzero input (7d3b64a2e3).
• Boolean lowering fixes on arm64/ppc64/riscv64 internal (9ae7dc3040, 90a11e921b, 7a574ff23f, d6e6140c98); PPC64 FPR/XER regalloc changes (e84a37068b, 33987b408c); Add64/Sub64 lowered in SSA on PPC64 (0c43878baa); more negation rules (e858c14f91).
• Walk/select/map tweaks internal — no unreachable branch for select cases (d9fd9201ad), map-literal hint counts all entries (aaa3d39f27), field tracking of unexported fields (7fd9564fcd).

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: user-visible riscv64 moves to register ABI: context register moved from X20 to X26 9faef5a654, duff device registers X10/X11→X24/X25 29b968e766, ABI register info caf5cd9da8, initial spill 4d2da99498, CALL ops 849e42f028, morestack/prologue 6c17529af7, enabled d3362fc124. sys.Arch gains LR and fixed frame size, replacing Ctxt.FixedFrameSize 8af7fac5a1,5f625de4d0. loopreschedchecks repaired for regabi 3b01a80319. Left open: loong64 and s390x still stack-based.
• Register allocator, scheduler and block-level backend passes — Done: XER made allocatable on PPC64 a4a0f9b148 (FPR31 reallocated 33987b408c, F0/F27-31 allocatable e84a37068b); better propagation of desired registers bdd0f0f780; merge (stack merging helper) uses applicative balanced trees to cut sets sharing (heap −95% on the pathological test) 857cda4625; carry chain scheduled disjointly c386269ed8 (1.7–2.4× on PPC64 crypto/elliptic multiplication).
• amd64 code generation and GOAMD64 microarchitecture levels — Done: LZCNT (avoids BSR zero special-case) a92ca51507, SHLX/SHRX/SARX incl. load forms and constant-shift folding (7fbabe8d57,d6320f1a58,517781b391,66f03f79da,cb702a2a56), MOVBE index/store 32de2b0d1c,ba6df85c7c, false dependency removed for TZCNT 96081f8545, BSRQ with nonzero input 7d3b64a2e3, v3 bit-length intrinsic fix for 16/8 bits 5a103ca5e9.
• arm64 code generation and assembler — Done: jump tables on ARM64 540f8c2b50 (following the amd64 jump-table CL); prologue/epilogue with STP/LDP c6d9b38dd8 and small-frame prologue changed to save LR+decrement SP in one instruction because glibc cannot block SIGSETXID and a signal on the old stack would clobber below SP (frame 0x1f0→0xf0) 64ef16e777; stacksplit optimized 31be6285a8; ANDconst+UBFX merge 8ab42a945a; TLBI, DC, TRN1/2 instructions; fix ADR/ADRP/BITCON/SYS encodings.
• riscv64 compiler and assembler (RVA profiles, vector, compressed) — Done: register ABI (see ABI thread); boolean comparison fix d6e6140c98; two-operand forms 94727bed02.
• loong64 backend and assembler — Done: arch bring-up (above), SPWRITE FuncInfo 654b03167f, division-constant folding fix a2bca290e7.
• PPC64 / Power10 backend (GOPPC64, prefixed instructions, PC-relative code) — Done: Add64/Sub64 lowered into SSA with XER CA elision and spill support, carry-chain scheduling disjoint 0c43878baa,3d7ca9f7c0,c386269ed8 (1.7–2.4× on native crypto/elliptic multiplication); ORN c570f0eda2; BI argument of BC fix 4a5711c3cf; bdnz mnemonics 7b1ba972dc; publicationBarrier c9f67c289f; preferred nop 86371b0360; ISEL CR bit arg 2f23364340.
• Prologue, frame pointer, stack split and function alignment (cmd/internal/obj) — Done: arm64 c6d9b38dd8,64ef16e777,31be6285a8; 3562977b6f (mips, s390x, riscv).
• Jump tables for switch statements on more architectures — Done: arm64 540f8c2b50.
• Multi-word arithmetic, intrinsics and carry-chain support — Done: Add64/Sub64 in SSA for PPC64 0c43878baa.

Other changes

• Boringcrypto-related build fixes internal 16215e5340,e5407501cb.
• -p flag required by cmd/asm user-visible 6e03de7b83; -d=pctab flag db3045b4be.
• obj sorting of relocations / flag to omit referenced symbol names internal 1a9972ec87,b89a194889.
• BlockKind widened internal 83ee6c1d16.
• 10 small obj/arm64 and arm64 rules commits internal — e.g. cmd/asm: refactor some operands that are not special registe; cmd/asm: add TLBI instruction on arm64; cmd/asm: add DC instruction on arm64. (f5290ef947,26ab215969,62d4c32b7e,44a0da4ff1,49f16625c8,ecee4a3291,9ae7dc3040,90a11e921b,e6b5949a75,160414ca6a)
• 1 small obj/x86 and amd64/386 rules commits internal — e.g. cc: use opregreg for x86.AXOR* ops. (a4ffeb9edd)
• 2 small obj/ppc64 and PPC64 rules commits internal — e.g. cc: fix PrefetchStreamed builtin implementation on PPC64; cc: fix boolean comparison on PPC64. (7b15e297a2,7a574ff23f)
• 2 small obj/riscv and riscv64 rules commits internal — e.g. obj/riscv: fix illegal form of MOV instructions; cc: cast riscv64 rewrite shifts to unsigned int. (5dbfa6e61a,95547aee8c)
• 1 small cmd/asm commits internal — e.g. cmd/asm: fix MOVK when constant has high bit set. (a6f6932b3e)
• 1 small ssa/regalloc/liveness/obj generic commits internal — e.g. cc: fix the missing size for FuncInfoSym. (e845750744)

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: stop sorting pclntab entries (the sort was a no-op because all values were 0) 1f97f960e7. Left open: nothing noted.
• DWARF quality for debuggers (types, variables, trampolines) — Done: no typedef DIE for noalg.struct{...} f79a983891; no label symbols for DWARF on Windows/ARM64 cccfb8ffdb. Left open: nothing noted.
• Nosplit stack checking and stack constants — Done: new algorithm: Dostkcheck 7.9 ms to 1.8 ms (−77%), total link −1.6% on cmd/go, at +430% pass memory (40 KiB to 212 KiB) e25f46e596; AIX output fix 5834024057. Left open: nothing noted.
• ELF/relro/hardening and external-link policy — Done: ELF compression default d34287a4f6; DT_NEEDED for all 64-bit a8f019e956; unlinkable object when compiled without -p e853464055; visibility-hidden fixes 2049649e8b; -Wl,-z arguments 38607c5538. Left open: nothing noted.
• Per-platform object formats and internal linking (Mach-O, PE, XCOFF, wasm, ppc64, riscv64, loong64) — Done: loong64 linker cc4957a5f6; PE COMDAT support and crt2.o 1edc2769ca, a9d13a9c23; ppc64 TOC trampolines caa46312ee, register save/restore 9c9090eb1d. Left open: nothing noted.

Other changes

• PE internal linking and cgo plumbing internal — loadpe __imp_*/COMDAT/ctor-list handling and ASLR recipe (0a5bbba366, 821420d6bb, cdee8004ab, cc3a3519af, 2fa45a4fcd), libsynchronization for -race and PIE disabled there (c3bea70d9b, 0c7fcf6bd1).
• Symbol handling internal — ABI-mangling for linker-generated symbols (9c7f0b1ccd), attributes preserved on cloning to external (df08c9a821), name expansion removed (e3f7816f0e), .TOC. relocations resolved (12420f9c01), carrier symbol alignment (c2c76c6f19, 1d9d99b7ce), plugin unexported methods marked (91631bc7e0), GOROOT stamping (9ac75d3951, 9a932c5712, 2c92b2349a), fuzz counters (3f571d1dea), loong64 relocs (af99c2092a), FuncID fix (7c45dafdb2), LR/frame size in sys.Arch (8af7fac5a1).
• boringcrypto linking internal — internal linking allowed for crypto/internal/boring, R_X86_64_PC64 (d1351fbc31, 19b89a22df).
• Fuzzing counters internal — libFuzzer 8-bit counters (7ec6ef432a).