0.624

What's Changed

• CodeGen: Fix a typo in X64 (dis)assembler by @zeux in #1238
• Optimize table.concat. This function is now 1.4x-2x faster. #1243
• Optimize table.maxn. This function is now 5-14x faster
• Add benchmarks for native compilation with type info enabled by @vegorov-rbx in #1244
• Reserve Luau stack space for error message.

New Solver

• Globals can be type-stated, but only if they are already in scope
• Fix a stack overflow that could occur when normalizing certain kinds of recursive unions of intersections (of unions of intersections...)
• Fix an assertion failure that would trigger when the __iter metamethod has a bad signature

Native Codegen

• Type propagation and temporary register type hints
• Direct vector property access should only happen for names of right length
• BytecodeAnalysis will only predict that some of the vector value fields are numbers

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Internal Contributors

Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com
Full Changelog: 0.623...0.624

0.623

What's changed?

New Type Solver

• Unification of two fresh types no longer binds them together.
• Replaced uses of raw emplace with emplaceType to catch cyclic bound types when they are created.
• SetIndexerConstraint is blocked until the indexer result type is not blocked.
• Fix a case where a blocked type got past the constraint solver.
• Searching for free types should no longer traverse into ClassTypes.
• Fix a corner case that could result in the non-testable type ~{}.
• Fix incorrect flagging when any was a parameter of some checked function in nonstrict type checker.
• IterableConstraint now consider tables without __iter to be iterables.

Native Code Generation

• Improve register type info lookup by program counter.
• Generate type information for locals and upvalues

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: James McNellis jmcnellis@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.622

What's changed?

• Improved the actual message for the type errors for cannot call non-function when attempting to call a union of functions/callable tables. The error now correctly explains the issue is an inability to determine the return type of the call in this situation.
• Resolve an issue where tables and metatables were not correctly being cloned during instantiation (fixes #1176).
• Refactor luaM_getnextgcopage to luaM_getnextpage (generally removing gco prefix where appropriate).
• Optimize table.move between tables for large ranges of elements.
• Reformat a bunch of code automatically using clang-format.

New Type Solver

• Clean up minimally-used or unused constraints in the constraint solver (InstantiationConstraint, SetOpConstraint, SingletonOrTopTypeConstraint).
• Add a builtin singleton type family to replace SingletonOrTopTypeConstraint when inferring refinements.
• Fixed a crash involving type path reasoning by recording when type family reduction has taken place in the path.
• Improved constraint ordering by blocking on unreduced types families that are not yet proven uninhabitable.
• Improved the handling of SetIndexerConstraints for both better inference quality and to resolve crashes.
• Fix a crash when normalizing cyclic unions of intersections.
• Fix a crash when normalizing an intersection with the negation of unknown.
• Fix a number of crashes caused by missing follow calls on TypeIds.
• Changed type family reduction to correctly use a semantic notion of uninhabited types, rather than checking for never types specifically.
• Refactor the union and intersect type families to be variadic.

Native Code Generation

• Improve translation for userdata key get/set and userdata/vector namecall.
• Provide [top level] and [anonymous] as function names to FunctionStats as appropriate when no function name is available.
• Disable unwind support on Android platforms since it is unsupported.

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.621

What's changed?

• Support for new 'require by string' RFC with relative paths and aliases in now enabled in Luau REPL application

New Type Solver

• Fixed assertion failure on generic table keys ([expr] = value)
• Fixed an issue with type substitution traversing into the substituted parts during type instantiation
• Fixed crash in union simplification when that union contained uninhabited unions and other types inside
• Union types in binary type families like add<a | b, c> are expanded into add<a, c> | add<b, c> to handle
• Added handling for type family solving creating new type families
• Fixed a bug with normalization operation caching types with unsolved parts
• Tables with uninhabited properties are now simplified to never
• Fixed failures found by fuzzer

Native Code Generation

• Added support for shared code generation between multiple Luau VM instances
• Fixed issue in load-store propagation and new tagged LOAD_TVALUE instructions
• Fixed issues with partial register dead store elimination causing failures in GC assists

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Full Changelog: 0.620...0.621

0.620

What's Changed

New Type Solver

• Many more fixes to crashes, assertions, and hangs
• Annotated locals now countermand the inferred types of locals, meaning that for a type type MyType = number | string, local foo : MyType = 5 behaves the same as local foo = 5 :: MyType, where before, foo would be assigned the type of the value on the rhs.
• Type Normalization now respects resource limits.
• Subtyping between classes and cyclic tables now supported

Native Code Generation

• Work on the Native Code Generation(NCG) allocator continues

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: James McNellis jmcnellis@roblox.com
Co-authored-by: Vighnesh Vijay vvijay@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.619

What's Changed

New Type Solver

• Many fixes to crashes, assertions, and hangs
• Binary type family aliases now have a default parameter
• Added a debug check for unsolved types escaping the constraint solver
• Overloaded functions are no longer inferred
• Unification creates additional subtyping constraints for blocked types
• Attempt to guess the result type for type families that are too large to resolve timely

Native Code Generation

• Fixed IrCmd::CHECK_TRUTHY lowering in a specific case
• Detailed compilation errors are now supported
• More work on the new allocator

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: James McNellis jmcnellis@roblox.com
Co-authored-by: Lily Brown lbrown@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.618

What's changed

Debugger

• Values after a 'continue' statement should not be accessible by debugger in the 'until' condition

New Type Solver

• Many fixes to crashes and hangs
• Better bidirectional inference of table literal expressions

Native Code Generation

• CodeGen: Preserve known tags for LOAD_TVALUE synthesized from LOADK (#1201)
• Initial steps toward a shared code allocator

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Lily Brown lbrown@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

Full Changelog: 0.617...0.618

0.617

What's Changed

• Fix a case where the stack wasn't completely cleaned up where debug.info errored when passed "f" option and a thread.
• Fix a case of uninitialized field in luaF_newproto.

New Type Solver

• When a local is captured in a function, don't add a new entry to the DfgScope::bindings if the capture occurs within a loop.
• Fix a poor performance characteristic during unification by not trying to simplify an intersection.
• Fix a case of multiple constraints mutating the same blocked type causing incorrect inferences.
• Fix a case of assertion failure when overload resolution encounters a return typepack mismatch.
• When refining a property of the top table type, we no longer signal an unknown property error.
• Fix a misuse of free types when trying to infer the type of a subscript expression.
• Fix a case of assertion failure when trying to resolve an overload from never.

Native Code Generation

• Fix dead store optimization issues caused by partial stores.

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: Aviral Goel agoel@roblox.com
Co-authored-by: David Cope dcope@roblox.com
Co-authored-by: Lily Brown lbrown@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.616

What's Changed

• Add a compiler hint to improve Luau memory allocation inlining

New Type Solver

• Added a system for recommending explicit type annotations to users in cases where we've inferred complex generic types with type families.
• Marked string library functions as @checked for use in new non-strict mode.
• Fixed a bug with new non-strict mode where we would incorrectly report arity mismatches when missing optional arguments.
• Implement an occurs check for unifications that would produce self-recursive types.
• Fix bug where overload resolution would fail when applied to non-overloaded functions.
• Fix bug that caused the subtyping to report an error whenever a generic was instantiated in an invariant context.
• Fix crash caused by SetPropConstraint not blocking properly.
• Fix bug where type checker forgot the refined rvalue when mutating a property.

Native Code Generation

• Implement optimization to eliminate dead stores
• Optimize vector ops for X64 when the source is computed (thanks, @zeux!)
• Use more efficient lowering for UNM_* (thanks, @zeux!)

---

Internal Contributors

Co-authored-by: Aaron Weiss aaronweiss@roblox.com
Co-authored-by: Alexander McCord amccord@roblox.com
Co-authored-by: Andy Friesen afriesen@roblox.com
Co-authored-by: David Cope dcope@roblox.com
Co-authored-by: Lily Brown lbrown@roblox.com
Co-authored-by: Vyacheslav Egorov vegorov@roblox.com

0.615

What's changed?

• Luau allocation scheme was changed to handle allocations in 513-1024 byte range internally without falling back to global allocator
  • coroutine/thread creation no longer requires any global allocations, making it up to 15% faster (vs libc malloc)
  • table construction for 17-32 keys or 33-64 array elements is up to 30% faster (vs libc malloc)
• luau-compile: Fix usage of vector-ctor without vector-lib by @zeux in #1172

New Type Solver

• Cyclic unary negation type families are reduced to number when possible
• Class types are skipped when searching for free types in unifier to improve performance
• Fixed issues with table type inference when metatables are present
• Improved inference of iteration loop types
• Fixed an issue with bidirectional inference of method calls
• Type simplification will now preserve error suppression markers

Native Code Generation

• Fixed TAG_VECTOR skip optimization to not break instruction use counts (broken optimization wasn't included in 614)
• Fixed missing side-effect when optimizing generic loop preparation instruction
• Optimized vector ops for X64 when the source is computed by @zeux in #1174

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Full Changelog: 0.614...0.615