Do not optimize only for table updates (key already present).
Creation of new short keys in new tables can be quite common in
programs that create lots of small tables, for instance with
constructors like {x=e1,y=e2}.
Protect stack top before possible stack reallocation. (In the current
implementation, a stack reallocation cannot call an emergency
collection, so there is no bug, but it is safer not to depend on that.)
Moreover, each function being parsed has its own table.
The code is cleaner when each table is used for one specific purpose:
The scanner uses its table to anchor and unify strings, mapping strings
to themselves; the parser uses it to reuse constants in the code,
mapping constants to their indices in the constant table. A different
table for each task avoids false collisions.
The extra check in checknoTM (versus only checking whether there is a
metatable) is cheap, and it is not that uncommon for a table to have a
metatable without a __newindex metafield.
Optimize this opcode for the common case. For long names or method
calls after too many constants, operation can be coded as a move
followed by 'gettable'.
When reinserting elements into a table during a rehash, the code does
not need to invoke all the complexity of a full 'luaH_set':
- The table has space for all keys.
- The key cannot exist in the new hash.
- The keys are valid (not NaN nor nil).
- The keys are normalized (1.0 -> 1).
- The values cannot be nil.
- No barrier needed (the table already pointed to the key and value).
The array at the end of a Lua closure has pointers to upvalues, not
to tagged values. This bug cannot cause any issue: The ISO C standard
requires that all pointers to structures have the same representation,
so sizeof(TValue*) must be equal to sizeof(UpVal*).
Instead of using 'alimit' for keeping the size of the array and at
the same time being a hint for '#t', a table now keeps these two
values separate. The Table structure has a field 'asize' with the
size of the array, while the length hint is kept in the array itself.
That way, tables with no array part waste no space with that field.
Moreover, the space for the hint may have zero cost for small arrays,
if the array of tags plus the hint still fits in a single word.
'debug.getinfo' can return number of extra arguments added to a call by
a chain of __call metavalues. That information is being used to improve
error messages about errors in these extra arguments.
Without this extra space, sequences of insertions/deletions (and
some other uses) can have unpexpected low performances. See the
added tests for an example, and *Mathematical Models to Analyze Lua
Hybrid Tables and Why They Need a Fix* (Martínez, Nicaud, Rotondo;
arXiv:2208.13602v2) for detais.
Array part needs 1/3 of its elements filled, instead of 1/2.
Array entries use ~1/3 the memory of hash entries, so this new rule
still ensures that array parts do not use more memory than keeping
the values in the hash, while allowing more uses of the array part,
which is more efficient than the hash.
If there are no integer keys outside the array part, there is no
reason to resize it, saving the time to count its elements. Moreover,
assignments to non-integer keys will not collapse a table created with
'table.create'.
Any call to 'va_start' must have a corresponding call to 'va_end';
so, functions called between them (luaO_pushvfstring in particular)
cannot raise errors.
Any call to 'va_start' must have a corresponding call to 'va_end';
so, functions called between them (luaO_pushvfstring in particular)
cannot raise errors.
The use of a pointer (not access, only for computations) after its
deallocation is forbiden in ISO C, but seems to work fine in all
platforms we are aware of. So, using that to correct stack pointers
after a stack reallocation seems safe and is much simpler than the
current implementation (first change all pointers to offsets and
then changing the offsets back to pointers). Anyway, for now that
option is disabled.
