Conceptually, all functions get their vararg arguments in a vararg
table. The storing of vararg arguments in the stack is always treated
as an optimization.
When calling 'luaK_storevar', the 'expdesc' for the variable must be
created before the one for the expression, to satisfy the assumptions
for register allocation. So, in a statement like 'global a = exp', where
'a' is actually '_ENV.a', this variable must be handled before the
initializing expression 'exp'.
The check for limit of local variables is made after generating code to
initialize them. If there are too many local variables not initialized,
the coding of instruction OP_LOADNIL could overflow an argument.
A vararg table can be virtual. If the vararg table is used only as
a base in indexing expressions, the code does not need to create an
actual table for it. Instead, it compiles the indexing expressions
into direct accesses to the internal vararg data.
In a constructor, each field generates at least one opcode, and the
number of opcodes is limited by INT_MAX. Therefore, the counters for
number of fields cannot exceed this limit. (The current limit for
items in the hash part of a table has a limit smaller than INT_MAX.
However, as long as there are no overflows, the logic for table
resizing will handle that limit.)
A goto cannot jump into the scope of any variable declaration,
including 'global *'. To report the error, it needs a "name" for
the scope it is entering.
The parser uses "break" as fake label to compile "break" as "goto
break". To avoid producing this string at each use, it keeps it
available in its state.
Added comments so that all braces pair correctly. (The parser has
several instances of unmatched braces as characters ('{' or '}'), which
hinders matching regular braces in the code.)
The compilation of a goto or a label just create an entry and generate
boilerplate code for the gotos. As we don't know yet whether it needs a
CLOSE, we code a jump followed by a CLOSE, which is then dead code.
When a block ends (and then we know for sure whether there are variables
that need to be closed), we check the goto's against the labels of that
block. When closing a goto against a label, if it needs a CLOSE, the
compiler swaps the order of the jump and the CLOSE, making the CLOSE
active.
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.
New instruction format 'ivABC' (a variant of iABC where parameter vC has
10 bits) allows constructors of up to 1024 elements to be coded without
EXTRAARG.
Instead of a fixed limit of 50 registers (which, in a bad worst case,
can limit the nesting of constructors to 5 levels), the compiler
computes an individual limit for each constructor based on how many
registers are available when it runs. This limit then controls the
frequency of SETLIST instructions.
Several definitions that don't need to be "global" (that is, that
concerns only specific parts of the code) moved out of llimits.h,
to more appropriate places.
