For now, this GC is non-generational, and much slower than the old
version. It tracks objects by a fixed object ID rather than changeable
memory address. Small object (eight bytes or less) are stored directly
in the array, indexed by object ID, while larger object are allocated
with malloc() (for now) and stored in the array as a pointer. Object
IDs are stored as 32-bit integers, even on 64-bit platforms.
Advantages:
- Simpler design
- Requires less memory on 64-bit platforms
- Object IDs don't change when running the GC
- No need to store a random "hash" value in vectors/strings/structs
- Can hash pairs by identity, not just value
- Can move objects individually, without fixing up all references
- Can determine object type from value, without another memory access
Disadvantages:
- Lower initial performance (non-generational, relies on malloc())
- 32-bit values place a (high) limit on total number of objects
- Must explicitly free unreachable object IDs after GC
The macro resembles (or x (fn x)) except:
1) The value is only evaluated once, and
2) Multiple (single-argument) functions can be chained.
If the original value or the result of any function is #f, the
final value is #f. Otherwise the result is ((compose ,@fns) x).
Short-circuit evaluation is employed.
Each transient identifies the value of the corresponding previous bytecode.
This change (a) frees up many bytecodes formerly used by the conditional
expression (if c t f); (b) regularizes the bytecode by always placing opcodes
before operands; and (c) causes the bytecode to conform to the Single Static
Assignment (SSA) form preferred by e.g. LLVM.
Includes updates to the hand-assembled files (*.rla) and the bytecode compiler.
Eliminate use of #="undefined" as an explicit initializer for boxes.
Do not allow #@ ("freeze") to be applied to references, for sanity's sake.
Inside compiler, builtins are now represented by (#%builtin "name") form.
Plain symbols are promoted to builtins; quoted symbols become structures.
Fix choice of continuation when function ends in (call/cc).
Change empty kw-args from '() to #%nil in (simplify-apply).
Improve error message when no match is found for a primitive form.
Add special variables for keyword arguments & values.
Add support for keyword arguments to (simplify-apply).
Implement full string parsing in src/reader.rls.
TODO: Support keywords in (simplify-lambda) and writer.
Fix assertion in gc_object_left_behind() to work in Gen-0 collection.
Add (weak-box?) and (make-weak-box) primitives. (unbox) now works for both.
Add option to just simplify the input (stops before reduce-function).
Default to writing .rla without indentation, comments, or newlines.
Add support for (fix=), (list), (and), (or), (cond), (when), and (unless).
Fix a mapper bug which could assign the same frame var to separate variables.
Update make-struct primitive for new structure type layout.
Change primitives to use #% as prefix instead of just %.
Add primitive operations for comparing byte-strings.
Pairs, boxes, and strings are hashed by values; vectors and structures
are "hashed" by reference. Takes into account the possibility of cycles.
This is a prelude to implementing hash-tables.
Jesse D. McDonald