This commit does four things:
* Adds "pb.ss" and "pb.c", which implement a portable bytecode
backend and interpreter that is intended for bootstrapping. A
single set of pb bootfiles can support bootstrapping on all
platforms --- as long as the C compiler supports a 64-bit integer
type. The pb machine supports foreign calls for only a small set of
recognized prototypes, and it does not support foriegn callables.
Use `./configure --pb` to build the pb variant.
* Changes the kernel's casts between `ptr` and `void*` types. In a pb
build, the `ptr` type can be a 64-bit integer type while `void*` is
a 32-bit pointer type, so casts must go through an intermediate
integer type.
* Adjusts the compiler to accomodate run-time-determined endianness.
Making the compiler agnostic to word size is not practical, but
only a few pieces depend on the target machine's endianness, and
those can generally be deferred to a run-time choice of byte-based
operations. The one exception is that ftype bit fields are not
allowed unless accompanied by an explicit endianness declaration.
* Start reducing duplication among platform-specific makefiles. For
example, `Mf-ta6osx` chains to `Mf-a6osx` to avoid repeating most
of it. A lot more can be done here.
original commit: 97533fa9d8b8400b0dc1a890768c7d30c91257e0
Change the GC so that it can mark and sweep objects in-place, instead
of always copying. This change is helpful for reducing peak memory
use while performing a collection on a large, old heap.
Some non-copying support was already in place for locked objects,
but the new implementation is faster and more general. As an
alternative to locking, the storage manager now provides "immobile"
allocation (currently only for bytevectors, vectors, and boxes),
which allocates an object that won't move but that can be GCed if
it's not referenced. A locked object is an object that has been
immobiled and that is on a global list --- mostly the old,
non-scalable implementation of locked objects brought back, since
immobile objects cover the cases that need to scale.
original commit: aecb7b736cb1d52764c292fa6364a674958dfde3
The `unlock-object` operation was O(N) with N currently locked objects
--- so, O(N^2) to lock N objects and then unlock them --- because
locked objects were stored in and searched in a global list. Also, GC
was O(N) at any generation with N locked objects across generations,
since every locked object was scanned.
Fix these poblems so that locking and unlocking is practically O(1)
and GC is not poportional to locked objects. More precisely, locking
and unlocking is now O(C) for locking an individual object C times to
be balanced by C unlocks. (Since multiple locks on a single object
is rare, this performance seems good enough.)
The implementation replaces the global list with segment-specific
lists. Backpointers are managed using the general generational
support, so that unmodified, old-generation locked objects do not
need to be swept duing a new-generation collection.
original commit: a57d256ca73a3d507792c471facb7e35afbe88b3
