* libguile/loader.c (scm_find_slot_map_unlocked): Rename from
scm_find_dead_slot_map_unlocked.
* libguile/vm.c (struct slot_map_cache_entry, struct slot_map_cache)
(find_slot_map): Rename, changing "dead_slot" to "slot".
(enum slot_desc): New type.
(scm_i_vm_mark_stack): Interpret slot maps as having two bits per
slot, allowing us to indicate that a slot is live but not a pointer.
* module/language/cps/compile-bytecode.scm (compile-function): Adapt to
emit-slot-map name change.
* module/system/vm/assembler.scm (<asm>): Rename dead-slot-maps field to
slot-maps.
(emit-slot-map): Rename from emit-dead-slot-map.
(link-frame-maps): 2 bits per slot.
* module/language/cps/slot-allocation.scm (lookup-slot-map): Rename from
lookup-dead-slot-map.
(compute-var-representations): New function.
(allocate-slots): Adapt to encode two-bit slot representations.
* libguile/loader.c (load_thunk_from_memory): Only load PT_LOAD
segments, as libc does. The PT_DYNAMIC segment should be inside some
other PT_LOAD segment.
* module/system/vm/linker.scm (segment-kind): Give the .dynamic segment
PT_LOAD kind, so that it is written in a PT_LOAD segment.
(count-segments): Add one if there is a SHT_DYNAMIC segment.
(allocate-segment): Set the paddr to the addr, as binutils do.
(record-special-segments): New routine, to write out special segments
like PT_DYNAMIC.
(allocate-elf): Call record-special-segments.
* module/language/cps/slot-allocation.scm (lookup-dead-slot-map)
(allocate-slots): For each non-tail call in a function, compute the
set of slots that are dead after the function has begun the call.
* module/language/cps/compile-bytecode.scm (compile-fun): Emit the
`dead-slot-map' macro instruction for non-tail calls.
* module/system/vm/assembler.scm (<asm>): Add `dead-slot-maps' member.
(dead-slot-map): New macro-instruction.
(link-frame-maps, link-dynamic-section, link-objects): Write dead
slots information into .guile.frame-maps sections of ELF files.
* module/system/vm/elf.scm (DT_GUILE_FRAME_MAPS): New definition.
* libguile/loader.h:
* libguile/loader.c (DT_GUILE_FRAME_MAPS, process_dynamic_segment):
(load_thunk_from_memory, register_elf): Arrange to parse
DT_GUILE_FRAME_MAPS out of the dynamic section.
(find_mapped_elf_image_unlocked, find_mapped_elf_image): New helpers.
(scm_find_mapped_elf_image): Refactor.
(scm_find_dead_slot_map_unlocked): New interface.
* libguile/vm.c (scm_i_vm_mark_stack): Mark the hottest frame
conservatively, as before. Otherwise use the dead slots map, if
available, to avoid marking data that isn't live.
