wingo pushed a commit to branch wip-whippet
in repository guile.
commit cd54bbc627bebd85af69421c7283968c3f5e2927
Author: Andy Wingo <wi...@igalia.com>
AuthorDate: Thu Jul 3 10:13:20 2025 +0200
nofl: Pin untagged pointerless allocations
This was the case before, but I forgot why and removed it :/
---
api/mmc-attrs.h | 4 +++-
src/mmc.c | 6 ++----
src/nofl-space.h | 13 ++++++++++---
3 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/api/mmc-attrs.h b/api/mmc-attrs.h
index 116c64036..a9fdcc844 100644
--- a/api/mmc-attrs.h
+++ b/api/mmc-attrs.h
@@ -35,6 +35,7 @@ static inline uint8_t
gc_allocator_alloc_table_begin_pattern(enum gc_allocation_
uint8_t trace_precisely = 0;
uint8_t trace_none = 8;
uint8_t trace_conservatively = 16;
+ uint8_t pinned = 16;
switch (kind) {
case GC_ALLOCATION_TAGGED:
return young | trace_precisely;
@@ -43,8 +44,9 @@ static inline uint8_t
gc_allocator_alloc_table_begin_pattern(enum gc_allocation_
GC_CRASH ();
return young | trace_conservatively;
case GC_ALLOCATION_TAGGED_POINTERLESS:
- case GC_ALLOCATION_UNTAGGED_POINTERLESS:
return young | trace_none;
+ case GC_ALLOCATION_UNTAGGED_POINTERLESS:
+ return young | trace_none | pinned;
default:
GC_CRASH();
}
diff --git a/src/mmc.c b/src/mmc.c
index 9b9b00046..65d076b06 100644
--- a/src/mmc.c
+++ b/src/mmc.c
@@ -617,7 +617,7 @@ grow_heap_if_necessary(struct gc_heap *heap,
// If we cannot defragment and are making no progress but have a
// growable heap, expand by 25% to add some headroom.
size_t needed_headroom =
- GC_CONSERVATIVE_TRACE
+ nofl_space_heap_has_ambiguous_edges (nofl)
? (progress ? 0 : nofl_active_block_count (nofl) * NOFL_BLOCK_SIZE / 4)
: 0;
size_t headroom = nofl_empty_block_count(nofl) * NOFL_BLOCK_SIZE;
@@ -1031,8 +1031,6 @@ compute_trace_kind(enum gc_allocation_kind kind) {
case GC_ALLOCATION_TAGGED:
return GC_TRACE_PRECISELY;
case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
- if (!GC_CONSERVATIVE_TRACE)
- GC_CRASH ();
return GC_TRACE_CONSERVATIVELY;
case GC_ALLOCATION_TAGGED_POINTERLESS:
case GC_ALLOCATION_UNTAGGED_POINTERLESS:
@@ -1359,7 +1357,7 @@ gc_init(const struct gc_options *options, struct
gc_stack_addr stack_base,
GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_UNTAGGED_CONSERVATIVE),
NOFL_METADATA_BYTE_YOUNG |
NOFL_METADATA_BYTE_TRACE_CONSERVATIVELY);
GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_UNTAGGED_POINTERLESS),
- NOFL_METADATA_BYTE_YOUNG | NOFL_METADATA_BYTE_TRACE_NONE);
+ NOFL_METADATA_BYTE_YOUNG | NOFL_METADATA_BYTE_TRACE_NONE |
NOFL_METADATA_BYTE_PINNED);
GC_ASSERT_EQ(gc_allocator_alloc_table_end_pattern(), NOFL_METADATA_BYTE_END);
if (GC_GENERATIONAL) {
GC_ASSERT_EQ(gc_write_barrier_field_table_alignment(), NOFL_SLAB_SIZE);
diff --git a/src/nofl-space.h b/src/nofl-space.h
index ce62c17d3..d9a3fd99a 100644
--- a/src/nofl-space.h
+++ b/src/nofl-space.h
@@ -1357,12 +1357,19 @@ nofl_metadata_byte_trace_kind(struct nofl_space *space,
uint8_t byte)
switch (byte & mask) {
case NOFL_METADATA_BYTE_TRACE_PRECISELY:
return GC_TRACE_PRECISELY;
- case NOFL_METADATA_BYTE_TRACE_NONE:
- return GC_TRACE_NONE;
case NOFL_METADATA_BYTE_TRACE_CONSERVATIVELY:
return GC_TRACE_CONSERVATIVELY;
+ case NOFL_METADATA_BYTE_TRACE_NONE:
+ return GC_TRACE_NONE;
default:
- GC_CRASH();
+ /* Untagged pointerless objects are allocated with the PINNED bit,
+ because we can't relocate them, because we don't have a tag word
+ to hold the forwarding state. Fortunately, this bit pattern is
+ different from NOFL_METADATA_BYTE_TRACE_CONSERVATIVELY; we can
+ just leave it as-is. */
+ GC_ASSERT_EQ (byte & mask,
+ NOFL_METADATA_BYTE_TRACE_NONE | NOFL_METADATA_BYTE_PINNED);
+ return GC_TRACE_NONE;
}
}
