wingo pushed a commit to branch wip-whippet
in repository guile.
commit b874ad5da60428a5c41c6792e4cf5955bfeb89fb
Author: Andy Wingo <wi...@igalia.com>
AuthorDate: Wed Jul 2 10:44:05 2025 +0200
Allow conservative mmc configs to trace some objects precisely
* api/mmc-attrs.h (gc_allocator_alloc_table_begin_pattern): Unify the
strategies between conservative and precise configurations. Notably
this mens that TAGGED allocations are traced precisely in
heap-conservative configurations. Don't pin untagged pointerless
allocations; that is the mutator's responsibility.
* src/mmc.c (compute_trace_kind): Trace tagged objects precisely in all
cases.
(gc_init): Update expectations for alloc table bytes.
---
api/mmc-attrs.h | 36 ++++++++++-------------------
benchmarks/simple-gc-embedder.h | 14 ++++-------
src/mmc.c | 51 ++++++++++++++---------------------------
3 files changed, 33 insertions(+), 68 deletions(-)
diff --git a/api/mmc-attrs.h b/api/mmc-attrs.h
index 749674343..116c64036 100644
--- a/api/mmc-attrs.h
+++ b/api/mmc-attrs.h
@@ -35,30 +35,18 @@ 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;
- if (GC_CONSERVATIVE_TRACE) {
- switch (kind) {
- case GC_ALLOCATION_TAGGED:
- case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
- return young | trace_conservatively;
- case GC_ALLOCATION_TAGGED_POINTERLESS:
- case GC_ALLOCATION_UNTAGGED_POINTERLESS:
- return young | trace_none;
- default:
- GC_CRASH();
- };
- } else {
- switch (kind) {
- case GC_ALLOCATION_TAGGED:
- return young | trace_precisely;
- case GC_ALLOCATION_TAGGED_POINTERLESS:
- return young | trace_none;
- case GC_ALLOCATION_UNTAGGED_POINTERLESS:
- return young | trace_none | pinned;
- case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
- default:
- GC_CRASH();
- };
+ switch (kind) {
+ case GC_ALLOCATION_TAGGED:
+ return young | trace_precisely;
+ case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
+ if (!GC_CONSERVATIVE_TRACE)
+ GC_CRASH ();
+ return young | trace_conservatively;
+ case GC_ALLOCATION_TAGGED_POINTERLESS:
+ case GC_ALLOCATION_UNTAGGED_POINTERLESS:
+ return young | trace_none;
+ default:
+ GC_CRASH();
}
}
static inline uint8_t gc_allocator_alloc_table_end_pattern(void) {
diff --git a/benchmarks/simple-gc-embedder.h b/benchmarks/simple-gc-embedder.h
index bf9f4e91f..26fcef444 100644
--- a/benchmarks/simple-gc-embedder.h
+++ b/benchmarks/simple-gc-embedder.h
@@ -12,13 +12,12 @@ static inline size_t gc_finalizer_priority_count(void) {
return 2; }
static inline int
gc_is_valid_conservative_ref_displacement(uintptr_t displacement) {
-#if GC_CONSERVATIVE_ROOTS || GC_CONSERVATIVE_TRACE
- // Here is where you would allow tagged heap object references.
- return displacement == 0;
-#else
+ if (GC_CONSERVATIVE_ROOTS || GC_CONSERVATIVE_TRACE)
+ // Here is where you would allow tagged heap object references.
+ return displacement == 0;
+
// Shouldn't get here.
GC_CRASH();
-#endif
}
// No external objects in simple benchmarks.
@@ -40,10 +39,6 @@ static inline void gc_trace_object(struct gc_ref ref,
struct gc_heap *heap,
void *trace_data,
size_t *size) {
-#if GC_CONSERVATIVE_TRACE
- // Shouldn't get here.
- GC_CRASH();
-#else
switch (tag_live_alloc_kind(*tag_word(ref))) {
#define SCAN_OBJECT(name, Name, NAME) \
case ALLOC_KIND_##NAME: \
@@ -58,7 +53,6 @@ static inline void gc_trace_object(struct gc_ref ref,
default:
GC_CRASH();
}
-#endif
}
static inline void visit_roots(struct handle *roots,
diff --git a/src/mmc.c b/src/mmc.c
index 279f56278..0dce510b3 100644
--- a/src/mmc.c
+++ b/src/mmc.c
@@ -1031,28 +1031,18 @@ void gc_safepoint_signal_reallow(struct gc_mutator
*mut) { GC_CRASH(); }
static enum gc_trace_kind
compute_trace_kind(enum gc_allocation_kind kind) {
- if (GC_CONSERVATIVE_TRACE) {
- switch (kind) {
- case GC_ALLOCATION_TAGGED:
- case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
- return GC_TRACE_CONSERVATIVELY;
- case GC_ALLOCATION_TAGGED_POINTERLESS:
- case GC_ALLOCATION_UNTAGGED_POINTERLESS:
- return GC_TRACE_NONE;
- default:
- GC_CRASH();
- };
- } else {
- switch (kind) {
- case GC_ALLOCATION_TAGGED:
- return GC_TRACE_PRECISELY;
- case GC_ALLOCATION_TAGGED_POINTERLESS:
- case GC_ALLOCATION_UNTAGGED_POINTERLESS:
- return GC_TRACE_NONE;
- case GC_ALLOCATION_UNTAGGED_CONSERVATIVE:
- default:
- GC_CRASH();
- };
+ switch (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:
+ return GC_TRACE_NONE;
+ default:
+ GC_CRASH();
}
}
@@ -1367,20 +1357,13 @@ gc_init(const struct gc_options *options, struct
gc_stack_addr stack_base,
GC_ASSERT_EQ(gc_allocator_alloc_table_alignment(), NOFL_SLAB_SIZE);
GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_TAGGED_POINTERLESS),
NOFL_METADATA_BYTE_YOUNG | NOFL_METADATA_BYTE_TRACE_NONE);
- if (GC_CONSERVATIVE_TRACE) {
- GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_TAGGED),
- NOFL_METADATA_BYTE_YOUNG |
NOFL_METADATA_BYTE_TRACE_CONSERVATIVELY);
+ GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_TAGGED),
+ NOFL_METADATA_BYTE_YOUNG | NOFL_METADATA_BYTE_TRACE_PRECISELY);
+ if (GC_CONSERVATIVE_TRACE)
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);
- } else {
- GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_TAGGED),
- NOFL_METADATA_BYTE_YOUNG |
NOFL_METADATA_BYTE_TRACE_PRECISELY);
-
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_PINNED);
- }
+
GC_ASSERT_EQ(gc_allocator_alloc_table_begin_pattern(GC_ALLOCATION_UNTAGGED_POINTERLESS),
+ NOFL_METADATA_BYTE_YOUNG | NOFL_METADATA_BYTE_TRACE_NONE);
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);
