enable inline allocation of structs with pointers (#34126)

NEWS.md

@@ -70,6 +70,16 @@ Language changes
 * The line number of function definitions is now added by the parser as an
  additional `LineNumberNode` at the start of each function body ([#35138]).
 
+Compiler/Runtime improvements
+-----------------------------
+
+* Immutable structs (including tuples) that contain references can now be allocated
+ on the stack, and allocated inline within arrays and other structs ([#33886]).
+ This significantly reduces the number of heap allocations in some workloads.
+ Code that requires assumptions about object layout and addresses (usually for
+ interoperability with C or other languages) might need to be updated; for
+ example any object that needs a stable address should be a `mutable struct`.
+
 Command-line option changes
 ---------------------------
 
@@ -79,9 +89,6 @@ Command-line option changes
 
 * Color now defaults to on when stdout and stderr are TTYs ([#34347])
 
-Command-line option changes
----------------------------
-
  * `-t N`, `--threads N` starts Julia with `N` threads. This option takes precedence over
  `JULIA_NUM_THREADS`. The specified number of threads also propagates to worker
  processes spawned using the `-p`/`--procs` or `--machine-file` command line arguments.

src/datatype.c

@@ -506,11 +506,10 @@ void jl_compute_field_offsets(jl_datatype_t *st)
  // now finish deciding if this instantiation qualifies for special properties
  assert(!isbitstype || st->layout->npointers == 0); // the definition of isbits
  if (isinlinealloc && st->layout->npointers > 0) {
- //if (st->ninitialized != nfields)
- // isinlinealloc = 0;
- //else if (st->layout->fielddesc_type != 0) // GC only implements support for this
- // isinlinealloc = 0;
- isinlinealloc = 0;
+ if (st->ninitialized != nfields)
+ isinlinealloc = 0;
+ else if (st->layout->fielddesc_type != 0) // GC only implements support for this
+ isinlinealloc = 0;
  }
  st->isbitstype = isbitstype;
  st->isinlinealloc = isinlinealloc;