bpart: When backdating replace the entire bpart chain

Rather than rewriting the `restriction` of the bparts. With this, I
believe this removes that last point where `restriction` is overwritten
after construction, hopefully allowing us to go back to the original
design where `restriction` is `const` after construction.

Author: Keno

src/module.c

@@ -248,6 +248,78 @@ JL_DLLEXPORT jl_module_t *jl_new_module_(jl_sym_t *name, jl_module_t *parent, ui
     return m;
 }
 
+// Precondition: world_counter_lock is held
+JL_DLLEXPORT jl_binding_partition_t *jl_declare_constant_val3(
+    jl_binding_t *b, jl_module_t *mod, jl_sym_t *var, jl_value_t *val,
+    enum jl_partition_kind constant_kind, size_t new_world)
+{
+    JL_GC_PUSH1(&val);
+    if (!b) {
+        b = jl_get_module_binding(mod, var, 1);
+    }
+    jl_binding_partition_t *new_bpart = NULL;
+    jl_binding_partition_t *bpart = jl_get_binding_partition(b, new_world);
+    jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
+    while (!new_bpart) {
+        enum jl_partition_kind kind = decode_restriction_kind(pku);
+        if (jl_bkind_is_some_constant(kind)) {
+            if (!val) {
+                new_bpart = bpart;
+                break;
+            }
+            jl_value_t *old = decode_restriction_value(pku);
+            JL_GC_PROMISE_ROOTED(old);
+            if (jl_egal(val, old)) {
+                new_bpart = bpart;
+                break;
+            }
+        } else if (jl_bkind_is_some_import(kind) && kind != BINDING_KIND_IMPLICIT) {
+            jl_errorf("cannot declare %s.%s constant; it was already declared as an import",
+                      jl_symbol_name(mod->name), jl_symbol_name(var));
+        } else if (kind == BINDING_KIND_GLOBAL) {
+            jl_errorf("cannot declare %s.%s constant; it was already declared global",
+                      jl_symbol_name(mod->name), jl_symbol_name(var));
+        }
+        if (bpart->min_world == new_world) {
+            if (!jl_atomic_cmpswap(&bpart->restriction, &pku, encode_restriction(val, constant_kind))) {
+                continue;
+            }
+            jl_gc_wb(bpart, val);
+            new_bpart = bpart;
+        } else {
+            new_bpart = jl_replace_binding_locked(b, bpart, val, constant_kind, new_world);
+        }
+        int need_backdate = new_world && val;
+        if (need_backdate) {
+            // We will backdate as long as this partition was never explicitly
+            // declared const, global, or imported.
+            jl_binding_partition_t *prev_bpart = bpart;
+            for (;;) {
+                jl_ptr_kind_union_t prev_pku = jl_atomic_load_relaxed(&prev_bpart->restriction);
+                enum jl_partition_kind prev_kind = decode_restriction_kind(prev_pku);
+                if (jl_bkind_is_some_constant(prev_kind) || prev_kind == BINDING_KIND_GLOBAL ||
+                    (jl_bkind_is_some_import(prev_kind))) {
+                    need_backdate = 0;
+                    break;
+                }
+                if (prev_bpart->min_world == 0)
+                    break;
+                prev_bpart = jl_get_binding_partition(b, prev_bpart->min_world - 1);
+            }
+        }
+        // If backdate is required, create one new binding partition to cover
+        // the entire backdate range.
+        if (need_backdate) {
+            jl_binding_partition_t *backdate_bpart = new_binding_partition();
+            jl_atomic_store_relaxed(&backdate_bpart->restriction, encode_restriction(val, BINDING_KIND_BACKDATED_CONST));
+            jl_atomic_store_relaxed(&backdate_bpart->max_world, new_world - 1);
+            jl_atomic_store_release(&new_bpart->next, backdate_bpart);
+        }
+    }
+    JL_GC_POP();
+    return new_bpart;
+}
+
 JL_DLLEXPORT jl_module_t *jl_new_module(jl_sym_t *name, jl_module_t *parent)
 {
     return jl_new_module_(name, parent, 1);

src/toplevel.c

@@ -754,82 +754,6 @@ static void jl_eval_errorf(jl_module_t *m, const char *filename, int lineno, con
     JL_GC_POP();
 }
 
-JL_DLLEXPORT jl_binding_partition_t *jl_declare_constant_val3(
-    jl_binding_t *b, jl_module_t *mod, jl_sym_t *var, jl_value_t *val,
-    enum jl_partition_kind constant_kind, size_t new_world)
-{
-    JL_GC_PUSH1(&val);
-    if (!b) {
-        b = jl_get_module_binding(mod, var, 1);
-    }
-    jl_binding_partition_t *new_bpart = NULL;
-    jl_binding_partition_t *bpart = jl_get_binding_partition(b, new_world);
-    jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
-    while (!new_bpart) {
-        enum jl_partition_kind kind = decode_restriction_kind(pku);
-        if (jl_bkind_is_some_constant(kind)) {
-            if (!val) {
-                new_bpart = bpart;
-                break;
-            }
-            jl_value_t *old = decode_restriction_value(pku);
-            JL_GC_PROMISE_ROOTED(old);
-            if (jl_egal(val, old)) {
-                new_bpart = bpart;
-                break;
-            }
-        } else if (jl_bkind_is_some_import(kind) && kind != BINDING_KIND_IMPLICIT) {
-            jl_errorf("cannot declare %s.%s constant; it was already declared as an import",
-                      jl_symbol_name(mod->name), jl_symbol_name(var));
-        } else if (kind == BINDING_KIND_GLOBAL) {
-            jl_errorf("cannot declare %s.%s constant; it was already declared global",
-                      jl_symbol_name(mod->name), jl_symbol_name(var));
-        }
-        if (bpart->min_world == new_world) {
-            if (!jl_atomic_cmpswap(&bpart->restriction, &pku, encode_restriction(val, constant_kind))) {
-                continue;
-            }
-            jl_gc_wb(bpart, val);
-            new_bpart = bpart;
-        } else {
-            new_bpart = jl_replace_binding_locked(b, bpart, val, constant_kind, new_world);
-        }
-        int need_backdate = new_world && val;
-        if (need_backdate) {
-            // We will backdate as long as this partition was never explicitly
-            // declared const, global, or imported.
-            jl_binding_partition_t *prev_bpart = bpart;
-            for (;;) {
-                jl_ptr_kind_union_t prev_pku = jl_atomic_load_relaxed(&prev_bpart->restriction);
-                enum jl_partition_kind prev_kind = decode_restriction_kind(prev_pku);
-                if (jl_bkind_is_some_constant(prev_kind) || prev_kind == BINDING_KIND_GLOBAL ||
-                    (jl_bkind_is_some_import(prev_kind))) {
-                    need_backdate = 0;
-                    break;
-                }
-                if (prev_bpart->min_world == 0)
-                    break;
-                prev_bpart = jl_get_binding_partition(b, prev_bpart->min_world - 1);
-            }
-        }
-        // If backdate is required, rewrite all previous binding partitions to
-        // backdated const
-        if (need_backdate) {
-            // We will backdate as long as this partition was never explicitly
-            // declared const, global, or *explicitly* imported.
-            jl_binding_partition_t *prev_bpart = bpart;
-            for (;;) {
-                jl_atomic_store_relaxed(&prev_bpart->restriction, encode_restriction(val, BINDING_KIND_BACKDATED_CONST));
-                if (prev_bpart->min_world == 0)
-                    break;
-                prev_bpart = jl_get_binding_partition(b, prev_bpart->min_world - 1);
-            }
-        }
-    }
-    JL_GC_POP();
-    return new_bpart;
-}
-
 JL_DLLEXPORT jl_binding_partition_t *jl_declare_constant_val2(
     jl_binding_t *b, jl_module_t *mod, jl_sym_t *var, jl_value_t *val,
     enum jl_partition_kind constant_kind)