Refactor Binding data structures in preparation for partition (#54788)

This is a re-worked extraction of #54654, adjusted to support the new
semantics arrived at over the course of that thread. Note that this is
the data-structure change only. The semantics in this PR still match
current master to the greatest extent possible.

The core idea here is to split `Binding` in two: A new `Binding` with
minimal data and a `BindingPartition` that holds all data that is
world-age partitioned. In the present PR, these are always in 1:1
correspondednce, but after #54654, there will be multiple
`BindingPartition`s for every `Binding`.

Essentially the `owner` and `ty` fields have been merged into a new
`restriction` field of `BindingPartition`, which may also hold the value
of a constant (consistent with the final semantics reached in #54654).
The non-partitioned binding->value field is now used exclusively for
non-constant globals. The disambiguation for how to interpret the
`restriction` field happens via flags. `->imported` grew to 2 bits and
can now be one of `NONE`/`IMPLICIT`/ `EXPLICIT`/`GUARD`. `GUARD`
corresponds to the old `b->owner == NULL` case. `NONE` corresponds to
the old `b->owner == b` case, while IMPLICIT/EXPLICIT correspond to
`b->owner != b` and the old `imported` flag. Other than that, the
behavior of the flags is unchanged.

Additionally, fields are provided for `min_world`/`max_world`/`next`,
but these are unused in this PR and prepratory only.

base/client.jl

@@ -417,7 +417,7 @@ function load_REPL()
     return nothing
 end
 
-global active_repl
+global active_repl::Any
 global active_repl_backend = nothing
 
 function run_fallback_repl(interactive::Bool)

base/reflection.jl

@@ -207,6 +207,27 @@ function _fieldnames(@nospecialize t)
     return t.name.names
 end
 
+const BINDING_KIND_GLOBAL       = 0x0
+const BINDING_KIND_CONST        = 0x1
+const BINDING_KIND_CONST_IMPORT = 0x2
+const BINDING_KIND_IMPLICIT     = 0x3
+const BINDING_KIND_EXPLICIT     = 0x4
+const BINDING_KIND_IMPORTED     = 0x5
+const BINDING_KIND_FAILED       = 0x6
+const BINDING_KIND_DECLARED     = 0x7
+const BINDING_KIND_GUARD        = 0x8
+
+function lookup_binding_partition(world::UInt, b::Core.Binding)
+    ccall(:jl_get_binding_partition, Ref{Core.BindingPartition}, (Any, UInt), b, world)
+end
+
+function lookup_binding_partition(world::UInt, gr::Core.GlobalRef)
+    ccall(:jl_get_globalref_partition, Ref{Core.BindingPartition}, (Any, UInt), gr, world)
+end
+
+binding_kind(bpart::Core.BindingPartition) = ccall(:jl_bpart_get_kind, UInt8, (Any,), bpart)
+binding_kind(m::Module, s::Symbol) = binding_kind(lookup_binding_partition(tls_world_age(), GlobalRef(m, s)))
+
 """
     fieldname(x::DataType, i::Integer)
 

doc/src/manual/variables-and-scoping.md

@@ -743,7 +743,7 @@ ERROR: invalid redefinition of constant x
 julia> const y = 1.0
 1.0
 
-julia> y = 2.0
+julia> const y = 2.0
 WARNING: redefinition of constant y. This may fail, cause incorrect answers, or produce other errors.
 2.0
 ```
@@ -761,7 +761,7 @@ julia> const a = [1]
 1-element Vector{Int64}:
  1
 
-julia> a = [1]
+julia> const a = [1]
 WARNING: redefinition of constant a. This may fail, cause incorrect answers, or produce other errors.
 1-element Vector{Int64}:
  1
@@ -782,7 +782,7 @@ f (generic function with 1 method)
 julia> f()
 1
 
-julia> x = 2
+julia> const x = 2
 WARNING: redefinition of constant x. This may fail, cause incorrect answers, or produce other errors.
 2
 

src/ast.c

@@ -175,7 +175,8 @@ static value_t fl_defined_julia_global(fl_context_t *fl_ctx, value_t *args, uint
     jl_ast_context_t *ctx = jl_ast_ctx(fl_ctx);
     jl_sym_t *var = scmsym_to_julia(fl_ctx, args[0]);
     jl_binding_t *b = jl_get_module_binding(ctx->module, var, 0);
-    return (b != NULL && jl_atomic_load_relaxed(&b->owner) == b) ? fl_ctx->T : fl_ctx->F;
+    jl_binding_partition_t *bpart = jl_get_binding_partition(b, jl_current_task->world_age);
+    return (bpart != NULL && decode_restriction_kind(jl_atomic_load_relaxed(&bpart->restriction)) == BINDING_KIND_GLOBAL) ? fl_ctx->T : fl_ctx->F;
 }
 
 static value_t fl_nothrow_julia_global(fl_context_t *fl_ctx, value_t *args, uint32_t nargs)
@@ -204,8 +205,14 @@ static value_t fl_nothrow_julia_global(fl_context_t *fl_ctx, value_t *args, uint
         var = scmsym_to_julia(fl_ctx, args[1]);
     }
     jl_binding_t *b = jl_get_module_binding(mod, var, 0);
-    b = b ? jl_atomic_load_relaxed(&b->owner) : NULL;
-    return b != NULL && jl_atomic_load_relaxed(&b->value) != NULL ? fl_ctx->T : fl_ctx->F;
+    jl_binding_partition_t *bpart = jl_get_binding_partition(b, jl_current_task->world_age);
+    jl_ptr_kind_union_t pku = jl_walk_binding_inplace(&b, &bpart, jl_current_task->world_age);
+    if (!bpart)
+        return fl_ctx->F;
+    if (jl_bkind_is_some_guard(decode_restriction_kind(pku)))
+        return fl_ctx->F;
+    return  (jl_bkind_is_some_constant(decode_restriction_kind(pku)) ?
+        decode_restriction_value(pku) : jl_atomic_load_relaxed(&b->value)) != NULL ? fl_ctx->T : fl_ctx->F;
 }
 
 static value_t fl_current_module_counter(fl_context_t *fl_ctx, value_t *args, uint32_t nargs) JL_NOTSAFEPOINT

src/builtins.c

@@ -1369,19 +1369,10 @@ JL_CALLABLE(jl_f_get_binding_type)
     jl_sym_t *var = (jl_sym_t*)args[1];
     JL_TYPECHK(get_binding_type, module, (jl_value_t*)mod);
     JL_TYPECHK(get_binding_type, symbol, (jl_value_t*)var);
-    jl_value_t *ty = jl_get_binding_type(mod, var);
-    if (ty == (jl_value_t*)jl_nothing) {
-        jl_binding_t *b = jl_get_module_binding(mod, var, 0);
-        if (b == NULL)
-            return (jl_value_t*)jl_any_type;
-        jl_binding_t *b2 = jl_atomic_load_relaxed(&b->owner);
-        if (b2 != b)
-            return (jl_value_t*)jl_any_type;
-        jl_value_t *old_ty = NULL;
-        jl_atomic_cmpswap_relaxed(&b->ty, &old_ty, (jl_value_t*)jl_any_type);
-        return jl_atomic_load_relaxed(&b->ty);
-    }
-    return ty;
+    jl_value_t *ret = jl_get_binding_type(mod, var);
+    if (ret == jl_nothing)
+        return (jl_value_t*)jl_any_type;
+    return ret;
 }
 
 JL_CALLABLE(jl_f_swapglobal)
@@ -2509,6 +2500,7 @@ void jl_init_primitives(void) JL_GC_DISABLED
     add_builtin("QuoteNode", (jl_value_t*)jl_quotenode_type);
     add_builtin("NewvarNode", (jl_value_t*)jl_newvarnode_type);
     add_builtin("Binding", (jl_value_t*)jl_binding_type);
+    add_builtin("BindingPartition", (jl_value_t*)jl_binding_partition_type);
     add_builtin("GlobalRef", (jl_value_t*)jl_globalref_type);
     add_builtin("NamedTuple", (jl_value_t*)jl_namedtuple_type);
 

src/cgutils.cpp

@@ -568,23 +568,6 @@ static Value *literal_pointer_val(jl_codectx_t &ctx, jl_value_t *p)
     return load;
 }
 
-// Returns ctx.types().T_pjlvalue
-static Value *literal_pointer_val(jl_codectx_t &ctx, jl_binding_t *p)
-{
-    // emit a pointer to any jl_value_t which will be valid across reloading code
-    if (p == NULL)
-        return Constant::getNullValue(ctx.types().T_pjlvalue);
-    // bindings are prefixed with jl_bnd#
-    jl_globalref_t *gr = p->globalref;
-    Value *pgv = gr ? julia_pgv(ctx, "jl_bnd#", gr->name, gr->mod, p) : julia_pgv(ctx, "jl_bnd#", p);
-    jl_aliasinfo_t ai = jl_aliasinfo_t::fromTBAA(ctx, ctx.tbaa().tbaa_const);
-    auto load = ai.decorateInst(maybe_mark_load_dereferenceable(
-            ctx.builder.CreateAlignedLoad(ctx.types().T_pjlvalue, pgv, Align(sizeof(void*))),
-            false, sizeof(jl_binding_t), alignof(jl_binding_t)));
-    setName(ctx.emission_context, load, pgv->getName());
-    return load;
-}
-
 // bitcast a value, but preserve its address space when dealing with pointer types
 static Value *emit_bitcast(jl_codectx_t &ctx, Value *v, Type *jl_value)
 {