bpart: Start enforcing min_world for global variable definitions (#57150)

This is the analog of #57102 for global variables. Unlike for consants,
there is no automatic global backdate mechanism. The reasoning for this
is that global variables can be declared at any time, unlike constants
which can only be decalared once their value is available. As a result
code patterns using `Core.eval` to declare globals are rarer and likely
incorrect.

Author: Keno

Compiler/test/abioverride.jl

@@ -46,7 +46,7 @@ let world = Base.tls_world_age()
     global new_ci = Core.CodeInstance(Core.ABIOverride(Tuple{typeof(myplus), Int}, mi),
         #=owner=#SecondArgConstOverride(1), new_source.rettype, Any#=new_source.exctype is missing=#,
         #=inferred_const=#nothing, #=code=#nothing, #=const_flags=#Int32(0),
-        new_source.min_world, new_source.max_world, #=new_source.ipo_purity_bits is missing=#UInt32(0),
+        new_source.min_world, typemax(UInt), #=new_source.ipo_purity_bits is missing=#UInt32(0),
         #=analysis_results=#nothing, new_source.debuginfo, new_source.edges)
 
     # Poke the CI into the global cache

base/docs/Docs.jl

@@ -75,18 +75,23 @@ const META    = gensym(:meta)
 const METAType = IdDict{Any,Any}
 
 function meta(m::Module; autoinit::Bool=true)
-    if !isdefined(m, META) || getfield(m, META) === nothing
-        autoinit ? initmeta(m) : return nothing
+    if !isdefinedglobal(m, META)
+        return autoinit ? invokelatest(initmeta, m) : nothing
     end
-    return getfield(m, META)::METAType
+    # TODO: This `invokelatest` is not technically required, but because
+    # of the automatic constant backdating is currently required to avoid
+    # a warning.
+    return invokelatest(getglobal, m, META)::METAType
 end
 
 function initmeta(m::Module)
-    if !isdefined(m, META) || getfield(m, META) === nothing
-        Core.eval(m, :($META = $(METAType())))
+    if !isdefinedglobal(m, META)
+        val = METAType()
+        Core.eval(m, :(const $META = $val))
         push!(modules, m)
+        return val
     end
-    nothing
+    return getglobal(m, META)
 end
 
 function signature!(tv::Vector{Any}, expr::Expr)

base/exports.jl

@@ -818,6 +818,7 @@ export
     @invoke,
     invokelatest,
     @invokelatest,
+    @world,
 
 # loading source files
     __precompile__,

base/loading.jl

@@ -1389,7 +1389,7 @@ function register_restored_modules(sv::SimpleVector, pkg::PkgId, path::String)
     restored = sv[1]::Vector{Any}
     for M in restored
         M = M::Module
-        if isdefined(M, Base.Docs.META) && getfield(M, Base.Docs.META) !== nothing
+        if isdefinedglobal(M, Base.Docs.META)
             push!(Base.Docs.modules, M)
         end
         if is_root_module(M)

src/builtins.c

@@ -1395,7 +1395,7 @@ JL_CALLABLE(jl_f_setglobal)
         jl_atomic_error("setglobal!: module binding cannot be written non-atomically");
     else if (order >= jl_memory_order_seq_cst)
         jl_fence();
-    jl_binding_t *b = jl_get_binding_wr(mod, var, 0);
+    jl_binding_t *b = jl_get_binding_wr(mod, var);
     jl_checked_assignment(b, mod, var, args[2]); // release store
     if (order >= jl_memory_order_seq_cst)
         jl_fence();
@@ -1430,7 +1430,7 @@ JL_CALLABLE(jl_f_swapglobal)
     if (order == jl_memory_order_notatomic)
         jl_atomic_error("swapglobal!: module binding cannot be written non-atomically");
     // is seq_cst already, no fence needed
-    jl_binding_t *b = jl_get_binding_wr(mod, var, 0);
+    jl_binding_t *b = jl_get_binding_wr(mod, var);
     return jl_checked_swap(b, mod, var, args[2]);
 }
 
@@ -1448,7 +1448,7 @@ JL_CALLABLE(jl_f_modifyglobal)
     JL_TYPECHK(modifyglobal!, symbol, (jl_value_t*)var);
     if (order == jl_memory_order_notatomic)
         jl_atomic_error("modifyglobal!: module binding cannot be written non-atomically");
-    jl_binding_t *b = jl_get_binding_wr(mod, var, 0);
+    jl_binding_t *b = jl_get_binding_wr(mod, var);
     // is seq_cst already, no fence needed
     return jl_checked_modify(b, mod, var, args[2], args[3]);
 }
@@ -1477,7 +1477,7 @@ JL_CALLABLE(jl_f_replaceglobal)
         jl_atomic_error("replaceglobal!: module binding cannot be written non-atomically");
     if (failure_order == jl_memory_order_notatomic)
         jl_atomic_error("replaceglobal!: module binding cannot be accessed non-atomically");
-    jl_binding_t *b = jl_get_binding_wr(mod, var, 0);
+    jl_binding_t *b = jl_get_binding_wr(mod, var);
     // is seq_cst already, no fence needed
     return jl_checked_replace(b, mod, var, args[2], args[3]);
 }
@@ -1506,7 +1506,7 @@ JL_CALLABLE(jl_f_setglobalonce)
         jl_atomic_error("setglobalonce!: module binding cannot be written non-atomically");
     if (failure_order == jl_memory_order_notatomic)
         jl_atomic_error("setglobalonce!: module binding cannot be accessed non-atomically");
-    jl_binding_t *b = jl_get_binding_wr(mod, var, 0);
+    jl_binding_t *b = jl_get_binding_wr(mod, var);
     // is seq_cst already, no fence needed
     jl_value_t *old = jl_checked_assignonce(b, mod, var, args[2]);
     return old == NULL ? jl_true : jl_false;

src/codegen.cpp

@@ -930,12 +930,12 @@ static const auto jlgetbindingorerror_func = new JuliaFunction<>{
     },
     nullptr,
 };
-static const auto jlgetbindingwrorerror_func = new JuliaFunction<>{
-    XSTR(jl_get_binding_wr),
+static const auto jlcheckbpwritable_func = new JuliaFunction<>{
+    XSTR(jl_check_binding_currently_writable),
     [](LLVMContext &C) {
         auto T_pjlvalue = JuliaType::get_pjlvalue_ty(C);
-        return FunctionType::get(T_pjlvalue,
-                {T_pjlvalue, T_pjlvalue, getInt32Ty(C)}, false);
+        return FunctionType::get(getVoidTy(C),
+                {T_pjlvalue, T_pjlvalue, T_pjlvalue}, false);
     },
     nullptr,
 };
@@ -2098,8 +2098,6 @@ static Type *julia_type_to_llvm(jl_codectx_t &ctx, jl_value_t *jt, bool *isboxed
 static jl_returninfo_t get_specsig_function(jl_codectx_t &ctx, Module *M, Value *fval, StringRef name, jl_value_t *sig, jl_value_t *jlrettype, bool is_opaque_closure, bool gcstack_arg,
         ArrayRef<const char*> ArgNames=None, unsigned nreq=0);
 static jl_cgval_t emit_expr(jl_codectx_t &ctx, jl_value_t *expr, ssize_t ssaval = -1);
-static Value *global_binding_pointer(jl_codectx_t &ctx, jl_module_t *m, jl_sym_t *s,
-                                     jl_binding_t **pbnd, bool assign, bool alloc);
 static jl_cgval_t emit_checked_var(jl_codectx_t &ctx, Value *bp, jl_sym_t *name, jl_value_t *scope, bool isvol, MDNode *tbaa);
 static jl_cgval_t emit_sparam(jl_codectx_t &ctx, size_t i);
 static Value *emit_condition(jl_codectx_t &ctx, const jl_cgval_t &condV, const Twine &msg);
@@ -3498,19 +3496,17 @@ static jl_cgval_t emit_globalop(jl_codectx_t &ctx, jl_module_t *mod, jl_sym_t *s
                                 bool issetglobal, bool isreplaceglobal, bool isswapglobal, bool ismodifyglobal, bool issetglobalonce,
                                 const jl_cgval_t *modifyop, bool alloc)
 {
-    jl_binding_t *bnd = NULL;
-    Value *bp = global_binding_pointer(ctx, mod, sym, &bnd, true, alloc);
+    jl_binding_t *bnd = jl_get_module_binding(mod, sym, 1);
     jl_binding_partition_t *bpart = jl_get_binding_partition_all(bnd, ctx.min_world, ctx.max_world);
-    if (bp == NULL)
-        return jl_cgval_t();
+    Value *bp = julia_binding_gv(ctx, bnd);
     if (bpart) {
         jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
-        if (!jl_bkind_is_some_constant(decode_restriction_kind(pku))) {
+        if (decode_restriction_kind(pku) == BINDING_KIND_GLOBAL) {
             jl_value_t *ty = decode_restriction_value(pku);
             if (ty != nullptr) {
                 const std::string fname = issetglobal ? "setglobal!" : isreplaceglobal ? "replaceglobal!" : isswapglobal ? "swapglobal!" : ismodifyglobal ? "modifyglobal!" : "setglobalonce!";
                 if (!ismodifyglobal) {
-                    // TODO: use typeassert in jl_check_binding_wr too
+                    // TODO: use typeassert in jl_check_binding_assign_value too
                     emit_typecheck(ctx, rval, ty, "typeassert");
                     rval = update_julia_type(ctx, rval, ty);
                     if (rval.typ == jl_bottom_type)
@@ -3545,6 +3541,8 @@ static jl_cgval_t emit_globalop(jl_codectx_t &ctx, jl_module_t *mod, jl_sym_t *s
     }
     Value *m = literal_pointer_val(ctx, (jl_value_t*)mod);
     Value *s = literal_pointer_val(ctx, (jl_value_t*)sym);
+    ctx.builder.CreateCall(prepare_call(jlcheckbpwritable_func),
+        { bp, m, s });
     if (issetglobal) {
         ctx.builder.CreateCall(prepare_call(jlcheckassign_func),
                 { bp, m, s, mark_callee_rooted(ctx, boxed(ctx, rval)) });
@@ -5991,85 +5989,6 @@ static void emit_hasnofield_error_ifnot(jl_codectx_t &ctx, Value *ok, jl_datatyp
     ctx.builder.SetInsertPoint(ifok);
 }
 
-// returns a jl_ppvalue_t location for the global variable m.s
-// if the reference currently bound or assign == true,
-//   pbnd will also be assigned with the binding address
-static Value *global_binding_pointer(jl_codectx_t &ctx, jl_module_t *m, jl_sym_t *s,
-                                     jl_binding_t **pbnd, bool assign, bool alloc)
-{
-    jl_binding_t *b = jl_get_module_binding(m, s, 1);
-    jl_binding_partition_t *bpart = jl_get_binding_partition_all(b, ctx.min_world, ctx.max_world);
-    jl_ptr_kind_union_t pku = jl_atomic_load_relaxed(&bpart->restriction);
-    if (assign) {
-        if (jl_bkind_is_some_guard(decode_restriction_kind(pku)))
-            // not yet declared
-            b = NULL;
-    }
-    else {
-        if (jl_bkind_is_some_guard(decode_restriction_kind(pku))) {
-            // try to look this up now
-            b = jl_get_binding(m, s);
-            bpart = jl_get_binding_partition_all(b, ctx.min_world, ctx.max_world);
-        }
-        pku = jl_walk_binding_inplace_all(&b, &bpart, ctx.min_world, ctx.max_world);
-    }
-    if (!b || !bpart) {
-        // var not found. switch to delayed lookup.
-        Constant *initnul = Constant::getNullValue(ctx.types().T_pjlvalue);
-        GlobalVariable *bindinggv = new GlobalVariable(*ctx.f->getParent(), ctx.types().T_pjlvalue,
-                false, GlobalVariable::PrivateLinkage, initnul, "jl_binding_ptr"); // LLVM has bugs with nameless globals
-        LoadInst *cachedval = ctx.builder.CreateAlignedLoad(ctx.types().T_pjlvalue, bindinggv, Align(sizeof(void*)));
-        setName(ctx.emission_context, cachedval, jl_symbol_name(m->name) + StringRef(".") + jl_symbol_name(s) + ".cached");
-        cachedval->setOrdering(AtomicOrdering::Unordered);
-        BasicBlock *have_val = BasicBlock::Create(ctx.builder.getContext(), "found");
-        BasicBlock *not_found = BasicBlock::Create(ctx.builder.getContext(), "notfound");
-        BasicBlock *currentbb = ctx.builder.GetInsertBlock();
-        auto iscached = ctx.builder.CreateICmpNE(cachedval, initnul);
-        setName(ctx.emission_context, iscached, "iscached");
-        ctx.builder.CreateCondBr(iscached, have_val, not_found);
-        not_found->insertInto(ctx.f);
-        ctx.builder.SetInsertPoint(not_found);
-        Value *bval = nullptr;
-        if (assign) {
-            bval = ctx.builder.CreateCall(prepare_call(jlgetbindingwrorerror_func),
-                    { literal_pointer_val(ctx, (jl_value_t*)m),
-                    literal_pointer_val(ctx, (jl_value_t*)s),
-                    ConstantInt::get(getInt32Ty(ctx.builder.getContext()), alloc)});
-        } else {
-            bval = ctx.builder.CreateCall(prepare_call(jlgetbindingorerror_func),
-                    { literal_pointer_val(ctx, (jl_value_t*)m),
-                    literal_pointer_val(ctx, (jl_value_t*)s)});
-        }
-        setName(ctx.emission_context, bval, jl_symbol_name(m->name) + StringRef(".") + jl_symbol_name(s) + ".found");
-        ctx.builder.CreateAlignedStore(bval, bindinggv, Align(sizeof(void*)))->setOrdering(AtomicOrdering::Release);
-        ctx.builder.CreateBr(have_val);
-        have_val->insertInto(ctx.f);
-        ctx.builder.SetInsertPoint(have_val);
-        PHINode *p = ctx.builder.CreatePHI(ctx.types().T_pjlvalue, 2);
-        p->addIncoming(cachedval, currentbb);
-        p->addIncoming(bval, not_found);
-        setName(ctx.emission_context, p, jl_symbol_name(m->name) + StringRef(".") + jl_symbol_name(s));
-        return p;
-    }
-    if (assign) {
-        if (decode_restriction_kind(pku) != BINDING_KIND_GLOBAL && !jl_bkind_is_some_guard(decode_restriction_kind(pku))) {
-            // this will fail at runtime, so defer to the runtime to create the error
-            ctx.builder.CreateCall(prepare_call(jlgetbindingwrorerror_func),
-                    { literal_pointer_val(ctx, (jl_value_t*)m),
-                      literal_pointer_val(ctx, (jl_value_t*)s),
-                      ConstantInt::get(getInt32Ty(ctx.builder.getContext()), alloc) });
-            CreateTrap(ctx.builder);
-            return NULL;
-        }
-    }
-    else {
-        if (b->deprecated)
-            cg_bdw(ctx, s, b);
-    }
-    *pbnd = b;
-    return julia_binding_gv(ctx, b);
-}
-
 static jl_cgval_t emit_checked_var(jl_codectx_t &ctx, Value *bp, jl_sym_t *name, jl_value_t *scope, bool isvol, MDNode *tbaa)
 {
     LoadInst *v = ctx.builder.CreateAlignedLoad(ctx.types().T_prjlvalue, bp, Align(sizeof(void*)));
@@ -10184,7 +10103,7 @@ static void init_jit_functions(void)
     add_named_global(jltypeerror_func, &jl_type_error);
     add_named_global(jlcheckassign_func, &jl_checked_assignment);
     add_named_global(jlgetbindingorerror_func, &jl_get_binding_or_error);
-    add_named_global(jlgetbindingwrorerror_func, &jl_get_binding_wr);
+    add_named_global(jlcheckbpwritable_func, &jl_check_binding_currently_writable);
     add_named_global(jlboundp_func, &jl_boundp);
     for (auto it : builtin_func_map())
         add_named_global(it.second, it.first);

src/jl_exported_funcs.inc

@@ -196,6 +196,7 @@
     XX(jl_get_binding_for_method_def) \
     XX(jl_get_binding_or_error) \
     XX(jl_get_binding_wr) \
+    XX(jl_check_binding_currently_writable) \
     XX(jl_get_cpu_name) \
     XX(jl_get_cpu_features) \
     XX(jl_cpu_has_fma) \

src/julia-syntax.scm

@@ -4626,6 +4626,8 @@ f(x) = yt(x)
       (if (globalref? lhs)
         (begin
           (emit `(global ,lhs))
+          (if (null? (cadr lam))
+            (emit `(latestworld)))
           (emit `(call (top setglobal!) ,(cadr lhs) (inert ,(caddr lhs)) ,rhs)))
         (emit `(= ,lhs ,rhs))))
     (define (emit-assignment lhs rhs)
@@ -4944,13 +4946,16 @@ f(x) = yt(x)
                  #f))
             ((global) ; keep global declarations as statements
              (if value (error "misplaced \"global\" declaration"))
-             (emit e))
+             (emit e)
+             (if (null? (cadr lam))
+               (emit `(latestworld))))
             ((globaldecl)
              (if value (error "misplaced \"global\" declaration"))
-             (if (atom? (caddr e)) (emit e)
+             (if (atom? (caddr e)) (begin (emit e) (emit `(latestworld)))
               (let ((rr (make-ssavalue)))
                 (emit `(= ,rr ,(caddr e)))
-                (emit `(globaldecl ,(cadr e) ,rr)))))
+                (emit `(globaldecl ,(cadr e) ,rr))
+                (emit `(latestworld)))))
             ((local-def) #f)
             ((local) #f)
             ((moved-local)

src/julia.h

@@ -2001,7 +2001,8 @@ JL_DLLEXPORT jl_binding_t *jl_get_binding_or_error(jl_module_t *m, jl_sym_t *var
 JL_DLLEXPORT jl_value_t *jl_module_globalref(jl_module_t *m, jl_sym_t *var);
 JL_DLLEXPORT jl_value_t *jl_get_binding_type(jl_module_t *m, jl_sym_t *var);
 // get binding for assignment
-JL_DLLEXPORT jl_binding_t *jl_get_binding_wr(jl_module_t *m JL_PROPAGATES_ROOT, jl_sym_t *var, int alloc);
+JL_DLLEXPORT void jl_check_binding_currently_writable(jl_binding_t *b, jl_module_t *m, jl_sym_t *s);
+JL_DLLEXPORT jl_binding_t *jl_get_binding_wr(jl_module_t *m JL_PROPAGATES_ROOT, jl_sym_t *var);
 JL_DLLEXPORT jl_binding_t *jl_get_binding_for_method_def(jl_module_t *m JL_PROPAGATES_ROOT, jl_sym_t *var);
 JL_DLLEXPORT int jl_boundp(jl_module_t *m, jl_sym_t *var, int allow_import);
 JL_DLLEXPORT int jl_defines_or_exports_p(jl_module_t *m, jl_sym_t *var);