Preserve the scope across the exception handler (JuliaLang#60647)

Fixes
JuliaLang#60620 (comment)
previously we were preserving the new scope across the exception
handler, instead of the scope that was actually stored in the eh
context.

The additionaly write_barriers are probably not necessary (the task
should always be young.

Alternative to JuliaLang#60620

Author: vchuravy

src/codegen.cpp

@@ -6159,6 +6159,7 @@ static void emit_stmtpos(jl_codectx_t &ctx, jl_value_t *expr, int ssaval_result)
             Value *scope_ptr = get_scope_field(ctx);
             jl_aliasinfo_t::fromTBAA(ctx, ctx.tbaa().tbaa_gcframe).decorateInst(
                 ctx.builder.CreateAlignedStore(scope_to_restore, scope_ptr, ctx.types().alignof_ptr));
+            emit_write_barrier(ctx, get_current_task(ctx), scope_to_restore);
         }
     }
     else if (head == jl_pop_exception_sym) {
@@ -9334,12 +9335,12 @@ static jl_llvm_functions_t
                 Value *scope_ptr = get_scope_field(ctx);
                 LoadInst *current_scope = ctx.builder.CreateAlignedLoad(ctx.types().T_prjlvalue, scope_ptr, ctx.types().alignof_ptr);
                 StoreInst *scope_store = ctx.builder.CreateAlignedStore(scope_boxed, scope_ptr, ctx.types().alignof_ptr);
+                // NOTE: wb not needed here, due to store to current_task (always young)
                 jl_aliasinfo_t::fromTBAA(ctx, ctx.tbaa().tbaa_gcframe).decorateInst(current_scope);
                 jl_aliasinfo_t::fromTBAA(ctx, ctx.tbaa().tbaa_gcframe).decorateInst(scope_store);
-                // GC preserve the scope, since it is not rooted in the `jl_handler_t *`
-                // and may be removed from jl_current_task by any nested block and then
-                // replaced later
-                Value *scope_token = ctx.builder.CreateCall(prepare_call(gc_preserve_begin_func), {scope_boxed});
+                // GC preserve the current_scope, since it is not rooted in the `jl_handler_t *`,
+                // the newly entered scope is preserved through the current_task.
+                Value *scope_token = ctx.builder.CreateCall(prepare_call(gc_preserve_begin_func), {current_scope});
                 ctx.scope_restore[cursor] = std::make_pair(scope_token, current_scope);
             }
         }

src/interpreter.c

@@ -539,12 +539,12 @@ static jl_value_t *eval_body(jl_array_t *stmts, interpreter_state *s, size_t ip,
             }
             s->locals[jl_source_nslots(s->src) + ip] = jl_box_ulong(jl_excstack_state(ct));
             if (jl_enternode_scope(stmt)) {
+                jl_value_t *old_scope = ct->scope; // Identical to __eh.scope
+                // GC preserve the old_scope, since it is not rooted in the `jl_handler_t *`,
+                // the newly entered scope is preserved through the current_task.
+                JL_GC_PUSH1(&old_scope);
                 jl_value_t *scope = eval_value(jl_enternode_scope(stmt), s);
-                // GC preserve the scope, since it is not rooted in the `jl_handler_t *`
-                // and may be removed from jl_current_task by any nested block and then
-                // replaced later
-                JL_GC_PUSH1(&scope);
-                ct->scope = scope;
+                ct->scope = scope; // NOTE: wb not needed here, due to store to current_task (always young)
                 if (!jl_setjmp(__eh.eh_ctx, 0)) {
                     ct->eh = &__eh;
                     eval_body(stmts, s, next_ip, toplevel);

src/task.c

@@ -1107,7 +1107,7 @@ JL_DLLEXPORT jl_task_t *jl_new_task(jl_function_t *start, jl_value_t *completion
     t->donenotify = completion_future;
     jl_atomic_store_relaxed(&t->_isexception, 0);
     // Inherit scope from parent task
-    t->scope = ct->scope;
+    t->scope = ct->scope; // NOTE: wb not needed here
     // Fork task-local random state from parent
     jl_rng_split(t->rngState, ct->rngState);
     // there is no active exception handler available on this stack yet