Re: [PATCH] c++: Disallow jumps into statement expressions

[Jason Merrill <jason@redhat.com>]

On 10/2/22 07:35, Jakub Jelinek wrote:
> On Fri, Sep 30, 2022 at 04:39:25PM -0400, Jason Merrill wrote:
>>> --- gcc/cp/decl.cc.jj	2022-09-22 00:14:55.478599363 +0200
>>> +++ gcc/cp/decl.cc	2022-09-22 00:24:01.121178256 +0200
>>> @@ -223,6 +223,7 @@ struct GTY((for_user)) named_label_entry
>>>      bool in_transaction_scope;
>>>      bool in_constexpr_if;
>>>      bool in_consteval_if;
>>> +  bool in_assume;
>>
>> I think it would be better to reject jumps into statement-expressions like
>> the C front-end.
> 
> Ok, here is a self-contained patch that does that.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK, thanks.

> 2022-10-01  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* cp-tree.h (BCS_STMT_EXPR): New enumerator.
> 	* name-lookup.h (enum scope_kind): Add sk_stmt_expr.
> 	* name-lookup.cc (begin_scope): Handle sk_stmt_expr like sk_block.
> 	* semantics.cc (begin_compound_stmt): For BCS_STMT_EXPR use
> 	sk_stmt_expr.
> 	* parser.cc (cp_parser_statement_expr): Use BCS_STMT_EXPR instead of
> 	BCS_NORMAL.
> 	* decl.cc (struct named_label_entry): Add in_stmt_expr.
> 	(poplevel_named_label_1): Handle sk_stmt_expr.
> 	(check_previous_goto_1): Diagnose entering of statement expression.
> 	(check_goto): Likewise.
> 
> 	* g++.dg/ext/stmtexpr24.C: New test.
> 
> --- gcc/cp/cp-tree.h.jj	2022-09-30 18:38:55.351607176 +0200
> +++ gcc/cp/cp-tree.h	2022-10-01 13:06:20.731720730 +0200
> @@ -7599,7 +7599,8 @@ enum {
>     BCS_NO_SCOPE = 1,
>     BCS_TRY_BLOCK = 2,
>     BCS_FN_BODY = 4,
> -  BCS_TRANSACTION = 8
> +  BCS_TRANSACTION = 8,
> +  BCS_STMT_EXPR = 16
>   };
>   extern tree begin_compound_stmt			(unsigned int);
>   
> --- gcc/cp/name-lookup.h.jj	2022-09-23 09:02:31.103668514 +0200
> +++ gcc/cp/name-lookup.h	2022-10-01 13:37:50.158404107 +0200
> @@ -200,6 +200,7 @@ enum scope_kind {
>   			init-statement.  */
>     sk_cond,	     /* The scope of the variable declared in the condition
>   			of an if or switch statement.  */
> +  sk_stmt_expr,	     /* GNU statement expression block.  */
>     sk_function_parms, /* The scope containing function parameters.  */
>     sk_class,	     /* The scope containing the members of a class.  */
>     sk_scoped_enum,    /* The scope containing the enumerators of a C++11
> --- gcc/cp/name-lookup.cc.jj	2022-09-13 09:21:28.123540623 +0200
> +++ gcc/cp/name-lookup.cc	2022-10-01 13:37:26.383732959 +0200
> @@ -4296,6 +4296,7 @@ begin_scope (scope_kind kind, tree entit
>       case sk_scoped_enum:
>       case sk_transaction:
>       case sk_omp:
> +    case sk_stmt_expr:
>         scope->keep = keep_next_level_flag;
>         break;
>   
> --- gcc/cp/semantics.cc.jj	2022-09-30 18:38:50.337675080 +0200
> +++ gcc/cp/semantics.cc	2022-10-01 13:09:34.958970367 +0200
> @@ -1761,6 +1761,8 @@ begin_compound_stmt (unsigned int flags)
>   	sk = sk_try;
>         else if (flags & BCS_TRANSACTION)
>   	sk = sk_transaction;
> +      else if (flags & BCS_STMT_EXPR)
> +	sk = sk_stmt_expr;
>         r = do_pushlevel (sk);
>       }
>   
> --- gcc/cp/parser.cc.jj	2022-09-30 18:38:55.374606864 +0200
> +++ gcc/cp/parser.cc	2022-10-01 13:08:27.367927479 +0200
> @@ -5272,7 +5272,7 @@ cp_parser_statement_expr (cp_parser *par
>     /* Start the statement-expression.  */
>     tree expr = begin_stmt_expr ();
>     /* Parse the compound-statement.  */
> -  cp_parser_compound_statement (parser, expr, BCS_NORMAL, false);
> +  cp_parser_compound_statement (parser, expr, BCS_STMT_EXPR, false);
>     /* Finish up.  */
>     expr = finish_stmt_expr (expr, false);
>     /* Consume the ')'.  */
> --- gcc/cp/decl.cc.jj	2022-09-27 08:27:47.671428567 +0200
> +++ gcc/cp/decl.cc	2022-10-01 13:14:57.990434730 +0200
> @@ -223,6 +223,7 @@ struct GTY((for_user)) named_label_entry
>     bool in_transaction_scope;
>     bool in_constexpr_if;
>     bool in_consteval_if;
> +  bool in_stmt_expr;
>   };
>   
>   #define named_labels cp_function_chain->x_named_labels
> @@ -538,6 +539,9 @@ poplevel_named_label_1 (named_label_entr
>   	case sk_transaction:
>   	  ent->in_transaction_scope = true;
>   	  break;
> +	case sk_stmt_expr:
> +	  ent->in_stmt_expr = true;
> +	  break;
>   	case sk_block:
>   	  if (level_for_constexpr_if (bl->level_chain))
>   	    ent->in_constexpr_if = true;
> @@ -3487,7 +3491,7 @@ check_previous_goto_1 (tree decl, cp_bin
>     bool complained = false;
>     int identified = 0;
>     bool saw_eh = false, saw_omp = false, saw_tm = false, saw_cxif = false;
> -  bool saw_ceif = false;
> +  bool saw_ceif = false, saw_se = false;
>   
>     if (exited_omp)
>       {
> @@ -3560,6 +3564,12 @@ check_previous_goto_1 (tree decl, cp_bin
>   	  saw_tm = true;
>   	  break;
>   
> +	case sk_stmt_expr:
> +	  if (!saw_se)
> +	    inf = G_("  enters statement expression");
> +	  saw_se = true;
> +	  break;
> +
>   	case sk_block:
>   	  if (!saw_cxif && level_for_constexpr_if (b->level_chain))
>   	    {
> @@ -3650,12 +3660,13 @@ check_goto (tree decl)
>   
>     if (ent->in_try_scope || ent->in_catch_scope || ent->in_transaction_scope
>         || ent->in_constexpr_if || ent->in_consteval_if
> -      || ent->in_omp_scope || !vec_safe_is_empty (ent->bad_decls))
> +      || ent->in_omp_scope || ent->in_stmt_expr
> +      || !vec_safe_is_empty (ent->bad_decls))
>       {
>         diagnostic_t diag_kind = DK_PERMERROR;
>         if (ent->in_try_scope || ent->in_catch_scope || ent->in_constexpr_if
>   	  || ent->in_consteval_if || ent->in_transaction_scope
> -	  || ent->in_omp_scope)
> +	  || ent->in_omp_scope || ent->in_stmt_expr)
>   	diag_kind = DK_ERROR;
>         complained = identify_goto (decl, DECL_SOURCE_LOCATION (decl),
>   				  &input_location, diag_kind);
> @@ -3703,6 +3714,8 @@ check_goto (tree decl)
>   	inform (input_location, "  enters %<constexpr if%> statement");
>         else if (ent->in_consteval_if)
>   	inform (input_location, "  enters %<consteval if%> statement");
> +      else if (ent->in_stmt_expr)
> +	inform (input_location, "  enters statement expression");
>       }
>   
>     if (ent->in_omp_scope)
> --- gcc/testsuite/g++.dg/ext/stmtexpr24.C.jj	2022-10-01 13:34:01.471565458 +0200
> +++ gcc/testsuite/g++.dg/ext/stmtexpr24.C	2022-10-01 13:39:56.078662362 +0200
> @@ -0,0 +1,27 @@
> +// { dg-do compile }
> +// { dg-options "" }
> +
> +void
> +foo (int x)
> +{
> +  bool a = false;
> +  if (x == 1)
> +    goto l1;						// { dg-message "from here" }
> +  a = ({ l0:; if (x == 0) goto l0; true; });
> +  a = ({ if (x == 0) throw 1; true; });
> +  a = ({ l1:; true; });					// { dg-error "jump to label 'l1'" }
> +							// { dg-message "enters statement expression" "" { target *-*-* } .-1 }
> +  a = ({ l2:; true; });					// { dg-error "jump to label 'l2'" }
> +  switch (x)
> +    {
> +    case 2:
> +      a = ({ case 3:; true; });				// { dg-error "jump to case label" }
> +							// { dg-message "enters statement expression" "" { target *-*-* } .-1 }
> +      a = ({ default:; true; });			// { dg-error "jump to case label" }
> +							// { dg-message "enters statement expression" "" { target *-*-* } .-1 }
> +      break;
> +    }
> +  if (x == 4)
> +    goto l2;						// { dg-message "from here" }
> +							// { dg-message "enters statement expression" "" { target *-*-* } .-1 }
> +}
> 
> 
> 	Jakub
>