c++: Disallow jumps into statement expressions

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.

2022-10-03  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.

7 files changed, 50 insertions, 5 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 67aea96..e734bf4 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -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);
 
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index fb85564..07148b9 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -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_entry **slot, cp_binding_level *bl)
 	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_binding_level* level, tree names,
   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_binding_level* level, tree names,
 	  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)
diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index 69d555d..d6757d1 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -4296,6 +4296,7 @@ begin_scope (scope_kind kind, tree entity)
     case sk_scoped_enum:
     case sk_transaction:
     case sk_omp:
+    case sk_stmt_expr:
       scope->keep = keep_next_level_flag;
       break;
 
diff --git a/gcc/cp/name-lookup.h b/gcc/cp/name-lookup.h
index 999db33..7201ae8 100644
--- a/gcc/cp/name-lookup.h
+++ b/gcc/cp/name-lookup.h
@@ -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
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 8d0e0fa..6c4f840 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -5272,7 +5272,7 @@ cp_parser_statement_expr (cp_parser *parser)
   /* 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 ')'.  */
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 5cc5a00..58b5b43 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -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);
     }
 
diff --git a/gcc/testsuite/g++.dg/ext/stmtexpr24.C b/gcc/testsuite/g++.dg/ext/stmtexpr24.C
new file mode 100644
index 0000000..907d027
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/stmtexpr24.C
@@ -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 }
+}