openmp: Diagnose syntax mismatches between declare target and end declare target

OpenMP 5.1 says:
For any directive that has a paired end directive, including those with a begin
and end pair, both directives must use either the attribute syntax or the
pragma syntax.

The following patch enforces it with the only pair so far recognized in C++
(Fortran has many, but on the other side doesn't have attribute syntax).

While I initially wanted to use vec<bool, va_gc> *member; in there, that
unfortunately doesn't work, one gets linker errors and I guess it is fixable,
but for begin declare target we'll need a struct anyway to store device_type
etc.

2021-08-12  Jakub Jelinek  <jakub@redhat.com>

	* cp-tree.h (omp_declare_target_attr): New type.
	(struct saved_scope): Change type of omp_declare_target_attribute
	from int to vec<omp_declare_target_attr, va_gc> * and move it.
	* parser.c (cp_parser_omp_declare_target): Instead of
	incrementing scope_chain->omp_declare_target_attribute, push
	a struct containing parser->lexer->in_omp_attribute_pragma to
	the vector.
	(cp_parser_omp_end_declare_target): Instead of decrementing
	scope_chain->omp_declare_target_attribute, pop a structure
	from it.  Diagnose mismatching declare target vs.
	end declare target syntax.
	* semantics.c (finish_translation_unit): Use vec_safe_length
	and vec_safe_truncate on scope_chain->omp_declare_target_attributes.
	* decl2.c (cplus_decl_attributes): Use vec_safe_length
	on scope_chain->omp_declare_target_attributes.

	* g++.dg/gomp/attrs-12.C: New test.

4 files changed, 28 insertions, 9 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 6a8264b..bd3f12a 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -1789,6 +1789,10 @@ union GTY((desc ("cp_tree_node_structure (&%h)"),
 };
 
 
+struct GTY(()) omp_declare_target_attr {
+  bool attr_syntax;
+};
+
 /* Global state.  */
 
 struct GTY(()) saved_scope {
@@ -1826,9 +1830,6 @@ struct GTY(()) saved_scope {
   int unevaluated_operand;
   int inhibit_evaluation_warnings;
   int noexcept_operand;
-  /* If non-zero, implicit "omp declare target" attribute is added into the
-     attribute lists.  */
-  int omp_declare_target_attribute;
   int ref_temp_count;
 
   struct stmt_tree_s x_stmt_tree;
@@ -1837,6 +1838,7 @@ struct GTY(()) saved_scope {
   cp_binding_level *bindings;
 
   hash_map<tree, tree> *GTY((skip)) x_local_specializations;
+  vec<omp_declare_target_attr, va_gc> *omp_declare_target_attribute;
 
   struct saved_scope *prev;
 };
diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index ba27388..0c9d2f4 100644
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -1551,7 +1551,7 @@ cplus_decl_attributes (tree *decl, tree attributes, int flags)
     return;
 
   /* Add implicit "omp declare target" attribute if requested.  */
-  if (scope_chain->omp_declare_target_attribute
+  if (vec_safe_length (scope_chain->omp_declare_target_attribute)
       && ((VAR_P (*decl)
 	   && (TREE_STATIC (*decl) || DECL_EXTERNAL (*decl)))
 	  || TREE_CODE (*decl) == FUNCTION_DECL))
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index fbb8130..74de529 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -44641,8 +44641,10 @@ cp_parser_omp_declare_target (cp_parser *parser, cp_token *pragma_tok)
     }
   else
     {
+      struct omp_declare_target_attr a
+	= { parser->lexer->in_omp_attribute_pragma };
+      vec_safe_push (scope_chain->omp_declare_target_attribute, a);
       cp_parser_require_pragma_eol (parser, pragma_tok);
-      scope_chain->omp_declare_target_attribute++;
       return;
     }
   for (tree c = clauses; c; c = OMP_CLAUSE_CHAIN (c))
@@ -44723,6 +44725,7 @@ static void
 cp_parser_omp_end_declare_target (cp_parser *parser, cp_token *pragma_tok)
 {
   const char *p = "";
+  bool in_omp_attribute_pragma = parser->lexer->in_omp_attribute_pragma;
   if (cp_lexer_next_token_is (parser->lexer, CPP_NAME))
     {
       tree id = cp_lexer_peek_token (parser->lexer)->u.value;
@@ -44753,12 +44756,26 @@ cp_parser_omp_end_declare_target (cp_parser *parser, cp_token *pragma_tok)
       return;
     }
   cp_parser_require_pragma_eol (parser, pragma_tok);
-  if (!scope_chain->omp_declare_target_attribute)
+  if (!vec_safe_length (scope_chain->omp_declare_target_attribute))
     error_at (pragma_tok->location,
 	      "%<#pragma omp end declare target%> without corresponding "
 	      "%<#pragma omp declare target%>");
   else
-    scope_chain->omp_declare_target_attribute--;
+    {
+      omp_declare_target_attr
+	a = scope_chain->omp_declare_target_attribute->pop ();
+      if (a.attr_syntax != in_omp_attribute_pragma)
+	{
+	  if (a.attr_syntax)
+	    error_at (pragma_tok->location,
+		      "%<declare target%> in attribute syntax terminated "
+		      "with %<end declare target%> in pragma syntax");
+	  else
+	    error_at (pragma_tok->location,
+		      "%<declare target%> in pragma syntax terminated "
+		      "with %<end declare target%> in attribute syntax");
+	}
+    }
 }
 
 /* Helper function of cp_parser_omp_declare_reduction.  Parse the combiner
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 34e5d76..2e23818 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -3271,12 +3271,12 @@ finish_translation_unit (void)
   /* Do file scope __FUNCTION__ et al.  */
   finish_fname_decls ();
 
-  if (scope_chain->omp_declare_target_attribute)
+  if (vec_safe_length (scope_chain->omp_declare_target_attribute))
     {
       if (!errorcount)
 	error ("%<#pragma omp declare target%> without corresponding "
 	       "%<#pragma omp end declare target%>");
-      scope_chain->omp_declare_target_attribute = 0;
+      vec_safe_truncate (scope_chain->omp_declare_target_attribute, 0);
     }
 }