Re: [PATCH v5 04/10] OpenMP: Robustify C front end handling of attribute-syntax pragmas

[Tobias Burnus]

Sandra Loosemore wrote:

[in https://gcc.gnu.org/pipermail/gcc-patches/2024-November/669055.html ]
Presently, the code to handle OpenMP attribute-syntax pragmas in the C
front end assumes nothing else is messing with redirecting
parser->tokens, and makes no provision for restoring it from anything
other than parser->tokens_buf when the buffer allocated for the pragma
is exhausted.  Adding support for metadirectives will change that,
since it also needs to buffer tokens for the metadirective
alternatives, and an attribute-syntax directive can appear inside a
metadirective.
(Cf. token->in_omp_attribute_pragma handling in 
c_parser_omp_metadirective, added in part 5 of the patch series, 
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/669058.html )
This patch adds a more general save/restore mechanism attached to the
parser via a pointer to a new struct omp_attribute_pragma_state.
gcc/c/ChangeLog

        * c-parser.cc (struct c_parser): Change in_omp_attribute_pragma
        field to be of type struct omp_attribute_pragma_state.
        (struct omp_attribute_pragma_state): New.
        (c_parser_skip_until_found): Use the new way to restore state
        on EOF.
        (c_parser_skip_to_pragma_eol): Likewise.
        (c_parser_handle_statement_omp_attributes): Create an
        omp_attribute_pragma_state to hold the restore state.
        (omp_maybe_parse_omp_decl): Likewise.
...
--- a/gcc/c/c-parser.cc
+++ b/gcc/c/c-parser.cc
@@ -262,13 +262,24 @@ struct GTY(()) c_parser {
    struct omp_for_parse_data * GTY((skip)) omp_for_parse_state;
  
    /* If we're in the context of OpenMP directives written as C23
-     attributes turned into pragma, vector of tokens created from that,
-     otherwise NULL.  */
-  vec<c_token, va_gc> *in_omp_attribute_pragma;
+     attributes turned into pragma, the tokens field is temporarily
+     redirected.  This holds data needed to restore state afterwards.
+     It's NULL otherwise.  */
+  struct omp_attribute_pragma_state *in_omp_attribute_pragma;
  
    /* Set for omp::decl attribute parsing to the decl to which it
       appertains.  */
    tree in_omp_decl_attribute;
+
+};

Can you remove the added empty line?

+/* Holds data needed to restore the token stream to its previous state
+   after parsing an OpenMP attribute-syntax pragma.  */
+struct GTY(()) omp_attribute_pragma_state
+{
+  vec<c_token, va_gc> *token_vec;
+  c_token * GTY((skip)) save_tokens;
+  unsigned int save_tokens_avail;
  };
...
@@ -7187,9 +7200,13 @@ c_parser_handle_statement_omp_attributes (c_parser *parser, 
tree &attrs,
    tok.flags = tokens_avail;
    toks->quick_push (tok);
IMHO, 'tok.flags = tokens_avail' is no longer needed.
+  gcc_assert (!parser->in_omp_attribute_pragma);
+  parser->in_omp_attribute_pragma = ggc_alloc<omp_attribute_pragma_state> ();
+  parser->in_omp_attribute_pragma->token_vec = toks;
+  parser->in_omp_attribute_pragma->save_tokens = parser->tokens;
+  parser->in_omp_attribute_pragma->save_tokens_avail = tokens_avail;
    parser->tokens = toks->address ();
    parser->tokens_avail = tokens;
-  parser->in_omp_attribute_pragma = toks;
    return true;
  }
  
@@ -27166,9 +27183,13 @@ c_maybe_parse_omp_decl (tree decl, tree d)
    tok.flags = tokens_avail;
    toks->quick_push (tok);

Likewise, IMHO, 'tok.flags = tokens_avail' is no longer needed.

Otherwise, LGTM.

Tobias