Re: C PATCH to fix bogus warning with -Wmultistatement-macros (PR c/81364)

[Marek Polacek <polacek at redhat dot com>]

I think David might be able to approve this one, so CCing.

On Tue, Jul 11, 2017 at 03:23:16PM +0200, Marek Polacek wrote:
> This patch fixes a bogus -Wmultistatement-macros warning.  The code didn't
> notice that what came after a guard such as else was actually wrapped in { }
> which is a correct use.  This bogus warning only triggered when the body of
> a conditional was coming from a different expansion than the conditional
> itself.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2017-07-11  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c/81364
> 	* c-parser.c (c_parser_else_body): Don't warn about multistatement
> 	macro expansion if the body is in { }.
> 	(c_parser_while_statement): Likewise.
> 	(c_parser_for_statement): Likewise.
> 
> 	* Wmultistatement-macros-12.c: New test.
> 
> diff --git gcc/c/c-parser.c gcc/c/c-parser.c
> index f8fbc92..7524a73 100644
> --- gcc/c/c-parser.c
> +++ gcc/c/c-parser.c
> @@ -5557,7 +5557,8 @@ c_parser_else_body (c_parser *parser, const token_indent_info &else_tinfo,
>      }
>    else
>      {
> -      body_loc_after_labels = c_parser_peek_token (parser)->location;
> +      if (!c_parser_next_token_is (parser, CPP_OPEN_BRACE))
> +	body_loc_after_labels = c_parser_peek_token (parser)->location;
>        c_parser_statement_after_labels (parser, NULL, chain);
>      }
>  
> @@ -5811,6 +5812,7 @@ c_parser_while_statement (c_parser *parser, bool ivdep, bool *if_p)
>      = get_token_indent_info (c_parser_peek_token (parser));
>  
>    location_t loc_after_labels;
> +  bool open_brace = c_parser_next_token_is (parser, CPP_OPEN_BRACE);
>    body = c_parser_c99_block_statement (parser, if_p, &loc_after_labels);
>    c_finish_loop (loc, cond, NULL, body, c_break_label, c_cont_label, true);
>    add_stmt (c_end_compound_stmt (loc, block, flag_isoc99));
> @@ -5820,7 +5822,7 @@ c_parser_while_statement (c_parser *parser, bool ivdep, bool *if_p)
>      = get_token_indent_info (c_parser_peek_token (parser));
>    warn_for_misleading_indentation (while_tinfo, body_tinfo, next_tinfo);
>  
> -  if (next_tinfo.type != CPP_SEMICOLON)
> +  if (next_tinfo.type != CPP_SEMICOLON && !open_brace)
>      warn_for_multistatement_macros (loc_after_labels, next_tinfo.location,
>  				    while_tinfo.location, RID_WHILE);
>  
> @@ -6109,6 +6111,7 @@ c_parser_for_statement (c_parser *parser, bool ivdep, bool *if_p)
>      = get_token_indent_info (c_parser_peek_token (parser));
>  
>    location_t loc_after_labels;
> +  bool open_brace = c_parser_next_token_is (parser, CPP_OPEN_BRACE);
>    body = c_parser_c99_block_statement (parser, if_p, &loc_after_labels);
>  
>    if (is_foreach_statement)
> @@ -6122,7 +6125,7 @@ c_parser_for_statement (c_parser *parser, bool ivdep, bool *if_p)
>      = get_token_indent_info (c_parser_peek_token (parser));
>    warn_for_misleading_indentation (for_tinfo, body_tinfo, next_tinfo);
>  
> -  if (next_tinfo.type != CPP_SEMICOLON)
> +  if (next_tinfo.type != CPP_SEMICOLON && !open_brace)
>      warn_for_multistatement_macros (loc_after_labels, next_tinfo.location,
>  				    for_tinfo.location, RID_FOR);
>  
> diff --git gcc/testsuite/c-c++-common/Wmultistatement-macros-12.c gcc/testsuite/c-c++-common/Wmultistatement-macros-12.c
> index e69de29..ac8915c 100644
> --- gcc/testsuite/c-c++-common/Wmultistatement-macros-12.c
> +++ gcc/testsuite/c-c++-common/Wmultistatement-macros-12.c
> @@ -0,0 +1,43 @@
> +/* PR c/81364 */
> +/* { dg-do compile } */
> +/* { dg-options "-Wmultistatement-macros" } */
> +
> +#define FOO0 if (1) { } else
> +#define TST0 \
> +void bar0 (void) \
> +{ \
> +  FOO0 { } /* { dg-bogus "macro expands to multiple statements" } */ \
> +}
> +TST0
> +
> +#define FOO1 for (;;)
> +#define TST1 \
> +void bar1 (void) \
> +{ \
> +  FOO1 { } /* { dg-bogus "macro expands to multiple statements" } */ \
> +}
> +TST1
> +
> +#define FOO2 while (1)
> +#define TST2 \
> +void bar2 (void) \
> +{ \
> +  FOO2 { } /* { dg-bogus "macro expands to multiple statements" } */ \
> +}
> +TST2
> +
> +#define FOO3 switch (1)
> +#define TST3 \
> +void bar3 (void) \
> +{ \
> +  FOO3 { } /* { dg-bogus "macro expands to multiple statements" } */ \
> +}
> +TST3
> +
> +#define FOO4 if (1)
> +#define TST4 \
> +void bar4 (void) \
> +{ \
> +  FOO4 { } /* { dg-bogus "macro expands to multiple statements" } */ \
> +}
> +TST4
> 
> 	Marek

	Marek