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

[David Malcolm <dmalcolm at redhat dot com>]

On Fri, 2017-07-14 at 15:38 +0200, Marek Polacek wrote:
> I think David might be able to approve this one, so CCing.

It's something of a stretch for my "diagnostic messages" maintainer
hat, but I've looked over these changes and they look good to me.

Dave

> 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