[Bug c/41517] New: Unexpected behaviour of #pragma in statement context

["stephen dot clarke at st dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Gcc behaviour looks like it might be incorrect on thefollowing example.
It relates to the treatment of the pragma.  (I cannot provide the .i file
here because then the pragma is stripped out, and this changes the
behaviour of the compiler.)

$ cat test22.c
#include <stdio.h>

int x;
void foo (void)
{
  int i, j;
  for (i = 0; i < 10; i++)
#pragma GCC visibility push(default)
    for (j = 0; j < 10; j++)
      x++;
}

int main(void)
{
  foo ();
  printf ("x = %d (should be 100)\n", x);
  return 0;
}


If I compile and run using gcc 4.3.3 I get:

$ gcc -Wall test22.c
$ ./a.out
x = 10 (should be 100)

If I compile it as C++ (same gcc version), I get the behaviour I was expecting:

$ g++ -Wall -xc++ test22.c
$ ./a.out
x = 100 (should be 100)

It seems that the C parser is treating the pragma as a statement
which becomes the entire body of the first for loop, whereas the
C++ parser is not treating the pragma as a statement.

(Disclaimer: I know the example is silly.  In the original code,
the pragma is one we have added locally to control the
degree of loop unrolling in the following loop.  But I wanted to
present here an example which is reproducible using stock gcc.)

Here's more complete information on the gcc I am using:
$ gcc -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: ../configure
--prefix=/sw/st/gnu_compil/gnu/Linux-RH-WS-3/.package/gcc-4.3.3 --with-gnu-as
--with-gnu-ld --enable-shared --enable-languages=c,c++ --disable-libgcj
--disable-nls --with-mpfr=/sw/st/gnu_compil/gnu/Linux-RH-WS-3
--with-gmp=/sw/st/gnu_compil/gnu/Linux-RH-WS-3
--with-local-prefix=/sw/st/gnu_compil/gnu/Linux-RH-WS-3
Thread model: posix
gcc version 4.3.3 (GCC)


-- 
           Summary: Unexpected behaviour of #pragma in statement context
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: stephen dot clarke at st dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41517