Cast on bitfield ignored in gcc 2.95.2

[Jennifer Anderson <jennifer at vmware dot com>]

It looks like gcc is ignoring a cast on a bitfield in the code below.
I have an unsigned bitfield of size one byte.  The bitfield is set to
0xff, cast to unsigned int and then shifted left 24 bits to give
0xff000000.  I then test this value to see if it's less than 1.  I
expect the test to fail, as it should be treated as an unsigned
quantity; however it is being treated as signed and the test succeeds.
For comparison, I do the same operations on an unsigned char and in
that case the resulting value is treated as unsigned, and the test
fails.

Here's the code:

#include <stdio.h>

typedef struct thestruct {
  unsigned field1 : 8;
} thestruct;

main(void)
{
  unsigned char c;
  thestruct x;

  x.field1 = 0xff;
  c = x.field1;


  if ((c << 24) < 1) {
    printf("good: unsigned char promoted to int: c = 0x%x\n", c);
  }
  if ((x.field1 << 24) < 1) {
    printf("good: unsigned bitfield promoted to int: field1 = 0x%x\n", 
	   x.field1);
  }
  if ((((unsigned int) c) << 24) < 1) {
    printf("bad: cast to unsigned int on char ignored: c = 0x%x\n", c);
  }

  /* 
   * This case has the error.
   */
  if ((((unsigned int) (x.field1)) << 24) < 1) {
    printf("bad: cast to unsigned int on bitfield ignored: field1 = 0x%x\n", 
	   x.field1);
  }
}

==============================

Here's what happens when I run it:

> gcc -o bitfield-cast bitfield-cast.c
> bitfield-cast

good: unsigned char promoted to int: c = 0xff
good: unsigned bitfield promoted to int: field1 = 0xff
bad: cast to unsigned int on bitfield ignored: field1 = 0xff

> gcc -v 
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.95.2/specs
gcc version 2.95.2 19991024 (release)


I'm running on a Pentium III box, with RedHat Linux 6.1.  I installed
gcc 2.95.2 from an RPM that I grabbed from http://www.rpmfind.net/.

-- Jennifer