[Bug c/50521] -fstrict-volatile-bitfields is not strict

[kikairoya at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50521

--- Comment #3 from Tomohiro Kashiwada <kikairoya at gmail dot com> 2011-09-27 
04:15:19 UTC ---
Other test case (gcc generates wrong code):

volatile union {
    // add volatiles tenaciously, but...
    volatile unsigned int all;
    volatile struct {
        volatile unsigned int a: 8;
        volatile unsigned int : 7;
        volatile unsigned int b: 1;
        volatile unsigned int : 8;
        volatile unsigned int c: 8;
    } bits;
} bitfield;

int main() {
    bitfield.bits.a = 1;
    bitfield.bits.b = 1;
    bitfield.bits.c = 1;
    return 0;
}


$ gcc -S -O -o - btf.c -fstrict-volatile-bitfields
        .file   "btf.c"
        .text
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        movl    $1, bitfield(%rip) ; **** breaks other area! ****
        movl    bitfield(%rip), %eax
        orb     $128, %ah
        movl    %eax, bitfield(%rip)
        movl    $1, bitfield+3(%rip) ; **** unaligned, and breaks other area!
****
        movl    $0, %eax
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .comm   bitfield,4,4
        .ident  "GCC: (Debian 4.6.1-3) 4.6.1"
        .section        .note.GNU-stack,"",@progbits



$ rx-elf-gcc -S -O -o - btf.c -fstrict-volatile-bitfields
        .file   "btf.c"
        .section P,"ax"
        .global _main
        .type   _main, @function
_main:
        mov.L   #_bitfield, r14
        mov.L   #1, [r14]        ; **** breaks other area! ****
        mov.L   [r14], r4
        bset    #15, r4
        mov.L   r4, [r14]
        mov.L   [r14], r4
        and     #0xffffff, r4
        or      #0x1000000, r4
        mov.L   r4, [r14]        ; ok, aligned (my misunderstanding).
        mov.L   #0, r1
        rts
        .size   _main, .-_main
        .comm   _bitfield,4,4
        .ident  "GCC: (GNU) 4.6.1"