In the example below, define T as "char" or "short". (probably "int" too on a 64-bit machine, with minor adjustment to the example code) Compile the code with "-Os -S" and observe the assembly. Even if there are no aliasing or alignment issues, the compiler fails to merge multiple stores into larger stores.

This is tested with three gcc 4.1 compilers:

i386 from Fedora Core 6 test2
x86-64 from Fedora Core 6 test2
ppc32 from Debian-unstable

BTW, I hope I guessed right in filing against "middle-end". I didn't know if it was tree-optimization or rtl-optimization, and there still isn't an obvious place to file bugs which are common to both C and C++.

-------------------------------------
tmp 0 $ cat e.c
#ifndef T
#define T short
#endif

typedef struct S{
        T a;
        T b;
        T c;
        T d;
}S;

S *structbug(S *s){
        s->a = 1;
        s->b = 2;
        s->c = 3;
        s->d = 4;
        return s;
}

T *arraybug(T *s){
        s[0] = 1;
        s[1] = 2;
        s[2] = 3;
        s[3] = 4;
        return s;
}

tmp 0 $ gcc -W -Wall -m32 -Os -fomit-frame-pointer -S e.c
tmp 0 $ cat e.s
        .file   "e.c"
        .text
.globl structbug
        .type   structbug, @function
structbug:
        movl    4(%esp), %eax
        movw    $1, (%eax)
        movw    $2, 2(%eax)
        movw    $3, 4(%eax)
        movw    $4, 6(%eax)
        ret
        .size   structbug, .-structbug
.globl arraybug
        .type   arraybug, @function
arraybug:
        movl    4(%esp), %eax
        movw    $1, (%eax)
        movw    $2, 2(%eax)
        movw    $3, 4(%eax)
        movw    $4, 6(%eax)
        ret
        .size   arraybug, .-arraybug
        .ident  "GCC: (GNU) 4.1.1 20060828 (Red Hat 4.1.1-20)"
        .section        .note.GNU-stack,"",@progbits
tmp 0 $