I tested an svn build from 20100813 with the following code: struct bar { unsigned int a:1, b:1, c:1, d:1, e:28; };
void foo(struct bar * __restrict__ src, struct bar * __restrict__ dst) { dst->a = src->a; dst->b = src->b; dst->c = src->c; dst->d = src->d; dst->e = src->e; } Built as 32bit, we see loads and stores as if the compiler is following pointer aliasing rules: # gcc -m32 -O2 -S foo.c foo: lwz 9,0(3) lwz 0,0(4) rlwimi 0,9,0,0,0 stw 0,0(4) lwz 9,0(3) rlwimi 0,9,0,1,1 stw 0,0(4) lwz 9,0(3) rlwimi 0,9,0,2,2 stw 0,0(4) lwz 9,0(3) rlwimi 0,9,0,3,3 stw 0,0(4) lwz 9,0(3) rlwimi 0,9,0,4,31 stw 0,0(4) blr Apologies if I am misusing or misinterpreting the use of __restrict__ here. Also, when built as 64bit things are considerably more complex. Is there a reason why we can't use the same code as 32bit? # gcc -m64 -O2 -S foo.c ... .L.foo: lwz 9,0(4) lwz 0,0(3) rlwinm 9,9,0,1,31 rlwinm 0,0,0,0,0 or 0,9,0 stw 0,0(4) rlwinm 0,0,1,1,31 rlwinm 0,0,31,0xffffffff lwz 9,0(3) rldicl 9,9,34,63 slwi 9,9,30 or 0,0,9 stw 0,0(4) rlwinm 9,0,2,1,31 rlwinm 9,9,30,0xffffffff lwz 0,0(3) rldicl 0,0,35,63 slwi 0,0,29 or 0,9,0 stw 0,0(4) rlwinm 0,0,3,1,31 rlwinm 0,0,29,0xffffffff lwz 9,0(3) rldicl 9,9,36,63 slwi 9,9,28 or 0,0,9 stw 0,0(4) rlwinm 0,0,0,0,3 lwz 9,0(3) rlwinm 9,9,0,4,31 or 0,0,9 stw 0,0(4) blr -- Summary: __restrict__ type qualifier does not work on pointers to bitfields Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: middle-end AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: anton at samba dot org GCC target triplet: powerpc64-unknown-linux-gnu http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45274