On Thu, Aug 06, 2009 at 01:56:12PM -0400, Matt Turner wrote: > I was researching different ways of writing unaligned load/store > macros, so I checked how the kernel did it -- the most general way > possible. See include/linux/unaligned.h. As such, very bad code is > generated, for example on alpha with BWX, we can implement all these > functions with a single instruction, whereas we get stuff like this > generated from the generic functions. > > __get_unaligned_le32: > .frame $30,0,$26,0 > .prologue 0 > ldbu $0,1($16) > ldbu $1,2($16) > ldbu $2,3($16) > ldbu $3,0($16) > sll $1,16,$1 > sll $0,8,$0 > bis $0,$1,$0 > sll $2,24,$2 > bis $0,$3,$0 > bis $0,$2,$0 > addl $31,$0,$0 > ret $31,($26),1 > > 4 load byte instructions, shift, shift, or, shift, or, or, sign extend > -- or ldl_u instruction. The code is more than doubly-bad for le64. > > Do we use the generic functions for a reason I don't see? It appears > that it would be easy enough to add architecture-specific unaligned > get/put functions in arch/*/include/asm/unaligned.h There should be no need for architecture specific code for Alpha. GCC can generate the optimal code sequence for reads from unaligned struct members as in linux/unaligned/packed_struct.h, and this code should be used. So you should try to find out why it isn't. Falk -- To unsubscribe from this list: send the line "unsubscribe linux-alpha" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
