On Thu, Jul 05, 2018 at 08:45:30AM -0400, Paul Koning wrote:
> I have a struct that looks like this:
>
> struct Xrb
> {
> uint16_t xrlen; /* Length of I/O buffer in bytes */
> uint16_t xrbc; /* Byte count for transfer */
> void * xrloc; /* Pointer to I/O buffer */
> uint8_t xrci; /* Channel number times 2 for transfer */
> uint32_t xrblk:24; /* Random access block number */
> uint16_t xrtime; /* Wait time for terminal input */
> uint16_t xrmod; /* Modifiers */
> };
>
> When I write to xrblk (that 24 bit field) on my 16 bit target, I get
> unexpectly inefficient output:
>
> XRB->xrblk = 5;
>
> movb #5,10(r0)
> clrb 11(r0)
> clrb 7(r0)
(7? not 12?)
> rather than the expected word write to the word-aligned lower half of that
> field.
>
> Looking at the dumps, I see it coming into the RTL expand phase as a single
> write, which expand then turns into the three insns corresponding to the
> above. But (of course) there is a word (HImode) move also, which has the
> same cost as the byte one.
>
> Is there something I have to do in my target definition to get this to come
> out right? This is a strict_alignment target, but alignment is satisfied in
> this example. Also, SLOW_BYTE_ACCESS is 1.
What is your MOVE_MAX? It should be 2 probably.
Segher
