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)
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.
paul
