Re: Inefficient code

[Paul Koning <paulkoning@comcast.net>]

> On Jul 6, 2018, at 6:18 AM, Bernd Edlinger <bernd.edlinger@hotmail.de> wrote:
> 
> You can get much better code if you make xrci a bit field.
> so the entire bit filed region can be accessed word-wise:
> 
> 
> #include <stdint.h>
> 
> 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:8;             /* 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 */
> };
> 
> void test(struct Xrb *XRB)
> {
>    XRB->xrblk = 5;
> }
> 
> 
> Bernd.

That helps with x86.  It makes no difference with xstormy16, and it makes things slightly worse with pdp11 (though I can fiddle with the patterns to help with that; there's a zero_extend optimization I haven't coded yet).

On the other hand, since the two are equivalent it's reasonable to call this a missed optimization.

	paul