[patch] clean up pdp11.md a bit

[Richard Henderson]

On 02/14/2012 02:08 PM, Steven Bosscher wrote:
> OK for trunk?

This can wait for stage1.

> +;; On PDP-11, DIV always produces a quotient and a remainder.  But CSE
> +;; cannot optimize the divmods away because the SET_DESTs are SUBREGs.
> +;
>  ;(define_expand "divmodhi4"
>  ;  [(parallel [(set (subreg:HI (match_dup 1) 0)

Which of course begs the question of why that's so.
The division patterns can be modeled similarly to s390.

Indeed, all of the appearances of subreg in the md file are errors:

Should be removed as unnecessary:

  (define_expand "truncsihi2"

Should be removed as generated by generic code:

  (define_insn "zero_extendqihi2"
  (define_expand "zero_extendhisi2"


r~