insert evaluation for multi-ifields broken

[Joern Rennecke]

When I want to put a constant into a multi-ifield, the
exact instructions how to set the subfields are apparently ignored, and the
total value is copied into the subfields.
I have found this while working on my machine desscription,
and I could reproduce this with a small synthetic testcase, attached as
foo.cpu.  I've put tis file into the cgen/cpu directory, and
then with the cgen directory as the cwd, invoked guile and evaluated:
(load "dev.scm")
(load-sim)
(cload #:arch "foo" #:machs "foo")
(cgen-decode.c)

note that the expected value to check entire_insn against is 0x1324,
but generated test is:
        if ((entire_insn & 0xffff) == 0x12424)
-------------- next part --------------
(include "simplify.inc")

(define-arch
  (name foo) ; name of cpu family
  (comment "")
  (default-alignment aligned)
  (insn-lsb0? #f)
  (machs foo)
  (isas foo)
)

(define-isa
  (name foo)

  ; The default size of an instruction in bits
  (default-insn-bitsize 16)

  (base-insn-bitsize 16)

  (default-insn-word-bitsize 16)
)

(define-cpu
  (name foo)
  (comment "")
  (endian either)
  (word-bitsize 16)
  ; Generated files have an "f" suffix.
  (file-transform "f")
)

(define-mach
  (name foo)
  (comment "")
  (cpu foo)
)

(dnf  f-a "op a" ()  0 4)
(dnf  f-b "op a" ()  4 4)
(dnf  f-c "op a" ()  8 4)
(dnf  f-d "op a" () 12 4)
(dnmf f-ac "op ac" () UINT
  (f-a f-c)
  (sequence () ; insert
    (set (ifield f-c) (and (ifield f-ac) (const 15)))
    (set (ifield f-a) (srl (ifield f-ac) (const  4)))
  )
  (sequence () ; extract
    (set (ifield f-ac) (or (ifield f-c) (sll (ifield f-a) 4)))
  )
)

(define-pmacro (dni xname xcomment xsyntax xformat xattrs xsemantics)
  (define-insn
    (name xname)
    (comment xcomment)
    (.splice attrs (.unsplice xattrs))
    (syntax xsyntax)
    (format xformat)
    (semantics xsemantics)
    )
)

(dnh h-pc "program counter" (PC PROFILE) (pc) () () ())

(dni
  swi
  ""
  "swi"
  (+ (f-ac 18) (f-b 3) (f-d 4))
  ()
  (sequence ()
    (set pc (c-call SI "foo_trap" pc 0)))
)