;;;; Type Definitions ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; Our high-level, RISC-y input IR.
(type HighLevelInst
  (enum (Add (a Value) (b Value))
        (Load (addr Value))
        (Const (c i32))))

;; A value in our high-level IR is a Rust `Copy` type. Values are either defined
;; by an instruction, or are a basic block argument.
(type Value (primitive Value))

;; Our low-level, CISC-y machine instructions.
(type LowLevelInst
  (enum (Add (mode AddrMode))
        (Load (offset i32) (addr Reg))
        (Const (c i32))))

;; Different kinds of addressing modes for operands to our low-level machine
;; instructions.
(type AddrMode
  (enum
    ;; Both operands in registers.
    (RegReg (a Reg) (b Reg))
    ;; The destination/first operand is a register; the second operand is in
    ;; memory at `[b + offset]`.
    (RegMem (a Reg) (b Reg) (offset i32))
    ;; The destination/first operand is a register, second operand is an
    ;; immediate.
    (RegImm (a Reg) (imm i32))))

;; The register type is a Rust `Copy` type.
(type Reg (primitive Reg))

;;;; Rules ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

;; Declare our top-level lowering function. We will attach rules to this
;; declaration for lowering various patterns of `HighLevelInst` inputs.
(decl lower (HighLevelInst) LowLevelInst)

;; Simple rule for lowering constants.
(rule (lower (HighLevelInst.Const c))
      (LowLevelInst.Const c))

;; Declare an external constructor that puts a high-level `Value` into a
;; low-level `Reg`.
(decl put_in_reg (Value) Reg)
(extern constructor put_in_reg put_in_reg)

;; Simple rule for lowering adds.
(rule -1 (lower (HighLevelInst.Add a b))
      (LowLevelInst.Add
        (AddrMode.RegReg (put_in_reg a) (put_in_reg b))))

;; Simple rule for lowering loads.
(rule -1 (lower (HighLevelInst.Load addr))
      (LowLevelInst.Load 0 (put_in_reg addr)))

;; Declare an external extractor for extracting the instruction that defined a
;; given operand value.
(decl inst_result (HighLevelInst) Value)
(extern extractor inst_result inst_result)

;; Rule to sink loads into adds.
(rule (lower (HighLevelInst.Add a (inst_result (HighLevelInst.Load addr))))
      (LowLevelInst.Add
        (AddrMode.RegMem (put_in_reg a)
                         (put_in_reg addr)
                         0)))

;; Rule to sink a load of a base address with a static offset into a single add.
(rule 1 (lower (HighLevelInst.Add
               a
               (inst_result (HighLevelInst.Load
                              (inst_result (HighLevelInst.Add
                                             base
                                             (inst_result (HighLevelInst.Const offset))))))))
      (LowLevelInst.Add
        (AddrMode.RegMem (put_in_reg a)
                         (put_in_reg base)
                         offset)))

;; Rule for sinking an immediate into an add.
(rule (lower (HighLevelInst.Add a (inst_result (HighLevelInst.Const c))))
      (LowLevelInst.Add
        (AddrMode.RegImm (put_in_reg a) c)))

;; Rule for lowering loads of a base address with a static offset.
(rule (lower (HighLevelInst.Load
               (inst_result (HighLevelInst.Add
                              base
                              (inst_result (HighLevelInst.Const offset))))))
      (LowLevelInst.Load offset (put_in_reg base)))