implements support for ARM Modified Immediate Constants (#1196)

Surprisingly we didn't support them, only when an explicit shift was
used.

Author: ivg

lib/arm/arm_mov.ml

@@ -9,6 +9,32 @@ open Arm_flags
 module Env = Arm_env
 module Shift = Arm_shift
 
+let width = 32
+
+
+(** Modified Immediate Constants  *)
+module MIC : sig
+  val decode : exp -> exp
+end = struct
+  let ror value bits =
+    let p1 = Word.(value lsr bits) in
+    let rs = Word.(of_int ~width 32 - bits) in
+    let p2 = Word.(value lsl rs) in
+    Word.(p1 lor p2)
+
+  let mic x =
+    let shift = Word.extract_exn ~hi:11 ~lo:8 x
+    and value = Word.extract_exn ~hi:7 ~lo:0 x in
+    if Word.is_zero shift then x
+    else
+      let shift = Word.extract_exn ~hi:31 shift in
+      let value = Word.extract_exn ~hi:31 value in
+      ror value Word.(shift + shift)
+
+  let decode = function
+    | Bil.Int x -> Bil.Int (mic x)
+    | other -> other
+end
 
 let lift ?dest src1 ?src2 (itype ) ?sreg ?simm raw ~wflag cond =
   let dest : var = match dest with
@@ -45,7 +71,7 @@ let lift ?dest src1 ?src2 (itype ) ?sreg ?simm raw ~wflag cond =
       let shifted, carry = Shift.lift_i
           ~src:Bil.(var unshifted) simm reg32_t in
       s1, shifted, [Bil.move unshifted s2], carry
-    | _ -> s1, s2, [], Bil.var Env.cf in
+    | _ -> s1, (MIC.decode s2), [], Bil.var Env.cf in
 
   let stmts, flags = match itype, src1, src2 with
     | `MOV, `Imm i64, _