[sledge] Add Llair.Term.branch wrapper for Switch

Summary:
The main motivation is to factor out the code that determines the test
condition, e.g. to uniformly test `!= 0` vs `= 1`.

Also a convenience, and there are enough uses to make it worthwhile
and a readability improvement.

Reviewed By: mbouaziz

Differential Revision: D10488408

fbshipit-source-id: 520e843f3

sledge/src/llair/frontend.ml

@@ -1082,11 +1082,10 @@ let xlate_instr :
         let thn_lbl = label_of_block thn in
         let thn_args = jump_args x instr thn in
         let thn = Llair.Jump.mk thn_lbl thn_args in
-        let tbl = Vector.of_array [|(Z.one, thn)|] in
         let els_lbl = label_of_block els in
         let els_args = jump_args x instr els in
         let els = Llair.Jump.mk els_lbl els_args in
-        terminal [] (Llair.Term.switch ~key ~tbl ~els ~loc) [] )
+        terminal [] (Llair.Term.branch ~key ~nzero:thn ~zero:els ~loc) [] )
   | Switch ->
       let key = xlate_value x (Llvm.operand instr 0) in
       let cases =
@@ -1200,18 +1199,16 @@ let xlate_instr :
                       else Exp.dq tiI ti
                     in
                     let key = xlate_filter 0 in
-                    let thn = match_filter in
+                    Llair.Term.branch ~loc ~key ~nzero:match_filter
-                    let tbl = Vector.of_array [|(Z.one, thn)|] in
+                      ~zero:(jump (i + 1))
-                    Llair.Term.switch ~key ~tbl ~els:(jump (i + 1)) ~loc
                 | _ -> fail "xlate_instr: %a" pp_llvalue instr () )
               | _ (* catch *) ->
                   let clause = xlate_value x clause in
                   let key =
                     Exp.or_ (Exp.eq clause Exp.null) (Exp.eq clause ti)
                   in
-                  let thn = jump_unwind typeid in
+                  Llair.Term.branch ~loc ~key ~nzero:(jump_unwind typeid)
-                  let tbl = Vector.of_array [|(Z.one, thn)|] in
+                    ~zero:(jump (i + 1))
-                  Llair.Term.switch ~key ~tbl ~els:(jump (i + 1)) ~loc
           in
           let rec rev_blocks i z =
             if i < num_clauses then

sledge/src/llair/llair.ml

@@ -130,9 +130,9 @@ let pp_term fs term =
   | Switch {key; tbl; els; loc} -> (
     match Vector.to_array tbl with
     | [||] -> pf "@[%a@]\t%a" pp_goto els Loc.pp loc
-    | [|(z, jmp)|] when Z.equal Z.one z ->
+    | [|(z, jmp)|] when Z.equal Z.zero z ->
         pf "@[if %a@;<1 2>%a@ @[else@;<1 2>%a@]@]\t%a" Exp.pp key pp_goto
-          jmp pp_goto els Loc.pp loc
+          els pp_goto jmp Loc.pp loc
     | _ ->
         pf "@[<2>switch %a@ @[%a@ else: %a@]@]\t%a" Exp.pp key
           (Vector.pp "@ " (fun fs (z, jmp) ->
@@ -277,6 +277,11 @@ module Term = struct
     Switch {key= Exp.integer Z.zero; tbl= Vector.empty; els= dst; loc}
     |> check invariant
 
+  let branch ~key ~nzero ~zero ~loc =
+    let tbl = Vector.of_array [|(Z.zero, zero)|] in
+    let els = nzero in
+    Switch {key; tbl; els; loc} |> check invariant
+
   let switch ~key ~tbl ~els ~loc =
     Switch {key; tbl; els; loc} |> check invariant
 

sledge/src/llair/llair.mli

@@ -157,6 +157,9 @@ module Term : sig
   val goto : dst:jump -> loc:Loc.t -> term
   (** Construct a [Switch] representing an unconditional branch. *)
 
+  val branch : key:Exp.t -> nzero:jump -> zero:jump -> loc:Loc.t -> term
+  (** Construct a [Switch] representing a conditional branch. *)
+
   val switch :
     key:Exp.t -> tbl:(Z.t * jump) vector -> els:jump -> loc:Loc.t -> term