[sledge] Do not consume names for non-call void instructions

Summary:
The names of instructions that produce void results, other than Call
instructions, are not used. So do not consume ids for them.

There are actually very many of these, so the saved work during
translation can be significant.

Reviewed By: jvillard

Differential Revision: D26250529

fbshipit-source-id: f9eea5684

sledge/cli/frontend.ml

@@ -105,6 +105,10 @@ open struct
         ~line:(Llvm.get_debug_loc_line i)
         ~col:(Llvm.get_debug_loc_column i)
 
+    let find_scope scope =
+      ScopeTbl.find_or_add scope_tbl scope ~default:(fun () ->
+          (ref 0, String.Tbl.create ()) )
+
     let add_sym llv loc =
       let maybe_scope =
         match Llvm.classify_value llv with
@@ -129,20 +133,14 @@ open struct
             if Loc.equal loc0 Loc.none then
               SymTbl.set sym_tbl ~key:llv ~data:(name, loc)
         | None ->
-            let next, void_tbl =
-              ScopeTbl.find_or_add scope_tbl scope ~default:(fun () ->
-                  (ref 0, String.Tbl.create ()) )
-            in
             let name =
-              if
-                Poly.(
-                  Llvm.classify_value llv = Instruction Call
-                  && Llvm.classify_type (Llvm.type_of llv) = Void)
-              then (
+              if Poly.(Llvm.classify_type (Llvm.type_of llv) = Void) then
+                if Poly.(Llvm.classify_value llv = Instruction Call) then (
                   (* LLVM does not give unique names to the result of
                      void-returning function calls. We need unique names for
                      these as they determine the labels of newly-created
                      return blocks. *)
+                  let next, void_tbl = find_scope scope in
                   let fname =
                     match
                       Llvm.(value_name (operand llv (num_operands llv - 1)))
@@ -158,10 +156,12 @@ open struct
                       String.Tbl.set void_tbl ~key:fname ~data:(count + 1) ;
                       String.concat ~sep:""
                         [fname; ".void."; Int.to_string count] )
+                else ""
               else
                 match Llvm.value_name llv with
                 | "" ->
                     (* anonymous values take the next SSA name *)
+                    let next, _ = find_scope scope in
                     let name = !next in
                     next := name + 1 ;
                     Int.to_string name
@@ -209,7 +209,9 @@ open struct
     Llvm.iter_functions scan_function m
 
   let find_name : Llvm.llvalue -> string =
-   fun v -> fst (SymTbl.find_exn sym_tbl v)
+   fun v ->
+    fst (SymTbl.find_exn sym_tbl v)
+    $> fun s -> assert (not (String.is_empty s))
 
   let find_loc : Llvm.llvalue -> Loc.t =
    fun v -> snd (SymTbl.find_exn sym_tbl v)
@@ -1063,7 +1065,6 @@ let xlate_instr :
     [%Trace.retn fun {pf} () -> pf "%a" pp_code (prefix, term, blocks)] () ;
     (prefix, term, blocks)
   in
-  let name = find_name instr in
   let loc = find_loc instr in
   let inline_or_move xlate =
     if should_inline instr then nop ()
@@ -1141,6 +1142,7 @@ let xlate_instr :
           (* general function call that may not throw *)
           | _ ->
               let typ = xlate_type x lltyp in
+              let name = find_name instr in
               let lbl = name ^ ".ret" in
               let pre_1, actuals =
                 xlate_values x num_actuals (Llvm.operand instr)
@@ -1283,6 +1285,7 @@ let xlate_instr :
          eventually jumping to the handler code following the landingpad,
          passing a value for the selector which the handler code tests to
          e.g. either cleanup or rethrow. *)
+      let name = find_name instr in
       let i32, tip, cxa_exception = landingpad_typs x instr in
       let pi8, _, exc_typ = exception_typs in
       let exc = Exp.reg (Reg.mk pi8 (find_name instr ^ ".exc")) in