examples/OCaml-Kaleidoscope/Chapter6/codegen.ml

   1 (*===----------------------------------------------------------------------===
   2  * Code Generation
   3  *===----------------------------------------------------------------------===*)
   4
   5 open Llvm
   6
   7 exception Error of string
   8
   9 let context = global_context ()
  10 let the_module = create_module context "my cool jit"
  11 let builder = builder context
  12 let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
  13 let double_type = double_type context
  14
  15 let rec codegen_expr = function
  16   | Ast.Number n -> const_float double_type n
  17   | Ast.Variable name ->
  18       (try Hashtbl.find named_values name with
  19         | Not_found -> raise (Error "unknown variable name"))
  20   | Ast.Unary (op, operand) ->
  21       let operand = codegen_expr operand in
  22       let callee = "unary" ^ (String.make 1 op) in
  23       let callee =
  24         match lookup_function callee the_module with
  25         | Some callee -> callee
  26         | None -> raise (Error "unknown unary operator")
  27       in
  28       build_call callee [|operand|] "unop" builder
  29   | Ast.Binary (op, lhs, rhs) ->
  30       let lhs_val = codegen_expr lhs in
  31       let rhs_val = codegen_expr rhs in
  32       begin
  33         match op with
  34         | '+' -> build_fadd lhs_val rhs_val "addtmp" builder
  35         | '-' -> build_fsub lhs_val rhs_val "subtmp" builder
  36         | '*' -> build_fmul lhs_val rhs_val "multmp" builder
  37         | '<' ->
  38             (* Convert bool 0/1 to double 0.0 or 1.0 *)
  39             let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
  40             build_uitofp i double_type "booltmp" builder
  41         | _ ->
  42             (* If it wasn't a builtin binary operator, it must be a user defined
  43              * one. Emit a call to it. *)
  44             let callee = "binary" ^ (String.make 1 op) in
  45             let callee =
  46               match lookup_function callee the_module with
  47               | Some callee -> callee
  48               | None -> raise (Error "binary operator not found!")
  49             in
  50             build_call callee [|lhs_val; rhs_val|] "binop" builder
  51       end
  52   | Ast.Call (callee, args) ->
  53       (* Look up the name in the module table. *)
  54       let callee =
  55         match lookup_function callee the_module with
  56         | Some callee -> callee
  57         | None -> raise (Error "unknown function referenced")
  58       in
  59       let params = params callee in
  60
  61       (* If argument mismatch error. *)
  62       if Array.length params == Array.length args then () else
  63         raise (Error "incorrect # arguments passed");
  64       let args = Array.map codegen_expr args in
  65       build_call callee args "calltmp" builder
  66   | Ast.If (cond, then_, else_) ->
  67       let cond = codegen_expr cond in
  68
  69       (* Convert condition to a bool by comparing equal to 0.0 *)
  70       let zero = const_float double_type 0.0 in
  71       let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in
  72
  73       (* Grab the first block so that we might later add the conditional branch
  74        * to it at the end of the function. *)
  75       let start_bb = insertion_block builder in
  76       let the_function = block_parent start_bb in
  77
  78       let then_bb = append_block context "then" the_function in
  79
  80       (* Emit 'then' value. *)
  81       position_at_end then_bb builder;
  82       let then_val = codegen_expr then_ in
  83
  84       (* Codegen of 'then' can change the current block, update then_bb for the
  85        * phi. We create a new name because one is used for the phi node, and the
  86        * other is used for the conditional branch. *)
  87       let new_then_bb = insertion_block builder in
  88
  89       (* Emit 'else' value. *)
  90       let else_bb = append_block context "else" the_function in
  91       position_at_end else_bb builder;
  92       let else_val = codegen_expr else_ in
  93
  94       (* Codegen of 'else' can change the current block, update else_bb for the
  95        * phi. *)
  96       let new_else_bb = insertion_block builder in
  97
  98       (* Emit merge block. *)
  99       let merge_bb = append_block context "ifcont" the_function in
 100       position_at_end merge_bb builder;
 101       let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in
 102       let phi = build_phi incoming "iftmp" builder in
 103
 104       (* Return to the start block to add the conditional branch. *)
 105       position_at_end start_bb builder;
 106       ignore (build_cond_br cond_val then_bb else_bb builder);
 107
 108       (* Set a unconditional branch at the end of the 'then' block and the
 109        * 'else' block to the 'merge' block. *)
 110       position_at_end new_then_bb builder; ignore (build_br merge_bb builder);
 111       position_at_end new_else_bb builder; ignore (build_br merge_bb builder);
 112
 113       (* Finally, set the builder to the end of the merge block. *)
 114       position_at_end merge_bb builder;
 115
 116       phi
 117   | Ast.For (var_name, start, end_, step, body) ->
 118       (* Emit the start code first, without 'variable' in scope. *)
 119       let start_val = codegen_expr start in
 120
 121       (* Make the new basic block for the loop header, inserting after current
 122        * block. *)
 123       let preheader_bb = insertion_block builder in
 124       let the_function = block_parent preheader_bb in
 125       let loop_bb = append_block context "loop" the_function in
 126
 127       (* Insert an explicit fall through from the current block to the
 128        * loop_bb. *)
 129       ignore (build_br loop_bb builder);
 130
 131       (* Start insertion in loop_bb. *)
 132       position_at_end loop_bb builder;
 133
 134       (* Start the PHI node with an entry for start. *)
 135       let variable = build_phi [(start_val, preheader_bb)] var_name builder in
 136
 137       (* Within the loop, the variable is defined equal to the PHI node. If it
 138        * shadows an existing variable, we have to restore it, so save it
 139        * now. *)
 140       let old_val =
 141         try Some (Hashtbl.find named_values var_name) with Not_found -> None
 142       in
 143       Hashtbl.add named_values var_name variable;
 144
 145       (* Emit the body of the loop.  This, like any other expr, can change the
 146        * current BB.  Note that we ignore the value computed by the body, but
 147        * don't allow an error *)
 148       ignore (codegen_expr body);
 149
 150       (* Emit the step value. *)
 151       let step_val =
 152         match step with
 153         | Some step -> codegen_expr step
 154         (* If not specified, use 1.0. *)
 155         | None -> const_float double_type 1.0
 156       in
 157
 158       let next_var = build_add variable step_val "nextvar" builder in
 159
 160       (* Compute the end condition. *)
 161       let end_cond = codegen_expr end_ in
 162
 163       (* Convert condition to a bool by comparing equal to 0.0. *)
 164       let zero = const_float double_type 0.0 in
 165       let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in
 166
 167       (* Create the "after loop" block and insert it. *)
 168       let loop_end_bb = insertion_block builder in
 169       let after_bb = append_block context "afterloop" the_function in
 170
 171       (* Insert the conditional branch into the end of loop_end_bb. *)
 172       ignore (build_cond_br end_cond loop_bb after_bb builder);
 173
 174       (* Any new code will be inserted in after_bb. *)
 175       position_at_end after_bb builder;
 176
 177       (* Add a new entry to the PHI node for the backedge. *)
 178       add_incoming (next_var, loop_end_bb) variable;
 179
 180       (* Restore the unshadowed variable. *)
 181       begin match old_val with
 182       | Some old_val -> Hashtbl.add named_values var_name old_val
 183       | None -> ()
 184       end;
 185
 186       (* for expr always returns 0.0. *)
 187       const_null double_type
 188
 189 let codegen_proto = function
 190   | Ast.Prototype (name, args) | Ast.BinOpPrototype (name, args, _) ->
 191       (* Make the function type: double(double,double) etc. *)
 192       let doubles = Array.make (Array.length args) double_type in
 193       let ft = function_type double_type doubles in
 194       let f =
 195         match lookup_function name the_module with
 196         | None -> declare_function name ft the_module
 197
 198         (* If 'f' conflicted, there was already something named 'name'. If it
 199          * has a body, don't allow redefinition or reextern. *)
 200         | Some f ->
 201             (* If 'f' already has a body, reject this. *)
 202             if block_begin f <> At_end f then
 203               raise (Error "redefinition of function");
 204
 205             (* If 'f' took a different number of arguments, reject. *)
 206             if element_type (type_of f) <> ft then
 207               raise (Error "redefinition of function with different # args");
 208             f
 209       in
 210
 211       (* Set names for all arguments. *)
 212       Array.iteri (fun i a ->
 213         let n = args.(i) in
 214         set_value_name n a;
 215         Hashtbl.add named_values n a;
 216       ) (params f);
 217       f
 218
 219 let codegen_func the_fpm = function
 220   | Ast.Function (proto, body) ->
 221       Hashtbl.clear named_values;
 222       let the_function = codegen_proto proto in
 223
 224       (* If this is an operator, install it. *)
 225       begin match proto with
 226       | Ast.BinOpPrototype (name, args, prec) ->
 227           let op = name.[String.length name - 1] in
 228           Hashtbl.add Parser.binop_precedence op prec;
 229       | _ -> ()
 230       end;
 231
 232       (* Create a new basic block to start insertion into. *)
 233       let bb = append_block context "entry" the_function in
 234       position_at_end bb builder;
 235
 236       try
 237         let ret_val = codegen_expr body in
 238
 239         (* Finish off the function. *)
 240         let _ = build_ret ret_val builder in
 241
 242         (* Validate the generated code, checking for consistency. *)
 243         Llvm_analysis.assert_valid_function the_function;
 244
 245         (* Optimize the function. *)
 246         let _ = PassManager.run_function the_function the_fpm in
 247
 248         the_function
 249       with e ->
 250         delete_function the_function;
 251         raise e