1(*===----------------------------------------------------------------------===
2 * Code Generation
3 *===----------------------------------------------------------------------===*)
4
5open Llvm
6
7exception Error of string
8
9let context = global_context ()
10let the_module = create_module context "my cool jit"
11let builder = builder context
12let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
13let double_type = double_type context
14
15(* Create an alloca instruction in the entry block of the function. This
16 * is used for mutable variables etc. *)
17let create_entry_block_alloca the_function var_name =
18  let builder = builder_at context (instr_begin (entry_block the_function)) in
19  build_alloca double_type var_name builder
20
21let rec codegen_expr = function
22  | Ast.Number n -> const_float double_type n
23  | Ast.Variable name ->
24      let v = try Hashtbl.find named_values name with
25        | Not_found -> raise (Error "unknown variable name")
26      in
27      (* Load the value. *)
28      build_load v name builder
29  | Ast.Unary (op, operand) ->
30      let operand = codegen_expr operand in
31      let callee = "unary" ^ (String.make 1 op) in
32      let callee =
33        match lookup_function callee the_module with
34        | Some callee -> callee
35        | None -> raise (Error "unknown unary operator")
36      in
37      build_call callee [|operand|] "unop" builder
38  | Ast.Binary (op, lhs, rhs) ->
39      begin match op with
40      | '=' ->
41          (* Special case '=' because we don't want to emit the LHS as an
42           * expression. *)
43          let name =
44            match lhs with
45            | Ast.Variable name -> name
46            | _ -> raise (Error "destination of '=' must be a variable")
47          in
48
49          (* Codegen the rhs. *)
50          let val_ = codegen_expr rhs in
51
52          (* Lookup the name. *)
53          let variable = try Hashtbl.find named_values name with
54          | Not_found -> raise (Error "unknown variable name")
55          in
56          ignore(build_store val_ variable builder);
57          val_
58      | _ ->
59          let lhs_val = codegen_expr lhs in
60          let rhs_val = codegen_expr rhs in
61          begin
62            match op with
63            | '+' -> build_fadd lhs_val rhs_val "addtmp" builder
64            | '-' -> build_fsub lhs_val rhs_val "subtmp" builder
65            | '*' -> build_fmul lhs_val rhs_val "multmp" builder
66            | '<' ->
67                (* Convert bool 0/1 to double 0.0 or 1.0 *)
68                let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
69                build_uitofp i double_type "booltmp" builder
70            | _ ->
71                (* If it wasn't a builtin binary operator, it must be a user defined
72                 * one. Emit a call to it. *)
73                let callee = "binary" ^ (String.make 1 op) in
74                let callee =
75                  match lookup_function callee the_module with
76                  | Some callee -> callee
77                  | None -> raise (Error "binary operator not found!")
78                in
79                build_call callee [|lhs_val; rhs_val|] "binop" builder
80          end
81      end
82  | Ast.Call (callee, args) ->
83      (* Look up the name in the module table. *)
84      let callee =
85        match lookup_function callee the_module with
86        | Some callee -> callee
87        | None -> raise (Error "unknown function referenced")
88      in
89      let params = params callee in
90
91      (* If argument mismatch error. *)
92      if Array.length params == Array.length args then () else
93        raise (Error "incorrect # arguments passed");
94      let args = Array.map codegen_expr args in
95      build_call callee args "calltmp" builder
96  | Ast.If (cond, then_, else_) ->
97      let cond = codegen_expr cond in
98
99      (* Convert condition to a bool by comparing equal to 0.0 *)
100      let zero = const_float double_type 0.0 in
101      let cond_val = build_fcmp Fcmp.One cond zero "ifcond" builder in
102
103      (* Grab the first block so that we might later add the conditional branch
104       * to it at the end of the function. *)
105      let start_bb = insertion_block builder in
106      let the_function = block_parent start_bb in
107
108      let then_bb = append_block context "then" the_function in
109
110      (* Emit 'then' value. *)
111      position_at_end then_bb builder;
112      let then_val = codegen_expr then_ in
113
114      (* Codegen of 'then' can change the current block, update then_bb for the
115       * phi. We create a new name because one is used for the phi node, and the
116       * other is used for the conditional branch. *)
117      let new_then_bb = insertion_block builder in
118
119      (* Emit 'else' value. *)
120      let else_bb = append_block context "else" the_function in
121      position_at_end else_bb builder;
122      let else_val = codegen_expr else_ in
123
124      (* Codegen of 'else' can change the current block, update else_bb for the
125       * phi. *)
126      let new_else_bb = insertion_block builder in
127
128      (* Emit merge block. *)
129      let merge_bb = append_block context "ifcont" the_function in
130      position_at_end merge_bb builder;
131      let incoming = [(then_val, new_then_bb); (else_val, new_else_bb)] in
132      let phi = build_phi incoming "iftmp" builder in
133
134      (* Return to the start block to add the conditional branch. *)
135      position_at_end start_bb builder;
136      ignore (build_cond_br cond_val then_bb else_bb builder);
137
138      (* Set a unconditional branch at the end of the 'then' block and the
139       * 'else' block to the 'merge' block. *)
140      position_at_end new_then_bb builder; ignore (build_br merge_bb builder);
141      position_at_end new_else_bb builder; ignore (build_br merge_bb builder);
142
143      (* Finally, set the builder to the end of the merge block. *)
144      position_at_end merge_bb builder;
145
146      phi
147  | Ast.For (var_name, start, end_, step, body) ->
148      (* Output this as:
149       *   var = alloca double
150       *   ...
151       *   start = startexpr
152       *   store start -> var
153       *   goto loop
154       * loop:
155       *   ...
156       *   bodyexpr
157       *   ...
158       * loopend:
159       *   step = stepexpr
160       *   endcond = endexpr
161       *
162       *   curvar = load var
163       *   nextvar = curvar + step
164       *   store nextvar -> var
165       *   br endcond, loop, endloop
166       * outloop: *)
167
168      let the_function = block_parent (insertion_block builder) in
169
170      (* Create an alloca for the variable in the entry block. *)
171      let alloca = create_entry_block_alloca the_function var_name in
172
173      (* Emit the start code first, without 'variable' in scope. *)
174      let start_val = codegen_expr start in
175
176      (* Store the value into the alloca. *)
177      ignore(build_store start_val alloca builder);
178
179      (* Make the new basic block for the loop header, inserting after current
180       * block. *)
181      let loop_bb = append_block context "loop" the_function in
182
183      (* Insert an explicit fall through from the current block to the
184       * loop_bb. *)
185      ignore (build_br loop_bb builder);
186
187      (* Start insertion in loop_bb. *)
188      position_at_end loop_bb builder;
189
190      (* Within the loop, the variable is defined equal to the PHI node. If it
191       * shadows an existing variable, we have to restore it, so save it
192       * now. *)
193      let old_val =
194        try Some (Hashtbl.find named_values var_name) with Not_found -> None
195      in
196      Hashtbl.add named_values var_name alloca;
197
198      (* Emit the body of the loop.  This, like any other expr, can change the
199       * current BB.  Note that we ignore the value computed by the body, but
200       * don't allow an error *)
201      ignore (codegen_expr body);
202
203      (* Emit the step value. *)
204      let step_val =
205        match step with
206        | Some step -> codegen_expr step
207        (* If not specified, use 1.0. *)
208        | None -> const_float double_type 1.0
209      in
210
211      (* Compute the end condition. *)
212      let end_cond = codegen_expr end_ in
213
214      (* Reload, increment, and restore the alloca. This handles the case where
215       * the body of the loop mutates the variable. *)
216      let cur_var = build_load alloca var_name builder in
217      let next_var = build_add cur_var step_val "nextvar" builder in
218      ignore(build_store next_var alloca builder);
219
220      (* Convert condition to a bool by comparing equal to 0.0. *)
221      let zero = const_float double_type 0.0 in
222      let end_cond = build_fcmp Fcmp.One end_cond zero "loopcond" builder in
223
224      (* Create the "after loop" block and insert it. *)
225      let after_bb = append_block context "afterloop" the_function in
226
227      (* Insert the conditional branch into the end of loop_end_bb. *)
228      ignore (build_cond_br end_cond loop_bb after_bb builder);
229
230      (* Any new code will be inserted in after_bb. *)
231      position_at_end after_bb builder;
232
233      (* Restore the unshadowed variable. *)
234      begin match old_val with
235      | Some old_val -> Hashtbl.add named_values var_name old_val
236      | None -> ()
237      end;
238
239      (* for expr always returns 0.0. *)
240      const_null double_type
241  | Ast.Var (var_names, body) ->
242      let old_bindings = ref [] in
243
244      let the_function = block_parent (insertion_block builder) in
245
246      (* Register all variables and emit their initializer. *)
247      Array.iter (fun (var_name, init) ->
248        (* Emit the initializer before adding the variable to scope, this
249         * prevents the initializer from referencing the variable itself, and
250         * permits stuff like this:
251         *   var a = 1 in
252         *     var a = a in ...   # refers to outer 'a'. *)
253        let init_val =
254          match init with
255          | Some init -> codegen_expr init
256          (* If not specified, use 0.0. *)
257          | None -> const_float double_type 0.0
258        in
259
260        let alloca = create_entry_block_alloca the_function var_name in
261        ignore(build_store init_val alloca builder);
262
263        (* Remember the old variable binding so that we can restore the binding
264         * when we unrecurse. *)
265        begin
266          try
267            let old_value = Hashtbl.find named_values var_name in
268            old_bindings := (var_name, old_value) :: !old_bindings;
269          with Not_found -> ()
270        end;
271
272        (* Remember this binding. *)
273        Hashtbl.add named_values var_name alloca;
274      ) var_names;
275
276      (* Codegen the body, now that all vars are in scope. *)
277      let body_val = codegen_expr body in
278
279      (* Pop all our variables from scope. *)
280      List.iter (fun (var_name, old_value) ->
281        Hashtbl.add named_values var_name old_value
282      ) !old_bindings;
283
284      (* Return the body computation. *)
285      body_val
286
287let codegen_proto = function
288  | Ast.Prototype (name, args) | Ast.BinOpPrototype (name, args, _) ->
289      (* Make the function type: double(double,double) etc. *)
290      let doubles = Array.make (Array.length args) double_type in
291      let ft = function_type double_type doubles in
292      let f =
293        match lookup_function name the_module with
294        | None -> declare_function name ft the_module
295
296        (* If 'f' conflicted, there was already something named 'name'. If it
297         * has a body, don't allow redefinition or reextern. *)
298        | Some f ->
299            (* If 'f' already has a body, reject this. *)
300            if block_begin f <> At_end f then
301              raise (Error "redefinition of function");
302
303            (* If 'f' took a different number of arguments, reject. *)
304            if element_type (type_of f) <> ft then
305              raise (Error "redefinition of function with different # args");
306            f
307      in
308
309      (* Set names for all arguments. *)
310      Array.iteri (fun i a ->
311        let n = args.(i) in
312        set_value_name n a;
313        Hashtbl.add named_values n a;
314      ) (params f);
315      f
316
317(* Create an alloca for each argument and register the argument in the symbol
318 * table so that references to it will succeed. *)
319let create_argument_allocas the_function proto =
320  let args = match proto with
321    | Ast.Prototype (_, args) | Ast.BinOpPrototype (_, args, _) -> args
322  in
323  Array.iteri (fun i ai ->
324    let var_name = args.(i) in
325    (* Create an alloca for this variable. *)
326    let alloca = create_entry_block_alloca the_function var_name in
327
328    (* Store the initial value into the alloca. *)
329    ignore(build_store ai alloca builder);
330
331    (* Add arguments to variable symbol table. *)
332    Hashtbl.add named_values var_name alloca;
333  ) (params the_function)
334
335let codegen_func the_fpm = function
336  | Ast.Function (proto, body) ->
337      Hashtbl.clear named_values;
338      let the_function = codegen_proto proto in
339
340      (* If this is an operator, install it. *)
341      begin match proto with
342      | Ast.BinOpPrototype (name, args, prec) ->
343          let op = name.[String.length name - 1] in
344          Hashtbl.add Parser.binop_precedence op prec;
345      | _ -> ()
346      end;
347
348      (* Create a new basic block to start insertion into. *)
349      let bb = append_block context "entry" the_function in
350      position_at_end bb builder;
351
352      try
353        (* Add all arguments to the symbol table and create their allocas. *)
354        create_argument_allocas the_function proto;
355
356        let ret_val = codegen_expr body in
357
358        (* Finish off the function. *)
359        let _ = build_ret ret_val builder in
360
361        (* Validate the generated code, checking for consistency. *)
362        Llvm_analysis.assert_valid_function the_function;
363
364        (* Optimize the function. *)
365        let _ = PassManager.run_function the_function the_fpm in
366
367        the_function
368      with e ->
369        delete_function the_function;
370        raise e
371