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4 <html>
5 <head>
11 </head>
13 <body>
17 <ul>
20 <ol>
26 </ol>
27 </li>
29 Flow</li>
30 </ul>
33 <p>
36 </p>
37 </div>
39 <!-- *********************************************************************** -->
41 <!-- *********************************************************************** -->
47 language and added support for generating LLVM IR. This chapter describes
48 two new techniques: adding optimizer support to your language, and adding JIT
49 compiler support. These additions will demonstrate how to get nice, efficient code
50 for the Kaleidoscope language.</p>
52 </div>
54 <!-- *********************************************************************** -->
56 Folding</a></div>
57 <!-- *********************************************************************** -->
62 folding optimisations below.<p>
64 <p>
65 Our demonstration for Chapter 3 is elegant and easy to extend. Unfortunately,
66 it does not produce wonderful code. For example, when compiling simple code,
67 we don't get obvious optimizations:</p>
70 <pre>
72 Read function definition:
73 define double @test(double %x) {
74 entry:
76 %addtmp1 = add double %addtmp, %x
77 ret double %addtmp1
78 }
79 </pre>
80 </div>
82 <p>This code is a very, very literal transcription of the AST built by parsing
83 the input. As such, this transcription lacks optimizations like constant folding
84 (we'd like to get "<tt>add x, 3.0</tt>" in the example above) as well as other
85 more important optimizations. Constant folding, in particular, is a very common
86 and very important optimization: so much so that many language implementors
87 implement constant folding support in their AST representation.</p>
89 <p>With LLVM, you don't need this support in the AST. Since all calls to build
90 LLVM IR go through the LLVM builder, it would be nice if the builder itself
91 checked to see if there was a constant folding opportunity when you call it.
92 If so, it could just do the constant fold and return the constant instead of
94 class does.
98 instructions implicitly constant folded without us having to do anything
99 about it. For example, the input above now compiles to:</p>
102 <pre>
104 Read function definition:
105 define double @test(double %x) {
106 entry:
107 %addtmp = add double 3.000000e+00, %x
108 ret double %addtmp
109 }
110 </pre>
111 </div>
113 <p>Well, that was easy :). In practice, we recommend always using
115 "syntactic overhead" for its use (you don't have to uglify your compiler with
116 constant checks everywhere) and it can dramatically reduce the amount of
117 LLVM IR that is generated in some cases (particular for languages with a macro
118 preprocessor or that use a lot of constants).</p>
121 that it does all of its analysis inline with the code as it is built. If you
122 take a slightly more complex example:</p>
125 <pre>
127 ready> Read function definition:
128 define double @test(double %x) {
129 entry:
130 %addtmp = add double 3.000000e+00, %x
131 %addtmp1 = add double %x, 3.000000e+00
132 %multmp = mul double %addtmp, %addtmp1
133 ret double %multmp
134 }
135 </pre>
136 </div>
138 <p>In this case, the LHS and RHS of the multiplication are the same value. We'd
139 really like to see this generate "<tt>tmp = x+3; result = tmp*tmp;</tt>" instead
142 <p>Unfortunately, no amount of local analysis will be able to detect and correct
143 this. This requires two transformations: reassociation of expressions (to
144 make the add's lexically identical) and Common Subexpression Elimination (CSE)
145 to delete the redundant add instruction. Fortunately, LLVM provides a broad
148 </div>
150 <!-- *********************************************************************** -->
152 Passes</a></div>
153 <!-- *********************************************************************** -->
157 <p>LLVM provides many optimization passes, which do many different sorts of
158 things and have different tradeoffs. Unlike other systems, LLVM doesn't hold
159 to the mistaken notion that one set of optimizations is right for all languages
160 and for all situations. LLVM allows a compiler implementor to make complete
161 decisions about what optimizations to use, in which order, and in what
162 situation.</p>
165 across as large of body of code as they can (often a whole file, but if run
166 at link time, this can be a substantial portion of the whole program). It also
167 supports and includes "per-function" passes which just operate on a single
168 function at a time, without looking at other functions. For more information
173 <p>For Kaleidoscope, we are currently generating functions on the fly, one at
174 a time, as the user types them in. We aren't shooting for the ultimate
175 optimization experience in this setting, but we also want to catch the easy and
176 quick stuff where possible. As such, we will choose to run a few per-function
177 optimizations as the user types the function in. If we wanted to make a "static
178 Kaleidoscope compiler", we would use exactly the code we have now, except that
179 we would defer running the optimizer until the entire file has been parsed.</p>
181 <p>In order to get per-function optimizations going, we need to set up a
183 organize the LLVM optimizations that we want to run. Once we have that, we can
184 add a set of optimizations to run. The code looks like this:</p>
187 <pre>
188 (* Create the JIT. *)
189 let the_module_provider = ModuleProvider.create Codegen.the_module in
190 let the_execution_engine = ExecutionEngine.create the_module_provider in
191 let the_fpm = PassManager.create_function the_module_provider in
193 (* Set up the optimizer pipeline. Start with registering info about how the
194 * target lays out data structures. *)
195 TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
197 (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
198 add_instruction_combining the_fpm;
200 (* reassociate expressions. *)
201 add_reassociation the_fpm;
203 (* Eliminate Common SubExpressions. *)
204 add_gvn the_fpm;
206 (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
207 add_cfg_simplification the_fpm;
209 (* Run the main "interpreter loop" now. *)
210 Toplevel.main_loop the_fpm the_execution_engine stream;
211 </pre>
212 </div>
217 provides certain flexibility that we're not going to take advantage of here,
218 so I won't dive into any details about it.</p>
223 series of "add" calls to add a bunch of LLVM passes. The first pass is
224 basically boilerplate, it adds a pass so that later optimizations know how the
225 data structures in the program are layed out. The
226 "<tt>the_execution_engine</tt>" variable is related to the JIT, which we will
227 get to in the next section.</p>
230 here are a pretty standard set of "cleanup" optimizations that are useful for
231 a wide variety of code. I won't delve into what they do but, believe me,
232 they are a good starting place :).</p>
235 We do this by running it after our newly created function is constructed (in
239 <pre>
240 let codegen_func the_fpm = function
241 ...
242 try
243 let ret_val = codegen_expr body in
245 (* Finish off the function. *)
246 let _ = build_ret ret_val builder in
248 (* Validate the generated code, checking for consistency. *)
249 Llvm_analysis.assert_valid_function the_function;
251 (* Optimize the function. *)
252 let _ = PassManager.run_function the_function the_fpm in
254 the_function
255 </pre>
256 </div>
259 optimizes and updates the LLVM Function* in place, improving (hopefully) its
260 body. With this in place, we can try our test above again:</p>
263 <pre>
265 ready> Read function definition:
266 define double @test(double %x) {
267 entry:
268 %addtmp = add double %x, 3.000000e+00
269 %multmp = mul double %addtmp, %addtmp
270 ret double %multmp
271 }
272 </pre>
273 </div>
275 <p>As expected, we now get our nicely optimized code, saving a floating point
276 add instruction from every execution of this function.</p>
278 <p>LLVM provides a wide variety of optimizations that can be used in certain
280 passes</a> is available, but it isn't very complete. Another good source of
283 experiment with passes from the command line, so you can see if they do
284 anything.</p>
286 <p>Now that we have reasonable code coming out of our front-end, lets talk about
287 executing it!</p>
289 </div>
291 <!-- *********************************************************************** -->
293 <!-- *********************************************************************** -->
297 <p>Code that is available in LLVM IR can have a wide variety of tools
298 applied to it. For example, you can run optimizations on it (as we did above),
299 you can dump it out in textual or binary forms, you can compile the code to an
300 assembly file (.s) for some target, or you can JIT compile it. The nice thing
301 about the LLVM IR representation is that it is the "common currency" between
302 many different parts of the compiler.
303 </p>
305 <p>In this section, we'll add JIT compiler support to our interpreter. The
306 basic idea that we want for Kaleidoscope is to have the user enter function
307 bodies as they do now, but immediately evaluate the top-level expressions they
308 type in. For example, if they type in "1 + 2;", we should evaluate and print
309 out 3. If they define a function, they should be able to call it from the
310 command line.</p>
312 <p>In order to do this, we first declare and initialize the JIT. This is done
316 <pre>
317 ...
318 let main () =
319 ...
320 <b>(* Create the JIT. *)
321 let the_module_provider = ModuleProvider.create Codegen.the_module in
322 let the_execution_engine = ExecutionEngine.create the_module_provider in</b>
323 ...
324 </pre>
325 </div>
328 compiler or the LLVM interpreter. LLVM will automatically pick a JIT compiler
329 for you if one is available for your platform, otherwise it will fall back to
330 the interpreter.</p>
333 is ready to be used. There are a variety of APIs that are useful, but the
334 simplest one is the "<tt>Llvm_executionengine.ExecutionEngine.run_function</tt>"
335 function. This method JIT compiles the specified LLVM Function and returns a
336 function pointer to the generated machine code. In our case, this means that we
337 can change the code that parses a top-level expression to look like this:</p>
340 <pre>
341 (* Evaluate a top-level expression into an anonymous function. *)
342 let e = Parser.parse_toplevel stream in
343 print_endline "parsed a top-level expr";
344 let the_function = Codegen.codegen_func the_fpm e in
345 dump_value the_function;
347 (* JIT the function, returning a function pointer. *)
348 let result = ExecutionEngine.run_function the_function [||]
349 the_execution_engine in
351 print_string "Evaluated to ";
352 print_float (GenericValue.as_float double_type result);
353 print_newline ();
354 </pre>
355 </div>
357 <p>Recall that we compile top-level expressions into a self-contained LLVM
358 function that takes no arguments and returns the computed double. Because the
359 LLVM JIT compiler matches the native platform ABI, this means that you can just
360 cast the result pointer to a function pointer of that type and call it directly.
361 This means, there is no difference between JIT compiled code and native machine
362 code that is statically linked into your application.</p>
367 <pre>
369 define double @""() {
370 entry:
371 ret double 9.000000e+00
372 }
375 </pre>
376 </div>
378 <p>Well this looks like it is basically working. The dump of the function
379 shows the "no argument function that always returns double" that we synthesize
380 for each top level expression that is typed in. This demonstrates very basic
381 functionality, but can we do more?</p>
384 <pre>
386 Read function definition:
387 define double @testfunc(double %x, double %y) {
388 entry:
389 %multmp = mul double %y, 2.000000e+00
390 %addtmp = add double %multmp, %x
391 ret double %addtmp
392 }
395 define double @""() {
396 entry:
398 ret double %calltmp
399 }
402 </pre>
403 </div>
405 <p>This illustrates that we can now call user code, but there is something a bit
406 subtle going on here. Note that we only invoke the JIT on the anonymous
410 <p>What actually happened here is that the anonymous function was JIT'd when
411 requested. When the Kaleidoscope app calls through the function pointer that is
412 returned, the anonymous function starts executing. It ends up making the call
413 to the "testfunc" function, and ends up in a stub that invokes the JIT, lazily,
414 on testfunc. Once the JIT finishes lazily compiling testfunc,
415 it returns and the code re-executes the call.</p>
417 <p>In summary, the JIT will lazily JIT code, on the fly, as it is needed. The
418 JIT provides a number of other more advanced interfaces for things like freeing
419 allocated machine code, rejit'ing functions to update them, etc. However, even
420 with this simple code, we get some surprisingly powerful capabilities - check
421 this out (I removed the dump of the anonymous functions, you should get the idea
422 by now :) :</p>
425 <pre>
427 Read extern:
428 declare double @sin(double)
431 Read extern:
432 declare double @cos(double)
438 Read function definition:
439 define double @foo(double %x) {
440 entry:
441 %calltmp = call double @sin( double %x )
442 %multmp = mul double %calltmp, %calltmp
443 %calltmp2 = call double @cos( double %x )
444 %multmp4 = mul double %calltmp2, %calltmp2
445 %addtmp = add double %multmp, %multmp4
446 ret double %addtmp
447 }
451 </pre>
452 </div>
454 <p>Whoa, how does the JIT know about sin and cos? The answer is surprisingly
455 simple: in this example, the JIT started execution of a function and got to a
456 function call. It realized that the function was not yet JIT compiled and
457 invoked the standard set of routines to resolve the function. In this case,
458 there is no body defined for the function, so the JIT ended up calling
460 "<tt>sin</tt>" is defined within the JIT's address space, it simply patches up
463 <p>The LLVM JIT provides a number of interfaces (look in the
465 get resolved. It allows you to establish explicit mappings between IR objects
466 and addresses (useful for LLVM global variables that you want to map to static
467 tables, for example), allows you to dynamically decide on the fly based on the
468 function name, and even allows you to have the JIT abort itself if any lazy
469 compilation is attempted.</p>
471 <p>One interesting application of this is that we can now extend the language
472 by writing arbitrary C code to implement operations. For example, if we add:
473 </p>
476 <pre>
477 /* putchard - putchar that takes a double and returns 0. */
478 extern "C"
479 double putchard(double X) {
480 putchar((char)X);
481 return 0;
482 }
483 </pre>
484 </div>
486 <p>Now we can produce simple output to the console by using things like:
487 "<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
488 the console (120 is the ASCII code for 'x'). Similar code could be used to
489 implement file I/O, console input, and many other capabilities in
490 Kaleidoscope.</p>
492 <p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
493 this point, we can compile a non-Turing-complete programming language, optimize
494 and JIT compile it in a user-driven way. Next up we'll look into <a
498 </div>
500 <!-- *********************************************************************** -->
502 <!-- *********************************************************************** -->
506 <p>
507 Here is the complete code listing for our running example, enhanced with the
508 LLVM JIT and optimizer. To build this example, use:
509 </p>
512 <pre>
513 # Compile
514 ocamlbuild toy.byte
515 # Run
516 ./toy.byte
517 </pre>
518 </div>
522 <dl>
525 <pre>
530 </pre>
531 </dd>
535 <pre>
536 open Ocamlbuild_plugin;;
538 ocaml_lib ~extern:true "llvm";;
539 ocaml_lib ~extern:true "llvm_analysis";;
540 ocaml_lib ~extern:true "llvm_executionengine";;
541 ocaml_lib ~extern:true "llvm_target";;
542 ocaml_lib ~extern:true "llvm_scalar_opts";;
546 </pre>
547 </dd>
551 <pre>
552 (*===----------------------------------------------------------------------===
553 * Lexer Tokens
554 *===----------------------------------------------------------------------===*)
556 (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of
557 * these others for known things. *)
558 type token =
559 (* commands *)
560 | Def | Extern
562 (* primary *)
563 | Ident of string | Number of float
565 (* unknown *)
566 | Kwd of char
567 </pre>
568 </dd>
572 <pre>
573 (*===----------------------------------------------------------------------===
574 * Lexer
575 *===----------------------------------------------------------------------===*)
577 let rec lex = parser
578 (* Skip any whitespace. *)
581 (* identifier: [a-zA-Z][a-zA-Z0-9] *)
583 let buffer = Buffer.create 1 in
584 Buffer.add_char buffer c;
585 lex_ident buffer stream
589 let buffer = Buffer.create 1 in
590 Buffer.add_char buffer c;
591 lex_number buffer stream
593 (* Comment until end of line. *)
595 lex_comment stream
597 (* Otherwise, just return the character as its ascii value. *)
601 (* end of stream. *)
604 and lex_number buffer = parser
606 Buffer.add_char buffer c;
607 lex_number buffer stream
611 and lex_ident buffer = parser
613 Buffer.add_char buffer c;
614 lex_ident buffer stream
616 match Buffer.contents buffer with
621 and lex_comment = parser
625 </pre>
626 </dd>
630 <pre>
631 (*===----------------------------------------------------------------------===
632 * Abstract Syntax Tree (aka Parse Tree)
633 *===----------------------------------------------------------------------===*)
635 (* expr - Base type for all expression nodes. *)
636 type expr =
637 (* variant for numeric literals like "1.0". *)
638 | Number of float
640 (* variant for referencing a variable, like "a". *)
641 | Variable of string
643 (* variant for a binary operator. *)
644 | Binary of char * expr * expr
646 (* variant for function calls. *)
647 | Call of string * expr array
649 (* proto - This type represents the "prototype" for a function, which captures
650 * its name, and its argument names (thus implicitly the number of arguments the
651 * function takes). *)
652 type proto = Prototype of string * string array
654 (* func - This type represents a function definition itself. *)
655 type func = Function of proto * expr
656 </pre>
657 </dd>
661 <pre>
662 (*===---------------------------------------------------------------------===
663 * Parser
664 *===---------------------------------------------------------------------===*)
666 (* binop_precedence - This holds the precedence for each binary operator that is
667 * defined *)
668 let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10
670 (* precedence - Get the precedence of the pending binary operator token. *)
673 (* primary
674 * ::= identifier
675 * ::= numberexpr
676 * ::= parenexpr *)
677 let rec parse_primary = parser
678 (* numberexpr ::= number *)
681 (* parenexpr ::= '(' expression ')' *)
684 (* identifierexpr
685 * ::= identifier
686 * ::= identifier '(' argumentexpr ')' *)
688 let rec parse_args accumulator = parser
690 begin parser
693 end stream
695 in
696 let rec parse_ident id = parser
697 (* Call. *)
698 | [< 'Token.Kwd '(';
699 args=parse_args [];
701 Ast.Call (id, Array.of_list (List.rev args))
703 (* Simple variable ref. *)
705 in
706 parse_ident id stream
710 (* binoprhs
711 * ::= ('+' primary)* *)
712 and parse_bin_rhs expr_prec lhs stream =
713 match Stream.peek stream with
714 (* If this is a binop, find its precedence. *)
715 | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c ->
716 let token_prec = precedence c in
718 (* If this is a binop that binds at least as tightly as the current binop,
719 * consume it, otherwise we are done. *)
720 if token_prec < expr_prec then lhs else begin
721 (* Eat the binop. *)
722 Stream.junk stream;
724 (* Parse the primary expression after the binary operator. *)
725 let rhs = parse_primary stream in
727 (* Okay, we know this is a binop. *)
728 let rhs =
729 match Stream.peek stream with
730 | Some (Token.Kwd c2) ->
731 (* If BinOp binds less tightly with rhs than the operator after
732 * rhs, let the pending operator take rhs as its lhs. *)
733 let next_prec = precedence c2 in
734 if token_prec < next_prec
735 then parse_bin_rhs (token_prec + 1) rhs stream
736 else rhs
737 | _ -> rhs
738 in
740 (* Merge lhs/rhs. *)
741 let lhs = Ast.Binary (c, lhs, rhs) in
742 parse_bin_rhs expr_prec lhs stream
743 end
744 | _ -> lhs
746 (* expression
747 * ::= primary binoprhs *)
748 and parse_expr = parser
751 (* prototype
752 * ::= id '(' id* ')' *)
753 let parse_prototype =
754 let rec parse_args accumulator = parser
757 in
759 parser
760 | [< 'Token.Ident id;
761 'Token.Kwd '(' ?? "expected '(' in prototype";
762 args=parse_args [];
764 (* success. *)
765 Ast.Prototype (id, Array.of_list (List.rev args))
768 raise (Stream.Error "expected function name in prototype")
770 (* definition ::= 'def' prototype expression *)
771 let parse_definition = parser
773 Ast.Function (p, e)
775 (* toplevelexpr ::= expression *)
776 let parse_toplevel = parser
778 (* Make an anonymous proto. *)
779 Ast.Function (Ast.Prototype ("", [||]), e)
781 (* external ::= 'extern' prototype *)
782 let parse_extern = parser
784 </pre>
785 </dd>
789 <pre>
790 (*===----------------------------------------------------------------------===
791 * Code Generation
792 *===----------------------------------------------------------------------===*)
794 open Llvm
796 exception Error of string
798 let the_module = create_module "my cool jit"
799 let builder = builder ()
800 let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10
802 let rec codegen_expr = function
803 | Ast.Number n -> const_float double_type n
804 | Ast.Variable name ->
805 (try Hashtbl.find named_values name with
807 | Ast.Binary (op, lhs, rhs) ->
808 let lhs_val = codegen_expr lhs in
809 let rhs_val = codegen_expr rhs in
810 begin
811 match op with
817 let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in
818 build_uitofp i double_type "booltmp" builder
820 end
821 | Ast.Call (callee, args) ->
822 (* Look up the name in the module table. *)
823 let callee =
824 match lookup_function callee the_module with
825 | Some callee -> callee
827 in
828 let params = params callee in
830 (* If argument mismatch error. *)
831 if Array.length params == Array.length args then () else
832 raise (Error "incorrect # arguments passed");
833 let args = Array.map codegen_expr args in
834 build_call callee args "calltmp" builder
836 let codegen_proto = function
837 | Ast.Prototype (name, args) ->
838 (* Make the function type: double(double,double) etc. *)
839 let doubles = Array.make (Array.length args) double_type in
840 let ft = function_type double_type doubles in
841 let f =
842 match lookup_function name the_module with
843 | None -> declare_function name ft the_module
845 (* If 'f' conflicted, there was already something named 'name'. If it
846 * has a body, don't allow redefinition or reextern. *)
847 | Some f ->
848 (* If 'f' already has a body, reject this. *)
849 if block_begin f <> At_end f then
850 raise (Error "redefinition of function");
852 (* If 'f' took a different number of arguments, reject. *)
853 if element_type (type_of f) <> ft then
854 raise (Error "redefinition of function with different # args");
855 f
856 in
858 (* Set names for all arguments. *)
859 Array.iteri (fun i a ->
860 let n = args.(i) in
861 set_value_name n a;
862 Hashtbl.add named_values n a;
863 ) (params f);
864 f
866 let codegen_func the_fpm = function
867 | Ast.Function (proto, body) ->
868 Hashtbl.clear named_values;
869 let the_function = codegen_proto proto in
871 (* Create a new basic block to start insertion into. *)
872 let bb = append_block "entry" the_function in
873 position_at_end bb builder;
875 try
876 let ret_val = codegen_expr body in
878 (* Finish off the function. *)
879 let _ = build_ret ret_val builder in
881 (* Validate the generated code, checking for consistency. *)
882 Llvm_analysis.assert_valid_function the_function;
884 (* Optimize the function. *)
885 let _ = PassManager.run_function the_function the_fpm in
887 the_function
888 with e ->
889 delete_function the_function;
890 raise e
891 </pre>
892 </dd>
896 <pre>
897 (*===----------------------------------------------------------------------===
898 * Top-Level parsing and JIT Driver
899 *===----------------------------------------------------------------------===*)
901 open Llvm
902 open Llvm_executionengine
904 (* top ::= definition | external | expression | ';' *)
905 let rec main_loop the_fpm the_execution_engine stream =
906 match Stream.peek stream with
907 | None -> ()
909 (* ignore top-level semicolons. *)
910 | Some (Token.Kwd ';') ->
911 Stream.junk stream;
912 main_loop the_fpm the_execution_engine stream
914 | Some token ->
915 begin
916 try match token with
917 | Token.Def ->
918 let e = Parser.parse_definition stream in
919 print_endline "parsed a function definition.";
920 dump_value (Codegen.codegen_func the_fpm e);
921 | Token.Extern ->
922 let e = Parser.parse_extern stream in
923 print_endline "parsed an extern.";
924 dump_value (Codegen.codegen_proto e);
925 | _ ->
926 (* Evaluate a top-level expression into an anonymous function. *)
927 let e = Parser.parse_toplevel stream in
928 print_endline "parsed a top-level expr";
929 let the_function = Codegen.codegen_func the_fpm e in
930 dump_value the_function;
932 (* JIT the function, returning a function pointer. *)
933 let result = ExecutionEngine.run_function the_function [||]
934 the_execution_engine in
936 print_string "Evaluated to ";
937 print_float (GenericValue.as_float double_type result);
938 print_newline ();
939 with Stream.Error s | Codegen.Error s ->
940 (* Skip token for error recovery. *)
941 Stream.junk stream;
942 print_endline s;
943 end;
944 print_string "ready> "; flush stdout;
945 main_loop the_fpm the_execution_engine stream
946 </pre>
947 </dd>
951 <pre>
952 (*===----------------------------------------------------------------------===
953 * Main driver code.
954 *===----------------------------------------------------------------------===*)
956 open Llvm
957 open Llvm_executionengine
958 open Llvm_target
959 open Llvm_scalar_opts
961 let main () =
962 (* Install standard binary operators.
963 * 1 is the lowest precedence. *)
965 Hashtbl.add Parser.binop_precedence '+' 20;
966 Hashtbl.add Parser.binop_precedence '-' 20;
967 Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *)
969 (* Prime the first token. *)
970 print_string "ready> "; flush stdout;
971 let stream = Lexer.lex (Stream.of_channel stdin) in
973 (* Create the JIT. *)
974 let the_module_provider = ModuleProvider.create Codegen.the_module in
975 let the_execution_engine = ExecutionEngine.create the_module_provider in
976 let the_fpm = PassManager.create_function the_module_provider in
978 (* Set up the optimizer pipeline. Start with registering info about how the
979 * target lays out data structures. *)
980 TargetData.add (ExecutionEngine.target_data the_execution_engine) the_fpm;
982 (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
983 add_instruction_combining the_fpm;
985 (* reassociate expressions. *)
986 add_reassociation the_fpm;
988 (* Eliminate Common SubExpressions. *)
989 add_gvn the_fpm;
991 (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
992 add_cfg_simplification the_fpm;
994 (* Run the main "interpreter loop" now. *)
995 Toplevel.main_loop the_fpm the_execution_engine stream;
997 (* Print out all the generated code. *)
998 dump_module Codegen.the_module
999 ;;
1001 main ()
1002 </pre>
1003 </dd>
1007 <pre>
1010 /* putchard - putchar that takes a double and returns 0. */
1011 extern double putchard(double X) {
1012 putchar((char)X);
1013 return 0;
1014 }
1015 </pre>
1016 </dd>
1017 </dl>
1020 </div>
1022 <!-- *********************************************************************** -->
1023 <hr>
1024 <address>
1034 </address>
1035 </body>
1036 </html>