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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" 2 "http://www.w3.org/TR/html4/strict.dtd"> 3 4<html> 5<head> 6 <title>Kaleidoscope: Implementing code generation to LLVM IR</title> 7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 8 <meta name="author" content="Chris Lattner"> 9 <meta name="author" content="Erick Tryzelaar"> 10 <link rel="stylesheet" href="../_static/llvm.css" type="text/css"> 11</head> 12 13<body> 14 15<h1>Kaleidoscope: Code generation to LLVM IR</h1> 16 17<ul> 18<li><a href="index.html">Up to Tutorial Index</a></li> 19<li>Chapter 3 20 <ol> 21 <li><a href="#intro">Chapter 3 Introduction</a></li> 22 <li><a href="#basics">Code Generation Setup</a></li> 23 <li><a href="#exprs">Expression Code Generation</a></li> 24 <li><a href="#funcs">Function Code Generation</a></li> 25 <li><a href="#driver">Driver Changes and Closing Thoughts</a></li> 26 <li><a href="#code">Full Code Listing</a></li> 27 </ol> 28</li> 29<li><a href="OCamlLangImpl4.html">Chapter 4</a>: Adding JIT and Optimizer 30Support</li> 31</ul> 32 33<div class="doc_author"> 34 <p> 35 Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> 36 and <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a> 37 </p> 38</div> 39 40<!-- *********************************************************************** --> 41<h2><a name="intro">Chapter 3 Introduction</a></h2> 42<!-- *********************************************************************** --> 43 44<div> 45 46<p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language 47with LLVM</a>" tutorial. This chapter shows you how to transform the <a 48href="OCamlLangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into 49LLVM IR. This will teach you a little bit about how LLVM does things, as well 50as demonstrate how easy it is to use. It's much more work to build a lexer and 51parser than it is to generate LLVM IR code. :) 52</p> 53 54<p><b>Please note</b>: the code in this chapter and later require LLVM 2.3 or 55LLVM SVN to work. LLVM 2.2 and before will not work with it.</p> 56 57</div> 58 59<!-- *********************************************************************** --> 60<h2><a name="basics">Code Generation Setup</a></h2> 61<!-- *********************************************************************** --> 62 63<div> 64 65<p> 66In order to generate LLVM IR, we want some simple setup to get started. First 67we define virtual code generation (codegen) methods in each AST class:</p> 68 69<div class="doc_code"> 70<pre> 71let rec codegen_expr = function 72 | Ast.Number n -> ... 73 | Ast.Variable name -> ... 74</pre> 75</div> 76 77<p>The <tt>Codegen.codegen_expr</tt> function says to emit IR for that AST node 78along with all the things it depends on, and they all return an LLVM Value 79object. "Value" is the class used to represent a "<a 80href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single 81Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect 82of SSA values is that their value is computed as the related instruction 83executes, and it does not get a new value until (and if) the instruction 84re-executes. In other words, there is no way to "change" an SSA value. For 85more information, please read up on <a 86href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single 87Assignment</a> - the concepts are really quite natural once you grok them.</p> 88 89<p>The 90second thing we want is an "Error" exception like we used for the parser, which 91will be used to report errors found during code generation (for example, use of 92an undeclared parameter):</p> 93 94<div class="doc_code"> 95<pre> 96exception Error of string 97 98let context = global_context () 99let the_module = create_module context "my cool jit" 100let builder = builder context 101let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 102let double_type = double_type context 103</pre> 104</div> 105 106<p>The static variables will be used during code generation. 107<tt>Codgen.the_module</tt> is the LLVM construct that contains all of the 108functions and global variables in a chunk of code. In many ways, it is the 109top-level structure that the LLVM IR uses to contain code.</p> 110 111<p>The <tt>Codegen.builder</tt> object is a helper object that makes it easy to 112generate LLVM instructions. Instances of the <a 113href="http://llvm.org/doxygen/IRBuilder_8h-source.html"><tt>IRBuilder</tt></a> 114class keep track of the current place to insert instructions and has methods to 115create new instructions.</p> 116 117<p>The <tt>Codegen.named_values</tt> map keeps track of which values are defined 118in the current scope and what their LLVM representation is. (In other words, it 119is a symbol table for the code). In this form of Kaleidoscope, the only things 120that can be referenced are function parameters. As such, function parameters 121will be in this map when generating code for their function body.</p> 122 123<p> 124With these basics in place, we can start talking about how to generate code for 125each expression. Note that this assumes that the <tt>Codgen.builder</tt> has 126been set up to generate code <em>into</em> something. For now, we'll assume 127that this has already been done, and we'll just use it to emit code.</p> 128 129</div> 130 131<!-- *********************************************************************** --> 132<h2><a name="exprs">Expression Code Generation</a></h2> 133<!-- *********************************************************************** --> 134 135<div> 136 137<p>Generating LLVM code for expression nodes is very straightforward: less 138than 30 lines of commented code for all four of our expression nodes. First 139we'll do numeric literals:</p> 140 141<div class="doc_code"> 142<pre> 143 | Ast.Number n -> const_float double_type n 144</pre> 145</div> 146 147<p>In the LLVM IR, numeric constants are represented with the 148<tt>ConstantFP</tt> class, which holds the numeric value in an <tt>APFloat</tt> 149internally (<tt>APFloat</tt> has the capability of holding floating point 150constants of <em>A</em>rbitrary <em>P</em>recision). This code basically just 151creates and returns a <tt>ConstantFP</tt>. Note that in the LLVM IR 152that constants are all uniqued together and shared. For this reason, the API 153uses "the foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)".</p> 154 155<div class="doc_code"> 156<pre> 157 | Ast.Variable name -> 158 (try Hashtbl.find named_values name with 159 | Not_found -> raise (Error "unknown variable name")) 160</pre> 161</div> 162 163<p>References to variables are also quite simple using LLVM. In the simple 164version of Kaleidoscope, we assume that the variable has already been emitted 165somewhere and its value is available. In practice, the only values that can be 166in the <tt>Codegen.named_values</tt> map are function arguments. This code 167simply checks to see that the specified name is in the map (if not, an unknown 168variable is being referenced) and returns the value for it. In future chapters, 169we'll add support for <a href="LangImpl5.html#for">loop induction variables</a> 170in the symbol table, and for <a href="LangImpl7.html#localvars">local 171variables</a>.</p> 172 173<div class="doc_code"> 174<pre> 175 | Ast.Binary (op, lhs, rhs) -> 176 let lhs_val = codegen_expr lhs in 177 let rhs_val = codegen_expr rhs in 178 begin 179 match op with 180 | '+' -> build_fadd lhs_val rhs_val "addtmp" builder 181 | '-' -> build_fsub lhs_val rhs_val "subtmp" builder 182 | '*' -> build_fmul lhs_val rhs_val "multmp" builder 183 | '<' -> 184 (* Convert bool 0/1 to double 0.0 or 1.0 *) 185 let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in 186 build_uitofp i double_type "booltmp" builder 187 | _ -> raise (Error "invalid binary operator") 188 end 189</pre> 190</div> 191 192<p>Binary operators start to get more interesting. The basic idea here is that 193we recursively emit code for the left-hand side of the expression, then the 194right-hand side, then we compute the result of the binary expression. In this 195code, we do a simple switch on the opcode to create the right LLVM instruction. 196</p> 197 198<p>In the example above, the LLVM builder class is starting to show its value. 199IRBuilder knows where to insert the newly created instruction, all you have to 200do is specify what instruction to create (e.g. with <tt>Llvm.create_add</tt>), 201which operands to use (<tt>lhs</tt> and <tt>rhs</tt> here) and optionally 202provide a name for the generated instruction.</p> 203 204<p>One nice thing about LLVM is that the name is just a hint. For instance, if 205the code above emits multiple "addtmp" variables, LLVM will automatically 206provide each one with an increasing, unique numeric suffix. Local value names 207for instructions are purely optional, but it makes it much easier to read the 208IR dumps.</p> 209 210<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by 211strict rules: for example, the Left and Right operators of 212an <a href="../LangRef.html#i_add">add instruction</a> must have the same 213type, and the result type of the add must match the operand types. Because 214all values in Kaleidoscope are doubles, this makes for very simple code for add, 215sub and mul.</p> 216 217<p>On the other hand, LLVM specifies that the <a 218href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value 219(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with 220a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction 221converts its input integer into a floating point value by treating the input 222as an unsigned value. In contrast, if we used the <a 223href="../LangRef.html#i_sitofp">sitofp instruction</a>, the Kaleidoscope '<' 224operator would return 0.0 and -1.0, depending on the input value.</p> 225 226<div class="doc_code"> 227<pre> 228 | Ast.Call (callee, args) -> 229 (* Look up the name in the module table. *) 230 let callee = 231 match lookup_function callee the_module with 232 | Some callee -> callee 233 | None -> raise (Error "unknown function referenced") 234 in 235 let params = params callee in 236 237 (* If argument mismatch error. *) 238 if Array.length params == Array.length args then () else 239 raise (Error "incorrect # arguments passed"); 240 let args = Array.map codegen_expr args in 241 build_call callee args "calltmp" builder 242</pre> 243</div> 244 245<p>Code generation for function calls is quite straightforward with LLVM. The 246code above initially does a function name lookup in the LLVM Module's symbol 247table. Recall that the LLVM Module is the container that holds all of the 248functions we are JIT'ing. By giving each function the same name as what the 249user specifies, we can use the LLVM symbol table to resolve function names for 250us.</p> 251 252<p>Once we have the function to call, we recursively codegen each argument that 253is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call 254instruction</a>. Note that LLVM uses the native C calling conventions by 255default, allowing these calls to also call into standard library functions like 256"sin" and "cos", with no additional effort.</p> 257 258<p>This wraps up our handling of the four basic expressions that we have so far 259in Kaleidoscope. Feel free to go in and add some more. For example, by 260browsing the <a href="../LangRef.html">LLVM language reference</a> you'll find 261several other interesting instructions that are really easy to plug into our 262basic framework.</p> 263 264</div> 265 266<!-- *********************************************************************** --> 267<h2><a name="funcs">Function Code Generation</a></h2> 268<!-- *********************************************************************** --> 269 270<div> 271 272<p>Code generation for prototypes and functions must handle a number of 273details, which make their code less beautiful than expression code 274generation, but allows us to illustrate some important points. First, lets 275talk about code generation for prototypes: they are used both for function 276bodies and external function declarations. The code starts with:</p> 277 278<div class="doc_code"> 279<pre> 280let codegen_proto = function 281 | Ast.Prototype (name, args) -> 282 (* Make the function type: double(double,double) etc. *) 283 let doubles = Array.make (Array.length args) double_type in 284 let ft = function_type double_type doubles in 285 let f = 286 match lookup_function name the_module with 287</pre> 288</div> 289 290<p>This code packs a lot of power into a few lines. Note first that this 291function returns a "Function*" instead of a "Value*" (although at the moment 292they both are modeled by <tt>llvalue</tt> in ocaml). Because a "prototype" 293really talks about the external interface for a function (not the value computed 294by an expression), it makes sense for it to return the LLVM Function it 295corresponds to when codegen'd.</p> 296 297<p>The call to <tt>Llvm.function_type</tt> creates the <tt>Llvm.llvalue</tt> 298that should be used for a given Prototype. Since all function arguments in 299Kaleidoscope are of type double, the first line creates a vector of "N" LLVM 300double types. It then uses the <tt>Llvm.function_type</tt> method to create a 301function type that takes "N" doubles as arguments, returns one double as a 302result, and that is not vararg (that uses the function 303<tt>Llvm.var_arg_function_type</tt>). Note that Types in LLVM are uniqued just 304like <tt>Constant</tt>s are, so you don't "new" a type, you "get" it.</p> 305 306<p>The final line above checks if the function has already been defined in 307<tt>Codegen.the_module</tt>. If not, we will create it.</p> 308 309<div class="doc_code"> 310<pre> 311 | None -> declare_function name ft the_module 312</pre> 313</div> 314 315<p>This indicates the type and name to use, as well as which module to insert 316into. By default we assume a function has 317<tt>Llvm.Linkage.ExternalLinkage</tt>. "<a href="LangRef.html#linkage">external 318linkage</a>" means that the function may be defined outside the current module 319and/or that it is callable by functions outside the module. The "<tt>name</tt>" 320passed in is the name the user specified: this name is registered in 321"<tt>Codegen.the_module</tt>"s symbol table, which is used by the function call 322code above.</p> 323 324<p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases: 325first, we want to allow 'extern'ing a function more than once, as long as the 326prototypes for the externs match (since all arguments have the same type, we 327just have to check that the number of arguments match). Second, we want to 328allow 'extern'ing a function and then defining a body for it. This is useful 329when defining mutually recursive functions.</p> 330 331<div class="doc_code"> 332<pre> 333 (* If 'f' conflicted, there was already something named 'name'. If it 334 * has a body, don't allow redefinition or reextern. *) 335 | Some f -> 336 (* If 'f' already has a body, reject this. *) 337 if Array.length (basic_blocks f) == 0 then () else 338 raise (Error "redefinition of function"); 339 340 (* If 'f' took a different number of arguments, reject. *) 341 if Array.length (params f) == Array.length args then () else 342 raise (Error "redefinition of function with different # args"); 343 f 344 in 345</pre> 346</div> 347 348<p>In order to verify the logic above, we first check to see if the pre-existing 349function is "empty". In this case, empty means that it has no basic blocks in 350it, which means it has no body. If it has no body, it is a forward 351declaration. Since we don't allow anything after a full definition of the 352function, the code rejects this case. If the previous reference to a function 353was an 'extern', we simply verify that the number of arguments for that 354definition and this one match up. If not, we emit an error.</p> 355 356<div class="doc_code"> 357<pre> 358 (* Set names for all arguments. *) 359 Array.iteri (fun i a -> 360 let n = args.(i) in 361 set_value_name n a; 362 Hashtbl.add named_values n a; 363 ) (params f); 364 f 365</pre> 366</div> 367 368<p>The last bit of code for prototypes loops over all of the arguments in the 369function, setting the name of the LLVM Argument objects to match, and registering 370the arguments in the <tt>Codegen.named_values</tt> map for future use by the 371<tt>Ast.Variable</tt> variant. Once this is set up, it returns the Function 372object to the caller. Note that we don't check for conflicting 373argument names here (e.g. "extern foo(a b a)"). Doing so would be very 374straight-forward with the mechanics we have already used above.</p> 375 376<div class="doc_code"> 377<pre> 378let codegen_func = function 379 | Ast.Function (proto, body) -> 380 Hashtbl.clear named_values; 381 let the_function = codegen_proto proto in 382</pre> 383</div> 384 385<p>Code generation for function definitions starts out simply enough: we just 386codegen the prototype (Proto) and verify that it is ok. We then clear out the 387<tt>Codegen.named_values</tt> map to make sure that there isn't anything in it 388from the last function we compiled. Code generation of the prototype ensures 389that there is an LLVM Function object that is ready to go for us.</p> 390 391<div class="doc_code"> 392<pre> 393 (* Create a new basic block to start insertion into. *) 394 let bb = append_block context "entry" the_function in 395 position_at_end bb builder; 396 397 try 398 let ret_val = codegen_expr body in 399</pre> 400</div> 401 402<p>Now we get to the point where the <tt>Codegen.builder</tt> is set up. The 403first line creates a new 404<a href="http://en.wikipedia.org/wiki/Basic_block">basic block</a> (named 405"entry"), which is inserted into <tt>the_function</tt>. The second line then 406tells the builder that new instructions should be inserted into the end of the 407new basic block. Basic blocks in LLVM are an important part of functions that 408define the <a 409href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>. 410Since we don't have any control flow, our functions will only contain one 411block at this point. We'll fix this in <a href="OCamlLangImpl5.html">Chapter 4125</a> :).</p> 413 414<div class="doc_code"> 415<pre> 416 let ret_val = codegen_expr body in 417 418 (* Finish off the function. *) 419 let _ = build_ret ret_val builder in 420 421 (* Validate the generated code, checking for consistency. *) 422 Llvm_analysis.assert_valid_function the_function; 423 424 the_function 425</pre> 426</div> 427 428<p>Once the insertion point is set up, we call the <tt>Codegen.codegen_func</tt> 429method for the root expression of the function. If no error happens, this emits 430code to compute the expression into the entry block and returns the value that 431was computed. Assuming no error, we then create an LLVM <a 432href="../LangRef.html#i_ret">ret instruction</a>, which completes the function. 433Once the function is built, we call 434<tt>Llvm_analysis.assert_valid_function</tt>, which is provided by LLVM. This 435function does a variety of consistency checks on the generated code, to 436determine if our compiler is doing everything right. Using this is important: 437it can catch a lot of bugs. Once the function is finished and validated, we 438return it.</p> 439 440<div class="doc_code"> 441<pre> 442 with e -> 443 delete_function the_function; 444 raise e 445</pre> 446</div> 447 448<p>The only piece left here is handling of the error case. For simplicity, we 449handle this by merely deleting the function we produced with the 450<tt>Llvm.delete_function</tt> method. This allows the user to redefine a 451function that they incorrectly typed in before: if we didn't delete it, it 452would live in the symbol table, with a body, preventing future redefinition.</p> 453 454<p>This code does have a bug, though. Since the <tt>Codegen.codegen_proto</tt> 455can return a previously defined forward declaration, our code can actually delete 456a forward declaration. There are a number of ways to fix this bug, see what you 457can come up with! Here is a testcase:</p> 458 459<div class="doc_code"> 460<pre> 461extern foo(a b); # ok, defines foo. 462def foo(a b) c; # error, 'c' is invalid. 463def bar() foo(1, 2); # error, unknown function "foo" 464</pre> 465</div> 466 467</div> 468 469<!-- *********************************************************************** --> 470<h2><a name="driver">Driver Changes and Closing Thoughts</a></h2> 471<!-- *********************************************************************** --> 472 473<div> 474 475<p> 476For now, code generation to LLVM doesn't really get us much, except that we can 477look at the pretty IR calls. The sample code inserts calls to Codegen into the 478"<tt>Toplevel.main_loop</tt>", and then dumps out the LLVM IR. This gives a 479nice way to look at the LLVM IR for simple functions. For example: 480</p> 481 482<div class="doc_code"> 483<pre> 484ready> <b>4+5</b>; 485Read top-level expression: 486define double @""() { 487entry: 488 %addtmp = fadd double 4.000000e+00, 5.000000e+00 489 ret double %addtmp 490} 491</pre> 492</div> 493 494<p>Note how the parser turns the top-level expression into anonymous functions 495for us. This will be handy when we add <a href="OCamlLangImpl4.html#jit">JIT 496support</a> in the next chapter. Also note that the code is very literally 497transcribed, no optimizations are being performed. We will 498<a href="OCamlLangImpl4.html#trivialconstfold">add optimizations</a> explicitly 499in the next chapter.</p> 500 501<div class="doc_code"> 502<pre> 503ready> <b>def foo(a b) a*a + 2*a*b + b*b;</b> 504Read function definition: 505define double @foo(double %a, double %b) { 506entry: 507 %multmp = fmul double %a, %a 508 %multmp1 = fmul double 2.000000e+00, %a 509 %multmp2 = fmul double %multmp1, %b 510 %addtmp = fadd double %multmp, %multmp2 511 %multmp3 = fmul double %b, %b 512 %addtmp4 = fadd double %addtmp, %multmp3 513 ret double %addtmp4 514} 515</pre> 516</div> 517 518<p>This shows some simple arithmetic. Notice the striking similarity to the 519LLVM builder calls that we use to create the instructions.</p> 520 521<div class="doc_code"> 522<pre> 523ready> <b>def bar(a) foo(a, 4.0) + bar(31337);</b> 524Read function definition: 525define double @bar(double %a) { 526entry: 527 %calltmp = call double @foo(double %a, double 4.000000e+00) 528 %calltmp1 = call double @bar(double 3.133700e+04) 529 %addtmp = fadd double %calltmp, %calltmp1 530 ret double %addtmp 531} 532</pre> 533</div> 534 535<p>This shows some function calls. Note that this function will take a long 536time to execute if you call it. In the future we'll add conditional control 537flow to actually make recursion useful :).</p> 538 539<div class="doc_code"> 540<pre> 541ready> <b>extern cos(x);</b> 542Read extern: 543declare double @cos(double) 544 545ready> <b>cos(1.234);</b> 546Read top-level expression: 547define double @""() { 548entry: 549 %calltmp = call double @cos(double 1.234000e+00) 550 ret double %calltmp 551} 552</pre> 553</div> 554 555<p>This shows an extern for the libm "cos" function, and a call to it.</p> 556 557 558<div class="doc_code"> 559<pre> 560ready> <b>^D</b> 561; ModuleID = 'my cool jit' 562 563define double @""() { 564entry: 565 %addtmp = fadd double 4.000000e+00, 5.000000e+00 566 ret double %addtmp 567} 568 569define double @foo(double %a, double %b) { 570entry: 571 %multmp = fmul double %a, %a 572 %multmp1 = fmul double 2.000000e+00, %a 573 %multmp2 = fmul double %multmp1, %b 574 %addtmp = fadd double %multmp, %multmp2 575 %multmp3 = fmul double %b, %b 576 %addtmp4 = fadd double %addtmp, %multmp3 577 ret double %addtmp4 578} 579 580define double @bar(double %a) { 581entry: 582 %calltmp = call double @foo(double %a, double 4.000000e+00) 583 %calltmp1 = call double @bar(double 3.133700e+04) 584 %addtmp = fadd double %calltmp, %calltmp1 585 ret double %addtmp 586} 587 588declare double @cos(double) 589 590define double @""() { 591entry: 592 %calltmp = call double @cos(double 1.234000e+00) 593 ret double %calltmp 594} 595</pre> 596</div> 597 598<p>When you quit the current demo, it dumps out the IR for the entire module 599generated. Here you can see the big picture with all the functions referencing 600each other.</p> 601 602<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll 603describe how to <a href="OCamlLangImpl4.html">add JIT codegen and optimizer 604support</a> to this so we can actually start running code!</p> 605 606</div> 607 608 609<!-- *********************************************************************** --> 610<h2><a name="code">Full Code Listing</a></h2> 611<!-- *********************************************************************** --> 612 613<div> 614 615<p> 616Here is the complete code listing for our running example, enhanced with the 617LLVM code generator. Because this uses the LLVM libraries, we need to link 618them in. To do this, we use the <a 619href="http://llvm.org/cmds/llvm-config.html">llvm-config</a> tool to inform 620our makefile/command line about which options to use:</p> 621 622<div class="doc_code"> 623<pre> 624# Compile 625ocamlbuild toy.byte 626# Run 627./toy.byte 628</pre> 629</div> 630 631<p>Here is the code:</p> 632 633<dl> 634<dt>_tags:</dt> 635<dd class="doc_code"> 636<pre> 637<{lexer,parser}.ml>: use_camlp4, pp(camlp4of) 638<*.{byte,native}>: g++, use_llvm, use_llvm_analysis 639</pre> 640</dd> 641 642<dt>myocamlbuild.ml:</dt> 643<dd class="doc_code"> 644<pre> 645open Ocamlbuild_plugin;; 646 647ocaml_lib ~extern:true "llvm";; 648ocaml_lib ~extern:true "llvm_analysis";; 649 650flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);; 651</pre> 652</dd> 653 654<dt>token.ml:</dt> 655<dd class="doc_code"> 656<pre> 657(*===----------------------------------------------------------------------=== 658 * Lexer Tokens 659 *===----------------------------------------------------------------------===*) 660 661(* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of 662 * these others for known things. *) 663type token = 664 (* commands *) 665 | Def | Extern 666 667 (* primary *) 668 | Ident of string | Number of float 669 670 (* unknown *) 671 | Kwd of char 672</pre> 673</dd> 674 675<dt>lexer.ml:</dt> 676<dd class="doc_code"> 677<pre> 678(*===----------------------------------------------------------------------=== 679 * Lexer 680 *===----------------------------------------------------------------------===*) 681 682let rec lex = parser 683 (* Skip any whitespace. *) 684 | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream 685 686 (* identifier: [a-zA-Z][a-zA-Z0-9] *) 687 | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] -> 688 let buffer = Buffer.create 1 in 689 Buffer.add_char buffer c; 690 lex_ident buffer stream 691 692 (* number: [0-9.]+ *) 693 | [< ' ('0' .. '9' as c); stream >] -> 694 let buffer = Buffer.create 1 in 695 Buffer.add_char buffer c; 696 lex_number buffer stream 697 698 (* Comment until end of line. *) 699 | [< ' ('#'); stream >] -> 700 lex_comment stream 701 702 (* Otherwise, just return the character as its ascii value. *) 703 | [< 'c; stream >] -> 704 [< 'Token.Kwd c; lex stream >] 705 706 (* end of stream. *) 707 | [< >] -> [< >] 708 709and lex_number buffer = parser 710 | [< ' ('0' .. '9' | '.' as c); stream >] -> 711 Buffer.add_char buffer c; 712 lex_number buffer stream 713 | [< stream=lex >] -> 714 [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >] 715 716and lex_ident buffer = parser 717 | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] -> 718 Buffer.add_char buffer c; 719 lex_ident buffer stream 720 | [< stream=lex >] -> 721 match Buffer.contents buffer with 722 | "def" -> [< 'Token.Def; stream >] 723 | "extern" -> [< 'Token.Extern; stream >] 724 | id -> [< 'Token.Ident id; stream >] 725 726and lex_comment = parser 727 | [< ' ('\n'); stream=lex >] -> stream 728 | [< 'c; e=lex_comment >] -> e 729 | [< >] -> [< >] 730</pre> 731</dd> 732 733<dt>ast.ml:</dt> 734<dd class="doc_code"> 735<pre> 736(*===----------------------------------------------------------------------=== 737 * Abstract Syntax Tree (aka Parse Tree) 738 *===----------------------------------------------------------------------===*) 739 740(* expr - Base type for all expression nodes. *) 741type expr = 742 (* variant for numeric literals like "1.0". *) 743 | Number of float 744 745 (* variant for referencing a variable, like "a". *) 746 | Variable of string 747 748 (* variant for a binary operator. *) 749 | Binary of char * expr * expr 750 751 (* variant for function calls. *) 752 | Call of string * expr array 753 754(* proto - This type represents the "prototype" for a function, which captures 755 * its name, and its argument names (thus implicitly the number of arguments the 756 * function takes). *) 757type proto = Prototype of string * string array 758 759(* func - This type represents a function definition itself. *) 760type func = Function of proto * expr 761</pre> 762</dd> 763 764<dt>parser.ml:</dt> 765<dd class="doc_code"> 766<pre> 767(*===---------------------------------------------------------------------=== 768 * Parser 769 *===---------------------------------------------------------------------===*) 770 771(* binop_precedence - This holds the precedence for each binary operator that is 772 * defined *) 773let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10 774 775(* precedence - Get the precedence of the pending binary operator token. *) 776let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1 777 778(* primary 779 * ::= identifier 780 * ::= numberexpr 781 * ::= parenexpr *) 782let rec parse_primary = parser 783 (* numberexpr ::= number *) 784 | [< 'Token.Number n >] -> Ast.Number n 785 786 (* parenexpr ::= '(' expression ')' *) 787 | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e 788 789 (* identifierexpr 790 * ::= identifier 791 * ::= identifier '(' argumentexpr ')' *) 792 | [< 'Token.Ident id; stream >] -> 793 let rec parse_args accumulator = parser 794 | [< e=parse_expr; stream >] -> 795 begin parser 796 | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e 797 | [< >] -> e :: accumulator 798 end stream 799 | [< >] -> accumulator 800 in 801 let rec parse_ident id = parser 802 (* Call. *) 803 | [< 'Token.Kwd '('; 804 args=parse_args []; 805 'Token.Kwd ')' ?? "expected ')'">] -> 806 Ast.Call (id, Array.of_list (List.rev args)) 807 808 (* Simple variable ref. *) 809 | [< >] -> Ast.Variable id 810 in 811 parse_ident id stream 812 813 | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") 814 815(* binoprhs 816 * ::= ('+' primary)* *) 817and parse_bin_rhs expr_prec lhs stream = 818 match Stream.peek stream with 819 (* If this is a binop, find its precedence. *) 820 | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c -> 821 let token_prec = precedence c in 822 823 (* If this is a binop that binds at least as tightly as the current binop, 824 * consume it, otherwise we are done. *) 825 if token_prec < expr_prec then lhs else begin 826 (* Eat the binop. *) 827 Stream.junk stream; 828 829 (* Parse the primary expression after the binary operator. *) 830 let rhs = parse_primary stream in 831 832 (* Okay, we know this is a binop. *) 833 let rhs = 834 match Stream.peek stream with 835 | Some (Token.Kwd c2) -> 836 (* If BinOp binds less tightly with rhs than the operator after 837 * rhs, let the pending operator take rhs as its lhs. *) 838 let next_prec = precedence c2 in 839 if token_prec < next_prec 840 then parse_bin_rhs (token_prec + 1) rhs stream 841 else rhs 842 | _ -> rhs 843 in 844 845 (* Merge lhs/rhs. *) 846 let lhs = Ast.Binary (c, lhs, rhs) in 847 parse_bin_rhs expr_prec lhs stream 848 end 849 | _ -> lhs 850 851(* expression 852 * ::= primary binoprhs *) 853and parse_expr = parser 854 | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream 855 856(* prototype 857 * ::= id '(' id* ')' *) 858let parse_prototype = 859 let rec parse_args accumulator = parser 860 | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e 861 | [< >] -> accumulator 862 in 863 864 parser 865 | [< 'Token.Ident id; 866 'Token.Kwd '(' ?? "expected '(' in prototype"; 867 args=parse_args []; 868 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> 869 (* success. *) 870 Ast.Prototype (id, Array.of_list (List.rev args)) 871 872 | [< >] -> 873 raise (Stream.Error "expected function name in prototype") 874 875(* definition ::= 'def' prototype expression *) 876let parse_definition = parser 877 | [< 'Token.Def; p=parse_prototype; e=parse_expr >] -> 878 Ast.Function (p, e) 879 880(* toplevelexpr ::= expression *) 881let parse_toplevel = parser 882 | [< e=parse_expr >] -> 883 (* Make an anonymous proto. *) 884 Ast.Function (Ast.Prototype ("", [||]), e) 885 886(* external ::= 'extern' prototype *) 887let parse_extern = parser 888 | [< 'Token.Extern; e=parse_prototype >] -> e 889</pre> 890</dd> 891 892<dt>codegen.ml:</dt> 893<dd class="doc_code"> 894<pre> 895(*===----------------------------------------------------------------------=== 896 * Code Generation 897 *===----------------------------------------------------------------------===*) 898 899open Llvm 900 901exception Error of string 902 903let context = global_context () 904let the_module = create_module context "my cool jit" 905let builder = builder context 906let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 907let double_type = double_type context 908 909let rec codegen_expr = function 910 | Ast.Number n -> const_float double_type n 911 | Ast.Variable name -> 912 (try Hashtbl.find named_values name with 913 | Not_found -> raise (Error "unknown variable name")) 914 | Ast.Binary (op, lhs, rhs) -> 915 let lhs_val = codegen_expr lhs in 916 let rhs_val = codegen_expr rhs in 917 begin 918 match op with 919 | '+' -> build_add lhs_val rhs_val "addtmp" builder 920 | '-' -> build_sub lhs_val rhs_val "subtmp" builder 921 | '*' -> build_mul lhs_val rhs_val "multmp" builder 922 | '<' -> 923 (* Convert bool 0/1 to double 0.0 or 1.0 *) 924 let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in 925 build_uitofp i double_type "booltmp" builder 926 | _ -> raise (Error "invalid binary operator") 927 end 928 | Ast.Call (callee, args) -> 929 (* Look up the name in the module table. *) 930 let callee = 931 match lookup_function callee the_module with 932 | Some callee -> callee 933 | None -> raise (Error "unknown function referenced") 934 in 935 let params = params callee in 936 937 (* If argument mismatch error. *) 938 if Array.length params == Array.length args then () else 939 raise (Error "incorrect # arguments passed"); 940 let args = Array.map codegen_expr args in 941 build_call callee args "calltmp" builder 942 943let codegen_proto = function 944 | Ast.Prototype (name, args) -> 945 (* Make the function type: double(double,double) etc. *) 946 let doubles = Array.make (Array.length args) double_type in 947 let ft = function_type double_type doubles in 948 let f = 949 match lookup_function name the_module with 950 | None -> declare_function name ft the_module 951 952 (* If 'f' conflicted, there was already something named 'name'. If it 953 * has a body, don't allow redefinition or reextern. *) 954 | Some f -> 955 (* If 'f' already has a body, reject this. *) 956 if block_begin f <> At_end f then 957 raise (Error "redefinition of function"); 958 959 (* If 'f' took a different number of arguments, reject. *) 960 if element_type (type_of f) <> ft then 961 raise (Error "redefinition of function with different # args"); 962 f 963 in 964 965 (* Set names for all arguments. *) 966 Array.iteri (fun i a -> 967 let n = args.(i) in 968 set_value_name n a; 969 Hashtbl.add named_values n a; 970 ) (params f); 971 f 972 973let codegen_func = function 974 | Ast.Function (proto, body) -> 975 Hashtbl.clear named_values; 976 let the_function = codegen_proto proto in 977 978 (* Create a new basic block to start insertion into. *) 979 let bb = append_block context "entry" the_function in 980 position_at_end bb builder; 981 982 try 983 let ret_val = codegen_expr body in 984 985 (* Finish off the function. *) 986 let _ = build_ret ret_val builder in 987 988 (* Validate the generated code, checking for consistency. *) 989 Llvm_analysis.assert_valid_function the_function; 990 991 the_function 992 with e -> 993 delete_function the_function; 994 raise e 995</pre> 996</dd> 997 998<dt>toplevel.ml:</dt> 999<dd class="doc_code"> 1000<pre> 1001(*===----------------------------------------------------------------------=== 1002 * Top-Level parsing and JIT Driver 1003 *===----------------------------------------------------------------------===*) 1004 1005open Llvm 1006 1007(* top ::= definition | external | expression | ';' *) 1008let rec main_loop stream = 1009 match Stream.peek stream with 1010 | None -> () 1011 1012 (* ignore top-level semicolons. *) 1013 | Some (Token.Kwd ';') -> 1014 Stream.junk stream; 1015 main_loop stream 1016 1017 | Some token -> 1018 begin 1019 try match token with 1020 | Token.Def -> 1021 let e = Parser.parse_definition stream in 1022 print_endline "parsed a function definition."; 1023 dump_value (Codegen.codegen_func e); 1024 | Token.Extern -> 1025 let e = Parser.parse_extern stream in 1026 print_endline "parsed an extern."; 1027 dump_value (Codegen.codegen_proto e); 1028 | _ -> 1029 (* Evaluate a top-level expression into an anonymous function. *) 1030 let e = Parser.parse_toplevel stream in 1031 print_endline "parsed a top-level expr"; 1032 dump_value (Codegen.codegen_func e); 1033 with Stream.Error s | Codegen.Error s -> 1034 (* Skip token for error recovery. *) 1035 Stream.junk stream; 1036 print_endline s; 1037 end; 1038 print_string "ready> "; flush stdout; 1039 main_loop stream 1040</pre> 1041</dd> 1042 1043<dt>toy.ml:</dt> 1044<dd class="doc_code"> 1045<pre> 1046(*===----------------------------------------------------------------------=== 1047 * Main driver code. 1048 *===----------------------------------------------------------------------===*) 1049 1050open Llvm 1051 1052let main () = 1053 (* Install standard binary operators. 1054 * 1 is the lowest precedence. *) 1055 Hashtbl.add Parser.binop_precedence '<' 10; 1056 Hashtbl.add Parser.binop_precedence '+' 20; 1057 Hashtbl.add Parser.binop_precedence '-' 20; 1058 Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *) 1059 1060 (* Prime the first token. *) 1061 print_string "ready> "; flush stdout; 1062 let stream = Lexer.lex (Stream.of_channel stdin) in 1063 1064 (* Run the main "interpreter loop" now. *) 1065 Toplevel.main_loop stream; 1066 1067 (* Print out all the generated code. *) 1068 dump_module Codegen.the_module 1069;; 1070 1071main () 1072</pre> 1073</dd> 1074</dl> 1075 1076<a href="OCamlLangImpl4.html">Next: Adding JIT and Optimizer Support</a> 1077</div> 1078 1079<!-- *********************************************************************** --> 1080<hr> 1081<address> 1082 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img 1083 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> 1084 <a href="http://validator.w3.org/check/referer"><img 1085 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a> 1086 1087 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> 1088 <a href="mailto:idadesub@users.sourceforge.net">Erick Tryzelaar</a><br> 1089 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br> 1090 Last modified: $Date: 2012-05-03 06:46:36 +0800 (ε¨ε, 03 δΊζ 2012) $ 1091</address> 1092</body> 1093</html>