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: Extending the Language: Mutable Variables / SSA 7 construction</title> 8 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 9 <meta name="author" content="Chris Lattner"> 10 <link rel="stylesheet" href="../llvm.css" type="text/css"> 11</head> 12 13<body> 14 15<h1>Kaleidoscope: Extending the Language: Mutable Variables</h1> 16 17<ul> 18<li><a href="index.html">Up to Tutorial Index</a></li> 19<li>Chapter 7 20 <ol> 21 <li><a href="#intro">Chapter 7 Introduction</a></li> 22 <li><a href="#why">Why is this a hard problem?</a></li> 23 <li><a href="#memory">Memory in LLVM</a></li> 24 <li><a href="#kalvars">Mutable Variables in Kaleidoscope</a></li> 25 <li><a href="#adjustments">Adjusting Existing Variables for 26 Mutation</a></li> 27 <li><a href="#assignment">New Assignment Operator</a></li> 28 <li><a href="#localvars">User-defined Local Variables</a></li> 29 <li><a href="#code">Full Code Listing</a></li> 30 </ol> 31</li> 32<li><a href="LangImpl8.html">Chapter 8</a>: Conclusion and other useful LLVM 33 tidbits</li> 34</ul> 35 36<div class="doc_author"> 37 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p> 38</div> 39 40<!-- *********************************************************************** --> 41<h2><a name="intro">Chapter 7 Introduction</a></h2> 42<!-- *********************************************************************** --> 43 44<div> 45 46<p>Welcome to Chapter 7 of the "<a href="index.html">Implementing a language 47with LLVM</a>" tutorial. In chapters 1 through 6, we've built a very 48respectable, albeit simple, <a 49href="http://en.wikipedia.org/wiki/Functional_programming">functional 50programming language</a>. In our journey, we learned some parsing techniques, 51how to build and represent an AST, how to build LLVM IR, and how to optimize 52the resultant code as well as JIT compile it.</p> 53 54<p>While Kaleidoscope is interesting as a functional language, the fact that it 55is functional makes it "too easy" to generate LLVM IR for it. In particular, a 56functional language makes it very easy to build LLVM IR directly in <a 57href="http://en.wikipedia.org/wiki/Static_single_assignment_form">SSA form</a>. 58Since LLVM requires that the input code be in SSA form, this is a very nice 59property and it is often unclear to newcomers how to generate code for an 60imperative language with mutable variables.</p> 61 62<p>The short (and happy) summary of this chapter is that there is no need for 63your front-end to build SSA form: LLVM provides highly tuned and well tested 64support for this, though the way it works is a bit unexpected for some.</p> 65 66</div> 67 68<!-- *********************************************************************** --> 69<h2><a name="why">Why is this a hard problem?</a></h2> 70<!-- *********************************************************************** --> 71 72<div> 73 74<p> 75To understand why mutable variables cause complexities in SSA construction, 76consider this extremely simple C example: 77</p> 78 79<div class="doc_code"> 80<pre> 81int G, H; 82int test(_Bool Condition) { 83 int X; 84 if (Condition) 85 X = G; 86 else 87 X = H; 88 return X; 89} 90</pre> 91</div> 92 93<p>In this case, we have the variable "X", whose value depends on the path 94executed in the program. Because there are two different possible values for X 95before the return instruction, a PHI node is inserted to merge the two values. 96The LLVM IR that we want for this example looks like this:</p> 97 98<div class="doc_code"> 99<pre> 100@G = weak global i32 0 ; type of @G is i32* 101@H = weak global i32 0 ; type of @H is i32* 102 103define i32 @test(i1 %Condition) { 104entry: 105 br i1 %Condition, label %cond_true, label %cond_false 106 107cond_true: 108 %X.0 = load i32* @G 109 br label %cond_next 110 111cond_false: 112 %X.1 = load i32* @H 113 br label %cond_next 114 115cond_next: 116 %X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ] 117 ret i32 %X.2 118} 119</pre> 120</div> 121 122<p>In this example, the loads from the G and H global variables are explicit in 123the LLVM IR, and they live in the then/else branches of the if statement 124(cond_true/cond_false). In order to merge the incoming values, the X.2 phi node 125in the cond_next block selects the right value to use based on where control 126flow is coming from: if control flow comes from the cond_false block, X.2 gets 127the value of X.1. Alternatively, if control flow comes from cond_true, it gets 128the value of X.0. The intent of this chapter is not to explain the details of 129SSA form. For more information, see one of the many <a 130href="http://en.wikipedia.org/wiki/Static_single_assignment_form">online 131references</a>.</p> 132 133<p>The question for this article is "who places the phi nodes when lowering 134assignments to mutable variables?". The issue here is that LLVM 135<em>requires</em> that its IR be in SSA form: there is no "non-ssa" mode for it. 136However, SSA construction requires non-trivial algorithms and data structures, 137so it is inconvenient and wasteful for every front-end to have to reproduce this 138logic.</p> 139 140</div> 141 142<!-- *********************************************************************** --> 143<h2><a name="memory">Memory in LLVM</a></h2> 144<!-- *********************************************************************** --> 145 146<div> 147 148<p>The 'trick' here is that while LLVM does require all register values to be 149in SSA form, it does not require (or permit) memory objects to be in SSA form. 150In the example above, note that the loads from G and H are direct accesses to 151G and H: they are not renamed or versioned. This differs from some other 152compiler systems, which do try to version memory objects. In LLVM, instead of 153encoding dataflow analysis of memory into the LLVM IR, it is handled with <a 154href="../WritingAnLLVMPass.html">Analysis Passes</a> which are computed on 155demand.</p> 156 157<p> 158With this in mind, the high-level idea is that we want to make a stack variable 159(which lives in memory, because it is on the stack) for each mutable object in 160a function. To take advantage of this trick, we need to talk about how LLVM 161represents stack variables. 162</p> 163 164<p>In LLVM, all memory accesses are explicit with load/store instructions, and 165it is carefully designed not to have (or need) an "address-of" operator. Notice 166how the type of the @G/@H global variables is actually "i32*" even though the 167variable is defined as "i32". What this means is that @G defines <em>space</em> 168for an i32 in the global data area, but its <em>name</em> actually refers to the 169address for that space. Stack variables work the same way, except that instead of 170being declared with global variable definitions, they are declared with the 171<a href="../LangRef.html#i_alloca">LLVM alloca instruction</a>:</p> 172 173<div class="doc_code"> 174<pre> 175define i32 @example() { 176entry: 177 %X = alloca i32 ; type of %X is i32*. 178 ... 179 %tmp = load i32* %X ; load the stack value %X from the stack. 180 %tmp2 = add i32 %tmp, 1 ; increment it 181 store i32 %tmp2, i32* %X ; store it back 182 ... 183</pre> 184</div> 185 186<p>This code shows an example of how you can declare and manipulate a stack 187variable in the LLVM IR. Stack memory allocated with the alloca instruction is 188fully general: you can pass the address of the stack slot to functions, you can 189store it in other variables, etc. In our example above, we could rewrite the 190example to use the alloca technique to avoid using a PHI node:</p> 191 192<div class="doc_code"> 193<pre> 194@G = weak global i32 0 ; type of @G is i32* 195@H = weak global i32 0 ; type of @H is i32* 196 197define i32 @test(i1 %Condition) { 198entry: 199 %X = alloca i32 ; type of %X is i32*. 200 br i1 %Condition, label %cond_true, label %cond_false 201 202cond_true: 203 %X.0 = load i32* @G 204 store i32 %X.0, i32* %X ; Update X 205 br label %cond_next 206 207cond_false: 208 %X.1 = load i32* @H 209 store i32 %X.1, i32* %X ; Update X 210 br label %cond_next 211 212cond_next: 213 %X.2 = load i32* %X ; Read X 214 ret i32 %X.2 215} 216</pre> 217</div> 218 219<p>With this, we have discovered a way to handle arbitrary mutable variables 220without the need to create Phi nodes at all:</p> 221 222<ol> 223<li>Each mutable variable becomes a stack allocation.</li> 224<li>Each read of the variable becomes a load from the stack.</li> 225<li>Each update of the variable becomes a store to the stack.</li> 226<li>Taking the address of a variable just uses the stack address directly.</li> 227</ol> 228 229<p>While this solution has solved our immediate problem, it introduced another 230one: we have now apparently introduced a lot of stack traffic for very simple 231and common operations, a major performance problem. Fortunately for us, the 232LLVM optimizer has a highly-tuned optimization pass named "mem2reg" that handles 233this case, promoting allocas like this into SSA registers, inserting Phi nodes 234as appropriate. If you run this example through the pass, for example, you'll 235get:</p> 236 237<div class="doc_code"> 238<pre> 239$ <b>llvm-as < example.ll | opt -mem2reg | llvm-dis</b> 240@G = weak global i32 0 241@H = weak global i32 0 242 243define i32 @test(i1 %Condition) { 244entry: 245 br i1 %Condition, label %cond_true, label %cond_false 246 247cond_true: 248 %X.0 = load i32* @G 249 br label %cond_next 250 251cond_false: 252 %X.1 = load i32* @H 253 br label %cond_next 254 255cond_next: 256 %X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ] 257 ret i32 %X.01 258} 259</pre> 260</div> 261 262<p>The mem2reg pass implements the standard "iterated dominance frontier" 263algorithm for constructing SSA form and has a number of optimizations that speed 264up (very common) degenerate cases. The mem2reg optimization pass is the answer to dealing 265with mutable variables, and we highly recommend that you depend on it. Note that 266mem2reg only works on variables in certain circumstances:</p> 267 268<ol> 269<li>mem2reg is alloca-driven: it looks for allocas and if it can handle them, it 270promotes them. It does not apply to global variables or heap allocations.</li> 271 272<li>mem2reg only looks for alloca instructions in the entry block of the 273function. Being in the entry block guarantees that the alloca is only executed 274once, which makes analysis simpler.</li> 275 276<li>mem2reg only promotes allocas whose uses are direct loads and stores. If 277the address of the stack object is passed to a function, or if any funny pointer 278arithmetic is involved, the alloca will not be promoted.</li> 279 280<li>mem2reg only works on allocas of <a 281href="../LangRef.html#t_classifications">first class</a> 282values (such as pointers, scalars and vectors), and only if the array size 283of the allocation is 1 (or missing in the .ll file). mem2reg is not capable of 284promoting structs or arrays to registers. Note that the "scalarrepl" pass is 285more powerful and can promote structs, "unions", and arrays in many cases.</li> 286 287</ol> 288 289<p> 290All of these properties are easy to satisfy for most imperative languages, and 291we'll illustrate it below with Kaleidoscope. The final question you may be 292asking is: should I bother with this nonsense for my front-end? Wouldn't it be 293better if I just did SSA construction directly, avoiding use of the mem2reg 294optimization pass? In short, we strongly recommend that you use this technique 295for building SSA form, unless there is an extremely good reason not to. Using 296this technique is:</p> 297 298<ul> 299<li>Proven and well tested: llvm-gcc and clang both use this technique for local 300mutable variables. As such, the most common clients of LLVM are using this to 301handle a bulk of their variables. You can be sure that bugs are found fast and 302fixed early.</li> 303 304<li>Extremely Fast: mem2reg has a number of special cases that make it fast in 305common cases as well as fully general. For example, it has fast-paths for 306variables that are only used in a single block, variables that only have one 307assignment point, good heuristics to avoid insertion of unneeded phi nodes, etc. 308</li> 309 310<li>Needed for debug info generation: <a href="../SourceLevelDebugging.html"> 311Debug information in LLVM</a> relies on having the address of the variable 312exposed so that debug info can be attached to it. This technique dovetails 313very naturally with this style of debug info.</li> 314</ul> 315 316<p>If nothing else, this makes it much easier to get your front-end up and 317running, and is very simple to implement. Lets extend Kaleidoscope with mutable 318variables now! 319</p> 320 321</div> 322 323<!-- *********************************************************************** --> 324<h2><a name="kalvars">Mutable Variables in Kaleidoscope</a></h2> 325<!-- *********************************************************************** --> 326 327<div> 328 329<p>Now that we know the sort of problem we want to tackle, lets see what this 330looks like in the context of our little Kaleidoscope language. We're going to 331add two features:</p> 332 333<ol> 334<li>The ability to mutate variables with the '=' operator.</li> 335<li>The ability to define new variables.</li> 336</ol> 337 338<p>While the first item is really what this is about, we only have variables 339for incoming arguments as well as for induction variables, and redefining those only 340goes so far :). Also, the ability to define new variables is a 341useful thing regardless of whether you will be mutating them. Here's a 342motivating example that shows how we could use these:</p> 343 344<div class="doc_code"> 345<pre> 346# Define ':' for sequencing: as a low-precedence operator that ignores operands 347# and just returns the RHS. 348def binary : 1 (x y) y; 349 350# Recursive fib, we could do this before. 351def fib(x) 352 if (x < 3) then 353 1 354 else 355 fib(x-1)+fib(x-2); 356 357# Iterative fib. 358def fibi(x) 359 <b>var a = 1, b = 1, c in</b> 360 (for i = 3, i < x in 361 <b>c = a + b</b> : 362 <b>a = b</b> : 363 <b>b = c</b>) : 364 b; 365 366# Call it. 367fibi(10); 368</pre> 369</div> 370 371<p> 372In order to mutate variables, we have to change our existing variables to use 373the "alloca trick". Once we have that, we'll add our new operator, then extend 374Kaleidoscope to support new variable definitions. 375</p> 376 377</div> 378 379<!-- *********************************************************************** --> 380<h2><a name="adjustments">Adjusting Existing Variables for Mutation</a></h2> 381<!-- *********************************************************************** --> 382 383<div> 384 385<p> 386The symbol table in Kaleidoscope is managed at code generation time by the 387'<tt>NamedValues</tt>' map. This map currently keeps track of the LLVM "Value*" 388that holds the double value for the named variable. In order to support 389mutation, we need to change this slightly, so that it <tt>NamedValues</tt> holds 390the <em>memory location</em> of the variable in question. Note that this 391change is a refactoring: it changes the structure of the code, but does not 392(by itself) change the behavior of the compiler. All of these changes are 393isolated in the Kaleidoscope code generator.</p> 394 395<p> 396At this point in Kaleidoscope's development, it only supports variables for two 397things: incoming arguments to functions and the induction variable of 'for' 398loops. For consistency, we'll allow mutation of these variables in addition to 399other user-defined variables. This means that these will both need memory 400locations. 401</p> 402 403<p>To start our transformation of Kaleidoscope, we'll change the NamedValues 404map so that it maps to AllocaInst* instead of Value*. Once we do this, the C++ 405compiler will tell us what parts of the code we need to update:</p> 406 407<div class="doc_code"> 408<pre> 409static std::map<std::string, AllocaInst*> NamedValues; 410</pre> 411</div> 412 413<p>Also, since we will need to create these alloca's, we'll use a helper 414function that ensures that the allocas are created in the entry block of the 415function:</p> 416 417<div class="doc_code"> 418<pre> 419/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of 420/// the function. This is used for mutable variables etc. 421static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction, 422 const std::string &VarName) { 423 IRBuilder<> TmpB(&TheFunction->getEntryBlock(), 424 TheFunction->getEntryBlock().begin()); 425 return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0, 426 VarName.c_str()); 427} 428</pre> 429</div> 430 431<p>This funny looking code creates an IRBuilder object that is pointing at 432the first instruction (.begin()) of the entry block. It then creates an alloca 433with the expected name and returns it. Because all values in Kaleidoscope are 434doubles, there is no need to pass in a type to use.</p> 435 436<p>With this in place, the first functionality change we want to make is to 437variable references. In our new scheme, variables live on the stack, so code 438generating a reference to them actually needs to produce a load from the stack 439slot:</p> 440 441<div class="doc_code"> 442<pre> 443Value *VariableExprAST::Codegen() { 444 // Look this variable up in the function. 445 Value *V = NamedValues[Name]; 446 if (V == 0) return ErrorV("Unknown variable name"); 447 448 <b>// Load the value. 449 return Builder.CreateLoad(V, Name.c_str());</b> 450} 451</pre> 452</div> 453 454<p>As you can see, this is pretty straightforward. Now we need to update the 455things that define the variables to set up the alloca. We'll start with 456<tt>ForExprAST::Codegen</tt> (see the <a href="#code">full code listing</a> for 457the unabridged code):</p> 458 459<div class="doc_code"> 460<pre> 461 Function *TheFunction = Builder.GetInsertBlock()->getParent(); 462 463 <b>// Create an alloca for the variable in the entry block. 464 AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);</b> 465 466 // Emit the start code first, without 'variable' in scope. 467 Value *StartVal = Start->Codegen(); 468 if (StartVal == 0) return 0; 469 470 <b>// Store the value into the alloca. 471 Builder.CreateStore(StartVal, Alloca);</b> 472 ... 473 474 // Compute the end condition. 475 Value *EndCond = End->Codegen(); 476 if (EndCond == 0) return EndCond; 477 478 <b>// Reload, increment, and restore the alloca. This handles the case where 479 // the body of the loop mutates the variable. 480 Value *CurVar = Builder.CreateLoad(Alloca); 481 Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar"); 482 Builder.CreateStore(NextVar, Alloca);</b> 483 ... 484</pre> 485</div> 486 487<p>This code is virtually identical to the code <a 488href="LangImpl5.html#forcodegen">before we allowed mutable variables</a>. The 489big difference is that we no longer have to construct a PHI node, and we use 490load/store to access the variable as needed.</p> 491 492<p>To support mutable argument variables, we need to also make allocas for them. 493The code for this is also pretty simple:</p> 494 495<div class="doc_code"> 496<pre> 497/// CreateArgumentAllocas - Create an alloca for each argument and register the 498/// argument in the symbol table so that references to it will succeed. 499void PrototypeAST::CreateArgumentAllocas(Function *F) { 500 Function::arg_iterator AI = F->arg_begin(); 501 for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) { 502 // Create an alloca for this variable. 503 AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]); 504 505 // Store the initial value into the alloca. 506 Builder.CreateStore(AI, Alloca); 507 508 // Add arguments to variable symbol table. 509 NamedValues[Args[Idx]] = Alloca; 510 } 511} 512</pre> 513</div> 514 515<p>For each argument, we make an alloca, store the input value to the function 516into the alloca, and register the alloca as the memory location for the 517argument. This method gets invoked by <tt>FunctionAST::Codegen</tt> right after 518it sets up the entry block for the function.</p> 519 520<p>The final missing piece is adding the mem2reg pass, which allows us to get 521good codegen once again:</p> 522 523<div class="doc_code"> 524<pre> 525 // Set up the optimizer pipeline. Start with registering info about how the 526 // target lays out data structures. 527 OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData())); 528 <b>// Promote allocas to registers. 529 OurFPM.add(createPromoteMemoryToRegisterPass());</b> 530 // Do simple "peephole" optimizations and bit-twiddling optzns. 531 OurFPM.add(createInstructionCombiningPass()); 532 // Reassociate expressions. 533 OurFPM.add(createReassociatePass()); 534</pre> 535</div> 536 537<p>It is interesting to see what the code looks like before and after the 538mem2reg optimization runs. For example, this is the before/after code for our 539recursive fib function. Before the optimization:</p> 540 541<div class="doc_code"> 542<pre> 543define double @fib(double %x) { 544entry: 545 <b>%x1 = alloca double 546 store double %x, double* %x1 547 %x2 = load double* %x1</b> 548 %cmptmp = fcmp ult double %x2, 3.000000e+00 549 %booltmp = uitofp i1 %cmptmp to double 550 %ifcond = fcmp one double %booltmp, 0.000000e+00 551 br i1 %ifcond, label %then, label %else 552 553then: ; preds = %entry 554 br label %ifcont 555 556else: ; preds = %entry 557 <b>%x3 = load double* %x1</b> 558 %subtmp = fsub double %x3, 1.000000e+00 559 %calltmp = call double @fib(double %subtmp) 560 <b>%x4 = load double* %x1</b> 561 %subtmp5 = fsub double %x4, 2.000000e+00 562 %calltmp6 = call double @fib(double %subtmp5) 563 %addtmp = fadd double %calltmp, %calltmp6 564 br label %ifcont 565 566ifcont: ; preds = %else, %then 567 %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ] 568 ret double %iftmp 569} 570</pre> 571</div> 572 573<p>Here there is only one variable (x, the input argument) but you can still 574see the extremely simple-minded code generation strategy we are using. In the 575entry block, an alloca is created, and the initial input value is stored into 576it. Each reference to the variable does a reload from the stack. Also, note 577that we didn't modify the if/then/else expression, so it still inserts a PHI 578node. While we could make an alloca for it, it is actually easier to create a 579PHI node for it, so we still just make the PHI.</p> 580 581<p>Here is the code after the mem2reg pass runs:</p> 582 583<div class="doc_code"> 584<pre> 585define double @fib(double %x) { 586entry: 587 %cmptmp = fcmp ult double <b>%x</b>, 3.000000e+00 588 %booltmp = uitofp i1 %cmptmp to double 589 %ifcond = fcmp one double %booltmp, 0.000000e+00 590 br i1 %ifcond, label %then, label %else 591 592then: 593 br label %ifcont 594 595else: 596 %subtmp = fsub double <b>%x</b>, 1.000000e+00 597 %calltmp = call double @fib(double %subtmp) 598 %subtmp5 = fsub double <b>%x</b>, 2.000000e+00 599 %calltmp6 = call double @fib(double %subtmp5) 600 %addtmp = fadd double %calltmp, %calltmp6 601 br label %ifcont 602 603ifcont: ; preds = %else, %then 604 %iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ] 605 ret double %iftmp 606} 607</pre> 608</div> 609 610<p>This is a trivial case for mem2reg, since there are no redefinitions of the 611variable. The point of showing this is to calm your tension about inserting 612such blatent inefficiencies :).</p> 613 614<p>After the rest of the optimizers run, we get:</p> 615 616<div class="doc_code"> 617<pre> 618define double @fib(double %x) { 619entry: 620 %cmptmp = fcmp ult double %x, 3.000000e+00 621 %booltmp = uitofp i1 %cmptmp to double 622 %ifcond = fcmp ueq double %booltmp, 0.000000e+00 623 br i1 %ifcond, label %else, label %ifcont 624 625else: 626 %subtmp = fsub double %x, 1.000000e+00 627 %calltmp = call double @fib(double %subtmp) 628 %subtmp5 = fsub double %x, 2.000000e+00 629 %calltmp6 = call double @fib(double %subtmp5) 630 %addtmp = fadd double %calltmp, %calltmp6 631 ret double %addtmp 632 633ifcont: 634 ret double 1.000000e+00 635} 636</pre> 637</div> 638 639<p>Here we see that the simplifycfg pass decided to clone the return instruction 640into the end of the 'else' block. This allowed it to eliminate some branches 641and the PHI node.</p> 642 643<p>Now that all symbol table references are updated to use stack variables, 644we'll add the assignment operator.</p> 645 646</div> 647 648<!-- *********************************************************************** --> 649<h2><a name="assignment">New Assignment Operator</a></h2> 650<!-- *********************************************************************** --> 651 652<div> 653 654<p>With our current framework, adding a new assignment operator is really 655simple. We will parse it just like any other binary operator, but handle it 656internally (instead of allowing the user to define it). The first step is to 657set a precedence:</p> 658 659<div class="doc_code"> 660<pre> 661 int main() { 662 // Install standard binary operators. 663 // 1 is lowest precedence. 664 <b>BinopPrecedence['='] = 2;</b> 665 BinopPrecedence['<'] = 10; 666 BinopPrecedence['+'] = 20; 667 BinopPrecedence['-'] = 20; 668</pre> 669</div> 670 671<p>Now that the parser knows the precedence of the binary operator, it takes 672care of all the parsing and AST generation. We just need to implement codegen 673for the assignment operator. This looks like:</p> 674 675<div class="doc_code"> 676<pre> 677Value *BinaryExprAST::Codegen() { 678 // Special case '=' because we don't want to emit the LHS as an expression. 679 if (Op == '=') { 680 // Assignment requires the LHS to be an identifier. 681 VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS); 682 if (!LHSE) 683 return ErrorV("destination of '=' must be a variable"); 684</pre> 685</div> 686 687<p>Unlike the rest of the binary operators, our assignment operator doesn't 688follow the "emit LHS, emit RHS, do computation" model. As such, it is handled 689as a special case before the other binary operators are handled. The other 690strange thing is that it requires the LHS to be a variable. It is invalid to 691have "(x+1) = expr" - only things like "x = expr" are allowed. 692</p> 693 694<div class="doc_code"> 695<pre> 696 // Codegen the RHS. 697 Value *Val = RHS->Codegen(); 698 if (Val == 0) return 0; 699 700 // Look up the name. 701 Value *Variable = NamedValues[LHSE->getName()]; 702 if (Variable == 0) return ErrorV("Unknown variable name"); 703 704 Builder.CreateStore(Val, Variable); 705 return Val; 706 } 707 ... 708</pre> 709</div> 710 711<p>Once we have the variable, codegen'ing the assignment is straightforward: 712we emit the RHS of the assignment, create a store, and return the computed 713value. Returning a value allows for chained assignments like "X = (Y = Z)".</p> 714 715<p>Now that we have an assignment operator, we can mutate loop variables and 716arguments. For example, we can now run code like this:</p> 717 718<div class="doc_code"> 719<pre> 720# Function to print a double. 721extern printd(x); 722 723# Define ':' for sequencing: as a low-precedence operator that ignores operands 724# and just returns the RHS. 725def binary : 1 (x y) y; 726 727def test(x) 728 printd(x) : 729 x = 4 : 730 printd(x); 731 732test(123); 733</pre> 734</div> 735 736<p>When run, this example prints "123" and then "4", showing that we did 737actually mutate the value! Okay, we have now officially implemented our goal: 738getting this to work requires SSA construction in the general case. However, 739to be really useful, we want the ability to define our own local variables, lets 740add this next! 741</p> 742 743</div> 744 745<!-- *********************************************************************** --> 746<h2><a name="localvars">User-defined Local Variables</a></h2> 747<!-- *********************************************************************** --> 748 749<div> 750 751<p>Adding var/in is just like any other other extensions we made to 752Kaleidoscope: we extend the lexer, the parser, the AST and the code generator. 753The first step for adding our new 'var/in' construct is to extend the lexer. 754As before, this is pretty trivial, the code looks like this:</p> 755 756<div class="doc_code"> 757<pre> 758enum Token { 759 ... 760 <b>// var definition 761 tok_var = -13</b> 762... 763} 764... 765static int gettok() { 766... 767 if (IdentifierStr == "in") return tok_in; 768 if (IdentifierStr == "binary") return tok_binary; 769 if (IdentifierStr == "unary") return tok_unary; 770 <b>if (IdentifierStr == "var") return tok_var;</b> 771 return tok_identifier; 772... 773</pre> 774</div> 775 776<p>The next step is to define the AST node that we will construct. For var/in, 777it looks like this:</p> 778 779<div class="doc_code"> 780<pre> 781/// VarExprAST - Expression class for var/in 782class VarExprAST : public ExprAST { 783 std::vector<std::pair<std::string, ExprAST*> > VarNames; 784 ExprAST *Body; 785public: 786 VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames, 787 ExprAST *body) 788 : VarNames(varnames), Body(body) {} 789 790 virtual Value *Codegen(); 791}; 792</pre> 793</div> 794 795<p>var/in allows a list of names to be defined all at once, and each name can 796optionally have an initializer value. As such, we capture this information in 797the VarNames vector. Also, var/in has a body, this body is allowed to access 798the variables defined by the var/in.</p> 799 800<p>With this in place, we can define the parser pieces. The first thing we do is add 801it as a primary expression:</p> 802 803<div class="doc_code"> 804<pre> 805/// primary 806/// ::= identifierexpr 807/// ::= numberexpr 808/// ::= parenexpr 809/// ::= ifexpr 810/// ::= forexpr 811<b>/// ::= varexpr</b> 812static ExprAST *ParsePrimary() { 813 switch (CurTok) { 814 default: return Error("unknown token when expecting an expression"); 815 case tok_identifier: return ParseIdentifierExpr(); 816 case tok_number: return ParseNumberExpr(); 817 case '(': return ParseParenExpr(); 818 case tok_if: return ParseIfExpr(); 819 case tok_for: return ParseForExpr(); 820 <b>case tok_var: return ParseVarExpr();</b> 821 } 822} 823</pre> 824</div> 825 826<p>Next we define ParseVarExpr:</p> 827 828<div class="doc_code"> 829<pre> 830/// varexpr ::= 'var' identifier ('=' expression)? 831// (',' identifier ('=' expression)?)* 'in' expression 832static ExprAST *ParseVarExpr() { 833 getNextToken(); // eat the var. 834 835 std::vector<std::pair<std::string, ExprAST*> > VarNames; 836 837 // At least one variable name is required. 838 if (CurTok != tok_identifier) 839 return Error("expected identifier after var"); 840</pre> 841</div> 842 843<p>The first part of this code parses the list of identifier/expr pairs into the 844local <tt>VarNames</tt> vector. 845 846<div class="doc_code"> 847<pre> 848 while (1) { 849 std::string Name = IdentifierStr; 850 getNextToken(); // eat identifier. 851 852 // Read the optional initializer. 853 ExprAST *Init = 0; 854 if (CurTok == '=') { 855 getNextToken(); // eat the '='. 856 857 Init = ParseExpression(); 858 if (Init == 0) return 0; 859 } 860 861 VarNames.push_back(std::make_pair(Name, Init)); 862 863 // End of var list, exit loop. 864 if (CurTok != ',') break; 865 getNextToken(); // eat the ','. 866 867 if (CurTok != tok_identifier) 868 return Error("expected identifier list after var"); 869 } 870</pre> 871</div> 872 873<p>Once all the variables are parsed, we then parse the body and create the 874AST node:</p> 875 876<div class="doc_code"> 877<pre> 878 // At this point, we have to have 'in'. 879 if (CurTok != tok_in) 880 return Error("expected 'in' keyword after 'var'"); 881 getNextToken(); // eat 'in'. 882 883 ExprAST *Body = ParseExpression(); 884 if (Body == 0) return 0; 885 886 return new VarExprAST(VarNames, Body); 887} 888</pre> 889</div> 890 891<p>Now that we can parse and represent the code, we need to support emission of 892LLVM IR for it. This code starts out with:</p> 893 894<div class="doc_code"> 895<pre> 896Value *VarExprAST::Codegen() { 897 std::vector<AllocaInst *> OldBindings; 898 899 Function *TheFunction = Builder.GetInsertBlock()->getParent(); 900 901 // Register all variables and emit their initializer. 902 for (unsigned i = 0, e = VarNames.size(); i != e; ++i) { 903 const std::string &VarName = VarNames[i].first; 904 ExprAST *Init = VarNames[i].second; 905</pre> 906</div> 907 908<p>Basically it loops over all the variables, installing them one at a time. 909For each variable we put into the symbol table, we remember the previous value 910that we replace in OldBindings.</p> 911 912<div class="doc_code"> 913<pre> 914 // Emit the initializer before adding the variable to scope, this prevents 915 // the initializer from referencing the variable itself, and permits stuff 916 // like this: 917 // var a = 1 in 918 // var a = a in ... # refers to outer 'a'. 919 Value *InitVal; 920 if (Init) { 921 InitVal = Init->Codegen(); 922 if (InitVal == 0) return 0; 923 } else { // If not specified, use 0.0. 924 InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0)); 925 } 926 927 AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName); 928 Builder.CreateStore(InitVal, Alloca); 929 930 // Remember the old variable binding so that we can restore the binding when 931 // we unrecurse. 932 OldBindings.push_back(NamedValues[VarName]); 933 934 // Remember this binding. 935 NamedValues[VarName] = Alloca; 936 } 937</pre> 938</div> 939 940<p>There are more comments here than code. The basic idea is that we emit the 941initializer, create the alloca, then update the symbol table to point to it. 942Once all the variables are installed in the symbol table, we evaluate the body 943of the var/in expression:</p> 944 945<div class="doc_code"> 946<pre> 947 // Codegen the body, now that all vars are in scope. 948 Value *BodyVal = Body->Codegen(); 949 if (BodyVal == 0) return 0; 950</pre> 951</div> 952 953<p>Finally, before returning, we restore the previous variable bindings:</p> 954 955<div class="doc_code"> 956<pre> 957 // Pop all our variables from scope. 958 for (unsigned i = 0, e = VarNames.size(); i != e; ++i) 959 NamedValues[VarNames[i].first] = OldBindings[i]; 960 961 // Return the body computation. 962 return BodyVal; 963} 964</pre> 965</div> 966 967<p>The end result of all of this is that we get properly scoped variable 968definitions, and we even (trivially) allow mutation of them :).</p> 969 970<p>With this, we completed what we set out to do. Our nice iterative fib 971example from the intro compiles and runs just fine. The mem2reg pass optimizes 972all of our stack variables into SSA registers, inserting PHI nodes where needed, 973and our front-end remains simple: no "iterated dominance frontier" computation 974anywhere in sight.</p> 975 976</div> 977 978<!-- *********************************************************************** --> 979<h2><a name="code">Full Code Listing</a></h2> 980<!-- *********************************************************************** --> 981 982<div> 983 984<p> 985Here is the complete code listing for our running example, enhanced with mutable 986variables and var/in support. To build this example, use: 987</p> 988 989<div class="doc_code"> 990<pre> 991# Compile 992clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy 993# Run 994./toy 995</pre> 996</div> 997 998<p>Here is the code:</p> 999 1000<div class="doc_code"> 1001<pre> 1002#include "llvm/DerivedTypes.h" 1003#include "llvm/ExecutionEngine/ExecutionEngine.h" 1004#include "llvm/ExecutionEngine/JIT.h" 1005#include "llvm/LLVMContext.h" 1006#include "llvm/Module.h" 1007#include "llvm/PassManager.h" 1008#include "llvm/Analysis/Verifier.h" 1009#include "llvm/Analysis/Passes.h" 1010#include "llvm/Target/TargetData.h" 1011#include "llvm/Transforms/Scalar.h" 1012#include "llvm/Support/IRBuilder.h" 1013#include "llvm/Support/TargetSelect.h" 1014#include <cstdio> 1015#include <string> 1016#include <map> 1017#include <vector> 1018using namespace llvm; 1019 1020//===----------------------------------------------------------------------===// 1021// Lexer 1022//===----------------------------------------------------------------------===// 1023 1024// The lexer returns tokens [0-255] if it is an unknown character, otherwise one 1025// of these for known things. 1026enum Token { 1027 tok_eof = -1, 1028 1029 // commands 1030 tok_def = -2, tok_extern = -3, 1031 1032 // primary 1033 tok_identifier = -4, tok_number = -5, 1034 1035 // control 1036 tok_if = -6, tok_then = -7, tok_else = -8, 1037 tok_for = -9, tok_in = -10, 1038 1039 // operators 1040 tok_binary = -11, tok_unary = -12, 1041 1042 // var definition 1043 tok_var = -13 1044}; 1045 1046static std::string IdentifierStr; // Filled in if tok_identifier 1047static double NumVal; // Filled in if tok_number 1048 1049/// gettok - Return the next token from standard input. 1050static int gettok() { 1051 static int LastChar = ' '; 1052 1053 // Skip any whitespace. 1054 while (isspace(LastChar)) 1055 LastChar = getchar(); 1056 1057 if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]* 1058 IdentifierStr = LastChar; 1059 while (isalnum((LastChar = getchar()))) 1060 IdentifierStr += LastChar; 1061 1062 if (IdentifierStr == "def") return tok_def; 1063 if (IdentifierStr == "extern") return tok_extern; 1064 if (IdentifierStr == "if") return tok_if; 1065 if (IdentifierStr == "then") return tok_then; 1066 if (IdentifierStr == "else") return tok_else; 1067 if (IdentifierStr == "for") return tok_for; 1068 if (IdentifierStr == "in") return tok_in; 1069 if (IdentifierStr == "binary") return tok_binary; 1070 if (IdentifierStr == "unary") return tok_unary; 1071 if (IdentifierStr == "var") return tok_var; 1072 return tok_identifier; 1073 } 1074 1075 if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+ 1076 std::string NumStr; 1077 do { 1078 NumStr += LastChar; 1079 LastChar = getchar(); 1080 } while (isdigit(LastChar) || LastChar == '.'); 1081 1082 NumVal = strtod(NumStr.c_str(), 0); 1083 return tok_number; 1084 } 1085 1086 if (LastChar == '#') { 1087 // Comment until end of line. 1088 do LastChar = getchar(); 1089 while (LastChar != EOF && LastChar != '\n' && LastChar != '\r'); 1090 1091 if (LastChar != EOF) 1092 return gettok(); 1093 } 1094 1095 // Check for end of file. Don't eat the EOF. 1096 if (LastChar == EOF) 1097 return tok_eof; 1098 1099 // Otherwise, just return the character as its ascii value. 1100 int ThisChar = LastChar; 1101 LastChar = getchar(); 1102 return ThisChar; 1103} 1104 1105//===----------------------------------------------------------------------===// 1106// Abstract Syntax Tree (aka Parse Tree) 1107//===----------------------------------------------------------------------===// 1108 1109/// ExprAST - Base class for all expression nodes. 1110class ExprAST { 1111public: 1112 virtual ~ExprAST() {} 1113 virtual Value *Codegen() = 0; 1114}; 1115 1116/// NumberExprAST - Expression class for numeric literals like "1.0". 1117class NumberExprAST : public ExprAST { 1118 double Val; 1119public: 1120 NumberExprAST(double val) : Val(val) {} 1121 virtual Value *Codegen(); 1122}; 1123 1124/// VariableExprAST - Expression class for referencing a variable, like "a". 1125class VariableExprAST : public ExprAST { 1126 std::string Name; 1127public: 1128 VariableExprAST(const std::string &name) : Name(name) {} 1129 const std::string &getName() const { return Name; } 1130 virtual Value *Codegen(); 1131}; 1132 1133/// UnaryExprAST - Expression class for a unary operator. 1134class UnaryExprAST : public ExprAST { 1135 char Opcode; 1136 ExprAST *Operand; 1137public: 1138 UnaryExprAST(char opcode, ExprAST *operand) 1139 : Opcode(opcode), Operand(operand) {} 1140 virtual Value *Codegen(); 1141}; 1142 1143/// BinaryExprAST - Expression class for a binary operator. 1144class BinaryExprAST : public ExprAST { 1145 char Op; 1146 ExprAST *LHS, *RHS; 1147public: 1148 BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs) 1149 : Op(op), LHS(lhs), RHS(rhs) {} 1150 virtual Value *Codegen(); 1151}; 1152 1153/// CallExprAST - Expression class for function calls. 1154class CallExprAST : public ExprAST { 1155 std::string Callee; 1156 std::vector<ExprAST*> Args; 1157public: 1158 CallExprAST(const std::string &callee, std::vector<ExprAST*> &args) 1159 : Callee(callee), Args(args) {} 1160 virtual Value *Codegen(); 1161}; 1162 1163/// IfExprAST - Expression class for if/then/else. 1164class IfExprAST : public ExprAST { 1165 ExprAST *Cond, *Then, *Else; 1166public: 1167 IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else) 1168 : Cond(cond), Then(then), Else(_else) {} 1169 virtual Value *Codegen(); 1170}; 1171 1172/// ForExprAST - Expression class for for/in. 1173class ForExprAST : public ExprAST { 1174 std::string VarName; 1175 ExprAST *Start, *End, *Step, *Body; 1176public: 1177 ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end, 1178 ExprAST *step, ExprAST *body) 1179 : VarName(varname), Start(start), End(end), Step(step), Body(body) {} 1180 virtual Value *Codegen(); 1181}; 1182 1183/// VarExprAST - Expression class for var/in 1184class VarExprAST : public ExprAST { 1185 std::vector<std::pair<std::string, ExprAST*> > VarNames; 1186 ExprAST *Body; 1187public: 1188 VarExprAST(const std::vector<std::pair<std::string, ExprAST*> > &varnames, 1189 ExprAST *body) 1190 : VarNames(varnames), Body(body) {} 1191 1192 virtual Value *Codegen(); 1193}; 1194 1195/// PrototypeAST - This class represents the "prototype" for a function, 1196/// which captures its name, and its argument names (thus implicitly the number 1197/// of arguments the function takes), as well as if it is an operator. 1198class PrototypeAST { 1199 std::string Name; 1200 std::vector<std::string> Args; 1201 bool isOperator; 1202 unsigned Precedence; // Precedence if a binary op. 1203public: 1204 PrototypeAST(const std::string &name, const std::vector<std::string> &args, 1205 bool isoperator = false, unsigned prec = 0) 1206 : Name(name), Args(args), isOperator(isoperator), Precedence(prec) {} 1207 1208 bool isUnaryOp() const { return isOperator && Args.size() == 1; } 1209 bool isBinaryOp() const { return isOperator && Args.size() == 2; } 1210 1211 char getOperatorName() const { 1212 assert(isUnaryOp() || isBinaryOp()); 1213 return Name[Name.size()-1]; 1214 } 1215 1216 unsigned getBinaryPrecedence() const { return Precedence; } 1217 1218 Function *Codegen(); 1219 1220 void CreateArgumentAllocas(Function *F); 1221}; 1222 1223/// FunctionAST - This class represents a function definition itself. 1224class FunctionAST { 1225 PrototypeAST *Proto; 1226 ExprAST *Body; 1227public: 1228 FunctionAST(PrototypeAST *proto, ExprAST *body) 1229 : Proto(proto), Body(body) {} 1230 1231 Function *Codegen(); 1232}; 1233 1234//===----------------------------------------------------------------------===// 1235// Parser 1236//===----------------------------------------------------------------------===// 1237 1238/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current 1239/// token the parser is looking at. getNextToken reads another token from the 1240/// lexer and updates CurTok with its results. 1241static int CurTok; 1242static int getNextToken() { 1243 return CurTok = gettok(); 1244} 1245 1246/// BinopPrecedence - This holds the precedence for each binary operator that is 1247/// defined. 1248static std::map<char, int> BinopPrecedence; 1249 1250/// GetTokPrecedence - Get the precedence of the pending binary operator token. 1251static int GetTokPrecedence() { 1252 if (!isascii(CurTok)) 1253 return -1; 1254 1255 // Make sure it's a declared binop. 1256 int TokPrec = BinopPrecedence[CurTok]; 1257 if (TokPrec <= 0) return -1; 1258 return TokPrec; 1259} 1260 1261/// Error* - These are little helper functions for error handling. 1262ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;} 1263PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; } 1264FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; } 1265 1266static ExprAST *ParseExpression(); 1267 1268/// identifierexpr 1269/// ::= identifier 1270/// ::= identifier '(' expression* ')' 1271static ExprAST *ParseIdentifierExpr() { 1272 std::string IdName = IdentifierStr; 1273 1274 getNextToken(); // eat identifier. 1275 1276 if (CurTok != '(') // Simple variable ref. 1277 return new VariableExprAST(IdName); 1278 1279 // Call. 1280 getNextToken(); // eat ( 1281 std::vector<ExprAST*> Args; 1282 if (CurTok != ')') { 1283 while (1) { 1284 ExprAST *Arg = ParseExpression(); 1285 if (!Arg) return 0; 1286 Args.push_back(Arg); 1287 1288 if (CurTok == ')') break; 1289 1290 if (CurTok != ',') 1291 return Error("Expected ')' or ',' in argument list"); 1292 getNextToken(); 1293 } 1294 } 1295 1296 // Eat the ')'. 1297 getNextToken(); 1298 1299 return new CallExprAST(IdName, Args); 1300} 1301 1302/// numberexpr ::= number 1303static ExprAST *ParseNumberExpr() { 1304 ExprAST *Result = new NumberExprAST(NumVal); 1305 getNextToken(); // consume the number 1306 return Result; 1307} 1308 1309/// parenexpr ::= '(' expression ')' 1310static ExprAST *ParseParenExpr() { 1311 getNextToken(); // eat (. 1312 ExprAST *V = ParseExpression(); 1313 if (!V) return 0; 1314 1315 if (CurTok != ')') 1316 return Error("expected ')'"); 1317 getNextToken(); // eat ). 1318 return V; 1319} 1320 1321/// ifexpr ::= 'if' expression 'then' expression 'else' expression 1322static ExprAST *ParseIfExpr() { 1323 getNextToken(); // eat the if. 1324 1325 // condition. 1326 ExprAST *Cond = ParseExpression(); 1327 if (!Cond) return 0; 1328 1329 if (CurTok != tok_then) 1330 return Error("expected then"); 1331 getNextToken(); // eat the then 1332 1333 ExprAST *Then = ParseExpression(); 1334 if (Then == 0) return 0; 1335 1336 if (CurTok != tok_else) 1337 return Error("expected else"); 1338 1339 getNextToken(); 1340 1341 ExprAST *Else = ParseExpression(); 1342 if (!Else) return 0; 1343 1344 return new IfExprAST(Cond, Then, Else); 1345} 1346 1347/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression 1348static ExprAST *ParseForExpr() { 1349 getNextToken(); // eat the for. 1350 1351 if (CurTok != tok_identifier) 1352 return Error("expected identifier after for"); 1353 1354 std::string IdName = IdentifierStr; 1355 getNextToken(); // eat identifier. 1356 1357 if (CurTok != '=') 1358 return Error("expected '=' after for"); 1359 getNextToken(); // eat '='. 1360 1361 1362 ExprAST *Start = ParseExpression(); 1363 if (Start == 0) return 0; 1364 if (CurTok != ',') 1365 return Error("expected ',' after for start value"); 1366 getNextToken(); 1367 1368 ExprAST *End = ParseExpression(); 1369 if (End == 0) return 0; 1370 1371 // The step value is optional. 1372 ExprAST *Step = 0; 1373 if (CurTok == ',') { 1374 getNextToken(); 1375 Step = ParseExpression(); 1376 if (Step == 0) return 0; 1377 } 1378 1379 if (CurTok != tok_in) 1380 return Error("expected 'in' after for"); 1381 getNextToken(); // eat 'in'. 1382 1383 ExprAST *Body = ParseExpression(); 1384 if (Body == 0) return 0; 1385 1386 return new ForExprAST(IdName, Start, End, Step, Body); 1387} 1388 1389/// varexpr ::= 'var' identifier ('=' expression)? 1390// (',' identifier ('=' expression)?)* 'in' expression 1391static ExprAST *ParseVarExpr() { 1392 getNextToken(); // eat the var. 1393 1394 std::vector<std::pair<std::string, ExprAST*> > VarNames; 1395 1396 // At least one variable name is required. 1397 if (CurTok != tok_identifier) 1398 return Error("expected identifier after var"); 1399 1400 while (1) { 1401 std::string Name = IdentifierStr; 1402 getNextToken(); // eat identifier. 1403 1404 // Read the optional initializer. 1405 ExprAST *Init = 0; 1406 if (CurTok == '=') { 1407 getNextToken(); // eat the '='. 1408 1409 Init = ParseExpression(); 1410 if (Init == 0) return 0; 1411 } 1412 1413 VarNames.push_back(std::make_pair(Name, Init)); 1414 1415 // End of var list, exit loop. 1416 if (CurTok != ',') break; 1417 getNextToken(); // eat the ','. 1418 1419 if (CurTok != tok_identifier) 1420 return Error("expected identifier list after var"); 1421 } 1422 1423 // At this point, we have to have 'in'. 1424 if (CurTok != tok_in) 1425 return Error("expected 'in' keyword after 'var'"); 1426 getNextToken(); // eat 'in'. 1427 1428 ExprAST *Body = ParseExpression(); 1429 if (Body == 0) return 0; 1430 1431 return new VarExprAST(VarNames, Body); 1432} 1433 1434/// primary 1435/// ::= identifierexpr 1436/// ::= numberexpr 1437/// ::= parenexpr 1438/// ::= ifexpr 1439/// ::= forexpr 1440/// ::= varexpr 1441static ExprAST *ParsePrimary() { 1442 switch (CurTok) { 1443 default: return Error("unknown token when expecting an expression"); 1444 case tok_identifier: return ParseIdentifierExpr(); 1445 case tok_number: return ParseNumberExpr(); 1446 case '(': return ParseParenExpr(); 1447 case tok_if: return ParseIfExpr(); 1448 case tok_for: return ParseForExpr(); 1449 case tok_var: return ParseVarExpr(); 1450 } 1451} 1452 1453/// unary 1454/// ::= primary 1455/// ::= '!' unary 1456static ExprAST *ParseUnary() { 1457 // If the current token is not an operator, it must be a primary expr. 1458 if (!isascii(CurTok) || CurTok == '(' || CurTok == ',') 1459 return ParsePrimary(); 1460 1461 // If this is a unary operator, read it. 1462 int Opc = CurTok; 1463 getNextToken(); 1464 if (ExprAST *Operand = ParseUnary()) 1465 return new UnaryExprAST(Opc, Operand); 1466 return 0; 1467} 1468 1469/// binoprhs 1470/// ::= ('+' unary)* 1471static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) { 1472 // If this is a binop, find its precedence. 1473 while (1) { 1474 int TokPrec = GetTokPrecedence(); 1475 1476 // If this is a binop that binds at least as tightly as the current binop, 1477 // consume it, otherwise we are done. 1478 if (TokPrec < ExprPrec) 1479 return LHS; 1480 1481 // Okay, we know this is a binop. 1482 int BinOp = CurTok; 1483 getNextToken(); // eat binop 1484 1485 // Parse the unary expression after the binary operator. 1486 ExprAST *RHS = ParseUnary(); 1487 if (!RHS) return 0; 1488 1489 // If BinOp binds less tightly with RHS than the operator after RHS, let 1490 // the pending operator take RHS as its LHS. 1491 int NextPrec = GetTokPrecedence(); 1492 if (TokPrec < NextPrec) { 1493 RHS = ParseBinOpRHS(TokPrec+1, RHS); 1494 if (RHS == 0) return 0; 1495 } 1496 1497 // Merge LHS/RHS. 1498 LHS = new BinaryExprAST(BinOp, LHS, RHS); 1499 } 1500} 1501 1502/// expression 1503/// ::= unary binoprhs 1504/// 1505static ExprAST *ParseExpression() { 1506 ExprAST *LHS = ParseUnary(); 1507 if (!LHS) return 0; 1508 1509 return ParseBinOpRHS(0, LHS); 1510} 1511 1512/// prototype 1513/// ::= id '(' id* ')' 1514/// ::= binary LETTER number? (id, id) 1515/// ::= unary LETTER (id) 1516static PrototypeAST *ParsePrototype() { 1517 std::string FnName; 1518 1519 unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary. 1520 unsigned BinaryPrecedence = 30; 1521 1522 switch (CurTok) { 1523 default: 1524 return ErrorP("Expected function name in prototype"); 1525 case tok_identifier: 1526 FnName = IdentifierStr; 1527 Kind = 0; 1528 getNextToken(); 1529 break; 1530 case tok_unary: 1531 getNextToken(); 1532 if (!isascii(CurTok)) 1533 return ErrorP("Expected unary operator"); 1534 FnName = "unary"; 1535 FnName += (char)CurTok; 1536 Kind = 1; 1537 getNextToken(); 1538 break; 1539 case tok_binary: 1540 getNextToken(); 1541 if (!isascii(CurTok)) 1542 return ErrorP("Expected binary operator"); 1543 FnName = "binary"; 1544 FnName += (char)CurTok; 1545 Kind = 2; 1546 getNextToken(); 1547 1548 // Read the precedence if present. 1549 if (CurTok == tok_number) { 1550 if (NumVal < 1 || NumVal > 100) 1551 return ErrorP("Invalid precedecnce: must be 1..100"); 1552 BinaryPrecedence = (unsigned)NumVal; 1553 getNextToken(); 1554 } 1555 break; 1556 } 1557 1558 if (CurTok != '(') 1559 return ErrorP("Expected '(' in prototype"); 1560 1561 std::vector<std::string> ArgNames; 1562 while (getNextToken() == tok_identifier) 1563 ArgNames.push_back(IdentifierStr); 1564 if (CurTok != ')') 1565 return ErrorP("Expected ')' in prototype"); 1566 1567 // success. 1568 getNextToken(); // eat ')'. 1569 1570 // Verify right number of names for operator. 1571 if (Kind && ArgNames.size() != Kind) 1572 return ErrorP("Invalid number of operands for operator"); 1573 1574 return new PrototypeAST(FnName, ArgNames, Kind != 0, BinaryPrecedence); 1575} 1576 1577/// definition ::= 'def' prototype expression 1578static FunctionAST *ParseDefinition() { 1579 getNextToken(); // eat def. 1580 PrototypeAST *Proto = ParsePrototype(); 1581 if (Proto == 0) return 0; 1582 1583 if (ExprAST *E = ParseExpression()) 1584 return new FunctionAST(Proto, E); 1585 return 0; 1586} 1587 1588/// toplevelexpr ::= expression 1589static FunctionAST *ParseTopLevelExpr() { 1590 if (ExprAST *E = ParseExpression()) { 1591 // Make an anonymous proto. 1592 PrototypeAST *Proto = new PrototypeAST("", std::vector<std::string>()); 1593 return new FunctionAST(Proto, E); 1594 } 1595 return 0; 1596} 1597 1598/// external ::= 'extern' prototype 1599static PrototypeAST *ParseExtern() { 1600 getNextToken(); // eat extern. 1601 return ParsePrototype(); 1602} 1603 1604//===----------------------------------------------------------------------===// 1605// Code Generation 1606//===----------------------------------------------------------------------===// 1607 1608static Module *TheModule; 1609static IRBuilder<> Builder(getGlobalContext()); 1610static std::map<std::string, AllocaInst*> NamedValues; 1611static FunctionPassManager *TheFPM; 1612 1613Value *ErrorV(const char *Str) { Error(Str); return 0; } 1614 1615/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of 1616/// the function. This is used for mutable variables etc. 1617static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction, 1618 const std::string &VarName) { 1619 IRBuilder<> TmpB(&TheFunction->getEntryBlock(), 1620 TheFunction->getEntryBlock().begin()); 1621 return TmpB.CreateAlloca(Type::getDoubleTy(getGlobalContext()), 0, 1622 VarName.c_str()); 1623} 1624 1625Value *NumberExprAST::Codegen() { 1626 return ConstantFP::get(getGlobalContext(), APFloat(Val)); 1627} 1628 1629Value *VariableExprAST::Codegen() { 1630 // Look this variable up in the function. 1631 Value *V = NamedValues[Name]; 1632 if (V == 0) return ErrorV("Unknown variable name"); 1633 1634 // Load the value. 1635 return Builder.CreateLoad(V, Name.c_str()); 1636} 1637 1638Value *UnaryExprAST::Codegen() { 1639 Value *OperandV = Operand->Codegen(); 1640 if (OperandV == 0) return 0; 1641 1642 Function *F = TheModule->getFunction(std::string("unary")+Opcode); 1643 if (F == 0) 1644 return ErrorV("Unknown unary operator"); 1645 1646 return Builder.CreateCall(F, OperandV, "unop"); 1647} 1648 1649Value *BinaryExprAST::Codegen() { 1650 // Special case '=' because we don't want to emit the LHS as an expression. 1651 if (Op == '=') { 1652 // Assignment requires the LHS to be an identifier. 1653 VariableExprAST *LHSE = dynamic_cast<VariableExprAST*>(LHS); 1654 if (!LHSE) 1655 return ErrorV("destination of '=' must be a variable"); 1656 // Codegen the RHS. 1657 Value *Val = RHS->Codegen(); 1658 if (Val == 0) return 0; 1659 1660 // Look up the name. 1661 Value *Variable = NamedValues[LHSE->getName()]; 1662 if (Variable == 0) return ErrorV("Unknown variable name"); 1663 1664 Builder.CreateStore(Val, Variable); 1665 return Val; 1666 } 1667 1668 Value *L = LHS->Codegen(); 1669 Value *R = RHS->Codegen(); 1670 if (L == 0 || R == 0) return 0; 1671 1672 switch (Op) { 1673 case '+': return Builder.CreateFAdd(L, R, "addtmp"); 1674 case '-': return Builder.CreateFSub(L, R, "subtmp"); 1675 case '*': return Builder.CreateFMul(L, R, "multmp"); 1676 case '<': 1677 L = Builder.CreateFCmpULT(L, R, "cmptmp"); 1678 // Convert bool 0/1 to double 0.0 or 1.0 1679 return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()), 1680 "booltmp"); 1681 default: break; 1682 } 1683 1684 // If it wasn't a builtin binary operator, it must be a user defined one. Emit 1685 // a call to it. 1686 Function *F = TheModule->getFunction(std::string("binary")+Op); 1687 assert(F && "binary operator not found!"); 1688 1689 Value *Ops[2] = { L, R }; 1690 return Builder.CreateCall(F, Ops, "binop"); 1691} 1692 1693Value *CallExprAST::Codegen() { 1694 // Look up the name in the global module table. 1695 Function *CalleeF = TheModule->getFunction(Callee); 1696 if (CalleeF == 0) 1697 return ErrorV("Unknown function referenced"); 1698 1699 // If argument mismatch error. 1700 if (CalleeF->arg_size() != Args.size()) 1701 return ErrorV("Incorrect # arguments passed"); 1702 1703 std::vector<Value*> ArgsV; 1704 for (unsigned i = 0, e = Args.size(); i != e; ++i) { 1705 ArgsV.push_back(Args[i]->Codegen()); 1706 if (ArgsV.back() == 0) return 0; 1707 } 1708 1709 return Builder.CreateCall(CalleeF, ArgsV, "calltmp"); 1710} 1711 1712Value *IfExprAST::Codegen() { 1713 Value *CondV = Cond->Codegen(); 1714 if (CondV == 0) return 0; 1715 1716 // Convert condition to a bool by comparing equal to 0.0. 1717 CondV = Builder.CreateFCmpONE(CondV, 1718 ConstantFP::get(getGlobalContext(), APFloat(0.0)), 1719 "ifcond"); 1720 1721 Function *TheFunction = Builder.GetInsertBlock()->getParent(); 1722 1723 // Create blocks for the then and else cases. Insert the 'then' block at the 1724 // end of the function. 1725 BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction); 1726 BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else"); 1727 BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont"); 1728 1729 Builder.CreateCondBr(CondV, ThenBB, ElseBB); 1730 1731 // Emit then value. 1732 Builder.SetInsertPoint(ThenBB); 1733 1734 Value *ThenV = Then->Codegen(); 1735 if (ThenV == 0) return 0; 1736 1737 Builder.CreateBr(MergeBB); 1738 // Codegen of 'Then' can change the current block, update ThenBB for the PHI. 1739 ThenBB = Builder.GetInsertBlock(); 1740 1741 // Emit else block. 1742 TheFunction->getBasicBlockList().push_back(ElseBB); 1743 Builder.SetInsertPoint(ElseBB); 1744 1745 Value *ElseV = Else->Codegen(); 1746 if (ElseV == 0) return 0; 1747 1748 Builder.CreateBr(MergeBB); 1749 // Codegen of 'Else' can change the current block, update ElseBB for the PHI. 1750 ElseBB = Builder.GetInsertBlock(); 1751 1752 // Emit merge block. 1753 TheFunction->getBasicBlockList().push_back(MergeBB); 1754 Builder.SetInsertPoint(MergeBB); 1755 PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, 1756 "iftmp"); 1757 1758 PN->addIncoming(ThenV, ThenBB); 1759 PN->addIncoming(ElseV, ElseBB); 1760 return PN; 1761} 1762 1763Value *ForExprAST::Codegen() { 1764 // Output this as: 1765 // var = alloca double 1766 // ... 1767 // start = startexpr 1768 // store start -> var 1769 // goto loop 1770 // loop: 1771 // ... 1772 // bodyexpr 1773 // ... 1774 // loopend: 1775 // step = stepexpr 1776 // endcond = endexpr 1777 // 1778 // curvar = load var 1779 // nextvar = curvar + step 1780 // store nextvar -> var 1781 // br endcond, loop, endloop 1782 // outloop: 1783 1784 Function *TheFunction = Builder.GetInsertBlock()->getParent(); 1785 1786 // Create an alloca for the variable in the entry block. 1787 AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName); 1788 1789 // Emit the start code first, without 'variable' in scope. 1790 Value *StartVal = Start->Codegen(); 1791 if (StartVal == 0) return 0; 1792 1793 // Store the value into the alloca. 1794 Builder.CreateStore(StartVal, Alloca); 1795 1796 // Make the new basic block for the loop header, inserting after current 1797 // block. 1798 BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction); 1799 1800 // Insert an explicit fall through from the current block to the LoopBB. 1801 Builder.CreateBr(LoopBB); 1802 1803 // Start insertion in LoopBB. 1804 Builder.SetInsertPoint(LoopBB); 1805 1806 // Within the loop, the variable is defined equal to the PHI node. If it 1807 // shadows an existing variable, we have to restore it, so save it now. 1808 AllocaInst *OldVal = NamedValues[VarName]; 1809 NamedValues[VarName] = Alloca; 1810 1811 // Emit the body of the loop. This, like any other expr, can change the 1812 // current BB. Note that we ignore the value computed by the body, but don't 1813 // allow an error. 1814 if (Body->Codegen() == 0) 1815 return 0; 1816 1817 // Emit the step value. 1818 Value *StepVal; 1819 if (Step) { 1820 StepVal = Step->Codegen(); 1821 if (StepVal == 0) return 0; 1822 } else { 1823 // If not specified, use 1.0. 1824 StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0)); 1825 } 1826 1827 // Compute the end condition. 1828 Value *EndCond = End->Codegen(); 1829 if (EndCond == 0) return EndCond; 1830 1831 // Reload, increment, and restore the alloca. This handles the case where 1832 // the body of the loop mutates the variable. 1833 Value *CurVar = Builder.CreateLoad(Alloca, VarName.c_str()); 1834 Value *NextVar = Builder.CreateFAdd(CurVar, StepVal, "nextvar"); 1835 Builder.CreateStore(NextVar, Alloca); 1836 1837 // Convert condition to a bool by comparing equal to 0.0. 1838 EndCond = Builder.CreateFCmpONE(EndCond, 1839 ConstantFP::get(getGlobalContext(), APFloat(0.0)), 1840 "loopcond"); 1841 1842 // Create the "after loop" block and insert it. 1843 BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction); 1844 1845 // Insert the conditional branch into the end of LoopEndBB. 1846 Builder.CreateCondBr(EndCond, LoopBB, AfterBB); 1847 1848 // Any new code will be inserted in AfterBB. 1849 Builder.SetInsertPoint(AfterBB); 1850 1851 // Restore the unshadowed variable. 1852 if (OldVal) 1853 NamedValues[VarName] = OldVal; 1854 else 1855 NamedValues.erase(VarName); 1856 1857 1858 // for expr always returns 0.0. 1859 return Constant::getNullValue(Type::getDoubleTy(getGlobalContext())); 1860} 1861 1862Value *VarExprAST::Codegen() { 1863 std::vector<AllocaInst *> OldBindings; 1864 1865 Function *TheFunction = Builder.GetInsertBlock()->getParent(); 1866 1867 // Register all variables and emit their initializer. 1868 for (unsigned i = 0, e = VarNames.size(); i != e; ++i) { 1869 const std::string &VarName = VarNames[i].first; 1870 ExprAST *Init = VarNames[i].second; 1871 1872 // Emit the initializer before adding the variable to scope, this prevents 1873 // the initializer from referencing the variable itself, and permits stuff 1874 // like this: 1875 // var a = 1 in 1876 // var a = a in ... # refers to outer 'a'. 1877 Value *InitVal; 1878 if (Init) { 1879 InitVal = Init->Codegen(); 1880 if (InitVal == 0) return 0; 1881 } else { // If not specified, use 0.0. 1882 InitVal = ConstantFP::get(getGlobalContext(), APFloat(0.0)); 1883 } 1884 1885 AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName); 1886 Builder.CreateStore(InitVal, Alloca); 1887 1888 // Remember the old variable binding so that we can restore the binding when 1889 // we unrecurse. 1890 OldBindings.push_back(NamedValues[VarName]); 1891 1892 // Remember this binding. 1893 NamedValues[VarName] = Alloca; 1894 } 1895 1896 // Codegen the body, now that all vars are in scope. 1897 Value *BodyVal = Body->Codegen(); 1898 if (BodyVal == 0) return 0; 1899 1900 // Pop all our variables from scope. 1901 for (unsigned i = 0, e = VarNames.size(); i != e; ++i) 1902 NamedValues[VarNames[i].first] = OldBindings[i]; 1903 1904 // Return the body computation. 1905 return BodyVal; 1906} 1907 1908Function *PrototypeAST::Codegen() { 1909 // Make the function type: double(double,double) etc. 1910 std::vector<Type*> Doubles(Args.size(), 1911 Type::getDoubleTy(getGlobalContext())); 1912 FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()), 1913 Doubles, false); 1914 1915 Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule); 1916 1917 // If F conflicted, there was already something named 'Name'. If it has a 1918 // body, don't allow redefinition or reextern. 1919 if (F->getName() != Name) { 1920 // Delete the one we just made and get the existing one. 1921 F->eraseFromParent(); 1922 F = TheModule->getFunction(Name); 1923 1924 // If F already has a body, reject this. 1925 if (!F->empty()) { 1926 ErrorF("redefinition of function"); 1927 return 0; 1928 } 1929 1930 // If F took a different number of args, reject. 1931 if (F->arg_size() != Args.size()) { 1932 ErrorF("redefinition of function with different # args"); 1933 return 0; 1934 } 1935 } 1936 1937 // Set names for all arguments. 1938 unsigned Idx = 0; 1939 for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size(); 1940 ++AI, ++Idx) 1941 AI->setName(Args[Idx]); 1942 1943 return F; 1944} 1945 1946/// CreateArgumentAllocas - Create an alloca for each argument and register the 1947/// argument in the symbol table so that references to it will succeed. 1948void PrototypeAST::CreateArgumentAllocas(Function *F) { 1949 Function::arg_iterator AI = F->arg_begin(); 1950 for (unsigned Idx = 0, e = Args.size(); Idx != e; ++Idx, ++AI) { 1951 // Create an alloca for this variable. 1952 AllocaInst *Alloca = CreateEntryBlockAlloca(F, Args[Idx]); 1953 1954 // Store the initial value into the alloca. 1955 Builder.CreateStore(AI, Alloca); 1956 1957 // Add arguments to variable symbol table. 1958 NamedValues[Args[Idx]] = Alloca; 1959 } 1960} 1961 1962Function *FunctionAST::Codegen() { 1963 NamedValues.clear(); 1964 1965 Function *TheFunction = Proto->Codegen(); 1966 if (TheFunction == 0) 1967 return 0; 1968 1969 // If this is an operator, install it. 1970 if (Proto->isBinaryOp()) 1971 BinopPrecedence[Proto->getOperatorName()] = Proto->getBinaryPrecedence(); 1972 1973 // Create a new basic block to start insertion into. 1974 BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction); 1975 Builder.SetInsertPoint(BB); 1976 1977 // Add all arguments to the symbol table and create their allocas. 1978 Proto->CreateArgumentAllocas(TheFunction); 1979 1980 if (Value *RetVal = Body->Codegen()) { 1981 // Finish off the function. 1982 Builder.CreateRet(RetVal); 1983 1984 // Validate the generated code, checking for consistency. 1985 verifyFunction(*TheFunction); 1986 1987 // Optimize the function. 1988 TheFPM->run(*TheFunction); 1989 1990 return TheFunction; 1991 } 1992 1993 // Error reading body, remove function. 1994 TheFunction->eraseFromParent(); 1995 1996 if (Proto->isBinaryOp()) 1997 BinopPrecedence.erase(Proto->getOperatorName()); 1998 return 0; 1999} 2000 2001//===----------------------------------------------------------------------===// 2002// Top-Level parsing and JIT Driver 2003//===----------------------------------------------------------------------===// 2004 2005static ExecutionEngine *TheExecutionEngine; 2006 2007static void HandleDefinition() { 2008 if (FunctionAST *F = ParseDefinition()) { 2009 if (Function *LF = F->Codegen()) { 2010 fprintf(stderr, "Read function definition:"); 2011 LF->dump(); 2012 } 2013 } else { 2014 // Skip token for error recovery. 2015 getNextToken(); 2016 } 2017} 2018 2019static void HandleExtern() { 2020 if (PrototypeAST *P = ParseExtern()) { 2021 if (Function *F = P->Codegen()) { 2022 fprintf(stderr, "Read extern: "); 2023 F->dump(); 2024 } 2025 } else { 2026 // Skip token for error recovery. 2027 getNextToken(); 2028 } 2029} 2030 2031static void HandleTopLevelExpression() { 2032 // Evaluate a top-level expression into an anonymous function. 2033 if (FunctionAST *F = ParseTopLevelExpr()) { 2034 if (Function *LF = F->Codegen()) { 2035 // JIT the function, returning a function pointer. 2036 void *FPtr = TheExecutionEngine->getPointerToFunction(LF); 2037 2038 // Cast it to the right type (takes no arguments, returns a double) so we 2039 // can call it as a native function. 2040 double (*FP)() = (double (*)())(intptr_t)FPtr; 2041 fprintf(stderr, "Evaluated to %f\n", FP()); 2042 } 2043 } else { 2044 // Skip token for error recovery. 2045 getNextToken(); 2046 } 2047} 2048 2049/// top ::= definition | external | expression | ';' 2050static void MainLoop() { 2051 while (1) { 2052 fprintf(stderr, "ready> "); 2053 switch (CurTok) { 2054 case tok_eof: return; 2055 case ';': getNextToken(); break; // ignore top-level semicolons. 2056 case tok_def: HandleDefinition(); break; 2057 case tok_extern: HandleExtern(); break; 2058 default: HandleTopLevelExpression(); break; 2059 } 2060 } 2061} 2062 2063//===----------------------------------------------------------------------===// 2064// "Library" functions that can be "extern'd" from user code. 2065//===----------------------------------------------------------------------===// 2066 2067/// putchard - putchar that takes a double and returns 0. 2068extern "C" 2069double putchard(double X) { 2070 putchar((char)X); 2071 return 0; 2072} 2073 2074/// printd - printf that takes a double prints it as "%f\n", returning 0. 2075extern "C" 2076double printd(double X) { 2077 printf("%f\n", X); 2078 return 0; 2079} 2080 2081//===----------------------------------------------------------------------===// 2082// Main driver code. 2083//===----------------------------------------------------------------------===// 2084 2085int main() { 2086 InitializeNativeTarget(); 2087 LLVMContext &Context = getGlobalContext(); 2088 2089 // Install standard binary operators. 2090 // 1 is lowest precedence. 2091 BinopPrecedence['='] = 2; 2092 BinopPrecedence['<'] = 10; 2093 BinopPrecedence['+'] = 20; 2094 BinopPrecedence['-'] = 20; 2095 BinopPrecedence['*'] = 40; // highest. 2096 2097 // Prime the first token. 2098 fprintf(stderr, "ready> "); 2099 getNextToken(); 2100 2101 // Make the module, which holds all the code. 2102 TheModule = new Module("my cool jit", Context); 2103 2104 // Create the JIT. This takes ownership of the module. 2105 std::string ErrStr; 2106 TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create(); 2107 if (!TheExecutionEngine) { 2108 fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str()); 2109 exit(1); 2110 } 2111 2112 FunctionPassManager OurFPM(TheModule); 2113 2114 // Set up the optimizer pipeline. Start with registering info about how the 2115 // target lays out data structures. 2116 OurFPM.add(new TargetData(*TheExecutionEngine->getTargetData())); 2117 // Provide basic AliasAnalysis support for GVN. 2118 OurFPM.add(createBasicAliasAnalysisPass()); 2119 // Promote allocas to registers. 2120 OurFPM.add(createPromoteMemoryToRegisterPass()); 2121 // Do simple "peephole" optimizations and bit-twiddling optzns. 2122 OurFPM.add(createInstructionCombiningPass()); 2123 // Reassociate expressions. 2124 OurFPM.add(createReassociatePass()); 2125 // Eliminate Common SubExpressions. 2126 OurFPM.add(createGVNPass()); 2127 // Simplify the control flow graph (deleting unreachable blocks, etc). 2128 OurFPM.add(createCFGSimplificationPass()); 2129 2130 OurFPM.doInitialization(); 2131 2132 // Set the global so the code gen can use this. 2133 TheFPM = &OurFPM; 2134 2135 // Run the main "interpreter loop" now. 2136 MainLoop(); 2137 2138 TheFPM = 0; 2139 2140 // Print out all of the generated code. 2141 TheModule->dump(); 2142 2143 return 0; 2144} 2145</pre> 2146</div> 2147 2148<a href="LangImpl8.html">Next: Conclusion and other useful LLVM tidbits</a> 2149</div> 2150 2151<!-- *********************************************************************** --> 2152<hr> 2153<address> 2154 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img 2155 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a> 2156 <a href="http://validator.w3.org/check/referer"><img 2157 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a> 2158 2159 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> 2160 <a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br> 2161 Last modified: $Date: 2011-10-16 04:07:38 -0400 (Sun, 16 Oct 2011) $ 2162</address> 2163</body> 2164</html> 2165