From ee47edfd8e2dd048522ebd47305aeefbe9d8729c Mon Sep 17 00:00:00 2001 From: Sean Silva Date: Wed, 5 Dec 2012 00:26:32 +0000 Subject: docs: Sphinxify `docs/tutorial/` Sorry for the massive commit, but I just wanted to knock this one down and it is really straightforward. There are still a couple trivial (i.e. not related to the content) things left to fix: - Use of raw HTML links where :doc:`...` and :ref:`...` could be used instead. If you are a newbie and want to help fix this it would make for some good bite-sized patches; more experienced developers should be focusing on adding new content (to this tutorial or elsewhere, but please _do not_ waste your time on formatting when there is such dire need for documentation (see docs/SphinxQuickstartTemplate.rst to get started writing)). - Highlighting of the kaleidoscope code blocks (currently left as bare `::`). I will be working on writing a custom Pygments highlighter for this, mostly as training for maintaining the `llvm` code-block's lexer in-tree. I want to do this because I am extremely unhappy with how it just "gives up" on the slightest deviation from the expected syntax and leaves the whole code-block un-highlighted. More generally I am looking at writing some Sphinx extensions and keeping them in-tree as well, to support common use cases that currently have no good solution (like "monospace text inside a link"). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169343 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/tutorial/LangImpl5.rst | 1609 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 1609 insertions(+) create mode 100644 docs/tutorial/LangImpl5.rst (limited to 'docs/tutorial/LangImpl5.rst') diff --git a/docs/tutorial/LangImpl5.rst b/docs/tutorial/LangImpl5.rst new file mode 100644 index 0000000000..8405e1a917 --- /dev/null +++ b/docs/tutorial/LangImpl5.rst @@ -0,0 +1,1609 @@ +================================================== +Kaleidoscope: Extending the Language: Control Flow +================================================== + +.. contents:: + :local: + +Written by `Chris Lattner `_ + +Chapter 5 Introduction +====================== + +Welcome to Chapter 5 of the "`Implementing a language with +LLVM `_" tutorial. Parts 1-4 described the implementation of +the simple Kaleidoscope language and included support for generating +LLVM IR, followed by optimizations and a JIT compiler. Unfortunately, as +presented, Kaleidoscope is mostly useless: it has no control flow other +than call and return. This means that you can't have conditional +branches in the code, significantly limiting its power. In this episode +of "build that compiler", we'll extend Kaleidoscope to have an +if/then/else expression plus a simple 'for' loop. + +If/Then/Else +============ + +Extending Kaleidoscope to support if/then/else is quite straightforward. +It basically requires adding support for this "new" concept to the +lexer, parser, AST, and LLVM code emitter. This example is nice, because +it shows how easy it is to "grow" a language over time, incrementally +extending it as new ideas are discovered. + +Before we get going on "how" we add this extension, lets talk about +"what" we want. The basic idea is that we want to be able to write this +sort of thing: + +:: + + def fib(x) + if x < 3 then + 1 + else + fib(x-1)+fib(x-2); + +In Kaleidoscope, every construct is an expression: there are no +statements. As such, the if/then/else expression needs to return a value +like any other. Since we're using a mostly functional form, we'll have +it evaluate its conditional, then return the 'then' or 'else' value +based on how the condition was resolved. This is very similar to the C +"?:" expression. + +The semantics of the if/then/else expression is that it evaluates the +condition to a boolean equality value: 0.0 is considered to be false and +everything else is considered to be true. If the condition is true, the +first subexpression is evaluated and returned, if the condition is +false, the second subexpression is evaluated and returned. Since +Kaleidoscope allows side-effects, this behavior is important to nail +down. + +Now that we know what we "want", lets break this down into its +constituent pieces. + +Lexer Extensions for If/Then/Else +--------------------------------- + +The lexer extensions are straightforward. First we add new enum values +for the relevant tokens: + +.. code-block:: c++ + + // control + tok_if = -6, tok_then = -7, tok_else = -8, + +Once we have that, we recognize the new keywords in the lexer. This is +pretty simple stuff: + +.. code-block:: c++ + + ... + if (IdentifierStr == "def") return tok_def; + if (IdentifierStr == "extern") return tok_extern; + if (IdentifierStr == "if") return tok_if; + if (IdentifierStr == "then") return tok_then; + if (IdentifierStr == "else") return tok_else; + return tok_identifier; + +AST Extensions for If/Then/Else +------------------------------- + +To represent the new expression we add a new AST node for it: + +.. code-block:: c++ + + /// IfExprAST - Expression class for if/then/else. + class IfExprAST : public ExprAST { + ExprAST *Cond, *Then, *Else; + public: + IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else) + : Cond(cond), Then(then), Else(_else) {} + virtual Value *Codegen(); + }; + +The AST node just has pointers to the various subexpressions. + +Parser Extensions for If/Then/Else +---------------------------------- + +Now that we have the relevant tokens coming from the lexer and we have +the AST node to build, our parsing logic is relatively straightforward. +First we define a new parsing function: + +.. code-block:: c++ + + /// ifexpr ::= 'if' expression 'then' expression 'else' expression + static ExprAST *ParseIfExpr() { + getNextToken(); // eat the if. + + // condition. + ExprAST *Cond = ParseExpression(); + if (!Cond) return 0; + + if (CurTok != tok_then) + return Error("expected then"); + getNextToken(); // eat the then + + ExprAST *Then = ParseExpression(); + if (Then == 0) return 0; + + if (CurTok != tok_else) + return Error("expected else"); + + getNextToken(); + + ExprAST *Else = ParseExpression(); + if (!Else) return 0; + + return new IfExprAST(Cond, Then, Else); + } + +Next we hook it up as a primary expression: + +.. code-block:: c++ + + static ExprAST *ParsePrimary() { + switch (CurTok) { + default: return Error("unknown token when expecting an expression"); + case tok_identifier: return ParseIdentifierExpr(); + case tok_number: return ParseNumberExpr(); + case '(': return ParseParenExpr(); + case tok_if: return ParseIfExpr(); + } + } + +LLVM IR for If/Then/Else +------------------------ + +Now that we have it parsing and building the AST, the final piece is +adding LLVM code generation support. This is the most interesting part +of the if/then/else example, because this is where it starts to +introduce new concepts. All of the code above has been thoroughly +described in previous chapters. + +To motivate the code we want to produce, lets take a look at a simple +example. Consider: + +:: + + extern foo(); + extern bar(); + def baz(x) if x then foo() else bar(); + +If you disable optimizations, the code you'll (soon) get from +Kaleidoscope looks like this: + +.. code-block:: llvm + + declare double @foo() + + declare double @bar() + + define double @baz(double %x) { + entry: + %ifcond = fcmp one double %x, 0.000000e+00 + br i1 %ifcond, label %then, label %else + + then: ; preds = %entry + %calltmp = call double @foo() + br label %ifcont + + else: ; preds = %entry + %calltmp1 = call double @bar() + br label %ifcont + + ifcont: ; preds = %else, %then + %iftmp = phi double [ %calltmp, %then ], [ %calltmp1, %else ] + ret double %iftmp + } + +To visualize the control flow graph, you can use a nifty feature of the +LLVM '`opt `_' tool. If you put this LLVM +IR into "t.ll" and run "``llvm-as < t.ll | opt -analyze -view-cfg``", `a +window will pop up <../ProgrammersManual.html#ViewGraph>`_ and you'll +see this graph: + +.. figure:: LangImpl5-cfg.png + :align: center + :alt: Example CFG + + Example CFG + +Another way to get this is to call "``F->viewCFG()``" or +"``F->viewCFGOnly()``" (where F is a "``Function*``") either by +inserting actual calls into the code and recompiling or by calling these +in the debugger. LLVM has many nice features for visualizing various +graphs. + +Getting back to the generated code, it is fairly simple: the entry block +evaluates the conditional expression ("x" in our case here) and compares +the result to 0.0 with the "``fcmp one``" instruction ('one' is "Ordered +and Not Equal"). Based on the result of this expression, the code jumps +to either the "then" or "else" blocks, which contain the expressions for +the true/false cases. + +Once the then/else blocks are finished executing, they both branch back +to the 'ifcont' block to execute the code that happens after the +if/then/else. In this case the only thing left to do is to return to the +caller of the function. The question then becomes: how does the code +know which expression to return? + +The answer to this question involves an important SSA operation: the +`Phi +operation `_. +If you're not familiar with SSA, `the wikipedia +article `_ +is a good introduction and there are various other introductions to it +available on your favorite search engine. The short version is that +"execution" of the Phi operation requires "remembering" which block +control came from. The Phi operation takes on the value corresponding to +the input control block. In this case, if control comes in from the +"then" block, it gets the value of "calltmp". If control comes from the +"else" block, it gets the value of "calltmp1". + +At this point, you are probably starting to think "Oh no! This means my +simple and elegant front-end will have to start generating SSA form in +order to use LLVM!". Fortunately, this is not the case, and we strongly +advise *not* implementing an SSA construction algorithm in your +front-end unless there is an amazingly good reason to do so. In +practice, there are two sorts of values that float around in code +written for your average imperative programming language that might need +Phi nodes: + +#. Code that involves user variables: ``x = 1; x = x + 1;`` +#. Values that are implicit in the structure of your AST, such as the + Phi node in this case. + +In `Chapter 7 `_ of this tutorial ("mutable variables"), +we'll talk about #1 in depth. For now, just believe me that you don't +need SSA construction to handle this case. For #2, you have the choice +of using the techniques that we will describe for #1, or you can insert +Phi nodes directly, if convenient. In this case, it is really really +easy to generate the Phi node, so we choose to do it directly. + +Okay, enough of the motivation and overview, lets generate code! + +Code Generation for If/Then/Else +-------------------------------- + +In order to generate code for this, we implement the ``Codegen`` method +for ``IfExprAST``: + +.. code-block:: c++ + + Value *IfExprAST::Codegen() { + Value *CondV = Cond->Codegen(); + if (CondV == 0) return 0; + + // Convert condition to a bool by comparing equal to 0.0. + CondV = Builder.CreateFCmpONE(CondV, + ConstantFP::get(getGlobalContext(), APFloat(0.0)), + "ifcond"); + +This code is straightforward and similar to what we saw before. We emit +the expression for the condition, then compare that value to zero to get +a truth value as a 1-bit (bool) value. + +.. code-block:: c++ + + Function *TheFunction = Builder.GetInsertBlock()->getParent(); + + // Create blocks for the then and else cases. Insert the 'then' block at the + // end of the function. + BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction); + BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else"); + BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont"); + + Builder.CreateCondBr(CondV, ThenBB, ElseBB); + +This code creates the basic blocks that are related to the if/then/else +statement, and correspond directly to the blocks in the example above. +The first line gets the current Function object that is being built. It +gets this by asking the builder for the current BasicBlock, and asking +that block for its "parent" (the function it is currently embedded +into). + +Once it has that, it creates three blocks. Note that it passes +"TheFunction" into the constructor for the "then" block. This causes the +constructor to automatically insert the new block into the end of the +specified function. The other two blocks are created, but aren't yet +inserted into the function. + +Once the blocks are created, we can emit the conditional branch that +chooses between them. Note that creating new blocks does not implicitly +affect the IRBuilder, so it is still inserting into the block that the +condition went into. Also note that it is creating a branch to the +"then" block and the "else" block, even though the "else" block isn't +inserted into the function yet. This is all ok: it is the standard way +that LLVM supports forward references. + +.. code-block:: c++ + + // Emit then value. + Builder.SetInsertPoint(ThenBB); + + Value *ThenV = Then->Codegen(); + if (ThenV == 0) return 0; + + Builder.CreateBr(MergeBB); + // Codegen of 'Then' can change the current block, update ThenBB for the PHI. + ThenBB = Builder.GetInsertBlock(); + +After the conditional branch is inserted, we move the builder to start +inserting into the "then" block. Strictly speaking, this call moves the +insertion point to be at the end of the specified block. However, since +the "then" block is empty, it also starts out by inserting at the +beginning of the block. :) + +Once the insertion point is set, we recursively codegen the "then" +expression from the AST. To finish off the "then" block, we create an +unconditional branch to the merge block. One interesting (and very +important) aspect of the LLVM IR is that it `requires all basic blocks +to be "terminated" <../LangRef.html#functionstructure>`_ with a `control +flow instruction <../LangRef.html#terminators>`_ such as return or +branch. This means that all control flow, *including fall throughs* must +be made explicit in the LLVM IR. If you violate this rule, the verifier +will emit an error. + +The final line here is quite subtle, but is very important. The basic +issue is that when we create the Phi node in the merge block, we need to +set up the block/value pairs that indicate how the Phi will work. +Importantly, the Phi node expects to have an entry for each predecessor +of the block in the CFG. Why then, are we getting the current block when +we just set it to ThenBB 5 lines above? The problem is that the "Then" +expression may actually itself change the block that the Builder is +emitting into if, for example, it contains a nested "if/then/else" +expression. Because calling Codegen recursively could arbitrarily change +the notion of the current block, we are required to get an up-to-date +value for code that will set up the Phi node. + +.. code-block:: c++ + + // Emit else block. + TheFunction->getBasicBlockList().push_back(ElseBB); + Builder.SetInsertPoint(ElseBB); + + Value *ElseV = Else->Codegen(); + if (ElseV == 0) return 0; + + Builder.CreateBr(MergeBB); + // Codegen of 'Else' can change the current block, update ElseBB for the PHI. + ElseBB = Builder.GetInsertBlock(); + +Code generation for the 'else' block is basically identical to codegen +for the 'then' block. The only significant difference is the first line, +which adds the 'else' block to the function. Recall previously that the +'else' block was created, but not added to the function. Now that the +'then' and 'else' blocks are emitted, we can finish up with the merge +code: + +.. code-block:: c++ + + // Emit merge block. + TheFunction->getBasicBlockList().push_back(MergeBB); + Builder.SetInsertPoint(MergeBB); + PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, + "iftmp"); + + PN->addIncoming(ThenV, ThenBB); + PN->addIncoming(ElseV, ElseBB); + return PN; + } + +The first two lines here are now familiar: the first adds the "merge" +block to the Function object (it was previously floating, like the else +block above). The second block changes the insertion point so that newly +created code will go into the "merge" block. Once that is done, we need +to create the PHI node and set up the block/value pairs for the PHI. + +Finally, the CodeGen function returns the phi node as the value computed +by the if/then/else expression. In our example above, this returned +value will feed into the code for the top-level function, which will +create the return instruction. + +Overall, we now have the ability to execute conditional code in +Kaleidoscope. With this extension, Kaleidoscope is a fairly complete +language that can calculate a wide variety of numeric functions. Next up +we'll add another useful expression that is familiar from non-functional +languages... + +'for' Loop Expression +===================== + +Now that we know how to add basic control flow constructs to the +language, we have the tools to add more powerful things. Lets add +something more aggressive, a 'for' expression: + +:: + + extern putchard(char) + def printstar(n) + for i = 1, i < n, 1.0 in + putchard(42); # ascii 42 = '*' + + # print 100 '*' characters + printstar(100); + +This expression defines a new variable ("i" in this case) which iterates +from a starting value, while the condition ("i < n" in this case) is +true, incrementing by an optional step value ("1.0" in this case). If +the step value is omitted, it defaults to 1.0. While the loop is true, +it executes its body expression. Because we don't have anything better +to return, we'll just define the loop as always returning 0.0. In the +future when we have mutable variables, it will get more useful. + +As before, lets talk about the changes that we need to Kaleidoscope to +support this. + +Lexer Extensions for the 'for' Loop +----------------------------------- + +The lexer extensions are the same sort of thing as for if/then/else: + +.. code-block:: c++ + + ... in enum Token ... + // control + tok_if = -6, tok_then = -7, tok_else = -8, + tok_for = -9, tok_in = -10 + + ... in gettok ... + if (IdentifierStr == "def") return tok_def; + if (IdentifierStr == "extern") return tok_extern; + if (IdentifierStr == "if") return tok_if; + if (IdentifierStr == "then") return tok_then; + if (IdentifierStr == "else") return tok_else; + if (IdentifierStr == "for") return tok_for; + if (IdentifierStr == "in") return tok_in; + return tok_identifier; + +AST Extensions for the 'for' Loop +--------------------------------- + +The AST node is just as simple. It basically boils down to capturing the +variable name and the constituent expressions in the node. + +.. code-block:: c++ + + /// ForExprAST - Expression class for for/in. + class ForExprAST : public ExprAST { + std::string VarName; + ExprAST *Start, *End, *Step, *Body; + public: + ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end, + ExprAST *step, ExprAST *body) + : VarName(varname), Start(start), End(end), Step(step), Body(body) {} + virtual Value *Codegen(); + }; + +Parser Extensions for the 'for' Loop +------------------------------------ + +The parser code is also fairly standard. The only interesting thing here +is handling of the optional step value. The parser code handles it by +checking to see if the second comma is present. If not, it sets the step +value to null in the AST node: + +.. code-block:: c++ + + /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression + static ExprAST *ParseForExpr() { + getNextToken(); // eat the for. + + if (CurTok != tok_identifier) + return Error("expected identifier after for"); + + std::string IdName = IdentifierStr; + getNextToken(); // eat identifier. + + if (CurTok != '=') + return Error("expected '=' after for"); + getNextToken(); // eat '='. + + + ExprAST *Start = ParseExpression(); + if (Start == 0) return 0; + if (CurTok != ',') + return Error("expected ',' after for start value"); + getNextToken(); + + ExprAST *End = ParseExpression(); + if (End == 0) return 0; + + // The step value is optional. + ExprAST *Step = 0; + if (CurTok == ',') { + getNextToken(); + Step = ParseExpression(); + if (Step == 0) return 0; + } + + if (CurTok != tok_in) + return Error("expected 'in' after for"); + getNextToken(); // eat 'in'. + + ExprAST *Body = ParseExpression(); + if (Body == 0) return 0; + + return new ForExprAST(IdName, Start, End, Step, Body); + } + +LLVM IR for the 'for' Loop +-------------------------- + +Now we get to the good part: the LLVM IR we want to generate for this +thing. With the simple example above, we get this LLVM IR (note that +this dump is generated with optimizations disabled for clarity): + +.. code-block:: llvm + + declare double @putchard(double) + + define double @printstar(double %n) { + entry: + ; initial value = 1.0 (inlined into phi) + br label %loop + + loop: ; preds = %loop, %entry + %i = phi double [ 1.000000e+00, %entry ], [ %nextvar, %loop ] + ; body + %calltmp = call double @putchard(double 4.200000e+01) + ; increment + %nextvar = fadd double %i, 1.000000e+00 + + ; termination test + %cmptmp = fcmp ult double %i, %n + %booltmp = uitofp i1 %cmptmp to double + %loopcond = fcmp one double %booltmp, 0.000000e+00 + br i1 %loopcond, label %loop, label %afterloop + + afterloop: ; preds = %loop + ; loop always returns 0.0 + ret double 0.000000e+00 + } + +This loop contains all the same constructs we saw before: a phi node, +several expressions, and some basic blocks. Lets see how this fits +together. + +Code Generation for the 'for' Loop +---------------------------------- + +The first part of Codegen is very simple: we just output the start +expression for the loop value: + +.. code-block:: c++ + + Value *ForExprAST::Codegen() { + // Emit the start code first, without 'variable' in scope. + Value *StartVal = Start->Codegen(); + if (StartVal == 0) return 0; + +With this out of the way, the next step is to set up the LLVM basic +block for the start of the loop body. In the case above, the whole loop +body is one block, but remember that the body code itself could consist +of multiple blocks (e.g. if it contains an if/then/else or a for/in +expression). + +.. code-block:: c++ + + // Make the new basic block for the loop header, inserting after current + // block. + Function *TheFunction = Builder.GetInsertBlock()->getParent(); + BasicBlock *PreheaderBB = Builder.GetInsertBlock(); + BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction); + + // Insert an explicit fall through from the current block to the LoopBB. + Builder.CreateBr(LoopBB); + +This code is similar to what we saw for if/then/else. Because we will +need it to create the Phi node, we remember the block that falls through +into the loop. Once we have that, we create the actual block that starts +the loop and create an unconditional branch for the fall-through between +the two blocks. + +.. code-block:: c++ + + // Start insertion in LoopBB. + Builder.SetInsertPoint(LoopBB); + + // Start the PHI node with an entry for Start. + PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str()); + Variable->addIncoming(StartVal, PreheaderBB); + +Now that the "preheader" for the loop is set up, we switch to emitting +code for the loop body. To begin with, we move the insertion point and +create the PHI node for the loop induction variable. Since we already +know the incoming value for the starting value, we add it to the Phi +node. Note that the Phi will eventually get a second value for the +backedge, but we can't set it up yet (because it doesn't exist!). + +.. code-block:: c++ + + // Within the loop, the variable is defined equal to the PHI node. If it + // shadows an existing variable, we have to restore it, so save it now. + Value *OldVal = NamedValues[VarName]; + NamedValues[VarName] = Variable; + + // Emit the body of the loop. This, like any other expr, can change the + // current BB. Note that we ignore the value computed by the body, but don't + // allow an error. + if (Body->Codegen() == 0) + return 0; + +Now the code starts to get more interesting. Our 'for' loop introduces a +new variable to the symbol table. This means that our symbol table can +now contain either function arguments or loop variables. To handle this, +before we codegen the body of the loop, we add the loop variable as the +current value for its name. Note that it is possible that there is a +variable of the same name in the outer scope. It would be easy to make +this an error (emit an error and return null if there is already an +entry for VarName) but we choose to allow shadowing of variables. In +order to handle this correctly, we remember the Value that we are +potentially shadowing in ``OldVal`` (which will be null if there is no +shadowed variable). + +Once the loop variable is set into the symbol table, the code +recursively codegen's the body. This allows the body to use the loop +variable: any references to it will naturally find it in the symbol +table. + +.. code-block:: c++ + + // Emit the step value. + Value *StepVal; + if (Step) { + StepVal = Step->Codegen(); + if (StepVal == 0) return 0; + } else { + // If not specified, use 1.0. + StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0)); + } + + Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar"); + +Now that the body is emitted, we compute the next value of the iteration +variable by adding the step value, or 1.0 if it isn't present. +'``NextVar``' will be the value of the loop variable on the next +iteration of the loop. + +.. code-block:: c++ + + // Compute the end condition. + Value *EndCond = End->Codegen(); + if (EndCond == 0) return EndCond; + + // Convert condition to a bool by comparing equal to 0.0. + EndCond = Builder.CreateFCmpONE(EndCond, + ConstantFP::get(getGlobalContext(), APFloat(0.0)), + "loopcond"); + +Finally, we evaluate the exit value of the loop, to determine whether +the loop should exit. This mirrors the condition evaluation for the +if/then/else statement. + +.. code-block:: c++ + + // Create the "after loop" block and insert it. + BasicBlock *LoopEndBB = Builder.GetInsertBlock(); + BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction); + + // Insert the conditional branch into the end of LoopEndBB. + Builder.CreateCondBr(EndCond, LoopBB, AfterBB); + + // Any new code will be inserted in AfterBB. + Builder.SetInsertPoint(AfterBB); + +With the code for the body of the loop complete, we just need to finish +up the control flow for it. This code remembers the end block (for the +phi node), then creates the block for the loop exit ("afterloop"). Based +on the value of the exit condition, it creates a conditional branch that +chooses between executing the loop again and exiting the loop. Any +future code is emitted in the "afterloop" block, so it sets the +insertion position to it. + +.. code-block:: c++ + + // Add a new entry to the PHI node for the backedge. + Variable->addIncoming(NextVar, LoopEndBB); + + // Restore the unshadowed variable. + if (OldVal) + NamedValues[VarName] = OldVal; + else + NamedValues.erase(VarName); + + // for expr always returns 0.0. + return Constant::getNullValue(Type::getDoubleTy(getGlobalContext())); + } + +The final code handles various cleanups: now that we have the "NextVar" +value, we can add the incoming value to the loop PHI node. After that, +we remove the loop variable from the symbol table, so that it isn't in +scope after the for loop. Finally, code generation of the for loop +always returns 0.0, so that is what we return from +``ForExprAST::Codegen``. + +With this, we conclude the "adding control flow to Kaleidoscope" chapter +of the tutorial. In this chapter we added two control flow constructs, +and used them to motivate a couple of aspects of the LLVM IR that are +important for front-end implementors to know. In the next chapter of our +saga, we will get a bit crazier and add `user-defined +operators `_ to our poor innocent language. + +Full Code Listing +================= + +Here is the complete code listing for our running example, enhanced with +the if/then/else and for expressions.. To build this example, use: + +.. code-block:: bash + + # Compile + clang++ -g toy.cpp `llvm-config --cppflags --ldflags --libs core jit native` -O3 -o toy + # Run + ./toy + +Here is the code: + +.. code-block:: c++ + + #include "llvm/DerivedTypes.h" + #include "llvm/ExecutionEngine/ExecutionEngine.h" + #include "llvm/ExecutionEngine/JIT.h" + #include "llvm/IRBuilder.h" + #include "llvm/LLVMContext.h" + #include "llvm/Module.h" + #include "llvm/PassManager.h" + #include "llvm/Analysis/Verifier.h" + #include "llvm/Analysis/Passes.h" + #include "llvm/DataLayout.h" + #include "llvm/Transforms/Scalar.h" + #include "llvm/Support/TargetSelect.h" + #include + #include + #include + #include + using namespace llvm; + + //===----------------------------------------------------------------------===// + // Lexer + //===----------------------------------------------------------------------===// + + // The lexer returns tokens [0-255] if it is an unknown character, otherwise one + // of these for known things. + enum Token { + tok_eof = -1, + + // commands + tok_def = -2, tok_extern = -3, + + // primary + tok_identifier = -4, tok_number = -5, + + // control + tok_if = -6, tok_then = -7, tok_else = -8, + tok_for = -9, tok_in = -10 + }; + + static std::string IdentifierStr; // Filled in if tok_identifier + static double NumVal; // Filled in if tok_number + + /// gettok - Return the next token from standard input. + static int gettok() { + static int LastChar = ' '; + + // Skip any whitespace. + while (isspace(LastChar)) + LastChar = getchar(); + + if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]* + IdentifierStr = LastChar; + while (isalnum((LastChar = getchar()))) + IdentifierStr += LastChar; + + if (IdentifierStr == "def") return tok_def; + if (IdentifierStr == "extern") return tok_extern; + if (IdentifierStr == "if") return tok_if; + if (IdentifierStr == "then") return tok_then; + if (IdentifierStr == "else") return tok_else; + if (IdentifierStr == "for") return tok_for; + if (IdentifierStr == "in") return tok_in; + return tok_identifier; + } + + if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+ + std::string NumStr; + do { + NumStr += LastChar; + LastChar = getchar(); + } while (isdigit(LastChar) || LastChar == '.'); + + NumVal = strtod(NumStr.c_str(), 0); + return tok_number; + } + + if (LastChar == '#') { + // Comment until end of line. + do LastChar = getchar(); + while (LastChar != EOF && LastChar != '\n' && LastChar != '\r'); + + if (LastChar != EOF) + return gettok(); + } + + // Check for end of file. Don't eat the EOF. + if (LastChar == EOF) + return tok_eof; + + // Otherwise, just return the character as its ascii value. + int ThisChar = LastChar; + LastChar = getchar(); + return ThisChar; + } + + //===----------------------------------------------------------------------===// + // Abstract Syntax Tree (aka Parse Tree) + //===----------------------------------------------------------------------===// + + /// ExprAST - Base class for all expression nodes. + class ExprAST { + public: + virtual ~ExprAST() {} + virtual Value *Codegen() = 0; + }; + + /// NumberExprAST - Expression class for numeric literals like "1.0". + class NumberExprAST : public ExprAST { + double Val; + public: + NumberExprAST(double val) : Val(val) {} + virtual Value *Codegen(); + }; + + /// VariableExprAST - Expression class for referencing a variable, like "a". + class VariableExprAST : public ExprAST { + std::string Name; + public: + VariableExprAST(const std::string &name) : Name(name) {} + virtual Value *Codegen(); + }; + + /// BinaryExprAST - Expression class for a binary operator. + class BinaryExprAST : public ExprAST { + char Op; + ExprAST *LHS, *RHS; + public: + BinaryExprAST(char op, ExprAST *lhs, ExprAST *rhs) + : Op(op), LHS(lhs), RHS(rhs) {} + virtual Value *Codegen(); + }; + + /// CallExprAST - Expression class for function calls. + class CallExprAST : public ExprAST { + std::string Callee; + std::vector Args; + public: + CallExprAST(const std::string &callee, std::vector &args) + : Callee(callee), Args(args) {} + virtual Value *Codegen(); + }; + + /// IfExprAST - Expression class for if/then/else. + class IfExprAST : public ExprAST { + ExprAST *Cond, *Then, *Else; + public: + IfExprAST(ExprAST *cond, ExprAST *then, ExprAST *_else) + : Cond(cond), Then(then), Else(_else) {} + virtual Value *Codegen(); + }; + + /// ForExprAST - Expression class for for/in. + class ForExprAST : public ExprAST { + std::string VarName; + ExprAST *Start, *End, *Step, *Body; + public: + ForExprAST(const std::string &varname, ExprAST *start, ExprAST *end, + ExprAST *step, ExprAST *body) + : VarName(varname), Start(start), End(end), Step(step), Body(body) {} + virtual Value *Codegen(); + }; + + /// PrototypeAST - This class represents the "prototype" for a function, + /// which captures its name, and its argument names (thus implicitly the number + /// of arguments the function takes). + class PrototypeAST { + std::string Name; + std::vector Args; + public: + PrototypeAST(const std::string &name, const std::vector &args) + : Name(name), Args(args) {} + + Function *Codegen(); + }; + + /// FunctionAST - This class represents a function definition itself. + class FunctionAST { + PrototypeAST *Proto; + ExprAST *Body; + public: + FunctionAST(PrototypeAST *proto, ExprAST *body) + : Proto(proto), Body(body) {} + + Function *Codegen(); + }; + + //===----------------------------------------------------------------------===// + // Parser + //===----------------------------------------------------------------------===// + + /// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current + /// token the parser is looking at. getNextToken reads another token from the + /// lexer and updates CurTok with its results. + static int CurTok; + static int getNextToken() { + return CurTok = gettok(); + } + + /// BinopPrecedence - This holds the precedence for each binary operator that is + /// defined. + static std::map BinopPrecedence; + + /// GetTokPrecedence - Get the precedence of the pending binary operator token. + static int GetTokPrecedence() { + if (!isascii(CurTok)) + return -1; + + // Make sure it's a declared binop. + int TokPrec = BinopPrecedence[CurTok]; + if (TokPrec <= 0) return -1; + return TokPrec; + } + + /// Error* - These are little helper functions for error handling. + ExprAST *Error(const char *Str) { fprintf(stderr, "Error: %s\n", Str);return 0;} + PrototypeAST *ErrorP(const char *Str) { Error(Str); return 0; } + FunctionAST *ErrorF(const char *Str) { Error(Str); return 0; } + + static ExprAST *ParseExpression(); + + /// identifierexpr + /// ::= identifier + /// ::= identifier '(' expression* ')' + static ExprAST *ParseIdentifierExpr() { + std::string IdName = IdentifierStr; + + getNextToken(); // eat identifier. + + if (CurTok != '(') // Simple variable ref. + return new VariableExprAST(IdName); + + // Call. + getNextToken(); // eat ( + std::vector Args; + if (CurTok != ')') { + while (1) { + ExprAST *Arg = ParseExpression(); + if (!Arg) return 0; + Args.push_back(Arg); + + if (CurTok == ')') break; + + if (CurTok != ',') + return Error("Expected ')' or ',' in argument list"); + getNextToken(); + } + } + + // Eat the ')'. + getNextToken(); + + return new CallExprAST(IdName, Args); + } + + /// numberexpr ::= number + static ExprAST *ParseNumberExpr() { + ExprAST *Result = new NumberExprAST(NumVal); + getNextToken(); // consume the number + return Result; + } + + /// parenexpr ::= '(' expression ')' + static ExprAST *ParseParenExpr() { + getNextToken(); // eat (. + ExprAST *V = ParseExpression(); + if (!V) return 0; + + if (CurTok != ')') + return Error("expected ')'"); + getNextToken(); // eat ). + return V; + } + + /// ifexpr ::= 'if' expression 'then' expression 'else' expression + static ExprAST *ParseIfExpr() { + getNextToken(); // eat the if. + + // condition. + ExprAST *Cond = ParseExpression(); + if (!Cond) return 0; + + if (CurTok != tok_then) + return Error("expected then"); + getNextToken(); // eat the then + + ExprAST *Then = ParseExpression(); + if (Then == 0) return 0; + + if (CurTok != tok_else) + return Error("expected else"); + + getNextToken(); + + ExprAST *Else = ParseExpression(); + if (!Else) return 0; + + return new IfExprAST(Cond, Then, Else); + } + + /// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression + static ExprAST *ParseForExpr() { + getNextToken(); // eat the for. + + if (CurTok != tok_identifier) + return Error("expected identifier after for"); + + std::string IdName = IdentifierStr; + getNextToken(); // eat identifier. + + if (CurTok != '=') + return Error("expected '=' after for"); + getNextToken(); // eat '='. + + + ExprAST *Start = ParseExpression(); + if (Start == 0) return 0; + if (CurTok != ',') + return Error("expected ',' after for start value"); + getNextToken(); + + ExprAST *End = ParseExpression(); + if (End == 0) return 0; + + // The step value is optional. + ExprAST *Step = 0; + if (CurTok == ',') { + getNextToken(); + Step = ParseExpression(); + if (Step == 0) return 0; + } + + if (CurTok != tok_in) + return Error("expected 'in' after for"); + getNextToken(); // eat 'in'. + + ExprAST *Body = ParseExpression(); + if (Body == 0) return 0; + + return new ForExprAST(IdName, Start, End, Step, Body); + } + + /// primary + /// ::= identifierexpr + /// ::= numberexpr + /// ::= parenexpr + /// ::= ifexpr + /// ::= forexpr + static ExprAST *ParsePrimary() { + switch (CurTok) { + default: return Error("unknown token when expecting an expression"); + case tok_identifier: return ParseIdentifierExpr(); + case tok_number: return ParseNumberExpr(); + case '(': return ParseParenExpr(); + case tok_if: return ParseIfExpr(); + case tok_for: return ParseForExpr(); + } + } + + /// binoprhs + /// ::= ('+' primary)* + static ExprAST *ParseBinOpRHS(int ExprPrec, ExprAST *LHS) { + // If this is a binop, find its precedence. + while (1) { + int TokPrec = GetTokPrecedence(); + + // If this is a binop that binds at least as tightly as the current binop, + // consume it, otherwise we are done. + if (TokPrec < ExprPrec) + return LHS; + + // Okay, we know this is a binop. + int BinOp = CurTok; + getNextToken(); // eat binop + + // Parse the primary expression after the binary operator. + ExprAST *RHS = ParsePrimary(); + if (!RHS) return 0; + + // If BinOp binds less tightly with RHS than the operator after RHS, let + // the pending operator take RHS as its LHS. + int NextPrec = GetTokPrecedence(); + if (TokPrec < NextPrec) { + RHS = ParseBinOpRHS(TokPrec+1, RHS); + if (RHS == 0) return 0; + } + + // Merge LHS/RHS. + LHS = new BinaryExprAST(BinOp, LHS, RHS); + } + } + + /// expression + /// ::= primary binoprhs + /// + static ExprAST *ParseExpression() { + ExprAST *LHS = ParsePrimary(); + if (!LHS) return 0; + + return ParseBinOpRHS(0, LHS); + } + + /// prototype + /// ::= id '(' id* ')' + static PrototypeAST *ParsePrototype() { + if (CurTok != tok_identifier) + return ErrorP("Expected function name in prototype"); + + std::string FnName = IdentifierStr; + getNextToken(); + + if (CurTok != '(') + return ErrorP("Expected '(' in prototype"); + + std::vector ArgNames; + while (getNextToken() == tok_identifier) + ArgNames.push_back(IdentifierStr); + if (CurTok != ')') + return ErrorP("Expected ')' in prototype"); + + // success. + getNextToken(); // eat ')'. + + return new PrototypeAST(FnName, ArgNames); + } + + /// definition ::= 'def' prototype expression + static FunctionAST *ParseDefinition() { + getNextToken(); // eat def. + PrototypeAST *Proto = ParsePrototype(); + if (Proto == 0) return 0; + + if (ExprAST *E = ParseExpression()) + return new FunctionAST(Proto, E); + return 0; + } + + /// toplevelexpr ::= expression + static FunctionAST *ParseTopLevelExpr() { + if (ExprAST *E = ParseExpression()) { + // Make an anonymous proto. + PrototypeAST *Proto = new PrototypeAST("", std::vector()); + return new FunctionAST(Proto, E); + } + return 0; + } + + /// external ::= 'extern' prototype + static PrototypeAST *ParseExtern() { + getNextToken(); // eat extern. + return ParsePrototype(); + } + + //===----------------------------------------------------------------------===// + // Code Generation + //===----------------------------------------------------------------------===// + + static Module *TheModule; + static IRBuilder<> Builder(getGlobalContext()); + static std::map NamedValues; + static FunctionPassManager *TheFPM; + + Value *ErrorV(const char *Str) { Error(Str); return 0; } + + Value *NumberExprAST::Codegen() { + return ConstantFP::get(getGlobalContext(), APFloat(Val)); + } + + Value *VariableExprAST::Codegen() { + // Look this variable up in the function. + Value *V = NamedValues[Name]; + return V ? V : ErrorV("Unknown variable name"); + } + + Value *BinaryExprAST::Codegen() { + Value *L = LHS->Codegen(); + Value *R = RHS->Codegen(); + if (L == 0 || R == 0) return 0; + + switch (Op) { + case '+': return Builder.CreateFAdd(L, R, "addtmp"); + case '-': return Builder.CreateFSub(L, R, "subtmp"); + case '*': return Builder.CreateFMul(L, R, "multmp"); + case '<': + L = Builder.CreateFCmpULT(L, R, "cmptmp"); + // Convert bool 0/1 to double 0.0 or 1.0 + return Builder.CreateUIToFP(L, Type::getDoubleTy(getGlobalContext()), + "booltmp"); + default: return ErrorV("invalid binary operator"); + } + } + + Value *CallExprAST::Codegen() { + // Look up the name in the global module table. + Function *CalleeF = TheModule->getFunction(Callee); + if (CalleeF == 0) + return ErrorV("Unknown function referenced"); + + // If argument mismatch error. + if (CalleeF->arg_size() != Args.size()) + return ErrorV("Incorrect # arguments passed"); + + std::vector ArgsV; + for (unsigned i = 0, e = Args.size(); i != e; ++i) { + ArgsV.push_back(Args[i]->Codegen()); + if (ArgsV.back() == 0) return 0; + } + + return Builder.CreateCall(CalleeF, ArgsV, "calltmp"); + } + + Value *IfExprAST::Codegen() { + Value *CondV = Cond->Codegen(); + if (CondV == 0) return 0; + + // Convert condition to a bool by comparing equal to 0.0. + CondV = Builder.CreateFCmpONE(CondV, + ConstantFP::get(getGlobalContext(), APFloat(0.0)), + "ifcond"); + + Function *TheFunction = Builder.GetInsertBlock()->getParent(); + + // Create blocks for the then and else cases. Insert the 'then' block at the + // end of the function. + BasicBlock *ThenBB = BasicBlock::Create(getGlobalContext(), "then", TheFunction); + BasicBlock *ElseBB = BasicBlock::Create(getGlobalContext(), "else"); + BasicBlock *MergeBB = BasicBlock::Create(getGlobalContext(), "ifcont"); + + Builder.CreateCondBr(CondV, ThenBB, ElseBB); + + // Emit then value. + Builder.SetInsertPoint(ThenBB); + + Value *ThenV = Then->Codegen(); + if (ThenV == 0) return 0; + + Builder.CreateBr(MergeBB); + // Codegen of 'Then' can change the current block, update ThenBB for the PHI. + ThenBB = Builder.GetInsertBlock(); + + // Emit else block. + TheFunction->getBasicBlockList().push_back(ElseBB); + Builder.SetInsertPoint(ElseBB); + + Value *ElseV = Else->Codegen(); + if (ElseV == 0) return 0; + + Builder.CreateBr(MergeBB); + // Codegen of 'Else' can change the current block, update ElseBB for the PHI. + ElseBB = Builder.GetInsertBlock(); + + // Emit merge block. + TheFunction->getBasicBlockList().push_back(MergeBB); + Builder.SetInsertPoint(MergeBB); + PHINode *PN = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, + "iftmp"); + + PN->addIncoming(ThenV, ThenBB); + PN->addIncoming(ElseV, ElseBB); + return PN; + } + + Value *ForExprAST::Codegen() { + // Output this as: + // ... + // start = startexpr + // goto loop + // loop: + // variable = phi [start, loopheader], [nextvariable, loopend] + // ... + // bodyexpr + // ... + // loopend: + // step = stepexpr + // nextvariable = variable + step + // endcond = endexpr + // br endcond, loop, endloop + // outloop: + + // Emit the start code first, without 'variable' in scope. + Value *StartVal = Start->Codegen(); + if (StartVal == 0) return 0; + + // Make the new basic block for the loop header, inserting after current + // block. + Function *TheFunction = Builder.GetInsertBlock()->getParent(); + BasicBlock *PreheaderBB = Builder.GetInsertBlock(); + BasicBlock *LoopBB = BasicBlock::Create(getGlobalContext(), "loop", TheFunction); + + // Insert an explicit fall through from the current block to the LoopBB. + Builder.CreateBr(LoopBB); + + // Start insertion in LoopBB. + Builder.SetInsertPoint(LoopBB); + + // Start the PHI node with an entry for Start. + PHINode *Variable = Builder.CreatePHI(Type::getDoubleTy(getGlobalContext()), 2, VarName.c_str()); + Variable->addIncoming(StartVal, PreheaderBB); + + // Within the loop, the variable is defined equal to the PHI node. If it + // shadows an existing variable, we have to restore it, so save it now. + Value *OldVal = NamedValues[VarName]; + NamedValues[VarName] = Variable; + + // Emit the body of the loop. This, like any other expr, can change the + // current BB. Note that we ignore the value computed by the body, but don't + // allow an error. + if (Body->Codegen() == 0) + return 0; + + // Emit the step value. + Value *StepVal; + if (Step) { + StepVal = Step->Codegen(); + if (StepVal == 0) return 0; + } else { + // If not specified, use 1.0. + StepVal = ConstantFP::get(getGlobalContext(), APFloat(1.0)); + } + + Value *NextVar = Builder.CreateFAdd(Variable, StepVal, "nextvar"); + + // Compute the end condition. + Value *EndCond = End->Codegen(); + if (EndCond == 0) return EndCond; + + // Convert condition to a bool by comparing equal to 0.0. + EndCond = Builder.CreateFCmpONE(EndCond, + ConstantFP::get(getGlobalContext(), APFloat(0.0)), + "loopcond"); + + // Create the "after loop" block and insert it. + BasicBlock *LoopEndBB = Builder.GetInsertBlock(); + BasicBlock *AfterBB = BasicBlock::Create(getGlobalContext(), "afterloop", TheFunction); + + // Insert the conditional branch into the end of LoopEndBB. + Builder.CreateCondBr(EndCond, LoopBB, AfterBB); + + // Any new code will be inserted in AfterBB. + Builder.SetInsertPoint(AfterBB); + + // Add a new entry to the PHI node for the backedge. + Variable->addIncoming(NextVar, LoopEndBB); + + // Restore the unshadowed variable. + if (OldVal) + NamedValues[VarName] = OldVal; + else + NamedValues.erase(VarName); + + + // for expr always returns 0.0. + return Constant::getNullValue(Type::getDoubleTy(getGlobalContext())); + } + + Function *PrototypeAST::Codegen() { + // Make the function type: double(double,double) etc. + std::vector Doubles(Args.size(), + Type::getDoubleTy(getGlobalContext())); + FunctionType *FT = FunctionType::get(Type::getDoubleTy(getGlobalContext()), + Doubles, false); + + Function *F = Function::Create(FT, Function::ExternalLinkage, Name, TheModule); + + // If F conflicted, there was already something named 'Name'. If it has a + // body, don't allow redefinition or reextern. + if (F->getName() != Name) { + // Delete the one we just made and get the existing one. + F->eraseFromParent(); + F = TheModule->getFunction(Name); + + // If F already has a body, reject this. + if (!F->empty()) { + ErrorF("redefinition of function"); + return 0; + } + + // If F took a different number of args, reject. + if (F->arg_size() != Args.size()) { + ErrorF("redefinition of function with different # args"); + return 0; + } + } + + // Set names for all arguments. + unsigned Idx = 0; + for (Function::arg_iterator AI = F->arg_begin(); Idx != Args.size(); + ++AI, ++Idx) { + AI->setName(Args[Idx]); + + // Add arguments to variable symbol table. + NamedValues[Args[Idx]] = AI; + } + + return F; + } + + Function *FunctionAST::Codegen() { + NamedValues.clear(); + + Function *TheFunction = Proto->Codegen(); + if (TheFunction == 0) + return 0; + + // Create a new basic block to start insertion into. + BasicBlock *BB = BasicBlock::Create(getGlobalContext(), "entry", TheFunction); + Builder.SetInsertPoint(BB); + + if (Value *RetVal = Body->Codegen()) { + // Finish off the function. + Builder.CreateRet(RetVal); + + // Validate the generated code, checking for consistency. + verifyFunction(*TheFunction); + + // Optimize the function. + TheFPM->run(*TheFunction); + + return TheFunction; + } + + // Error reading body, remove function. + TheFunction->eraseFromParent(); + return 0; + } + + //===----------------------------------------------------------------------===// + // Top-Level parsing and JIT Driver + //===----------------------------------------------------------------------===// + + static ExecutionEngine *TheExecutionEngine; + + static void HandleDefinition() { + if (FunctionAST *F = ParseDefinition()) { + if (Function *LF = F->Codegen()) { + fprintf(stderr, "Read function definition:"); + LF->dump(); + } + } else { + // Skip token for error recovery. + getNextToken(); + } + } + + static void HandleExtern() { + if (PrototypeAST *P = ParseExtern()) { + if (Function *F = P->Codegen()) { + fprintf(stderr, "Read extern: "); + F->dump(); + } + } else { + // Skip token for error recovery. + getNextToken(); + } + } + + static void HandleTopLevelExpression() { + // Evaluate a top-level expression into an anonymous function. + if (FunctionAST *F = ParseTopLevelExpr()) { + if (Function *LF = F->Codegen()) { + // JIT the function, returning a function pointer. + void *FPtr = TheExecutionEngine->getPointerToFunction(LF); + + // Cast it to the right type (takes no arguments, returns a double) so we + // can call it as a native function. + double (*FP)() = (double (*)())(intptr_t)FPtr; + fprintf(stderr, "Evaluated to %f\n", FP()); + } + } else { + // Skip token for error recovery. + getNextToken(); + } + } + + /// top ::= definition | external | expression | ';' + static void MainLoop() { + while (1) { + fprintf(stderr, "ready> "); + switch (CurTok) { + case tok_eof: return; + case ';': getNextToken(); break; // ignore top-level semicolons. + case tok_def: HandleDefinition(); break; + case tok_extern: HandleExtern(); break; + default: HandleTopLevelExpression(); break; + } + } + } + + //===----------------------------------------------------------------------===// + // "Library" functions that can be "extern'd" from user code. + //===----------------------------------------------------------------------===// + + /// putchard - putchar that takes a double and returns 0. + extern "C" + double putchard(double X) { + putchar((char)X); + return 0; + } + + //===----------------------------------------------------------------------===// + // Main driver code. + //===----------------------------------------------------------------------===// + + int main() { + InitializeNativeTarget(); + LLVMContext &Context = getGlobalContext(); + + // Install standard binary operators. + // 1 is lowest precedence. + BinopPrecedence['<'] = 10; + BinopPrecedence['+'] = 20; + BinopPrecedence['-'] = 20; + BinopPrecedence['*'] = 40; // highest. + + // Prime the first token. + fprintf(stderr, "ready> "); + getNextToken(); + + // Make the module, which holds all the code. + TheModule = new Module("my cool jit", Context); + + // Create the JIT. This takes ownership of the module. + std::string ErrStr; + TheExecutionEngine = EngineBuilder(TheModule).setErrorStr(&ErrStr).create(); + if (!TheExecutionEngine) { + fprintf(stderr, "Could not create ExecutionEngine: %s\n", ErrStr.c_str()); + exit(1); + } + + FunctionPassManager OurFPM(TheModule); + + // Set up the optimizer pipeline. Start with registering info about how the + // target lays out data structures. + OurFPM.add(new DataLayout(*TheExecutionEngine->getDataLayout())); + // Provide basic AliasAnalysis support for GVN. + OurFPM.add(createBasicAliasAnalysisPass()); + // Do simple "peephole" optimizations and bit-twiddling optzns. + OurFPM.add(createInstructionCombiningPass()); + // Reassociate expressions. + OurFPM.add(createReassociatePass()); + // Eliminate Common SubExpressions. + OurFPM.add(createGVNPass()); + // Simplify the control flow graph (deleting unreachable blocks, etc). + OurFPM.add(createCFGSimplificationPass()); + + OurFPM.doInitialization(); + + // Set the global so the code gen can use this. + TheFPM = &OurFPM; + + // Run the main "interpreter loop" now. + MainLoop(); + + TheFPM = 0; + + // Print out all of the generated code. + TheModule->dump(); + + return 0; + } + +`Next: Extending the language: user-defined operators `_ + -- cgit v1.2.3