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author | Chris Lattner <sabre@nondot.org> | 2007-11-13 07:06:30 +0000 |
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committer | Chris Lattner <sabre@nondot.org> | 2007-11-13 07:06:30 +0000 |
commit | 41fcea3bdb0b05f16bbb6413370079e0d096578e (patch) | |
tree | b5bf4f143cb5d5fcd02e4029c61b390c3fc9e332 /docs/tutorial | |
parent | 0f8d9c04d9feef86cee35cf5fecfb348a6b3de50 (diff) | |
download | external_llvm-41fcea3bdb0b05f16bbb6413370079e0d096578e.zip external_llvm-41fcea3bdb0b05f16bbb6413370079e0d096578e.tar.gz external_llvm-41fcea3bdb0b05f16bbb6413370079e0d096578e.tar.bz2 |
Many typos, grammaro, and wording fixes. Patch by
Kelly Wilson, thanks!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44043 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/tutorial')
-rw-r--r-- | docs/tutorial/LangImpl3.html | 59 | ||||
-rw-r--r-- | docs/tutorial/LangImpl4.html | 55 | ||||
-rw-r--r-- | docs/tutorial/LangImpl5.html | 52 |
3 files changed, 81 insertions, 85 deletions
diff --git a/docs/tutorial/LangImpl3.html b/docs/tutorial/LangImpl3.html index 3d19188..0258961 100644 --- a/docs/tutorial/LangImpl3.html +++ b/docs/tutorial/LangImpl3.html @@ -41,7 +41,7 @@ Support</li> <p>Welcome to Chapter 3 of the "<a href="index.html">Implementing a language with LLVM</a>" tutorial. This chapter shows you how to transform the <a -href="LangImpl2.html">Abstract Syntax Tree built in Chapter 2</a> into LLVM IR. +href="LangImpl2.html">Abstract Syntax Tree</a>, built in Chapter 2, into LLVM IR. This will teach you a little bit about how LLVM does things, as well as demonstrate how easy it is to use. It's much more work to build a lexer and parser than it is to generate LLVM IR code. :) @@ -79,14 +79,14 @@ public: </pre> </div> -<p>The Codegen() method says to emit IR for that AST node and all things it +<p>The Codegen() method says to emit IR for that AST node along with all the things it depends on, and they all return an LLVM Value object. "Value" is the class used to represent a "<a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single Assignment (SSA)</a> register" or "SSA value" in LLVM. The most distinct aspect of SSA values is that their value is computed as the related instruction executes, and it does not get a new value until (and if) the instruction -re-executes. In order words, there is no way to "change" an SSA value. For +re-executes. In other words, there is no way to "change" an SSA value. For more information, please read up on <a href="http://en.wikipedia.org/wiki/Static_single_assignment_form">Static Single Assignment</a> - the concepts are really quite natural once you grok them.</p> @@ -97,7 +97,7 @@ this. Again, this tutorial won't dwell on good software engineering practices: for our purposes, adding a virtual method is simplest.</p> <p>The -second thing we want is an "Error" method like we used for parser, which will +second thing we want is an "Error" method like we used for the parser, which will be used to report errors found during code generation (for example, use of an undeclared parameter):</p> @@ -144,7 +144,7 @@ has already been done, and we'll just use it to emit code. <div class="doc_text"> -<p>Generating LLVM code for expression nodes is very straight-forward: less +<p>Generating LLVM code for expression nodes is very straightforward: less than 45 lines of commented code for all four of our expression nodes. First, we'll do numeric literals:</p> @@ -174,7 +174,7 @@ Value *VariableExprAST::Codegen() { </pre> </div> -<p>References to variables are also quite simple here. In the simple version +<p>References to variables are also quite simple using LLVM. In the simple version of Kaleidoscope, we assume that the variable has already been emited somewhere and its value is available. In practice, the only values that can be in the <tt>NamedValues</tt> map are function arguments. This @@ -211,9 +211,9 @@ right-hand side, then we compute the result of the binary expression. In this code, we do a simple switch on the opcode to create the right LLVM instruction. </p> -<p>In this example, the LLVM builder class is starting to show its value. -Because it knows where to insert the newly created instruction, you just have to -specify what instruction to create (e.g. with <tt>CreateAdd</tt>), which +<p>In the example above, the LLVM builder class is starting to show its value. +LLVMBuilder knows where to insert the newly created instruction, all you have to +do is specify what instruction to create (e.g. with <tt>CreateAdd</tt>), which operands to use (<tt>L</tt> and <tt>R</tt> here) and optionally provide a name for the generated instruction. One nice thing about LLVM is that the name is just a hint: if there are multiple additions in a single function, the first @@ -221,17 +221,16 @@ will be named "addtmp" and the second will be "autorenamed" by adding a suffix, giving it a name like "addtmp42". Local value names for instructions are purely optional, but it makes it much easier to read the IR dumps.</p> -<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained with +<p><a href="../LangRef.html#instref">LLVM instructions</a> are constrained by strict rules: for example, the Left and Right operators of -an <a href="../LangRef.html#i_add">add instruction</a> have to have the same -type, and that the result type of the add must match the operand types. Because +an <a href="../LangRef.html#i_add">add instruction</a> must have the same +type, and the result type of the add must match the operand types. Because all values in Kaleidoscope are doubles, this makes for very simple code for add, sub and mul.</p> <p>On the other hand, LLVM specifies that the <a href="../LangRef.html#i_fcmp">fcmp instruction</a> always returns an 'i1' value -(a one bit integer). However, Kaleidoscope wants the value to be a 0.0 or 1.0 -value. In order to get these semantics, we combine the fcmp instruction with +(a one bit integer). The problem with this is that Kaleidoscope wants the value to be a 0.0 or 1.0 value. In order to get these semantics, we combine the fcmp instruction with a <a href="../LangRef.html#i_uitofp">uitofp instruction</a>. This instruction converts its input integer into a floating point value by treating the input as an unsigned value. In contrast, if we used the <a @@ -261,8 +260,8 @@ Value *CallExprAST::Codegen() { </pre> </div> -<p>Code generation for function calls is quite straight-forward with LLVM. The -code above first looks the name of the function up in the LLVM Module's symbol +<p>Code generation for function calls is quite straightforward with LLVM. The +code above initially does a function name lookup in the LLVM Module's symbol table. Recall that the LLVM Module is the container that holds all of the functions we are JIT'ing. By giving each function the same name as what the user specifies, we can use the LLVM symbol table to resolve function names for @@ -271,8 +270,8 @@ us.</p> <p>Once we have the function to call, we recursively codegen each argument that is to be passed in, and create an LLVM <a href="../LangRef.html#i_call">call instruction</a>. Note that LLVM uses the native C calling conventions by -default, allowing these calls to call into standard library functions like -"sin" and "cos" with no additional effort.</p> +default, allowing these calls to also call into standard library functions like +"sin" and "cos", with no additional effort.</p> <p>This wraps up our handling of the four basic expressions that we have so far in Kaleidoscope. Feel free to go in and add some more. For example, by @@ -321,7 +320,7 @@ this). Note that Types in LLVM are uniqued just like Constants are, so you don't "new" a type, you "get" it.</p> <p>The final line above actually creates the function that the prototype will -correspond to. This indicates which type, linkage, and name to use, and which +correspond to. This indicates the type, linkage and name to use, as well as which module to insert into. "<a href="LangRef.html#linkage">external linkage</a>" means that the function may be defined outside the current module and/or that it is callable by functions outside the module. The Name passed in is the name the @@ -343,7 +342,7 @@ above.</p> <p>The Module symbol table works just like the Function symbol table when it comes to name conflicts: if a new function is created with a name was previously added to the symbol table, it will get implicitly renamed when added to the -Module. The code above exploits this fact to tell if there was a previous +Module. The code above exploits this fact to determine if there was a previous definition of this function.</p> <p>In Kaleidoscope, I choose to allow redefinitions of functions in two cases: @@ -403,7 +402,7 @@ definition and this one match up. If not, we emit an error.</p> </div> <p>The last bit of code for prototypes loops over all of the arguments in the -function, setting the name of the LLVM Argument objects to match and registering +function, setting the name of the LLVM Argument objects to match, and registering the arguments in the <tt>NamedValues</tt> map for future use by the <tt>VariableExprAST</tt> AST node. Once this is set up, it returns the Function object to the caller. Note that we don't check for conflicting @@ -421,8 +420,8 @@ Function *FunctionAST::Codegen() { </pre> </div> -<p>Code generation for function definitions starts out simply enough: first we -codegen the prototype (Proto) and verify that it is ok. We also clear out the +<p>Code generation for function definitions starts out simply enough: we just +codegen the prototype (Proto) and verify that it is ok. We then clear out the <tt>NamedValues</tt> map to make sure that there isn't anything in it from the last function we compiled. Code generation of the prototype ensures that there is an LLVM Function object that is ready to go for us.</p> @@ -445,7 +444,7 @@ the end of the new basic block. Basic blocks in LLVM are an important part of functions that define the <a href="http://en.wikipedia.org/wiki/Control_flow_graph">Control Flow Graph</a>. Since we don't have any control flow, our functions will only contain one -block so far. We'll fix this in <a href="LangImpl5.html">Chapter 5</a> :).</p> +block at this point. We'll fix this in <a href="LangImpl5.html">Chapter 5</a> :).</p> <div class="doc_code"> <pre> @@ -465,7 +464,7 @@ the root expression of the function. If no error happens, this emits code to compute the expression into the entry block and returns the value that was computed. Assuming no error, we then create an LLVM <a href="../LangRef.html#i_ret">ret instruction</a>, which completes the function. -Once the function is built, we call the <tt>verifyFunction</tt> function, which +Once the function is built, we call <tt>verifyFunction</tt>, which is provided by LLVM. This function does a variety of consistency checks on the generated code, to determine if our compiler is doing everything right. Using this is important: it can catch a lot of bugs. Once the function is finished @@ -481,13 +480,13 @@ and validated, we return it.</p> </div> <p>The only piece left here is handling of the error case. For simplicity, we -simply handle this by deleting the function we produced with the +handle this by merely deleting the function we produced with the <tt>eraseFromParent</tt> method. This allows the user to redefine a function that they incorrectly typed in before: if we didn't delete it, it would live in the symbol table, with a body, preventing future redefinition.</p> -<p>This code does have a bug though. Since the <tt>PrototypeAST::Codegen</tt> -can return a previously defined forward declaration, this can actually delete +<p>This code does have a bug, though. Since the <tt>PrototypeAST::Codegen</tt> +can return a previously defined forward declaration, our code can actually delete a forward declaration. There are a number of ways to fix this bug, see what you can come up with! Here is a testcase:</p> @@ -571,7 +570,7 @@ entry: <p>This shows some function calls. Note that this function will take a long time to execute if you call it. In the future we'll add conditional control -flow to make recursion actually be useful :).</p> +flow to actually make recursion useful :).</p> <div class="doc_code"> <pre> @@ -636,7 +635,7 @@ entry: generated. Here you can see the big picture with all the functions referencing each other.</p> -<p>This wraps up this chapter of the Kaleidoscope tutorial. Up next we'll +<p>This wraps up the third chapter of the Kaleidoscope tutorial. Up next, we'll describe how to <a href="LangImpl4.html">add JIT codegen and optimizer support</a> to this so we can actually start running code!</p> diff --git a/docs/tutorial/LangImpl4.html b/docs/tutorial/LangImpl4.html index 04475e6..378b29b 100644 --- a/docs/tutorial/LangImpl4.html +++ b/docs/tutorial/LangImpl4.html @@ -42,8 +42,8 @@ Flow</li> with LLVM</a>" tutorial. Chapters 1-3 described the implementation of a simple language and added support for generating LLVM IR. This chapter describes two new techniques: adding optimizer support to your language, and adding JIT -compiler support. This shows how to get nice efficient code for your -language.</p> +compiler support. These additions will demonstrate how to get nice, efficient code +for the Kaleidoscope language.</p> </div> @@ -72,14 +72,13 @@ entry: </pre> </div> -<p>This code is a very very literal transcription of the AST built by parsing -our code, and as such, lacks optimizations like constant folding (we'd like to -get "<tt>add x, 3.0</tt>" in the example above) as well as other more important -optimizations. Constant folding in particular is a very common and very +<p>This code is a very, very literal transcription of the AST built by parsing +the input. As such, this transcription lacks optimizations like constant folding (we'd like to get "<tt>add x, 3.0</tt>" in the example above) as well as other more important +optimizations. Constant folding, in particular, is a very common and very important optimization: so much so that many language implementors implement constant folding support in their AST representation.</p> -<p>With LLVM, you don't need to. Since all calls to build LLVM IR go through +<p>With LLVM, you don't need this support in the AST. Since all calls to build LLVM IR go through the LLVM builder, it would be nice if the builder itself checked to see if there was a constant folding opportunity when you call it. If so, it could just do the constant fold and return the constant instead of creating an instruction. @@ -93,9 +92,9 @@ static LLVMFoldingBuilder Builder; </div> <p>All we did was switch from <tt>LLVMBuilder</tt> to -<tt>LLVMFoldingBuilder</tt>. Though we change no other code, now all of our -instructions are implicitly constant folded without us having to do anything -about it. For example, our example above now compiles to:</p> +<tt>LLVMFoldingBuilder</tt>. Though we change no other code, we now have all of our +instructions implicitly constant folded without us having to do anything +about it. For example, the input above now compiles to:</p> <div class="doc_code"> <pre> @@ -153,7 +152,7 @@ range of optimizations that you can use, in the form of "passes".</p> <div class="doc_text"> -<p>LLVM provides many optimization passes which do many different sorts of +<p>LLVM provides many optimization passes, which do many different sorts of things and have different tradeoffs. Unlike other systems, LLVM doesn't hold to the mistaken notion that one set of optimizations is right for all languages and for all situations. LLVM allows a compiler implementor to make complete @@ -165,7 +164,7 @@ across as large of body of code as they can (often a whole file, but if run at link time, this can be a substantial portion of the whole program). It also supports and includes "per-function" passes which just operate on a single function at a time, without looking at other functions. For more information -on passes and how the get run, see the <a href="../WritingAnLLVMPass.html">How +on passes and how they are run, see the <a href="../WritingAnLLVMPass.html">How to Write a Pass</a> document and the <a href="../Passes.html">List of LLVM Passes</a>.</p> @@ -207,13 +206,13 @@ add a set of optimizations to run. The code looks like this:</p> </pre> </div> -<p>This code defines two objects, a <tt>ExistingModuleProvider</tt> and a +<p>This code defines two objects, an <tt>ExistingModuleProvider</tt> and a <tt>FunctionPassManager</tt>. The former is basically a wrapper around our <tt>Module</tt> that the PassManager requires. It provides certain flexibility -that we're not going to take advantage of here, so I won't dive into what it is -all about.</p> +that we're not going to take advantage of here, so I won't dive into any details +about it.</p> -<p>The meat of the matter is the definition of "<tt>OurFPM</tt>". It +<p>The meat of the matter here, is the definition of "<tt>OurFPM</tt>". It requires a pointer to the <tt>Module</tt> (through the <tt>ModuleProvider</tt>) to construct itself. Once it is set up, we use a series of "add" calls to add a bunch of LLVM passes. The first pass is basically boilerplate, it adds a pass @@ -223,7 +222,7 @@ which we will get to in the next section.</p> <p>In this case, we choose to add 4 optimization passes. The passes we chose here are a pretty standard set of "cleanup" optimizations that are useful for -a wide variety of code. I won't delve into what they do, but believe me that +a wide variety of code. I won't delve into what they do but, believe me, they are a good starting place :).</p> <p>Once the PassManager is set up, we need to make use of it. We do this by @@ -247,7 +246,7 @@ running it after our newly created function is constructed (in </pre> </div> -<p>As you can see, this is pretty straight-forward. The +<p>As you can see, this is pretty straightforward. The <tt>FunctionPassManager</tt> optimizes and updates the LLVM Function* in place, improving (hopefully) its body. With this in place, we can try our test above again:</p> @@ -271,7 +270,7 @@ add instruction from every execution of this function.</p> <p>LLVM provides a wide variety of optimizations that can be used in certain circumstances. Some <a href="../Passes.html">documentation about the various passes</a> is available, but it isn't very complete. Another good source of -ideas is to look at the passes that <tt>llvm-gcc</tt> or +ideas can come from looking at the passes that <tt>llvm-gcc</tt> or <tt>llvm-ld</tt> run to get started. The "<tt>opt</tt>" tool allows you to experiment with passes from the command line, so you can see if they do anything.</p> @@ -324,7 +323,7 @@ for you if one is available for your platform, otherwise it will fall back to the interpreter.</p> <p>Once the <tt>ExecutionEngine</tt> is created, the JIT is ready to be used. -There are a variety of APIs that are useful, but the most simple one is the +There are a variety of APIs that are useful, but the simplest one is the "<tt>getPointerToFunction(F)</tt>" method. This method JIT compiles the specified LLVM Function and returns a function pointer to the generated machine code. In our case, this means that we can change the code that parses a @@ -353,7 +352,7 @@ static void HandleTopLevelExpression() { function that takes no arguments and returns the computed double. Because the LLVM JIT compiler matches the native platform ABI, this means that you can just cast the result pointer to a function pointer of that type and call it directly. -As such, there is no difference between JIT compiled code and native machine +This means, there is no difference between JIT compiled code and native machine code that is statically linked into your application.</p> <p>With just these two changes, lets see how Kaleidoscope works now!</p> @@ -372,7 +371,7 @@ entry: <p>Well this looks like it is basically working. The dump of the function shows the "no argument function that always returns double" that we synthesize -for each top level expression that is typed it. This demonstrates very basic +for each top level expression that is typed in. This demonstrates very basic functionality, but can we do more?</p> <div class="doc_code"> @@ -397,19 +396,19 @@ entry: </pre> </div> -<p>This illustrates that we can now call user code, but it is a bit subtle what -is going on here. Note that we only invoke the JIT on the anonymous functions -that <em>calls testfunc</em>, but we never invoked it on <em>testfunc -itself</em>.</p> +<p>This illustrates that we can now call user code, but there is something a bit subtle +going on here. Note that we only invoke the JIT on the anonymous functions +that <em>call testfunc</em>, but we never invoked it on <em>testfunc +</em>itself.</p> -<p>What actually happened here is that the anonymous function is +<p>What actually happened here is that the anonymous function was JIT'd when requested. When the Kaleidoscope app calls through the function pointer that is returned, the anonymous function starts executing. It ends up making the call to the "testfunc" function, and ends up in a stub that invokes the JIT, lazily, on testfunc. Once the JIT finishes lazily compiling testfunc, it returns and the code re-executes the call.</p> -<p>In summary, the JIT will lazily JIT code on the fly as it is needed. The +<p>In summary, the JIT will lazily JIT code, on the fly, as it is needed. The JIT provides a number of other more advanced interfaces for things like freeing allocated machine code, rejit'ing functions to update them, etc. However, even with this simple code, we get some surprisingly powerful capabilities - check diff --git a/docs/tutorial/LangImpl5.html b/docs/tutorial/LangImpl5.html index 837815a..9826844 100644 --- a/docs/tutorial/LangImpl5.html +++ b/docs/tutorial/LangImpl5.html @@ -55,7 +55,7 @@ User-defined Operators</li> <p>Welcome to Chapter 5 of the "<a href="index.html">Implementing a language with LLVM</a>" tutorial. Parts 1-4 described the implementation of the simple -Kaleidoscope language and included support for generating LLVM IR, following by +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 @@ -71,13 +71,13 @@ have an if/then/else expression plus a simple 'for' loop.</p> <div class="doc_text"> <p> -Extending Kaleidoscope to support if/then/else is quite straight-forward. It +Extending Kaleidoscope to support if/then/else is quite straightforward. It basically requires adding lexer 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.</p> -<p>Before we get going on "how" we do this extension, lets talk about what we +<p>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: </p> @@ -97,7 +97,7 @@ 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.</p> -<p>The semantics of the if/then/else expression is that it first evaluates the +<p>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 @@ -105,7 +105,7 @@ the condition is false, the second subexpression is evaluated and returned. Since Kaleidoscope allows side-effects, this behavior is important to nail down. </p> -<p>Now that we know what we want, lets break this down into its constituent +<p>Now that we know what we "want", lets break this down into its constituent pieces.</p> </div> @@ -118,7 +118,7 @@ If/Then/Else</a></div> <div class="doc_text"> -<p>The lexer extensions are straight-forward. First we add new enum values +<p>The lexer extensions are straightforward. First we add new enum values for the relevant tokens:</p> <div class="doc_code"> @@ -128,7 +128,7 @@ for the relevant tokens:</p> </pre> </div> -<p>Once we have that, we recognize the new keywords in the lexer, pretty simple +<p>Once we have that, we recognize the new keywords in the lexer. This is pretty simple stuff:</p> <div class="doc_code"> @@ -179,7 +179,7 @@ If/Then/Else</a></div> <div class="doc_text"> <p>Now that we have the relevant tokens coming from the lexer and we have the -AST node to build, our parsing logic is relatively straight-forward. First we +AST node to build, our parsing logic is relatively straightforward. First we define a new parsing function:</p> <div class="doc_code"> @@ -296,14 +296,14 @@ height="315"></center> inserting actual calls into the code and recompiling or by calling these in the debugger. LLVM has many nice features for visualizing various graphs.</p> -<p>Coming back to the generated code, it is fairly simple: the entry block +<p>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 "<tt><a href="../LangRef.html#i_fcmp">fcmp</a> one</tt>" 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.</p> -<p>Once the then/else blocks is finished executing, they both branch back to the +<p>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?</p> @@ -320,25 +320,25 @@ 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".</p> -<p>At this point, you are probably starting to think "oh no! this means my +<p>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 <em>not</em> 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 in your average imperative +sorts of values that float around in code written for your average imperative programming language that might need Phi nodes:</p> <ol> <li>Code that involves user variables: <tt>x = 1; x = x + 1; </tt></li> -<li>Values that are implicit in the structure of your AST, such as the phi node +<li>Values that are implicit in the structure of your AST, such as the Phi node in this case.</li> </ol> <p>In <a href="LangImpl7.html">Chapter 7</a> 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 them. 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 +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.</p> @@ -369,7 +369,7 @@ Value *IfExprAST::Codegen() { </pre> </div> -<p>This code is straight-forward and similar to what we saw before. We emit the +<p>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.</p> @@ -395,7 +395,7 @@ block for its "parent" (the function it is currently embedded into).</p> <p>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 onto the end of the specified function. The +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.</p> <p>Once the blocks are created, we can emit the conditional branch that chooses @@ -427,7 +427,7 @@ insertion point to be at the end of the specified block. However, since the block. :)</p> <p>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 +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 <a href="../LangRef.html#functionstructure">requires all basic blocks to be "terminated"</a> with a <a href="../LangRef.html#terminators">control flow @@ -439,7 +439,7 @@ violate this rule, the verifier will emit an error.</p> 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 +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 @@ -492,7 +492,7 @@ 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.</p> -<p>Overall, we now have the ability to execution conditional code in +<p>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...</p> @@ -571,7 +571,7 @@ the 'for' Loop</a></div> <div class="doc_text"> -<p>The AST node is similarly simple. It basically boils down to capturing +<p>The AST node is just as simple. It basically boils down to capturing the variable name and the constituent expressions in the node.</p> <div class="doc_code"> @@ -704,7 +704,7 @@ the 'for' Loop</a></div> <div class="doc_text"> -<p>The first part of codegen is very simple: we just output the start expression +<p>The first part of Codegen is very simple: we just output the start expression for the loop value:</p> <div class="doc_code"> @@ -804,7 +804,7 @@ references to it will naturally find it in the symbol table.</p> </div> <p>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. '<tt>NextVar</tt>' +variable by adding the step value, or 1.0 if it isn't present. '<tt>NextVar</tt>' will be the value of the loop variable on the next iteration of the loop.</p> <div class="doc_code"> @@ -839,8 +839,7 @@ statement.</p> </div> <p>With the code for the body of the loop complete, we just need to finish up -the control flow for it. This remembers the end block (for the phi node), then -creates the block for the loop exit ("afterloop"). Based on the value of the +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.</p> @@ -869,8 +868,7 @@ the for loop. Finally, code generation of the for loop always returns 0.0, so that is what we return from <tt>ForExprAST::Codegen</tt>.</p> <p>With this, we conclude the "adding control flow to Kaleidoscope" chapter of -the tutorial. 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 +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 <a href="LangImpl6.html">user-defined operators</a> to our poor innocent language.</p> |