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diff --git a/docs/tutorial/OCamlLangImpl3.rst b/docs/tutorial/OCamlLangImpl3.rst new file mode 100644 index 0000000..d2a47b4 --- /dev/null +++ b/docs/tutorial/OCamlLangImpl3.rst @@ -0,0 +1,964 @@ +======================================== +Kaleidoscope: Code generation to LLVM IR +======================================== + +.. contents:: + :local: + +Written by `Chris Lattner <mailto:sabre@nondot.org>`_ and `Erick +Tryzelaar <mailto:idadesub@users.sourceforge.net>`_ + +Chapter 3 Introduction +====================== + +Welcome to Chapter 3 of the "`Implementing a language with +LLVM <index.html>`_" tutorial. This chapter shows you how to transform +the `Abstract Syntax Tree <OCamlLangImpl2.html>`_, 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. :) + +**Please note**: the code in this chapter and later require LLVM 2.3 or +LLVM SVN to work. LLVM 2.2 and before will not work with it. + +Code Generation Setup +===================== + +In order to generate LLVM IR, we want some simple setup to get started. +First we define virtual code generation (codegen) methods in each AST +class: + +.. code-block:: ocaml + + let rec codegen_expr = function + | Ast.Number n -> ... + | Ast.Variable name -> ... + +The ``Codegen.codegen_expr`` function 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 "`Static Single +Assignment +(SSA) <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_ +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 other words, there is no way to "change" an SSA value. For more +information, please read up on `Static Single +Assignment <http://en.wikipedia.org/wiki/Static_single_assignment_form>`_ +- the concepts are really quite natural once you grok them. + +The second thing we want is an "Error" exception like we used for the +parser, which will be used to report errors found during code generation +(for example, use of an undeclared parameter): + +.. code-block:: ocaml + + exception Error of string + + let context = global_context () + let the_module = create_module context "my cool jit" + let builder = builder context + let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 + let double_type = double_type context + +The static variables will be used during code generation. +``Codgen.the_module`` is the LLVM construct that contains all of the +functions and global variables in a chunk of code. In many ways, it is +the top-level structure that the LLVM IR uses to contain code. + +The ``Codegen.builder`` object is a helper object that makes it easy to +generate LLVM instructions. Instances of the +```IRBuilder`` <http://llvm.org/doxygen/IRBuilder_8h-source.html>`_ +class keep track of the current place to insert instructions and has +methods to create new instructions. + +The ``Codegen.named_values`` map keeps track of which values are defined +in the current scope and what their LLVM representation is. (In other +words, it is a symbol table for the code). In this form of Kaleidoscope, +the only things that can be referenced are function parameters. As such, +function parameters will be in this map when generating code for their +function body. + +With these basics in place, we can start talking about how to generate +code for each expression. Note that this assumes that the +``Codgen.builder`` has been set up to generate code *into* something. +For now, we'll assume that this has already been done, and we'll just +use it to emit code. + +Expression Code Generation +========================== + +Generating LLVM code for expression nodes is very straightforward: less +than 30 lines of commented code for all four of our expression nodes. +First we'll do numeric literals: + +.. code-block:: ocaml + + | Ast.Number n -> const_float double_type n + +In the LLVM IR, numeric constants are represented with the +``ConstantFP`` class, which holds the numeric value in an ``APFloat`` +internally (``APFloat`` has the capability of holding floating point +constants of Arbitrary Precision). This code basically just creates +and returns a ``ConstantFP``. Note that in the LLVM IR that constants +are all uniqued together and shared. For this reason, the API uses "the +foo::get(..)" idiom instead of "new foo(..)" or "foo::Create(..)". + +.. code-block:: ocaml + + | Ast.Variable name -> + (try Hashtbl.find named_values name with + | Not_found -> raise (Error "unknown variable name")) + +References to variables are also quite simple using LLVM. In the simple +version of Kaleidoscope, we assume that the variable has already been +emitted somewhere and its value is available. In practice, the only +values that can be in the ``Codegen.named_values`` map are function +arguments. This code simply checks to see that the specified name is in +the map (if not, an unknown variable is being referenced) and returns +the value for it. In future chapters, we'll add support for `loop +induction variables <LangImpl5.html#for>`_ in the symbol table, and for +`local variables <LangImpl7.html#localvars>`_. + +.. code-block:: ocaml + + | Ast.Binary (op, lhs, rhs) -> + let lhs_val = codegen_expr lhs in + let rhs_val = codegen_expr rhs in + begin + match op with + | '+' -> build_fadd lhs_val rhs_val "addtmp" builder + | '-' -> build_fsub lhs_val rhs_val "subtmp" builder + | '*' -> build_fmul lhs_val rhs_val "multmp" builder + | '<' -> + (* Convert bool 0/1 to double 0.0 or 1.0 *) + let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in + build_uitofp i double_type "booltmp" builder + | _ -> raise (Error "invalid binary operator") + end + +Binary operators start to get more interesting. The basic idea here is +that we recursively emit code for the left-hand side of the expression, +then the 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. + +In the example above, the LLVM builder class is starting to show its +value. IRBuilder knows where to insert the newly created instruction, +all you have to do is specify what instruction to create (e.g. with +``Llvm.create_add``), which operands to use (``lhs`` and ``rhs`` here) +and optionally provide a name for the generated instruction. + +One nice thing about LLVM is that the name is just a hint. For instance, +if the code above emits multiple "addtmp" variables, LLVM will +automatically provide each one with an increasing, unique numeric +suffix. Local value names for instructions are purely optional, but it +makes it much easier to read the IR dumps. + +`LLVM instructions <../LangRef.html#instref>`_ are constrained by strict +rules: for example, the Left and Right operators of an `add +instruction <../LangRef.html#i_add>`_ 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. + +On the other hand, LLVM specifies that the `fcmp +instruction <../LangRef.html#i_fcmp>`_ always returns an 'i1' value (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 `uitofp +instruction <../LangRef.html#i_uitofp>`_. 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 `sitofp +instruction <../LangRef.html#i_sitofp>`_, the Kaleidoscope '<' operator +would return 0.0 and -1.0, depending on the input value. + +.. code-block:: ocaml + + | Ast.Call (callee, args) -> + (* Look up the name in the module table. *) + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown function referenced") + in + let params = params callee in + + (* If argument mismatch error. *) + if Array.length params == Array.length args then () else + raise (Error "incorrect # arguments passed"); + let args = Array.map codegen_expr args in + build_call callee args "calltmp" builder + +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 us. + +Once we have the function to call, we recursively codegen each argument +that is to be passed in, and create an LLVM `call +instruction <../LangRef.html#i_call>`_. Note that LLVM uses the native C +calling conventions by default, allowing these calls to also call into +standard library functions like "sin" and "cos", with no additional +effort. + +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 browsing the `LLVM language reference <../LangRef.html>`_ you'll find +several other interesting instructions that are really easy to plug into +our basic framework. + +Function Code Generation +======================== + +Code generation for prototypes and functions must handle a number of +details, which make their code less beautiful than expression code +generation, but allows us to illustrate some important points. First, +lets talk about code generation for prototypes: they are used both for +function bodies and external function declarations. The code starts +with: + +.. code-block:: ocaml + + let codegen_proto = function + | Ast.Prototype (name, args) -> + (* Make the function type: double(double,double) etc. *) + let doubles = Array.make (Array.length args) double_type in + let ft = function_type double_type doubles in + let f = + match lookup_function name the_module with + +This code packs a lot of power into a few lines. Note first that this +function returns a "Function\*" instead of a "Value\*" (although at the +moment they both are modeled by ``llvalue`` in ocaml). Because a +"prototype" really talks about the external interface for a function +(not the value computed by an expression), it makes sense for it to +return the LLVM Function it corresponds to when codegen'd. + +The call to ``Llvm.function_type`` creates the ``Llvm.llvalue`` that +should be used for a given Prototype. Since all function arguments in +Kaleidoscope are of type double, the first line creates a vector of "N" +LLVM double types. It then uses the ``Llvm.function_type`` method to +create a function type that takes "N" doubles as arguments, returns one +double as a result, and that is not vararg (that uses the function +``Llvm.var_arg_function_type``). Note that Types in LLVM are uniqued +just like ``Constant``'s are, so you don't "new" a type, you "get" it. + +The final line above checks if the function has already been defined in +``Codegen.the_module``. If not, we will create it. + +.. code-block:: ocaml + + | None -> declare_function name ft the_module + +This indicates the type and name to use, as well as which module to +insert into. By default we assume a function has +``Llvm.Linkage.ExternalLinkage``. "`external +linkage <LangRef.html#linkage>`_" 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 user +specified: this name is registered in "``Codegen.the_module``"s symbol +table, which is used by the function call code above. + +In Kaleidoscope, I choose to allow redefinitions of functions in two +cases: first, we want to allow 'extern'ing a function more than once, as +long as the prototypes for the externs match (since all arguments have +the same type, we just have to check that the number of arguments +match). Second, we want to allow 'extern'ing a function and then +defining a body for it. This is useful when defining mutually recursive +functions. + +.. code-block:: ocaml + + (* If 'f' conflicted, there was already something named 'name'. If it + * has a body, don't allow redefinition or reextern. *) + | Some f -> + (* If 'f' already has a body, reject this. *) + if Array.length (basic_blocks f) == 0 then () else + raise (Error "redefinition of function"); + + (* If 'f' took a different number of arguments, reject. *) + if Array.length (params f) == Array.length args then () else + raise (Error "redefinition of function with different # args"); + f + in + +In order to verify the logic above, we first check to see if the +pre-existing function is "empty". In this case, empty means that it has +no basic blocks in it, which means it has no body. If it has no body, it +is a forward declaration. Since we don't allow anything after a full +definition of the function, the code rejects this case. If the previous +reference to a function was an 'extern', we simply verify that the +number of arguments for that definition and this one match up. If not, +we emit an error. + +.. code-block:: ocaml + + (* Set names for all arguments. *) + Array.iteri (fun i a -> + let n = args.(i) in + set_value_name n a; + Hashtbl.add named_values n a; + ) (params f); + f + +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 the arguments in the ``Codegen.named_values`` map for +future use by the ``Ast.Variable`` variant. Once this is set up, it +returns the Function object to the caller. Note that we don't check for +conflicting argument names here (e.g. "extern foo(a b a)"). Doing so +would be very straight-forward with the mechanics we have already used +above. + +.. code-block:: ocaml + + let codegen_func = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in + +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 ``Codegen.named_values`` 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. + +.. code-block:: ocaml + + (* Create a new basic block to start insertion into. *) + let bb = append_block context "entry" the_function in + position_at_end bb builder; + + try + let ret_val = codegen_expr body in + +Now we get to the point where the ``Codegen.builder`` is set up. The +first line creates a new `basic +block <http://en.wikipedia.org/wiki/Basic_block>`_ (named "entry"), +which is inserted into ``the_function``. The second line then tells the +builder that new instructions should be inserted into the end of the new +basic block. Basic blocks in LLVM are an important part of functions +that define the `Control Flow +Graph <http://en.wikipedia.org/wiki/Control_flow_graph>`_. Since we +don't have any control flow, our functions will only contain one block +at this point. We'll fix this in `Chapter 5 <OCamlLangImpl5.html>`_ :). + +.. code-block:: ocaml + + let ret_val = codegen_expr body in + + (* Finish off the function. *) + let _ = build_ret ret_val builder in + + (* Validate the generated code, checking for consistency. *) + Llvm_analysis.assert_valid_function the_function; + + the_function + +Once the insertion point is set up, we call the ``Codegen.codegen_func`` +method for 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 `ret instruction <../LangRef.html#i_ret>`_, which completes the +function. Once the function is built, we call +``Llvm_analysis.assert_valid_function``, 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 and +validated, we return it. + +.. code-block:: ocaml + + with e -> + delete_function the_function; + raise e + +The only piece left here is handling of the error case. For simplicity, +we handle this by merely deleting the function we produced with the +``Llvm.delete_function`` 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. + +This code does have a bug, though. Since the ``Codegen.codegen_proto`` +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: + +:: + + extern foo(a b); # ok, defines foo. + def foo(a b) c; # error, 'c' is invalid. + def bar() foo(1, 2); # error, unknown function "foo" + +Driver Changes and Closing Thoughts +=================================== + +For now, code generation to LLVM doesn't really get us much, except that +we can look at the pretty IR calls. The sample code inserts calls to +Codegen into the "``Toplevel.main_loop``", and then dumps out the LLVM +IR. This gives a nice way to look at the LLVM IR for simple functions. +For example: + +:: + + ready> 4+5; + Read top-level expression: + define double @""() { + entry: + %addtmp = fadd double 4.000000e+00, 5.000000e+00 + ret double %addtmp + } + +Note how the parser turns the top-level expression into anonymous +functions for us. This will be handy when we add `JIT +support <OCamlLangImpl4.html#jit>`_ in the next chapter. Also note that +the code is very literally transcribed, no optimizations are being +performed. We will `add +optimizations <OCamlLangImpl4.html#trivialconstfold>`_ explicitly in the +next chapter. + +:: + + ready> def foo(a b) a*a + 2*a*b + b*b; + Read function definition: + define double @foo(double %a, double %b) { + entry: + %multmp = fmul double %a, %a + %multmp1 = fmul double 2.000000e+00, %a + %multmp2 = fmul double %multmp1, %b + %addtmp = fadd double %multmp, %multmp2 + %multmp3 = fmul double %b, %b + %addtmp4 = fadd double %addtmp, %multmp3 + ret double %addtmp4 + } + +This shows some simple arithmetic. Notice the striking similarity to the +LLVM builder calls that we use to create the instructions. + +:: + + ready> def bar(a) foo(a, 4.0) + bar(31337); + Read function definition: + define double @bar(double %a) { + entry: + %calltmp = call double @foo(double %a, double 4.000000e+00) + %calltmp1 = call double @bar(double 3.133700e+04) + %addtmp = fadd double %calltmp, %calltmp1 + ret double %addtmp + } + +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 actually make recursion useful :). + +:: + + ready> extern cos(x); + Read extern: + declare double @cos(double) + + ready> cos(1.234); + Read top-level expression: + define double @""() { + entry: + %calltmp = call double @cos(double 1.234000e+00) + ret double %calltmp + } + +This shows an extern for the libm "cos" function, and a call to it. + +:: + + ready> ^D + ; ModuleID = 'my cool jit' + + define double @""() { + entry: + %addtmp = fadd double 4.000000e+00, 5.000000e+00 + ret double %addtmp + } + + define double @foo(double %a, double %b) { + entry: + %multmp = fmul double %a, %a + %multmp1 = fmul double 2.000000e+00, %a + %multmp2 = fmul double %multmp1, %b + %addtmp = fadd double %multmp, %multmp2 + %multmp3 = fmul double %b, %b + %addtmp4 = fadd double %addtmp, %multmp3 + ret double %addtmp4 + } + + define double @bar(double %a) { + entry: + %calltmp = call double @foo(double %a, double 4.000000e+00) + %calltmp1 = call double @bar(double 3.133700e+04) + %addtmp = fadd double %calltmp, %calltmp1 + ret double %addtmp + } + + declare double @cos(double) + + define double @""() { + entry: + %calltmp = call double @cos(double 1.234000e+00) + ret double %calltmp + } + +When you quit the current demo, it dumps out the IR for the entire +module generated. Here you can see the big picture with all the +functions referencing each other. + +This wraps up the third chapter of the Kaleidoscope tutorial. Up next, +we'll describe how to `add JIT codegen and optimizer +support <OCamlLangImpl4.html>`_ to this so we can actually start running +code! + +Full Code Listing +================= + +Here is the complete code listing for our running example, enhanced with +the LLVM code generator. Because this uses the LLVM libraries, we need +to link them in. To do this, we use the +`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform +our makefile/command line about which options to use: + +.. code-block:: bash + + # Compile + ocamlbuild toy.byte + # Run + ./toy.byte + +Here is the code: + +\_tags: + :: + + <{lexer,parser}.ml>: use_camlp4, pp(camlp4of) + <*.{byte,native}>: g++, use_llvm, use_llvm_analysis + +myocamlbuild.ml: + .. code-block:: ocaml + + open Ocamlbuild_plugin;; + + ocaml_lib ~extern:true "llvm";; + ocaml_lib ~extern:true "llvm_analysis";; + + flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);; + +token.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Lexer Tokens + *===----------------------------------------------------------------------===*) + + (* The lexer returns these 'Kwd' if it is an unknown character, otherwise one of + * these others for known things. *) + type token = + (* commands *) + | Def | Extern + + (* primary *) + | Ident of string | Number of float + + (* unknown *) + | Kwd of char + +lexer.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Lexer + *===----------------------------------------------------------------------===*) + + let rec lex = parser + (* Skip any whitespace. *) + | [< ' (' ' | '\n' | '\r' | '\t'); stream >] -> lex stream + + (* identifier: [a-zA-Z][a-zA-Z0-9] *) + | [< ' ('A' .. 'Z' | 'a' .. 'z' as c); stream >] -> + let buffer = Buffer.create 1 in + Buffer.add_char buffer c; + lex_ident buffer stream + + (* number: [0-9.]+ *) + | [< ' ('0' .. '9' as c); stream >] -> + let buffer = Buffer.create 1 in + Buffer.add_char buffer c; + lex_number buffer stream + + (* Comment until end of line. *) + | [< ' ('#'); stream >] -> + lex_comment stream + + (* Otherwise, just return the character as its ascii value. *) + | [< 'c; stream >] -> + [< 'Token.Kwd c; lex stream >] + + (* end of stream. *) + | [< >] -> [< >] + + and lex_number buffer = parser + | [< ' ('0' .. '9' | '.' as c); stream >] -> + Buffer.add_char buffer c; + lex_number buffer stream + | [< stream=lex >] -> + [< 'Token.Number (float_of_string (Buffer.contents buffer)); stream >] + + and lex_ident buffer = parser + | [< ' ('A' .. 'Z' | 'a' .. 'z' | '0' .. '9' as c); stream >] -> + Buffer.add_char buffer c; + lex_ident buffer stream + | [< stream=lex >] -> + match Buffer.contents buffer with + | "def" -> [< 'Token.Def; stream >] + | "extern" -> [< 'Token.Extern; stream >] + | id -> [< 'Token.Ident id; stream >] + + and lex_comment = parser + | [< ' ('\n'); stream=lex >] -> stream + | [< 'c; e=lex_comment >] -> e + | [< >] -> [< >] + +ast.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Abstract Syntax Tree (aka Parse Tree) + *===----------------------------------------------------------------------===*) + + (* expr - Base type for all expression nodes. *) + type expr = + (* variant for numeric literals like "1.0". *) + | Number of float + + (* variant for referencing a variable, like "a". *) + | Variable of string + + (* variant for a binary operator. *) + | Binary of char * expr * expr + + (* variant for function calls. *) + | Call of string * expr array + + (* proto - This type represents the "prototype" for a function, which captures + * its name, and its argument names (thus implicitly the number of arguments the + * function takes). *) + type proto = Prototype of string * string array + + (* func - This type represents a function definition itself. *) + type func = Function of proto * expr + +parser.ml: + .. code-block:: ocaml + + (*===---------------------------------------------------------------------=== + * Parser + *===---------------------------------------------------------------------===*) + + (* binop_precedence - This holds the precedence for each binary operator that is + * defined *) + let binop_precedence:(char, int) Hashtbl.t = Hashtbl.create 10 + + (* precedence - Get the precedence of the pending binary operator token. *) + let precedence c = try Hashtbl.find binop_precedence c with Not_found -> -1 + + (* primary + * ::= identifier + * ::= numberexpr + * ::= parenexpr *) + let rec parse_primary = parser + (* numberexpr ::= number *) + | [< 'Token.Number n >] -> Ast.Number n + + (* parenexpr ::= '(' expression ')' *) + | [< 'Token.Kwd '('; e=parse_expr; 'Token.Kwd ')' ?? "expected ')'" >] -> e + + (* identifierexpr + * ::= identifier + * ::= identifier '(' argumentexpr ')' *) + | [< 'Token.Ident id; stream >] -> + let rec parse_args accumulator = parser + | [< e=parse_expr; stream >] -> + begin parser + | [< 'Token.Kwd ','; e=parse_args (e :: accumulator) >] -> e + | [< >] -> e :: accumulator + end stream + | [< >] -> accumulator + in + let rec parse_ident id = parser + (* Call. *) + | [< 'Token.Kwd '('; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')'">] -> + Ast.Call (id, Array.of_list (List.rev args)) + + (* Simple variable ref. *) + | [< >] -> Ast.Variable id + in + parse_ident id stream + + | [< >] -> raise (Stream.Error "unknown token when expecting an expression.") + + (* binoprhs + * ::= ('+' primary)* *) + and parse_bin_rhs expr_prec lhs stream = + match Stream.peek stream with + (* If this is a binop, find its precedence. *) + | Some (Token.Kwd c) when Hashtbl.mem binop_precedence c -> + let token_prec = precedence c in + + (* If this is a binop that binds at least as tightly as the current binop, + * consume it, otherwise we are done. *) + if token_prec < expr_prec then lhs else begin + (* Eat the binop. *) + Stream.junk stream; + + (* Parse the primary expression after the binary operator. *) + let rhs = parse_primary stream in + + (* Okay, we know this is a binop. *) + let rhs = + match Stream.peek stream with + | Some (Token.Kwd c2) -> + (* If BinOp binds less tightly with rhs than the operator after + * rhs, let the pending operator take rhs as its lhs. *) + let next_prec = precedence c2 in + if token_prec < next_prec + then parse_bin_rhs (token_prec + 1) rhs stream + else rhs + | _ -> rhs + in + + (* Merge lhs/rhs. *) + let lhs = Ast.Binary (c, lhs, rhs) in + parse_bin_rhs expr_prec lhs stream + end + | _ -> lhs + + (* expression + * ::= primary binoprhs *) + and parse_expr = parser + | [< lhs=parse_primary; stream >] -> parse_bin_rhs 0 lhs stream + + (* prototype + * ::= id '(' id* ')' *) + let parse_prototype = + let rec parse_args accumulator = parser + | [< 'Token.Ident id; e=parse_args (id::accumulator) >] -> e + | [< >] -> accumulator + in + + parser + | [< 'Token.Ident id; + 'Token.Kwd '(' ?? "expected '(' in prototype"; + args=parse_args []; + 'Token.Kwd ')' ?? "expected ')' in prototype" >] -> + (* success. *) + Ast.Prototype (id, Array.of_list (List.rev args)) + + | [< >] -> + raise (Stream.Error "expected function name in prototype") + + (* definition ::= 'def' prototype expression *) + let parse_definition = parser + | [< 'Token.Def; p=parse_prototype; e=parse_expr >] -> + Ast.Function (p, e) + + (* toplevelexpr ::= expression *) + let parse_toplevel = parser + | [< e=parse_expr >] -> + (* Make an anonymous proto. *) + Ast.Function (Ast.Prototype ("", [||]), e) + + (* external ::= 'extern' prototype *) + let parse_extern = parser + | [< 'Token.Extern; e=parse_prototype >] -> e + +codegen.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Code Generation + *===----------------------------------------------------------------------===*) + + open Llvm + + exception Error of string + + let context = global_context () + let the_module = create_module context "my cool jit" + let builder = builder context + let named_values:(string, llvalue) Hashtbl.t = Hashtbl.create 10 + let double_type = double_type context + + let rec codegen_expr = function + | Ast.Number n -> const_float double_type n + | Ast.Variable name -> + (try Hashtbl.find named_values name with + | Not_found -> raise (Error "unknown variable name")) + | Ast.Binary (op, lhs, rhs) -> + let lhs_val = codegen_expr lhs in + let rhs_val = codegen_expr rhs in + begin + match op with + | '+' -> build_add lhs_val rhs_val "addtmp" builder + | '-' -> build_sub lhs_val rhs_val "subtmp" builder + | '*' -> build_mul lhs_val rhs_val "multmp" builder + | '<' -> + (* Convert bool 0/1 to double 0.0 or 1.0 *) + let i = build_fcmp Fcmp.Ult lhs_val rhs_val "cmptmp" builder in + build_uitofp i double_type "booltmp" builder + | _ -> raise (Error "invalid binary operator") + end + | Ast.Call (callee, args) -> + (* Look up the name in the module table. *) + let callee = + match lookup_function callee the_module with + | Some callee -> callee + | None -> raise (Error "unknown function referenced") + in + let params = params callee in + + (* If argument mismatch error. *) + if Array.length params == Array.length args then () else + raise (Error "incorrect # arguments passed"); + let args = Array.map codegen_expr args in + build_call callee args "calltmp" builder + + let codegen_proto = function + | Ast.Prototype (name, args) -> + (* Make the function type: double(double,double) etc. *) + let doubles = Array.make (Array.length args) double_type in + let ft = function_type double_type doubles in + let f = + match lookup_function name the_module with + | None -> declare_function name ft the_module + + (* If 'f' conflicted, there was already something named 'name'. If it + * has a body, don't allow redefinition or reextern. *) + | Some f -> + (* If 'f' already has a body, reject this. *) + if block_begin f <> At_end f then + raise (Error "redefinition of function"); + + (* If 'f' took a different number of arguments, reject. *) + if element_type (type_of f) <> ft then + raise (Error "redefinition of function with different # args"); + f + in + + (* Set names for all arguments. *) + Array.iteri (fun i a -> + let n = args.(i) in + set_value_name n a; + Hashtbl.add named_values n a; + ) (params f); + f + + let codegen_func = function + | Ast.Function (proto, body) -> + Hashtbl.clear named_values; + let the_function = codegen_proto proto in + + (* Create a new basic block to start insertion into. *) + let bb = append_block context "entry" the_function in + position_at_end bb builder; + + try + let ret_val = codegen_expr body in + + (* Finish off the function. *) + let _ = build_ret ret_val builder in + + (* Validate the generated code, checking for consistency. *) + Llvm_analysis.assert_valid_function the_function; + + the_function + with e -> + delete_function the_function; + raise e + +toplevel.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Top-Level parsing and JIT Driver + *===----------------------------------------------------------------------===*) + + open Llvm + + (* top ::= definition | external | expression | ';' *) + let rec main_loop stream = + match Stream.peek stream with + | None -> () + + (* ignore top-level semicolons. *) + | Some (Token.Kwd ';') -> + Stream.junk stream; + main_loop stream + + | Some token -> + begin + try match token with + | Token.Def -> + let e = Parser.parse_definition stream in + print_endline "parsed a function definition."; + dump_value (Codegen.codegen_func e); + | Token.Extern -> + let e = Parser.parse_extern stream in + print_endline "parsed an extern."; + dump_value (Codegen.codegen_proto e); + | _ -> + (* Evaluate a top-level expression into an anonymous function. *) + let e = Parser.parse_toplevel stream in + print_endline "parsed a top-level expr"; + dump_value (Codegen.codegen_func e); + with Stream.Error s | Codegen.Error s -> + (* Skip token for error recovery. *) + Stream.junk stream; + print_endline s; + end; + print_string "ready> "; flush stdout; + main_loop stream + +toy.ml: + .. code-block:: ocaml + + (*===----------------------------------------------------------------------=== + * Main driver code. + *===----------------------------------------------------------------------===*) + + open Llvm + + let main () = + (* Install standard binary operators. + * 1 is the lowest precedence. *) + Hashtbl.add Parser.binop_precedence '<' 10; + Hashtbl.add Parser.binop_precedence '+' 20; + Hashtbl.add Parser.binop_precedence '-' 20; + Hashtbl.add Parser.binop_precedence '*' 40; (* highest. *) + + (* Prime the first token. *) + print_string "ready> "; flush stdout; + let stream = Lexer.lex (Stream.of_channel stdin) in + + (* Run the main "interpreter loop" now. *) + Toplevel.main_loop stream; + + (* Print out all the generated code. *) + dump_module Codegen.the_module + ;; + + main () + +`Next: Adding JIT and Optimizer Support <OCamlLangImpl4.html>`_ + |