| ======================================== |
| Kaleidoscope: Code generation to LLVM IR |
| ======================================== |
| |
| .. contents:: |
| :local: |
| |
| 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>`_ |
| |
