| ============================================== |
| Kaleidoscope: Adding JIT and Optimizer Support |
| ============================================== |
| |
| .. contents:: |
| :local: |
| |
| Chapter 4 Introduction |
| ====================== |
| |
| Welcome to Chapter 4 of the "`Implementing a language with |
| LLVM <index.html>`_" 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. These additions will |
| demonstrate how to get nice, efficient code for the Kaleidoscope |
| language. |
| |
| Trivial Constant Folding |
| ======================== |
| |
| **Note:** the default ``IRBuilder`` now always includes the constant |
| folding optimisations below. |
| |
| Our demonstration for Chapter 3 is elegant and easy to extend. |
| Unfortunately, it does not produce wonderful code. For example, when |
| compiling simple code, we don't get obvious optimizations: |
| |
| :: |
| |
| ready> def test(x) 1+2+x; |
| Read function definition: |
| define double @test(double %x) { |
| entry: |
| %addtmp = fadd double 1.000000e+00, 2.000000e+00 |
| %addtmp1 = fadd double %addtmp, %x |
| ret double %addtmp1 |
| } |
| |
| 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 "``add x, 3.0``" 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. |
| |
| 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. This is |
| exactly what the ``LLVMFoldingBuilder`` class does. |
| |
| All we did was switch from ``LLVMBuilder`` to ``LLVMFoldingBuilder``. |
| 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: |
| |
| :: |
| |
| ready> def test(x) 1+2+x; |
| Read function definition: |
| define double @test(double %x) { |
| entry: |
| %addtmp = fadd double 3.000000e+00, %x |
| ret double %addtmp |
| } |
| |
| Well, that was easy :). In practice, we recommend always using |
| ``LLVMFoldingBuilder`` when generating code like this. It has no |
| "syntactic overhead" for its use (you don't have to uglify your compiler |
| with constant checks everywhere) and it can dramatically reduce the |
| amount of LLVM IR that is generated in some cases (particular for |
| languages with a macro preprocessor or that use a lot of constants). |
| |
| On the other hand, the ``LLVMFoldingBuilder`` is limited by the fact |
| that it does all of its analysis inline with the code as it is built. If |
| you take a slightly more complex example: |
| |
| :: |
| |
| ready> def test(x) (1+2+x)*(x+(1+2)); |
| ready> Read function definition: |
| define double @test(double %x) { |
| entry: |
| %addtmp = fadd double 3.000000e+00, %x |
| %addtmp1 = fadd double %x, 3.000000e+00 |
| %multmp = fmul double %addtmp, %addtmp1 |
| ret double %multmp |
| } |
| |
| In this case, the LHS and RHS of the multiplication are the same value. |
| We'd really like to see this generate "``tmp = x+3; result = tmp*tmp;``" |
| instead of computing "``x*3``" twice. |
| |
| Unfortunately, no amount of local analysis will be able to detect and |
| correct this. This requires two transformations: reassociation of |
| expressions (to make the add's lexically identical) and Common |
| Subexpression Elimination (CSE) to delete the redundant add instruction. |
| Fortunately, LLVM provides a broad range of optimizations that you can |
| use, in the form of "passes". |
| |
| LLVM Optimization Passes |
| ======================== |
| |
| 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 decisions about what optimizations to use, in which |
| order, and in what situation. |
| |
| As a concrete example, LLVM supports both "whole module" passes, which |
| look 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 they are run, see the |
| `How to Write a Pass <../WritingAnLLVMPass.html>`_ document and the |
| `List of LLVM Passes <../Passes.html>`_. |
| |
| For Kaleidoscope, we are currently generating functions on the fly, one |
| at a time, as the user types them in. We aren't shooting for the |
| ultimate optimization experience in this setting, but we also want to |
| catch the easy and quick stuff where possible. As such, we will choose |
| to run a few per-function optimizations as the user types the function |
| in. If we wanted to make a "static Kaleidoscope compiler", we would use |
| exactly the code we have now, except that we would defer running the |
| optimizer until the entire file has been parsed. |
| |
| In order to get per-function optimizations going, we need to set up a |
| `Llvm.PassManager <../WritingAnLLVMPass.html#passmanager>`_ to hold and |
| organize the LLVM optimizations that we want to run. Once we have that, |
| we can add a set of optimizations to run. The code looks like this: |
| |
| .. code-block:: ocaml |
| |
| (* Create the JIT. *) |
| let the_execution_engine = ExecutionEngine.create Codegen.the_module in |
| let the_fpm = PassManager.create_function Codegen.the_module in |
| |
| (* Set up the optimizer pipeline. Start with registering info about how the |
| * target lays out data structures. *) |
| DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm; |
| |
| (* Do simple "peephole" optimizations and bit-twiddling optzn. *) |
| add_instruction_combining the_fpm; |
| |
| (* reassociate expressions. *) |
| add_reassociation the_fpm; |
| |
| (* Eliminate Common SubExpressions. *) |
| add_gvn the_fpm; |
| |
| (* Simplify the control flow graph (deleting unreachable blocks, etc). *) |
| add_cfg_simplification the_fpm; |
| |
| ignore (PassManager.initialize the_fpm); |
| |
| (* Run the main "interpreter loop" now. *) |
| Toplevel.main_loop the_fpm the_execution_engine stream; |
| |
| The meat of the matter here, is the definition of "``the_fpm``". It |
| requires a pointer to the ``the_module`` 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 so that later |
| optimizations know how the data structures in the program are laid out. |
| The "``the_execution_engine``" variable is related to the JIT, which we |
| will get to in the next section. |
| |
| 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, they are a good starting place :). |
| |
| Once the ``Llvm.PassManager.`` is set up, we need to make use of it. We |
| do this by running it after our newly created function is constructed |
| (in ``Codegen.codegen_func``), but before it is returned to the client: |
| |
| .. code-block:: ocaml |
| |
| let codegen_func the_fpm = function |
| ... |
| 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; |
| |
| (* Optimize the function. *) |
| let _ = PassManager.run_function the_function the_fpm in |
| |
| the_function |
| |
| As you can see, this is pretty straightforward. The ``the_fpm`` |
| optimizes and updates the LLVM Function\* in place, improving |
| (hopefully) its body. With this in place, we can try our test above |
| again: |
| |
| :: |
| |
| ready> def test(x) (1+2+x)*(x+(1+2)); |
| ready> Read function definition: |
| define double @test(double %x) { |
| entry: |
| %addtmp = fadd double %x, 3.000000e+00 |
| %multmp = fmul double %addtmp, %addtmp |
| ret double %multmp |
| } |
| |
| As expected, we now get our nicely optimized code, saving a floating |
| point add instruction from every execution of this function. |
| |
| LLVM provides a wide variety of optimizations that can be used in |
| certain circumstances. Some `documentation about the various |
| passes <../Passes.html>`_ is available, but it isn't very complete. |
| Another good source of ideas can come from looking at the passes that |
| ``Clang`` runs to get started. The "``opt``" tool allows you to |
| experiment with passes from the command line, so you can see if they do |
| anything. |
| |
| Now that we have reasonable code coming out of our front-end, lets talk |
| about executing it! |
| |
| Adding a JIT Compiler |
| ===================== |
| |
| Code that is available in LLVM IR can have a wide variety of tools |
| applied to it. For example, you can run optimizations on it (as we did |
| above), you can dump it out in textual or binary forms, you can compile |
| the code to an assembly file (.s) for some target, or you can JIT |
| compile it. The nice thing about the LLVM IR representation is that it |
| is the "common currency" between many different parts of the compiler. |
| |
| In this section, we'll add JIT compiler support to our interpreter. The |
| basic idea that we want for Kaleidoscope is to have the user enter |
| function bodies as they do now, but immediately evaluate the top-level |
| expressions they type in. For example, if they type in "1 + 2;", we |
| should evaluate and print out 3. If they define a function, they should |
| be able to call it from the command line. |
| |
| In order to do this, we first declare and initialize the JIT. This is |
| done by adding a global variable and a call in ``main``: |
| |
| .. code-block:: ocaml |
| |
| ... |
| let main () = |
| ... |
| (* Create the JIT. *) |
| let the_execution_engine = ExecutionEngine.create Codegen.the_module in |
| ... |
| |
| This creates an abstract "Execution Engine" which can be either a JIT |
| compiler or the LLVM interpreter. LLVM will automatically pick a JIT |
| compiler for you if one is available for your platform, otherwise it |
| will fall back to the interpreter. |
| |
| Once the ``Llvm_executionengine.ExecutionEngine.t`` is created, the JIT |
| is ready to be used. There are a variety of APIs that are useful, but |
| the simplest one is the |
| "``Llvm_executionengine.ExecutionEngine.run_function``" function. 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 top-level expression to look like |
| this: |
| |
| .. code-block:: ocaml |
| |
| (* Evaluate a top-level expression into an anonymous function. *) |
| let e = Parser.parse_toplevel stream in |
| print_endline "parsed a top-level expr"; |
| let the_function = Codegen.codegen_func the_fpm e in |
| dump_value the_function; |
| |
| (* JIT the function, returning a function pointer. *) |
| let result = ExecutionEngine.run_function the_function [||] |
| the_execution_engine in |
| |
| print_string "Evaluated to "; |
| print_float (GenericValue.as_float Codegen.double_type result); |
| print_newline (); |
| |
| Recall that we compile top-level expressions into a self-contained LLVM |
| 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. This means, there is no difference |
| between JIT compiled code and native machine code that is statically |
| linked into your application. |
| |
| With just these two changes, lets see how Kaleidoscope works now! |
| |
| :: |
| |
| ready> 4+5; |
| define double @""() { |
| entry: |
| ret double 9.000000e+00 |
| } |
| |
| Evaluated to 9.000000 |
| |
| 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 in. This |
| demonstrates very basic functionality, but can we do more? |
| |
| :: |
| |
| ready> def testfunc(x y) x + y*2; |
| Read function definition: |
| define double @testfunc(double %x, double %y) { |
| entry: |
| %multmp = fmul double %y, 2.000000e+00 |
| %addtmp = fadd double %multmp, %x |
| ret double %addtmp |
| } |
| |
| ready> testfunc(4, 10); |
| define double @""() { |
| entry: |
| %calltmp = call double @testfunc(double 4.000000e+00, double 1.000000e+01) |
| ret double %calltmp |
| } |
| |
| Evaluated to 24.000000 |
| |
| 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 *call testfunc*, but we never invoked it on |
| *testfunc* itself. What actually happened here is that the JIT scanned |
| for all non-JIT'd functions transitively called from the anonymous |
| function and compiled all of them before returning from |
| ``run_function``. |
| |
| 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 this out (I removed the dump of the |
| anonymous functions, you should get the idea by now :) : |
| |
| :: |
| |
| ready> extern sin(x); |
| Read extern: |
| declare double @sin(double) |
| |
| ready> extern cos(x); |
| Read extern: |
| declare double @cos(double) |
| |
| ready> sin(1.0); |
| Evaluated to 0.841471 |
| |
| ready> def foo(x) sin(x)*sin(x) + cos(x)*cos(x); |
| Read function definition: |
| define double @foo(double %x) { |
| entry: |
| %calltmp = call double @sin(double %x) |
| %multmp = fmul double %calltmp, %calltmp |
| %calltmp2 = call double @cos(double %x) |
| %multmp4 = fmul double %calltmp2, %calltmp2 |
| %addtmp = fadd double %multmp, %multmp4 |
| ret double %addtmp |
| } |
| |
| ready> foo(4.0); |
| Evaluated to 1.000000 |
| |
| Whoa, how does the JIT know about sin and cos? The answer is |
| surprisingly simple: in this example, the JIT started execution of a |
| function and got to a function call. It realized that the function was |
| not yet JIT compiled and invoked the standard set of routines to resolve |
| the function. In this case, there is no body defined for the function, |
| so the JIT ended up calling "``dlsym("sin")``" on the Kaleidoscope |
| process itself. Since "``sin``" is defined within the JIT's address |
| space, it simply patches up calls in the module to call the libm version |
| of ``sin`` directly. |
| |
| The LLVM JIT provides a number of interfaces (look in the |
| ``llvm_executionengine.mli`` file) for controlling how unknown functions |
| get resolved. It allows you to establish explicit mappings between IR |
| objects and addresses (useful for LLVM global variables that you want to |
| map to static tables, for example), allows you to dynamically decide on |
| the fly based on the function name, and even allows you to have the JIT |
| compile functions lazily the first time they're called. |
| |
| One interesting application of this is that we can now extend the |
| language by writing arbitrary C code to implement operations. For |
| example, if we add: |
| |
| .. code-block:: c++ |
| |
| /* putchard - putchar that takes a double and returns 0. */ |
| extern "C" |
| double putchard(double X) { |
| putchar((char)X); |
| return 0; |
| } |
| |
| Now we can produce simple output to the console by using things like: |
| "``extern putchard(x); putchard(120);``", which prints a lowercase 'x' |
| on the console (120 is the ASCII code for 'x'). Similar code could be |
| used to implement file I/O, console input, and many other capabilities |
| in Kaleidoscope. |
| |
| This completes the JIT and optimizer chapter of the Kaleidoscope |
| tutorial. At this point, we can compile a non-Turing-complete |
| programming language, optimize and JIT compile it in a user-driven way. |
| Next up we'll look into `extending the language with control flow |
| constructs <OCamlLangImpl5.html>`_, tackling some interesting LLVM IR |
| issues along the way. |
| |
| Full Code Listing |
| ================= |
| |
| Here is the complete code listing for our running example, enhanced with |
| the LLVM JIT and optimizer. To build this example, 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 |
| <*.{byte,native}>: use_llvm_executionengine, use_llvm_target |
| <*.{byte,native}>: use_llvm_scalar_opts, use_bindings |
| |
| myocamlbuild.ml: |
| .. code-block:: ocaml |
| |
| open Ocamlbuild_plugin;; |
| |
| ocaml_lib ~extern:true "llvm";; |
| ocaml_lib ~extern:true "llvm_analysis";; |
| ocaml_lib ~extern:true "llvm_executionengine";; |
| ocaml_lib ~extern:true "llvm_target";; |
| ocaml_lib ~extern:true "llvm_scalar_opts";; |
| |
| flag ["link"; "ocaml"; "g++"] (S[A"-cc"; A"g++"]);; |
| dep ["link"; "ocaml"; "use_bindings"] ["bindings.o"];; |
| |
| 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 the_fpm = 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; |
| |
| (* Optimize the function. *) |
| let _ = PassManager.run_function the_function the_fpm in |
| |
| the_function |
| with e -> |
| delete_function the_function; |
| raise e |
| |
| toplevel.ml: |
| .. code-block:: ocaml |
| |
| (*===----------------------------------------------------------------------=== |
| * Top-Level parsing and JIT Driver |
| *===----------------------------------------------------------------------===*) |
| |
| open Llvm |
| open Llvm_executionengine |
| |
| (* top ::= definition | external | expression | ';' *) |
| let rec main_loop the_fpm the_execution_engine stream = |
| match Stream.peek stream with |
| | None -> () |
| |
| (* ignore top-level semicolons. *) |
| | Some (Token.Kwd ';') -> |
| Stream.junk stream; |
| main_loop the_fpm the_execution_engine 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 the_fpm 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"; |
| let the_function = Codegen.codegen_func the_fpm e in |
| dump_value the_function; |
| |
| (* JIT the function, returning a function pointer. *) |
| let result = ExecutionEngine.run_function the_function [||] |
| the_execution_engine in |
| |
| print_string "Evaluated to "; |
| print_float (GenericValue.as_float Codegen.double_type result); |
| print_newline (); |
| 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 the_fpm the_execution_engine stream |
| |
| toy.ml: |
| .. code-block:: ocaml |
| |
| (*===----------------------------------------------------------------------=== |
| * Main driver code. |
| *===----------------------------------------------------------------------===*) |
| |
| open Llvm |
| open Llvm_executionengine |
| open Llvm_target |
| open Llvm_scalar_opts |
| |
| let main () = |
| ignore (initialize_native_target ()); |
| |
| (* 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 |
| |
| (* Create the JIT. *) |
| let the_execution_engine = ExecutionEngine.create Codegen.the_module in |
| let the_fpm = PassManager.create_function Codegen.the_module in |
| |
| (* Set up the optimizer pipeline. Start with registering info about how the |
| * target lays out data structures. *) |
| DataLayout.add (ExecutionEngine.target_data the_execution_engine) the_fpm; |
| |
| (* Do simple "peephole" optimizations and bit-twiddling optzn. *) |
| add_instruction_combination the_fpm; |
| |
| (* reassociate expressions. *) |
| add_reassociation the_fpm; |
| |
| (* Eliminate Common SubExpressions. *) |
| add_gvn the_fpm; |
| |
| (* Simplify the control flow graph (deleting unreachable blocks, etc). *) |
| add_cfg_simplification the_fpm; |
| |
| ignore (PassManager.initialize the_fpm); |
| |
| (* Run the main "interpreter loop" now. *) |
| Toplevel.main_loop the_fpm the_execution_engine stream; |
| |
| (* Print out all the generated code. *) |
| dump_module Codegen.the_module |
| ;; |
| |
| main () |
| |
| bindings.c |
| .. code-block:: c |
| |
| #include <stdio.h> |
| |
| /* putchard - putchar that takes a double and returns 0. */ |
| extern double putchard(double X) { |
| putchar((char)X); |
| return 0; |
| } |
| |
| `Next: Extending the language: control flow <OCamlLangImpl5.html>`_ |
| |
