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diff --git a/llvm/docs/tutorial/LangImpl08.rst b/llvm/docs/tutorial/LangImpl08.rst index 4f28a2adc64..1ff4dc8af44 100644 --- a/llvm/docs/tutorial/LangImpl08.rst +++ b/llvm/docs/tutorial/LangImpl08.rst @@ -1,218 +1,7 @@ -======================================== - Kaleidoscope: Compiling to Object Code -======================================== +:orphan: -.. contents:: - :local: +===================== +Kaleidoscope Tutorial +===================== -Chapter 8 Introduction -====================== - -Welcome to Chapter 8 of the "`Implementing a language with LLVM -<index.html>`_" tutorial. This chapter describes how to compile our -language down to object files. - -Choosing a target -================= - -LLVM has native support for cross-compilation. You can compile to the -architecture of your current machine, or just as easily compile for -other architectures. In this tutorial, we'll target the current -machine. - -To specify the architecture that you want to target, we use a string -called a "target triple". This takes the form -``<arch><sub>-<vendor>-<sys>-<abi>`` (see the `cross compilation docs -<http://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_). - -As an example, we can see what clang thinks is our current target -triple: - -:: - - $ clang --version | grep Target - Target: x86_64-unknown-linux-gnu - -Running this command may show something different on your machine as -you might be using a different architecture or operating system to me. - -Fortunately, we don't need to hard-code a target triple to target the -current machine. LLVM provides ``sys::getDefaultTargetTriple``, which -returns the target triple of the current machine. - -.. code-block:: c++ - - auto TargetTriple = sys::getDefaultTargetTriple(); - -LLVM doesn't require us to link in all the target -functionality. For example, if we're just using the JIT, we don't need -the assembly printers. Similarly, if we're only targeting certain -architectures, we can only link in the functionality for those -architectures. - -For this example, we'll initialize all the targets for emitting object -code. - -.. code-block:: c++ - - InitializeAllTargetInfos(); - InitializeAllTargets(); - InitializeAllTargetMCs(); - InitializeAllAsmParsers(); - InitializeAllAsmPrinters(); - -We can now use our target triple to get a ``Target``: - -.. code-block:: c++ - - std::string Error; - auto Target = TargetRegistry::lookupTarget(TargetTriple, Error); - - // Print an error and exit if we couldn't find the requested target. - // This generally occurs if we've forgotten to initialise the - // TargetRegistry or we have a bogus target triple. - if (!Target) { - errs() << Error; - return 1; - } - -Target Machine -============== - -We will also need a ``TargetMachine``. This class provides a complete -machine description of the machine we're targeting. If we want to -target a specific feature (such as SSE) or a specific CPU (such as -Intel's Sandylake), we do so now. - -To see which features and CPUs that LLVM knows about, we can use -``llc``. For example, let's look at x86: - -:: - - $ llvm-as < /dev/null | llc -march=x86 -mattr=help - Available CPUs for this target: - - amdfam10 - Select the amdfam10 processor. - athlon - Select the athlon processor. - athlon-4 - Select the athlon-4 processor. - ... - - Available features for this target: - - 16bit-mode - 16-bit mode (i8086). - 32bit-mode - 32-bit mode (80386). - 3dnow - Enable 3DNow! instructions. - 3dnowa - Enable 3DNow! Athlon instructions. - ... - -For our example, we'll use the generic CPU without any additional -features, options or relocation model. - -.. code-block:: c++ - - auto CPU = "generic"; - auto Features = ""; - - TargetOptions opt; - auto RM = Optional<Reloc::Model>(); - auto TargetMachine = Target->createTargetMachine(TargetTriple, CPU, Features, opt, RM); - - -Configuring the Module -====================== - -We're now ready to configure our module, to specify the target and -data layout. This isn't strictly necessary, but the `frontend -performance guide <../Frontend/PerformanceTips.html>`_ recommends -this. Optimizations benefit from knowing about the target and data -layout. - -.. code-block:: c++ - - TheModule->setDataLayout(TargetMachine->createDataLayout()); - TheModule->setTargetTriple(TargetTriple); - -Emit Object Code -================ - -We're ready to emit object code! Let's define where we want to write -our file to: - -.. code-block:: c++ - - auto Filename = "output.o"; - std::error_code EC; - raw_fd_ostream dest(Filename, EC, sys::fs::F_None); - - if (EC) { - errs() << "Could not open file: " << EC.message(); - return 1; - } - -Finally, we define a pass that emits object code, then we run that -pass: - -.. code-block:: c++ - - legacy::PassManager pass; - auto FileType = TargetMachine::CGFT_ObjectFile; - - if (TargetMachine->addPassesToEmitFile(pass, dest, nullptr, FileType)) { - errs() << "TargetMachine can't emit a file of this type"; - return 1; - } - - pass.run(*TheModule); - dest.flush(); - -Putting It All Together -======================= - -Does it work? Let's give it a try. We need to compile our code, but -note that the arguments to ``llvm-config`` are different to the previous chapters. - -:: - - $ clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs all` -o toy - -Let's run it, and define a simple ``average`` function. Press Ctrl-D -when you're done. - -:: - - $ ./toy - ready> def average(x y) (x + y) * 0.5; - ^D - Wrote output.o - -We have an object file! To test it, let's write a simple program and -link it with our output. Here's the source code: - -.. code-block:: c++ - - #include <iostream> - - extern "C" { - double average(double, double); - } - - int main() { - std::cout << "average of 3.0 and 4.0: " << average(3.0, 4.0) << std::endl; - } - -We link our program to output.o and check the result is what we -expected: - -:: - - $ clang++ main.cpp output.o -o main - $ ./main - average of 3.0 and 4.0: 3.5 - -Full Code Listing -================= - -.. literalinclude:: ../../examples/Kaleidoscope/Chapter8/toy.cpp - :language: c++ - -`Next: Adding Debug Information <LangImpl09.html>`_ +The Kaleidoscope Tutorial has `moved to another location <MyFirstLanguageFrontend/index>`_ . |
