README.md

JavaCPP Presets for LLVM

^{Build status for all platforms: Commercial support:}

Introduction

This directory contains the JavaCPP Presets module for:

• LLVM 13.0.1 http://llvm.org/

Please refer to the parent README.md file for more detailed information about the JavaCPP Presets.

Documentation

Java API documentation is available here:

• http://bytedeco.org/javacpp-presets/llvm/apidocs/

∗ Bindings are currently available only for the C APIs of LLVM and Clang.
∗ In the case of Clang, we might need to disable crash recovery with the LIBCLANG_DISABLE_CRASH_RECOVERY=1 environment variable to prevent clashes with the JVM's own signal handlers.

Sample Usage

Here is a simple example showing how to calculate the factorial of a number with LLVM, initially based on this C source file:

• https://github.com/wickedchicken/llvm-c-example/blob/master/fac.c

We can use Maven 3 to download and install automatically all the class files as well as the native binaries. To run this sample code, after creating the pom.xml and Factorial.java source files below, simply execute on the command line:

 $ mvn compile exec:java

The pom.xml build file

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.bytedeco.llvm</groupId>
    <artifactId>Factorial</artifactId>
    <version>1.5.7</version>
    <properties>
        <exec.mainClass>Factorial</exec.mainClass>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.bytedeco</groupId>
            <artifactId>llvm-platform</artifactId>
            <version>13.0.1-1.5.7</version>
        </dependency>
    </dependencies>
    <build>
        <sourceDirectory>.</sourceDirectory>
    </build>
</project>

The Factorial.java source file

import org.bytedeco.javacpp.*;
import org.bytedeco.llvm.LLVM.*;

import static org.bytedeco.llvm.global.LLVM.*;

public class Factorial {
    // a 'char *' used to retrieve error messages from LLVM
    private static final BytePointer error = new BytePointer();

    public static void main(String[] args) {
        // Stage 1: Initialize LLVM components
        LLVMInitializeCore(LLVMGetGlobalPassRegistry());
        LLVMLinkInMCJIT();
        LLVMInitializeNativeAsmPrinter();
        LLVMInitializeNativeAsmParser();
        LLVMInitializeNativeTarget();

        // Stage 2: Build the factorial function.
        LLVMContextRef context = LLVMContextCreate();
        LLVMModuleRef module = LLVMModuleCreateWithNameInContext("factorial", context);
        LLVMBuilderRef builder = LLVMCreateBuilderInContext(context);
        LLVMTypeRef i32Type = LLVMInt32TypeInContext(context);
        LLVMTypeRef factorialType = LLVMFunctionType(i32Type, i32Type, /* argumentCount */ 1, /* isVariadic */ 0);

        LLVMValueRef factorial = LLVMAddFunction(module, "factorial", factorialType);
        LLVMSetFunctionCallConv(factorial, LLVMCCallConv);

        LLVMValueRef n = LLVMGetParam(factorial, /* parameterIndex */0);
        LLVMValueRef zero = LLVMConstInt(i32Type, 0, /* signExtend */ 0);
        LLVMValueRef one = LLVMConstInt(i32Type, 1, /* signExtend */ 0);
        LLVMBasicBlockRef entry = LLVMAppendBasicBlockInContext(context, factorial, "entry");
        LLVMBasicBlockRef ifFalse = LLVMAppendBasicBlockInContext(context, factorial, "if_false");
        LLVMBasicBlockRef exit = LLVMAppendBasicBlockInContext(context, factorial, "exit");

        LLVMPositionBuilderAtEnd(builder, entry);
        LLVMValueRef condition = LLVMBuildICmp(builder, LLVMIntEQ, n, zero, "condition = n == 0");
        LLVMBuildCondBr(builder, condition, exit, ifFalse);

        LLVMPositionBuilderAtEnd(builder, ifFalse);
        LLVMValueRef nMinusOne = LLVMBuildSub(builder, n, one, "nMinusOne = n - 1");
        PointerPointer<Pointer> arguments = new PointerPointer<>(1)
            .put(0, nMinusOne);
        LLVMValueRef factorialResult = LLVMBuildCall(builder, factorial, arguments, 1, "factorialResult = factorial(nMinusOne)");
        LLVMValueRef resultIfFalse = LLVMBuildMul(builder, n, factorialResult, "resultIfFalse = n * factorialResult");
        LLVMBuildBr(builder, exit);

        LLVMPositionBuilderAtEnd(builder, exit);
        LLVMValueRef phi = LLVMBuildPhi(builder, i32Type, "result");
        PointerPointer<Pointer> phiValues = new PointerPointer<>(2)
            .put(0, one)
            .put(1, resultIfFalse);
        PointerPointer<Pointer> phiBlocks = new PointerPointer<>(2)
            .put(0, entry)
            .put(1, ifFalse);
        LLVMAddIncoming(phi, phiValues, phiBlocks, /* pairCount */ 2);
        LLVMBuildRet(builder, phi);

        // Stage 3: Verify the module using LLVMVerifier
        if (LLVMVerifyModule(module, LLVMPrintMessageAction, error) != 0) {
            LLVMDisposeMessage(error);
            return;
        }

        // Stage 4: Create a pass pipeline using the legacy pass manager
        LLVMPassManagerRef pm = LLVMCreatePassManager();
        LLVMAddAggressiveInstCombinerPass(pm);
        LLVMAddNewGVNPass(pm);
        LLVMAddCFGSimplificationPass(pm);
        LLVMRunPassManager(pm, module);
        LLVMDumpModule(module);

        // Stage 5: Execute the code using MCJIT
        LLVMExecutionEngineRef engine = new LLVMExecutionEngineRef();
        LLVMMCJITCompilerOptions options = new LLVMMCJITCompilerOptions();
        if (LLVMCreateMCJITCompilerForModule(engine, module, options, 3, error) != 0) {
            System.err.println("Failed to create JIT compiler: " + error.getString());
            LLVMDisposeMessage(error);
            return;
        }

        LLVMGenericValueRef argument = LLVMCreateGenericValueOfInt(i32Type, 10, /* signExtend */ 0);
        LLVMGenericValueRef result = LLVMRunFunction(engine, factorial, /* argumentCount */ 1, argument);
        System.out.println();
        System.out.println("; Running factorial(10) with MCJIT...");
        System.out.println("; Result: " + LLVMGenericValueToInt(result, /* signExtend */ 0));

        // Stage 6: Dispose of the allocated resources
        LLVMDisposeExecutionEngine(engine);
        LLVMDisposePassManager(pm);
        LLVMDisposeBuilder(builder);
        LLVMContextDispose(context);
    }
}

More samples showing off LLVM usage from Java can be found in the samples/ subdirectory.