[llvm-dev] JIT compiler, Windows, external functions like cos (original) (raw)

Stefan Gränitz via llvm-dev llvm-dev at lists.llvm.org
Wed Jan 2 12🔞23 PST 2019

Hi Marcus

If I understand correctly, you are creating a module with a declaration for an external function. Then you compile and load the module with the ExecutionEngine JIT interface. The loader is supposed to resolve your declaration to an existing definition in the host program, right? Do you get the error message "Program used external function '...' which could not be resolved!"?

There is a variety of potential reasons here. The mystery that it works for sqrt, but not for cos or sin, may be that something in your host program exposes a definition with its unmangled name only for sqrt, while the others are mangled or not exposed at all. After all, your host program links to the C++ stdlib, which provides multiple versions of all these functions with different signatures!

In general, using host-process symbols directly can be dangerous and hard to debug. Basically, you are relying on details of your host compiler and linker. The correct way may be adding another module with the stdlib implementation that your JITed code should use. The simplest way may be keeping the host-process calls, but expose your own wrappers explicitly by address. Using the Orc JIT interface directly, a QND implementation with LLVM 5.0 looked like this: https://github.com/weliveindetail/JitFromScratch/commit/e9988a834dd6c35c93268da6ece73a7cc472100a

Note that on Windows you want to declare the wrappers as: extern "C" __declspec(dllexport)

After many trials and errors we found out that no LLVM example works (“4. Kaleidoscope: Adding JIT and Optimizer Support”, “The Fibonacci project“). [...] It seems that the LLVM JIT compiler cannot find external functions like “sin” and “cos” nor intrinsic functions under Windows. Every (tutorial) example crashes using them. I can imagine this doesn't get tested so much on Windows.

Best Stefan

Am 02.01.19 um 19:05 schrieb Dr. Marcus Hoffmann:

Hello Stefan,

our software FluidSIM (www.fluidsim.de) simulates pneumatic, hydraulic and electric circuits. For the mathematical models we use the language Modelica (www.modelica.org). We developed our own Modelica simulator which solves the dynamical created algebraic differential equation systems. One tool is our small JIT compiler, which compiles mathematical expressions like “2*x0 + sin(x1)” at runtime. In the future we want to compile more complex expressions, especially entire blocks, like X1 = 2*x0 +4 X2 = 3*sin(x1) X3 = x1 + x2 At the moment, we are evaluating the LLVM suite to replace our JIT compiler. Our software runs under the Windows platform (32 and 64 Bit). We are using the Microsoft Visual Studio 2017 Version 15.9.4. For our evaluation we use LLVM 7.0.1. We created the LLVM suite for 32 Bit with the cmake tools. We wrote a small parser and took the LLVM tutorials as starting point to implement our LLVM JIT compiler. All arithmetic expressions work fine. But we failed to integrate external functions like “cos” and “sin”. Only “sqrt” worked. After many trials and errors we found out that no LLVM example works (“4. Kaleidoscope: Adding JIT and Optimizer Support”, “The Fibonacci project“). It seems that the LLVM JIT compiler cannot find external functions like “sin” and “cos” nor intrinsic functions under Windows. Every (tutorial) example crashes using them. Is there any solution for this problem (compiler switches, libraries to include, a simple Visual Studio project)? The following code works for “sqrt” but not for “cos”. It just encapsulates an external call. We use Microsoft Visual Studio 2017 Version 15.9.4. LLVM 7.0.1 Solution Configuration: Debug, 32 Bit, Switch: /MTd using namespace llvm; _typedef double(cdecl *JitCompiledFn)(double); int main() { // "sqrt" works. //const char externalFnName[] = "sqrt"; // "cos", "sin", etc. fails. const char externalFnName[] = "cos"; InitializeNativeTarget(); InitializeNativeTargetAsmPrinter(); InitializeNativeTargetAsmParser(); LLVMContext context; IRBuilder<> builder(context); std::uniqueptrllvm::Module module(new Module("TestModule", context)); Module* pModule = module.get(); auto externalFnIR = cast(pModule->getOrInsertFunction("externalFn", Type::getDoubleTy(context), Type::getDoubleTy(context))); Value* x = externalFnIR->argbegin(); x->setName("x"); BasicBlock *entryBlock = BasicBlock::Create(context, "EntryBlock", externalFnIR); builder.SetInsertPoint(entryBlock); std::vector<Type *> args(1, Type::getDoubleTy(context)); FunctionType *FT = FunctionType::get(Type::getDoubleTy(context), args, false); auto externalFnllvm = Function::Create(FT, Function::ExternalLinkage, externalFnName, pModule); auto ret = builder.CreateCall(externalFnllvm, x); builder.CreateRet(ret); errs() << "Created Module:\n\n" << *pModule; auto jitCompiler = EngineBuilder(std::move(module)).setOptLevel(CodeGenOpt::Level::Default).create();

JitCompiledFn externalFn = (JitCompiledFn)jitCompiler->getFunctionAddress(externalFnIR->getName()); errs() << "\n\nexternalFn(9.0) = "; double y = externalFn(9.0); errs() << y << "\n\n"; return 0; }

Kind regards Marcus Hoffmann -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190102/09533477/attachment.html>

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