[LLVMdev] Set up ExecutionEngine according to actual machine capabilities

[Mueller-Roemer, Johannes Sebastian]

It has no AVX according to CPUz (which I assume uses cpuid?), but it reports as an E5-2680, which normally does have AVX.

--
Johannes S. Mueller-Roemer, MSc
Wiss. Mitarbeiter - Interactive Engineering Technologies (IET)

Fraunhofer-Institut für Graphische Datenverarbeitung IGD
Fraunhoferstr. 5  |  64283 Darmstadt  |  Germany
Tel +49 6151 155-606  |  Fax +49 6151 155-139
johannes.mueller-roemer at igd.fraunhofer.de  |  www.igd.fraunhofer.de

From: Yaron Keren [mailto:yaron.keren at gmail.com]
Sent: Monday, May 11, 2015 11:18
To: Mueller-Roemer, Johannes Sebastian
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Set up ExecutionEngine according to actual machine capabilities

That's odd. getHostCPUName uses cpuid to get the actual capabilities of the CPU before selecting the name.
Does cpuid reports incorrect information in these virtual machines?

In any case you can further tune CPU capabilities with EngineBuilder::setMAttrs.


2015-05-11 11:59 GMT+03:00 Mueller-Roemer, Johannes Sebastian <Johannes.Sebastian.Mueller-Roemer at igd.fraunhofer.de<mailto:Johannes.Sebastian.Mueller-Roemer at igd.fraunhofer.de>>:
I am currently setting up my Module with

module->setTargetTriple(llvm::sys::getProcessTriple()
#ifdef _WIN32
                               + "-elf"
#endif
);

And my ExecutionEngine with

llvm::EngineBuilder(std::move(module))
                                               .setErrorStr(&err)
                                               .setMCPU(llvm::sys::getHostCPUName())
                                               .create()

This works fine on most machines, however on some virtualized machines this fails because the host CPU name implies AVX, however AVX is in fact disabled, leading to an illegal instruction when running JIT-compiled functions.

Is there a better way to set up the executionengine so that such failure do not occur (but all available features are used)?

--
Johannes S. Mueller-Roemer, MSc
Wiss. Mitarbeiter - Interactive Engineering Technologies (IET)

Fraunhofer-Institut für Graphische Datenverarbeitung IGD
Fraunhoferstr. 5  |  64283 Darmstadt  |  Germany
Tel +49 6151 155-606  |  Fax +49 6151 155-139
johannes.mueller-roemer at igd.fraunhofer.de<mailto:johannes.mueller-roemer at igd.fraunhofer.de>  |  www.igd.fraunhofer.de<http://www.igd.fraunhofer.de>


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