[LLVMdev] Set up ExecutionEngine according to actual machine capabilities

[Mueller-Roemer, Johannes Sebastian]

Ok I now have something like the following, which appears to work (at least it doesn't crash)

auto host_features = llvm::StringMap<bool>{};
if(!llvm::sys::getHostCPUFeatures(host_features))
	throw std::runtime_error("could not retrieve host CPU features");
auto host_attrs = llvm::SmallVector<llvm::StringRef, 16>{};
for(auto const & pair : host_features)
	if(pair.second)
		host_attrs.emplace_back(pair.first());
auto ee = std::unique_ptr<llvm::ExecutionEngine>{
	llvm::EngineBuilder(std::move(module))
		.setErrorStr(&err)
		.setMAttrs(host_attrs)
		.create()
};

Too bad setMattrs doesn't take a StringMap directly

--
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


-----Original Message-----
From: Benjamin Kramer [mailto:benny.kra at gmail.com] 
Sent: Monday, May 11, 2015 11:24
To: Mueller-Roemer, Johannes Sebastian
Cc: llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] Set up ExecutionEngine according to actual machine capabilities

On Mon, May 11, 2015 at 10:59 AM, Mueller-Roemer, Johannes Sebastian <Johannes.Sebastian.Mueller-Roemer at igd.fraunhofer.de> wrote:
> 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)?

The proper way to do this in LLVM trunk is to use sys::getHostCPUFeatures instead of the name and set the individual feature bits via setMAttrs. getHostCPUName used to be aware of AVX-disabled environments but that was a bit of a hack and was removed recently.

- Ben