Execution Engine: CodeGenOpt level

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1

Hi,

How can I dynamically change the code generation optimization level (e.g.,
None) of a JIT in other to recompile a function with a new optimization
level (e.g., Default)?

Thank you.

Best regards,
Nurudeen.

2

How can I dynamically change the code generation optimization level (e.g.,
None) of a JIT in other to recompile a function with a new optimization
level (e.g., Default)?

  From the source code I'm reading, you might have to creat another JIT with
different opt level.

Regards,
chenwj

3

Hi Chenwj,

Thank you for your response.

The problem with this approach is that global mappings have to be
recreated in the new JIT. Can this be somehow avoided?

Best regards,
Nurudeen.

4

The problem with this approach is that global mappings have to be
recreated in the new JIT. Can this be somehow avoided?

  I am afraid not. Besides, when you create another ExecutionEngine, it'll
take ownership of the module which contains the function you want to compile.
Maybe you have creat another module, perhaps. But I am not a LLVM expert, I
leave for other's comment.

Regards,
chenwj

5

From: llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] On Behalf Of nlamee@cs.mcgill.ca
Subject: [LLVMdev] Execution Engine: CodeGenOpt level

How can I dynamically change the code generation optimization level (e.g.,
None) of a JIT in other to recompile a function with a new optimization
level (e.g., Default)?

We set the optimization level with a PassManagerBuilder, which is initialized for each function compilation:

    PassManagerBuilder PMBuilder;
...
    PMBuilder.OptLevel = conf.value_of(CF_OPTLEVEL);
    PMBuilder.SizeLevel = conf.is_set(CF_OPTSIZE) ? 1 : 0;
    PMBuilder.DisableUnitAtATime = !conf.is_set(CF_OPTUNIT);
    PMBuilder.DisableUnrollLoops = !conf.is_set(CF_UNROLL);
    PMBuilder.DisableSimplifyLibCalls = !conf.is_set(CF_SIMPLIB);
    if (Opt != CodeGenOpt::None) {
        PMBuilder.Inliner = createFunctionInliningPass(Opt == CodeGenOpt::Aggressive ? 250 : 200);
    }
    pFPasses = new FunctionPassManager(pMod);
    pFPasses->add(new TargetData(*TD));
    PMBuilder.populateFunctionPassManager(*pFPasses);
    pFPasses->doInitialization();
    pFPasses->run(*pFun);
    pFPasses->doFinalization();
    delete pFPasses;
    pMPasses = new PassManager();
    pMPasses->add(new TargetData(*TD));
    pMPasses->add(createCFGSimplificationPass());
    pMPasses->add(createBlockPlacementPass());
    PMBuilder.populateModulePassManager(*pMPasses);
    pMPasses->run(*pMod);
    delete pMPasses;

(There is likely some redundancy and unnecessary steps in the above.)

- Chuck

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6

Neat approach, I think. So you set PassManagers's Opt level rather
then ExecutionEngine's one?

Regards,
chenwj

7

From: 陳韋任 [mailto:chenwj@iis.sinica.edu.tw]
Subject: Re: [LLVMdev] Execution Engine: CodeGenOpt level

So you set PassManagers's Opt level rather then ExecutionEngine's one?

That's correct. I have no idea what difference doing one or the other (or both) makes.

- Chuck

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8

Thank you.
Nurudeen.