[LLVMdev] how to get TargetData?

[Zonr Chang]

For those targets supported by LLVM, you can get their TargetData by
creating TargetMachine first (take X86 as example):

==== BEGIN CODE SNIPPET ====
    const std::string TripleStr = "i686-unknown-linux"; // hard coded for
example
    const std::string FeatureStr = ""; // hard coded for example
    std::string Err;
    const Target* T;
    TargetMachine* TM = NULL;
    const TargetData* TD;

    // Or just call InitializeAllTargetInfos() and InitializeAllTargets()
for all targets enabled by your LLVM build.
    LLVMInitializeX86TargetInfo();
    LLVMInitializeX86Target();

    T = TargetRegistry::lookupTarget(TripleStr, Err);
    if(!Err.empty())
        // error handling

    // Create TargetMachine
    TM = T->createTargetMachine(TripleStr, FeatureStr);
    if(TM == NULL)
        // error handling

    // TD is what you want.
    TD = TM->getTargetData();

    [...]

    // Free TM
    delete TM;
==== END CODE SNIPPET ====

For your case, you should be able to find TripleStr and FeatureStr in
somewhere.

And also there's a constructor in TargetData (
http://llvm.org/doxygen/classllvm_1_1TargetData.html#a0d7acb06af9665b54fc74480e2c6c707)
takeing a string "TargetDescription". The string specifies the data layout
of a target and its format is described here
http://llvm.org/docs/LangRef.html#datalayout. Thus, if you are developing a
customized target and/or you are really know the data layout specification
about your target, you can get a TargetData instance by simply passing
the hand-coded data layout string to the constructor of TargetData.

Hope this will be helpful to you.

Zonr


On Fri, May 28, 2010 at 11:27 PM, Victor Zverovich <
victor.zverovich at googlemail.com> wrote:

> Dear all
>
> I am trying to get the size of an LLVM pointer type.
> getPrimitiveSizeInBits() returns 0 for it and the documentation for
> isSized() suggest to use TargetData.
> I figured out from Kaleidoscope example that one can get a pointer to
> TagetData object through the execution engine but it seems to be an
> overkill.
> What is the right way to do it?
>
> Best regards,
> Victor
>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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