[llvm-dev] How to find variable names from LLVM IR?

[David Blaikie via llvm-dev]

Optimized debug info is best effort & not terribly accurate in LLVM
currently (it'll always be best effort, it's just that best could be better
than it is today), so it's quite possible that a Value you know is in a
variable isn't being tracked by debug info anymore because it got lost
somewhere along the way.

When you look at the IR, does it seem that it has debug info intrinsics
describing the value you're interested in? If not, did it start out that
way & lose it due to optimization somewhere? Which optimization?
(print-after-all can help track this sort of thing through an optimization
pipeline) Perhaps you can improve the debug info quality of the
optimization so it preserves what you need. But realize/remember it'll
never be perfect, there's lots of lossy things that optimizations do.

On Sun, May 29, 2016 at 3:41 AM, Dhriti Khanna via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> If I have an operand as a Value from an instruction like: Value* V =
> opnd->get(); and I am sure this is a variable, I want to know the
> variable name (in source code) for this Value object. I am doing it like
> this:
>
>                                    const Function* Func;
>                 if (const Argument* Arg = dyn_cast<Argument>(V))
>                 {
>                   Func = Arg->getParent();
>                 }
>                 else if (const Instruction* I = dyn_cast<Instruction>(V))
>                 {
>                   Func = I->getParent()->getParent();
>                 }
>
>                 StringRef name;
>                 if (!Func)
>                    name = V->getName();
>
>                 else
>                 {
>                   const DILocalVariable* Var = NULL;
>
>                   for (const_inst_iterator Iter = inst_begin(Func), End =
> inst_end(Func); Iter != End; ++Iter)
>                   {
>                     if (const DbgDeclareInst* DbgDeclare =
> dyn_cast<DbgDeclareInst>(&*Iter))
>                     {
>                       if (DbgDeclare->getAddress() == V) Var =
> DbgDeclare->getVariable();
>                     }
>                     else if (const DbgValueInst* DbgValue =
> dyn_cast<DbgValueInst>(&*Iter))
>                     {
>                       if (DbgValue->getValue() == V) Var =
> DbgValue->getVariable();
>                     }
>                   }
>
>                   name = Var->getName();
>                 }
>                 errs() << "\nVariableName: " << name.str() << "\n";
>
> But  this condition: if(DbgDeclare->getAddress() == V) produces false
> result as the address for the Value object differs from every Value object
> found in dbg.declare intrinsic. Is this not how one finds the variable
> name??
> What am I doing wrong?
>
> --
> Regards
> Dhriti Khanna
>
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>
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