[LLVMdev] The use iterator not working...

[Zack Waters]

Thanks Dan and Jon. I made an incorrect assumption that the "use" iterator
was actually giving me the "user" when de-referencing it.

Did it always have this behavior in previous LLVM versions? I've seen lots
of examples of the "use" iterator being dereferenced and resulting
Instruction pointer being treated as the "user"?

Thanks,
Zack


On Tue, Jun 9, 2015 at 7:25 PM, Jonathan Roelofs <jonathan at codesourcery.com>
wrote:

>
>
> On 6/9/15 8:02 PM, Zack Waters wrote:
>
>> Hi,
>>
>> I'm having a problem with the use iterator. Each "use" that I see, when
>> using the use_iterator, is the same as the "def". Meaning, in the code
>> below the pDef is always equal to pUse pointer for every instruction in
>> all basic blocks (except terminators).
>>
>>              for (auto i = inst_begin(f), ie = inst_end(f); i != ie; ++i)
>>                  Instruction* pDef = &(*i);
>>                  errs() << "Def: " << *pDef << "\n";
>>
>>                  for (auto ui = pDef->use_begin(), uie =
>> pDef->use_end(); ui != uie; ++ui)
>>                  {
>>
>
> 'user' != 'use'.
>
> Think of llvm::Use as the edge between the place where a value is
> produced, and the place where that value is consumed. The consumer is the
> 'User', and the Use points at it.
>
> http://llvm.org/docs/doxygen/html/classllvm_1_1Use.html
>
> The confusing thing that's happening below is that the llvm::Use is
> implicitly converted via `llvm::Use::operator Value *() const` to a
> `Value*`, and that `Value*` is `pDef`.
>
>
> HTH,
>
> Jon
>
>                       Instruction* pUse = dyn_cast<Instruction>(*ui);
>>                      errs() << "  Use: \t" << *pUse << "\n";
>>                  }
>>              }
>>
>> However, everything works as expected when using the range-based use
>> iterator with the following code.
>>
>>              for (auto i = inst_begin(f), ie = inst_end(f); i != ie; ++i)
>>              {
>>                  Instruction* pDef = &(*i);
>>                  errs() << "Def: " << *pDef << "\n";
>>
>>                  for (User* pUser : pDef->users())
>>                  {
>>                      Instruction* pUse = dyn_cast<Instruction>(pUser);
>>                      errs() << "  Use: \t" << *pUse << "\n";
>>                  }
>>              }
>>
>> Also, the code is executed inside a function pass. So was initially
>> thinking I somehow screwed up the use information in a previous pass.
>> However, I would assume the range-based iterator would not work as well
>> but it does.
>>
>> Finally, I'm currently using LLVM 3.5.1 built for Windows. Google hasn't
>> been much help. Anybody have any suggestions as to why the first example
>> above doesn't work?
>>
>> Thanks,
>> Zack
>>
>>
>> _______________________________________________
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>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
> --
> Jon Roelofs
> jonathan at codesourcery.com
> CodeSourcery / Mentor Embedded
>
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