llvm dev - Jan 2022 - getting providers of a llvm instruction

Hi

Analyzing llvm IR file ( .bc or .ll ) for every instruction it is 
possible, using the provided functions, to determine the list of 
instructions that consume it result. What about the other way around – 
are there llvm functions that allow for every instruction ( or better – 
for every operand of an instruction ) to determine the list of 
instructions that provide it with the necessary resources. Being able to 
know the users of the result of an instruction it is possible to 
calculate such a data. The question is if it is already calculated and, 
if yes, how to obtain it.

Thank you
David

-- 
David Livshin
david.livshin at dalsoft.com

www.dalsoft.com
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Hi David,

On Sun, 16 Jan 2022 at 21:06, David Livshin via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Analyzing llvm IR file ( .bc or .ll ) for every instruction it is possible,
using the provided functions, to determine the list of instructions that consume
it result.
Yes, this information is tracked pretty efficiently by the LLVM data
structures. You can iterate using Value::users (Instruction inherits
from Value). So something like:

    for (auto &U : MyInst->users()) {
      [...]
    }

ought to work.
> What about the other way around – are there llvm functions that allow for
every instruction ( or better – for every operand of an instruction ) to
determine the list of instructions that provide it with the necessary resources.
I think the confusingly named `Value::uses` gives you this information:

    for (auto &U : MyInst->uses()) {
      // U is the graph edge between the two values, U.get() is the
Value actually being used.
      Value *V = U.get();
      [...]
    }

Cheers.

Tim.