llvm dev - Feb 2016 - Difference between “uses” and “user”

Hi everyone,

Instruction and Value classes have "Uses" and "User". What
is the
difference between them?

I think that "Uses" gives all the instructions/values that a
particular
Value depends on and "User" gives all the instructions/values that
depend
on that particular value. Is that right?

Best,
Carlo
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2016-02-16 10:24 GMT+01:00 Carlos Alba via llvm-dev <llvm-dev at
lists.llvm.org>:
> Hi everyone,
>
> Instruction and Value classes have "Uses" and "User".
What is the difference
> between them?
>
> I think that "Uses" gives all the instructions/values that a
particular
> Value depends on and "User" gives all the instructions/values
that depend on
> that particular value. Is that right?
Given as example the instruction %add in

%add = add i32 %1, 1
[...]
%sub = sub i32 %add, 1

You can think of an llvm::Use as a tuple (Instruction,ArgumentNo)
Take for example the first argument of the add: (%add,0)
Use::getUser() returns that Instruction (%add)
Use::getOperandNo() returns that ArgumentNo (0)
Use::get() returns the argument itself (%1); llvm::Use operator
overloads may make the llvm::Use appear like it is the argument's
llvm::Value itself

add->operands() enumerates the llvm::Use(s), i.e. (%add,0) for the
first argument (which is "%1") and (%add,1) for the second (which is
"1")
add->uses() enumerates where %add is used, i.e. (%sub,0) in this example.
add->users() enumerates only the instructions which use %add, i.e.
%sub in this example (without specifying the ArgumentNo)

llvm::User is a base class of llvm::Instruction that implements the
argument list mechanism (Lists of llvm::Value(s)).

Hope that helps any corrections/additions are welcome.

Michael

So, according to your explanation, do you think that it is possible to get
the value produced by an instruction? something like the following
(roughly):

for(auto operand : instruction->getOperandList())
      if( operand -> getUser == instruction )
           return true;
      else
           continue;

Best,
Carlo


On Tue, Feb 16, 2016 at 1:01 PM, Michael Kruse <llvmdev at meinersbur.de>
wrote:
> 2016-02-16 10:24 GMT+01:00 Carlos Alba via llvm-dev <
> llvm-dev at lists.llvm.org>:
> > Hi everyone,
> >
> > Instruction and Value classes have "Uses" and
"User". What is the
> difference
> > between them?
> >
> > I think that "Uses" gives all the instructions/values that a
particular
> > Value depends on and "User" gives all the
instructions/values that
> depend on
> > that particular value. Is that right?
>
> Given as example the instruction %add in
>
> %add = add i32 %1, 1
> [...]
> %sub = sub i32 %add, 1
>
> You can think of an llvm::Use as a tuple (Instruction,ArgumentNo)
> Take for example the first argument of the add: (%add,0)
> Use::getUser() returns that Instruction (%add)
> Use::getOperandNo() returns that ArgumentNo (0)
> Use::get() returns the argument itself (%1); llvm::Use operator
> overloads may make the llvm::Use appear like it is the argument's
> llvm::Value itself
>
> add->operands() enumerates the llvm::Use(s), i.e. (%add,0) for the
> first argument (which is "%1") and (%add,1) for the second (which
is
> "1")
> add->uses() enumerates where %add is used, i.e. (%sub,0) in this
example.
> add->users() enumerates only the instructions which use %add, i.e.
> %sub in this example (without specifying the ArgumentNo)
>
> llvm::User is a base class of llvm::Instruction that implements the
> argument list mechanism (Lists of llvm::Value(s)).
>
> Hope that helps any corrections/additions are welcome.
>
> Michael
>
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