[llvm] r202802 - [cleanup] Use early exit and simpler temporary variables to clarify the

[David Blaikie]

On Tue, Mar 4, 2014 at 1:00 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
> Author: chandlerc
> Date: Tue Mar  4 03:00:15 2014
> New Revision: 202802
>
> URL: http://llvm.org/viewvc/llvm-project?rev=202802&view=rev
> Log:
> [cleanup] Use early exit and simpler temporary variables to clarify the
> swap implementation.

As an aside (not a priority): Do you reckon most of the clients of
swap really just want/need move assignment? I imagine move assignment
would be a little easier/clearer to implement (but maybe not much?),
and just implement swap in terms of move would be only a slight
pessimization of swap (which would only be an issue if clients
/really/ care about swap perf, rather than just wanting move
assignment)?

> Modified:
>     llvm/trunk/lib/IR/Use.cpp
>
> Modified: llvm/trunk/lib/IR/Use.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Use.cpp?rev=202802&r1=202801&r2=202802&view=diff
> ==============================================================================
> --- llvm/trunk/lib/IR/Use.cpp (original)
> +++ llvm/trunk/lib/IR/Use.cpp Tue Mar  4 03:00:15 2014
> @@ -14,27 +14,26 @@
>  namespace llvm {
>
>  void Use::swap(Use &RHS) {
> -  Value *V1(Val);
> -  Value *V2(RHS.Val);
> -  if (V1 != V2) {
> -    if (V1) {
> -      removeFromList();
> -    }
> +  if (Val == RHS.Val)
> +    return;
>
> -    if (V2) {
> -      RHS.removeFromList();
> -      Val = V2;
> -      V2->addUse(*this);
> -    } else {
> -      Val = 0;
> -    }
> +  if (Val)
> +    removeFromList();
>
> -    if (V1) {
> -      RHS.Val = V1;
> -      V1->addUse(RHS);
> -    } else {
> -      RHS.Val = 0;
> -    }
> +  Value *OldVal = Val;
> +  if (RHS.Val) {
> +    RHS.removeFromList();
> +    Val = RHS.Val;
> +    Val->addUse(*this);
> +  } else {
> +    Val = 0;
> +  }
> +
> +  if (OldVal) {
> +    RHS.Val = OldVal;
> +    RHS.Val->addUse(RHS);
> +  } else {
> +    RHS.Val = 0;
>    }
>  }
>
>
>
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