[llvm] r204857 - Simplify PBQP graph removeAdjEdgeId implementation.

[Lang Hames]

Correct on all points. Well - I made the last cosmetic fixes - I think it's
your turn to make these. ;)

It's about time you got your name on the blame list for this thing anyway.

- Lang.



On Wed, Mar 26, 2014 at 2:55 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Wed, Mar 26, 2014 at 2:21 PM, Lang Hames <lhames at gmail.com> wrote:
> > Author: lhames
> > Date: Wed Mar 26 16:21:53 2014
> > New Revision: 204857
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=204857&view=rev
> > Log:
> > Simplify PBQP graph removeAdjEdgeId implementation.
> >
> > Modified:
> >     llvm/trunk/include/llvm/CodeGen/PBQP/Graph.h
> >
> > Modified: llvm/trunk/include/llvm/CodeGen/PBQP/Graph.h
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/PBQP/Graph.h?rev=204857&r1=204856&r2=204857&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/include/llvm/CodeGen/PBQP/Graph.h (original)
> > +++ llvm/trunk/include/llvm/CodeGen/PBQP/Graph.h Wed Mar 26 16:21:53 2014
> > @@ -67,16 +67,16 @@ namespace PBQP {
> >          return Idx;
> >        }
> >
> > -      // If a swap is performed, returns the new EdgeId that must be
> > -      // updated, otherwise returns invalidEdgeId().
> > -      EdgeId removeAdjEdgeId(AdjEdgeIdx Idx) {
> > -        EdgeId EIdToUpdate = Graph::invalidEdgeId();
> > -        if (Idx < AdjEdgeIds.size() - 1) {
> > -          std::swap(AdjEdgeIds[Idx], AdjEdgeIds.back());
> > -          EIdToUpdate = AdjEdgeIds[Idx];
> > -        }
> > +      void removeAdjEdgeId(Graph &G, NodeId ThisNId, AdjEdgeIdx Idx) {
> > +        // Swap-and-pop for fast removal.
> > +        //   1) Update the adj index of the edge currently at back().
> > +        //   2) Swap Edge at Idx with back().
> > +        //   3) pop_back()
> > +        // If Idx == size() - 1 then the updateAdjEdgeIdx and swap are
> > +        // redundant, but both operations are cheap.
> > +        G.getEdge(AdjEdgeIds.back()).updateAdjEdgeIdx(ThisNId, Idx);
>
> Is there more to this "updateAdjEdgeIdx" function or is it just a
> trivial (indexed/mapped) setter? "update" rather than "set" makes me
> wonder what work it's doing...
>
> > +        std::swap(AdjEdgeIds[Idx], AdjEdgeIds.back());
>
> Since you're about to pop the back anyway, this could just be
> AdjEdgeIds[Idx] = AdjEdgeIds.back(); right? (if they were movable, you
> could add a std::move() around the RHS, but they're just indexes,
> right?)
>
> (& comment 2 would be "move back() down to fill the hole at Idx" or
> something like that)
>
> >          AdjEdgeIds.pop_back();
> > -        return EIdToUpdate;
> >        }
> >
> >        const AdjEdgeList& getAdjEdgeIds() const { return AdjEdgeIds; }
> > @@ -138,9 +138,7 @@ namespace PBQP {
> >          assert(ThisEdgeAdjIdxs[NIdx] !=
> NodeEntry::getInvalidAdjEdgeIdx() &&
> >                 "Edge not connected to NIds[NIdx].");
> >          NodeEntry &N = G.getNode(NIds[NIdx]);
> > -        EdgeId EIdToUpdate = N.removeAdjEdgeId(ThisEdgeAdjIdxs[NIdx]);
> > -        if (EIdToUpdate != Graph::invalidEdgeId())
> > -          G.getEdge(EIdToUpdate).updateAdjEdgeIdx(NIds[NIdx],
> ThisEdgeAdjIdxs[NIdx]);
> > +        N.removeAdjEdgeId(G, NIds[NIdx], ThisEdgeAdjIdxs[NIdx]);
> >          ThisEdgeAdjIdxs[NIdx] = NodeEntry::getInvalidAdjEdgeIdx();
> >        }
> >
> >
> >
> > _______________________________________________
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> > llvm-commits at cs.uiuc.edu
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>
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