[llvm] r230904 - [PBQP] Do not add an edge between nodes with totally disjoint allowed registers
Arnaud A. de Grandmaison
arnaud.degrandmaison at arm.com
Sun Mar 1 13:27:33 PST 2015
Addressed with r230908. Thanks David !
Cheers,
Arnaud
From: David Blaikie [mailto:dblaikie at gmail.com]
Sent: 01 March 2015 21:59
To: Arnaud De Grandmaison
Cc: llvm-commits at cs.uiuc.edu
Subject: Re: [llvm] r230904 - [PBQP] Do not add an edge between nodes with totally disjoint allowed registers
On Mar 1, 2015 12:42 PM, "Arnaud A. de Grandmaison" <arnaud.degrandmaison at arm.com> wrote:
>
> Author: aadg
> Date: Sun Mar 1 14:39:34 2015
> New Revision: 230904
>
> URL: http://llvm.org/viewvc/llvm-project?rev=230904 <http://llvm.org/viewvc/llvm-project?rev=230904&view=rev> &view=rev
> Log:
> [PBQP] Do not add an edge between nodes with totally disjoint allowed registers
>
> Such edges are zero matrix, and they bring no additional info to the
> allocation problem, apart from contributing to nodes' degree. Removing
> those edges is expected to improve allocation time.
>
> Tune the spill cost comparison, as this gives better average performances
> now that the nodes' degrees has changed.
>
> Modified:
> llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h
> llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp
>
> Modified: llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h?rev=230904 <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h?rev=230904&r1=230903&r2=230904&view=diff> &r1=230903&r2=230904&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h (original)
> +++ llvm/trunk/include/llvm/CodeGen/RegAllocPBQP.h Sun Mar 1 14:39:34 2015
> @@ -544,8 +544,10 @@ private:
> public:
> SpillCostComparator(const Graph& G) : G(G) {}
> bool operator()(NodeId N1Id, NodeId N2Id) {
> - PBQPNum N1SC = G.getNodeCosts(N1Id)[0] / G.getNodeDegree(N1Id);
> - PBQPNum N2SC = G.getNodeCosts(N2Id)[0] / G.getNodeDegree(N2Id);
> + PBQPNum N1SC = G.getNodeCosts(N1Id)[0];
> + PBQPNum N2SC = G.getNodeCosts(N2Id)[0];
> + if (N1SC == N2SC)
> + return G.getNodeDegree(N1Id) < G.getNodeDegree(N2Id);
> return N1SC < N2SC;
> }
> private:
>
> Modified: llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp?rev=230904 <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp?rev=230904&r1=230903&r2=230904&view=diff> &r1=230903&r2=230904&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp (original)
> +++ llvm/trunk/lib/CodeGen/RegAllocPBQP.cpp Sun Mar 1 14:39:34 2015
> @@ -178,8 +178,38 @@ class Interference : public PBQPRAConstr
> private:
>
> typedef const PBQP::RegAlloc::AllowedRegVector* AllowedRegVecPtr;
> - typedef std::pair<AllowedRegVecPtr, AllowedRegVecPtr> IMatrixKey;
> - typedef DenseMap<IMatrixKey, PBQPRAGraph::MatrixPtr> IMatrixCache;
> + typedef std::pair<AllowedRegVecPtr, AllowedRegVecPtr> IKey;
> + typedef DenseMap<IKey, PBQPRAGraph::MatrixPtr> IMatrixCache;
> + typedef DenseSet<IKey> DisjointAllowedRegsCache;
> +
> + bool haveDisjointAllowedRegs(const PBQPRAGraph &G, PBQPRAGraph::NodeId NId,
> + PBQPRAGraph::NodeId MId,
> + const DisjointAllowedRegsCache &D) const {
> + const auto *NRegs = &G.getNodeMetadata(NId).getAllowedRegs();
> + const auto *MRegs = &G.getNodeMetadata(MId).getAllowedRegs();
> +
> + if (NRegs == MRegs)
> + return false;
> +
> + if (NRegs < MRegs)
> + return D.count(IKey(NRegs, MRegs)) > 0;
> + else
You can drop the else after return (per style guide)
> + return D.count(IKey(MRegs, NRegs)) > 0;
> + }
> +
> + void setDisjointAllowedRegs(const PBQPRAGraph &G, PBQPRAGraph::NodeId NId,
> + PBQPRAGraph::NodeId MId,
> + DisjointAllowedRegsCache &D) {
> + const auto *NRegs = &G.getNodeMetadata(NId).getAllowedRegs();
> + const auto *MRegs = &G.getNodeMetadata(MId).getAllowedRegs();
> +
> + assert(NRegs != MRegs && "AllowedRegs can not be disjoint with itself");
> +
> + if (NRegs < MRegs)
> + D.insert(IKey(NRegs, MRegs));
> + else
> + D.insert(IKey(MRegs, NRegs));
> + }
>
> // Holds (Interval, CurrentSegmentID, and NodeId). The first two are required
> // for the fast interference graph construction algorithm. The last is there
> @@ -247,6 +277,9 @@ public:
> // and uniquing them.
> IMatrixCache C;
>
> + // Cache known disjoint allowed registers pairs
> + DisjointAllowedRegsCache D;
> +
> typedef std::set<IntervalInfo, decltype(&lowestEndPoint)> IntervalSet;
> typedef std::priority_queue<IntervalInfo, std::vector<IntervalInfo>,
> decltype(&lowestStartPoint)> IntervalQueue;
> @@ -290,6 +323,11 @@ public:
> for (const auto &A : Active) {
> PBQP::GraphBase::NodeId MId = getNodeId(A);
>
> + // Do not add an edge when the nodes' allowed registers do not
> + // intersect: there is obviously no interference.
> + if (haveDisjointAllowedRegs(G, NId, MId, D))
> + continue;
> +
> // Check that we haven't already added this edge
> // FIXME: findEdge is expensive in the worst case (O(max_clique(G))).
> // It might be better to replace this with a local bit-matrix.
> @@ -297,7 +335,8 @@ public:
> continue;
>
> // This is a new edge - add it to the graph.
> - createInterferenceEdge(G, NId, MId, C);
> + if (!createInterferenceEdge(G, NId, MId, C))
> + setDisjointAllowedRegs(G, NId, MId, D);
> }
>
> // Finally, add Cur to the Active set.
> @@ -307,35 +346,48 @@ public:
>
> private:
>
> - void createInterferenceEdge(PBQPRAGraph &G, PBQPRAGraph::NodeId NId,
> - PBQPRAGraph::NodeId MId, IMatrixCache &C) {
> + // Create an Interference edge and add it to the graph, unless it is
> + // a null matrix, meaning the nodes' allowed registers do not have any
> + // interference. This case occurs frequently between integer and floating
> + // point registers for example.
> + // return true iff both nodes interferes.
> + bool createInterferenceEdge(PBQPRAGraph &G,
> + PBQPRAGraph::NodeId NId, PBQPRAGraph::NodeId MId,
> + IMatrixCache &C) {
>
> const TargetRegisterInfo &TRI =
> *G.getMetadata().MF.getSubtarget().getRegisterInfo();
> -
> const auto &NRegs = G.getNodeMetadata(NId).getAllowedRegs();
> const auto &MRegs = G.getNodeMetadata(MId).getAllowedRegs();
>
> // Try looking the edge costs up in the IMatrixCache first.
> - IMatrixKey K(&NRegs, &MRegs);
> + IKey K(&NRegs, &MRegs);
> IMatrixCache::iterator I = C.find(K);
> if (I != C.end()) {
> G.addEdgeBypassingCostAllocator(NId, MId, I->second);
> - return;
> + return true;
> }
>
> PBQPRAGraph::RawMatrix M(NRegs.size() + 1, MRegs.size() + 1, 0);
> + bool NodesInterfere = false;
> for (unsigned I = 0; I != NRegs.size(); ++I) {
> unsigned PRegN = NRegs[I];
> for (unsigned J = 0; J != MRegs.size(); ++J) {
> unsigned PRegM = MRegs[J];
> - if (TRI.regsOverlap(PRegN, PRegM))
> + if (TRI.regsOverlap(PRegN, PRegM)) {
> M[I + 1][J + 1] = std::numeric_limits<PBQP::PBQPNum>::infinity();
> + NodesInterfere = true;
> + }
> }
> }
>
> + if (!NodesInterfere)
> + return false;
> +
> PBQPRAGraph::EdgeId EId = G.addEdge(NId, MId, std::move(M));
> C[K] = G.getEdgeCostsPtr(EId);
> +
> + return true;
> }
> };
>
>
>
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