[PATCH] D120780: speeding up ext-tsp for huge instances

[Sergey Pupyrev via Phabricator via llvm-commits]

spupyrev created this revision.
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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D120780

Files:
  llvm/lib/Transforms/Utils/CodeLayout.cpp


Index: llvm/lib/Transforms/Utils/CodeLayout.cpp
===================================================================
--- llvm/lib/Transforms/Utils/CodeLayout.cpp
+++ llvm/lib/Transforms/Utils/CodeLayout.cpp
@@ -67,6 +67,12 @@
     "ext-tsp-backward-distance", cl::Hidden, cl::init(640),
     cl::desc("The maximum distance (in bytes) of a backward jump for ExtTSP"));
 
+// The maximum size of a chain created by the algorithm. The size is bounded
+// so that the algorithm can efficiently process extremely large instance.
+static cl::opt<unsigned>
+    MaxChainSize("ext-tsp-max-chain-size", cl::Hidden, cl::init(4096),
+                 cl::desc("The maximum size of a chain to create."));
+
 // The maximum size of a chain for splitting. Larger values of the threshold
 // may yield better quality at the cost of worsen run-time.
 static cl::opt<unsigned> ChainSplitThreshold(
@@ -226,6 +232,8 @@
 
   const std::vector<Block *> &blocks() const { return Blocks; }
 
+  size_t numBlocks() const { return Blocks.size(); }
+
   const std::vector<std::pair<Chain *, ChainEdge *>> &edges() const {
     return Edges;
   }
@@ -502,7 +510,7 @@
     AllEdges.reserve(AllJumps.size());
     for (auto &Block : AllBlocks) {
       for (auto &Jump : Block.OutJumps) {
-        const auto SuccBlock = Jump->Target;
+        auto SuccBlock = Jump->Target;
         auto CurEdge = Block.CurChain->getEdge(SuccBlock->CurChain);
         // this edge is already present in the graph
         if (CurEdge != nullptr) {
@@ -592,6 +600,10 @@
           if (ChainPred == ChainSucc)
             continue;
 
+          // Stop early if the combined chain violates the maximum allowed size
+          if (ChainPred->numBlocks() + ChainSucc->numBlocks() >= MaxChainSize)
+            continue;
+
           // Compute the gain of merging the two chains
           auto CurGain = getBestMergeGain(ChainPred, ChainSucc, ChainEdge);
           if (CurGain.score() <= EPS)


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