[PATCH] D54442: [llvm-exegesis] Optimize ToProcess in dbScan

[Fangrui Song via Phabricator via llvm-commits]

MaskRay marked an inline comment as done.
MaskRay added inline comments.


================
Comment at: tools/llvm-exegesis/lib/Clustering.cpp:120
     // Process P's neighbors.
-    llvm::SetVector<size_t, std::deque<size_t>> ToProcess;
-    ToProcess.insert(Neighbors.begin(), Neighbors.end());
-    while (!ToProcess.empty()) {
+    size_t Tail = 0;
+    for (size_t Q : Neighbors)
----------------
courbet wrote:
> All of this makes the dbscan implementation harder to follow. Please move all this to a separate struct:
> 
> ```
> // This is long-lived.
> struct WorkSetStorage {
>   public:
>    WorkSetStorage(size_t NumPoints) : ToProcess(NumPoints), Added(NumPoints) {}
> 
>    void setProcessed(size_t P) { Added[P] = 1; }
> 
>   private:
>    friend class WorkSet;
>    std::vector<size_t> ToProcess;
>    std::vector<char> Added;
> };
> 
> // This is short-lived and replaces  llvm::SetVector<size_t, std::deque<size_t>> ToProcess;
> class WorkSet {
>   public:
>    WorkSet(WorkSetStorage& Storage) : Storage(Storage), Head(0), Tail(0) {}
> 
>    // Inserts a point if not already processed.
>    void insert(size_t P);
> 
>    // returns the first element from the work set and pops it.
>    size_t pop();
> 
>   private:
>    WorkSetStorage& Storage;
>    size_t Head;
>    size_t Tail;
> };
> ```
Sorry I don't think making the abstraction is very necessary. The use of `Head/Tail` is very local and takes very few lines of code. The dbscan algorithm is in essence a variant of Dijkstra or FIFO Bellman-Ford. There is not much fantasy here. Keeping these lines inline is IMHO more readable.


Repository:
  rL LLVM

https://reviews.llvm.org/D54442