[llvm] [LV] Vectorize histogram operations (PR #99851)

[Florian Hahn via llvm-commits]

================
@@ -1054,6 +1058,110 @@ bool LoopVectorizationLegality::canVectorizeInstrs() {
   return true;
 }
 
+/// Find Histogram counts that match high-level code in loops:
+/// \code
+/// buckets[indices[i]]+=step;
+/// \endcode
+///
+/// It matches a pattern starting from \p HSt, which Stores to the 'buckets'
+/// array the computed histogram. It uses a BinOp to sum all counts, storing
+/// them using a loop-variant index Load from the 'indices' input array.
+///
+/// On successful matches it updates the STATISTIC 'HistogramsDetected',
+/// regardless of hardware support. When there is support, it additionally
+/// stores the BinOp/Load pairs in \p HistogramCounts, as well the pointers
+/// used to update histogram in \p HistogramPtrs.
+
+static bool findHistograms(LoadInst *LI, StoreInst *HSt, Loop *TheLoop,
----------------
fhahn wrote:

nit: findHistograms as this only looks for a single one?

https://github.com/llvm/llvm-project/pull/99851