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Author: huntergr-arm

llvm/lib/Transforms/Vectorize/VPRecipeBuilder.h

@@ -103,8 +103,9 @@ class VPRecipeBuilder {
                             VPBasicBlock *VPBB);
 
   /// Makes Histogram count operations safe for vectorization, by emitting a
-  /// Histogram LLVM Intrinsic before the BinOp (Add/Sub) that does the actual
-  /// counting.
+  /// llvm.experimental.vector.histogram.add intrinsic in place of the
+  /// Load + Add|Sub + Store operations that perform the histogram in the
+  /// original scalar loop.
   VPHistogramRecipe *tryToWidenHistogram(const HistogramInfo *HI,
                                          ArrayRef<VPValue *> Operands);
 

llvm/test/Transforms/LoopVectorize/AArch64/sve2-histcnt.ll

@@ -319,6 +319,7 @@ for.exit:
   ret void
 }
 
+;; We don't support histograms with a update value that's not loop-invariant.
 define void @histogram_varying_increment(ptr noalias %buckets, ptr readonly %indices, ptr readonly %incvals, i64 %N) #0 {
 ; CHECK-LABEL: define void @histogram_varying_increment(
 ; CHECK-SAME: ptr noalias [[BUCKETS:%.*]], ptr readonly [[INDICES:%.*]], ptr readonly [[INCVALS:%.*]], i64 [[N:%.*]]) #[[ATTR0]] {