[llvm] [LV] Autovectorization for the all-in-one histogram intrinsic (PR #91458)

[Florian Hahn via llvm-commits]

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@@ -144,7 +144,9 @@ class MemoryDepChecker {
       // on MinDepDistBytes.
       BackwardVectorizable,
       // Same, but may prevent store-to-load forwarding.
-      BackwardVectorizableButPreventsForwarding
+      BackwardVectorizableButPreventsForwarding,
+      // Access is to a loop loaded value, but is part of a histogram operation.
+      Histogram
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fhahn wrote:

Hmm but the current version still has to analyze all stores for histograms even if the option is off?. Just trying to see if there are alternatives to avoid pulling some very specific analysis logic into LAA. 

IIUC without the histogram analysis, we would have an unknown dependence, that LV could analyze separately if histograms are supported, like other passes like LoopDistribute or LoopLoadeleimination do?

Would be great if it would be possible to support this without needing to increase the complexity of dependence analysis in LAA

https://github.com/llvm/llvm-project/pull/91458