[PATCH] D132261: [SLP]Do not reduce repeated values, use scalar red ops instead.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added inline comments.


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Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:12560
+      MapVector<Value *, unsigned> SameValuesCounter;
+      for (Value *V : Candidates)
+        ++SameValuesCounter.insert(std::make_pair(V, 0)).first->second;
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vdmitrie wrote:
> We don't need to collect repeating counters if IsSupportedreusedRdxOp is false.
No, still need it, it is used to produce vector of unique scalars, see line 12577.


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Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:12566
+          RdxKind != RecurKind::FMul && RdxKind != RecurKind::FMulAdd;
+      bool SameScaleFactor = false;
+      bool HasReusedScalars = SameValuesCounter.size() != Candidates.size();
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vdmitrie wrote:
> This needs a comment. Are you trying to catch a case for special processing when each value used same times? Please describe what is the benefit of catching such cases?
> Why are you trying to calculate it this early?
It may help to produce better vector ops. Say, we have 8 x aabbccdd. It will require reduction of 8 elements + the built tree still will operate on 4 x element, but the last node will have reshuffle from 4 x vector to 8 x vector + red(8 x ). Instead we may have just red(4 x abcd)*2.


Repository:
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  https://reviews.llvm.org/D132261/new/

https://reviews.llvm.org/D132261