[llvm] [RISCV][LoopVectorize] Use DataWithEVL as the preferred tail folding style (PR #148686)

[Philip Reames via llvm-commits]

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@@ -116,8 +116,7 @@ class RISCVTTIImpl final : public BasicTTIImplBase<RISCVTTIImpl> {
   }
   TailFoldingStyle
   getPreferredTailFoldingStyle(bool IVUpdateMayOverflow) const override {
-    return ST->hasVInstructions() ? TailFoldingStyle::Data
-                                  : TailFoldingStyle::DataWithoutLaneMask;
+    return TailFoldingStyle::DataWithEVL;
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preames wrote:

Just FYI, the comment references above is fairly misleading in my view.  From my experimentation, Data performs much worse than DataWithoutLaneMask for RISCV.  Both are much worse than EVL tail folding, but I think the data (without lane mask) is very over specialized for AArch64.  It's really not clear to me that's the right general direction.  

https://github.com/llvm/llvm-project/pull/148686