[llvm] [LV][EVL] Fix the check for legality of folding with EVL. (PR #125678)

[Florian Hahn via llvm-commits]

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@@ -1454,9 +1454,10 @@ class LoopVectorizationCostModel {
     // FIXME: Investigate opportunity for fixed vector factor.
     // FIXME: support fixed-order recurrences by fixing splice of non VFxUF
     // penultimate EVL.
-    bool EVLIsLegal =
-        UserIC <= 1 && TTI.hasActiveVectorLength(0, nullptr, Align()) &&
-        !EnableVPlanNativePath && Legal->getFixedOrderRecurrences().empty();
+    bool EVLIsLegal = UserIC <= 1 && IsScalableVF &&
+                      TTI.hasActiveVectorLength(0, nullptr, Align()) &&
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fhahn wrote:

It is not clear to me what claiming it currently isn't support means here. If we assume EVL == RISCV-EVL than we should be at least clear with a comment saying why it is limited to scalable vectors.

It would also be good if someone could clarify with someone familiar with PPC. If they don't support EVL, they shouldn't claim that it has ActiveVectorLength support?

https://github.com/llvm/llvm-project/pull/125678