[llvm] [LV] Vectorize fmin/fmax reductions (PR #198300)

[Florian Hahn via llvm-commits]

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@@ -1680,6 +1682,20 @@ bool VPlanTransforms::handleMaxMinNumReductions(VPlan &Plan) {
   if (MinOrMaxNumReductionsToHandle.empty())
     return true;
 
+  // Unsupported VP reduction Phis should be handled by handleMultiUseReductions
+  // if the unsupported phi is part of a FindIV chain which qualifies,
+  // regardless if it's a min/max or minnum/maxnum reduction op.
+  bool AllUnsupportedPhisInMultiUseChain =
+      all_of(UnsupportedVPRdxPhis, [&](VPReductionPHIRecipe *R) {
+        return R->hasOneUse() && all_of(R->users(), [](VPUser *U) {
+                 CmpPredicate Pred;
+                 return match(U, m_Select(m_Cmp(Pred, m_VPValue(), m_VPValue()),
+                                          m_VPValue(), m_VPValue()));
+               });
+      });
+  if (!UnsupportedVPRdxPhis.empty() && AllUnsupportedPhisInMultiUseChain)
+    return true;
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fhahn wrote:

I don't think this is correct; IIRC min/maxnum reductions need special handling due to the way they handle signaling NaN.

https://github.com/llvm/llvm-project/pull/198300