[llvm] [SLP] Support ordered FAdd reductions in SLPVectorizer (PR #146570)

[Alexey Bataev via llvm-commits]

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@@ -22066,6 +22089,68 @@ class HorizontalReduction {
            (I && !isa<LoadInst>(I) && isValidForAlternation(I->getOpcode()));
   }
 
+  bool checkOperandsOrder() const {
+    auto OpsVec = reverse(ReductionOps[0]);
+    if (!isOrderedFaddReduction() || empty(OpsVec))
+      return false;
+    Value *PrevOperand = *OpsVec.begin();
+    for (auto *I : drop_begin(OpsVec)) {
+      Value *Op1 = cast<BinaryOperator>(I)->getOperand(0);
+      if (Op1 != PrevOperand)
+        return false;
+      PrevOperand = I;
+    }
+    return true;
+  }
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alexey-bataev wrote:

No need for this function, if you'll preserve the order during building list of the values/operands. That's why I asked to separate this from the existing processing for the associative reduction

https://github.com/llvm/llvm-project/pull/146570