[llvm] Add `llvm.vector.partial.reduce.fadd` intrinsic (PR #159776)

[Sander de Smalen via llvm-commits]

================
@@ -12062,22 +12062,29 @@ SDValue TargetLowering::expandPartialReduceMLA(SDNode *N,
       EVT::getVectorVT(*DAG.getContext(), AccVT.getVectorElementType(),
                        MulOpVT.getVectorElementCount());
 
-  unsigned ExtOpcLHS = N->getOpcode() == ISD::PARTIAL_REDUCE_UMLA
-                      ? ISD::ZERO_EXTEND
-                      : ISD::SIGN_EXTEND;
-  unsigned ExtOpcRHS = N->getOpcode() == ISD::PARTIAL_REDUCE_SMLA
-                      ? ISD::SIGN_EXTEND
-                      : ISD::ZERO_EXTEND;
+  unsigned ExtOpcLHS =
+      N->getOpcode() == ISD::PARTIAL_REDUCE_FMLA   ? ISD::FP_EXTEND
+      : N->getOpcode() == ISD::PARTIAL_REDUCE_UMLA ? ISD::ZERO_EXTEND
+                                                   : ISD::SIGN_EXTEND;
+  unsigned ExtOpcRHS =
+      N->getOpcode() == ISD::PARTIAL_REDUCE_FMLA   ? ISD::FP_EXTEND
+      : N->getOpcode() == ISD::PARTIAL_REDUCE_SMLA ? ISD::SIGN_EXTEND
+                                                   : ISD::ZERO_EXTEND;
 
   if (ExtMulOpVT != MulOpVT) {
     MulLHS = DAG.getNode(ExtOpcLHS, DL, ExtMulOpVT, MulLHS);
     MulRHS = DAG.getNode(ExtOpcRHS, DL, ExtMulOpVT, MulRHS);
   }
   SDValue Input = MulLHS;
   APInt ConstantOne;
-  if (!ISD::isConstantSplatVector(MulRHS.getNode(), ConstantOne) ||
-      !ConstantOne.isOne())
+  if (N->getOpcode() == ISD::PARTIAL_REDUCE_FMLA) {
+    ConstantFPSDNode *C = llvm::isConstOrConstSplatFP(MulRHS, false);
+    if (!(C && C->isExactlyValue(1.0)))
+      Input = DAG.getNode(ISD::FMUL, DL, ExtMulOpVT, MulLHS, MulRHS);
+  } else if (!(ISD::isConstantSplatVector(MulRHS.getNode(), ConstantOne) &&
+               ConstantOne.isOne())) {
----------------
sdesmalen-arm wrote:

```suggestion
  } else if (!llvm::isOneConstant(MulRHS)) {
```

https://github.com/llvm/llvm-project/pull/159776