[llvm] [SLP] Fix canConvertToFMA fmul costing (PR #216425)

[Alexey Bataev via llvm-commits]

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@@ -14489,16 +14489,40 @@ static InstructionCost canConvertToFMA(ArrayRef<Value *> VL,
   // Compare the costs.
   InstructionCost FMulPlusFAddCost = 0;
   InstructionCost FMACost = 0;
+  // Price the fmul as not fused with its user. Passing a context instruction
+  // would let targets that model the fusion discount the unfused side of the
+  // comparison as well.
+  auto GetUnfusedFMulCost = [&](Instruction *I) {
+    assert(I->getOpcode() == Instruction::FMul && "Expected an fmul");
+    TTI::OperandValueInfo Op1Info = TTI::getOperandInfo(I->getOperand(0));
+    TTI::OperandValueInfo Op2Info = TTI::getOperandInfo(I->getOperand(1));
+    return TTI.getArithmeticInstrCost(Instruction::FMul, I->getType(), CostKind,
----------------
alexey-bataev wrote:

```suggestion
    return TTI.getArithmeticInstrCost(I->getOpcode(), I->getType(), CostKind,
```

https://github.com/llvm/llvm-project/pull/216425