[llvm] [AArch64] Change f128 costs to 10 * legalization factor. (PR #202555)

[David Sherwood via llvm-commits]

================
@@ -4389,6 +4389,11 @@ InstructionCost AArch64TTIImpl::getArithmeticInstrCost(
             }))
       return *PromotedCost;
 
+    // fp128 all go via libcalls
+    if (Ty->getScalarType()->isFP128Ty())
+      return CostKind == TTI::TCK_CodeSize ? 1 : 10 * LT.first;
----------------
david-arm wrote:

Is this right? For the code size case we presumably want to return LT.first to reflect the number of calls required? I was expecting something like:

```
  return CostKind == LT.first * (TTI::TCK_CodeSize ? 1 : 10);
```

https://github.com/llvm/llvm-project/pull/202555