[llvm] [FastIsel] Get the right register type for call instruction (PR #164565)

[Matt Arsenault via llvm-commits]

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@@ -1977,8 +1977,13 @@ SDValue SelectionDAGBuilder::getValueImpl(const Value *V) {
   if (const Instruction *Inst = dyn_cast<Instruction>(V)) {
     Register InReg = FuncInfo.InitializeRegForValue(Inst);
 
+    std::optional<CallingConv::ID> CallConv = std::nullopt;
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arsenm wrote:

```suggestion
    std::optional<CallingConv::ID> CallConv;
```

https://github.com/llvm/llvm-project/pull/164565