[llvm] [DirectX][DXIL] Distinguish return type for overload type resolution. (PR #85646)

[Chris B via llvm-commits]

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@@ -398,10 +398,20 @@ static void emitDXILOperationTable(std::vector<DXILOperationDesc> &Ops,
 
   OS << "  static const OpCodeProperty OpCodeProps[] = {\n";
   for (auto &Op : Ops) {
+    // Consider Op.OverloadParamIndex as the overload parameter index, by
+    // default
+    auto OLParamIdx = Op.OverloadParamIndex;
+    // If no overload parameter index is set, treat first parameter type as
+    // overload type - unless the Op has no parameters, in which case treat the
+    // return type - as overload parameter to emit the appropriate overload kind
+    // enum.
+    if (OLParamIdx < 0) {
+      OLParamIdx = (Op.OpTypes.size() > 1) ? 1 : 0;
+    }
----------------
llvm-beanz wrote:

I think this still might not be right. Take for example a barrier intrinsic. It takes 0 parameters, returns void. It has no overload type at all:

```llvm
define void @"\01?barrier_wrapper@@YAXXZ"() #0 {
  call void @dx.op.barrier(i32 80, i32 9), !dbg !20 ; line:2 col:3  ; Barrier(barrierMode)
  ret void, !dbg !21 ; line:3 col:1
}
```
https://godbolt.org/z/49fW8hKh5

Are there any cases where the overload isn't the first parameter and we have an overload type?

https://github.com/llvm/llvm-project/pull/85646