[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;
+    }
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llvm-beanz wrote:

Thanks @python3kgae!
So supporting the index being arbitrary is necessary.

I still can't think of any case where we have no parameters and an overload type, so if `Op.OpTypes.size() == 0` we should just not have an overload rather than overloading to the return type.

The cases where we overload on return type like `bufferLoad` and `cbufferLoadLegacy` all have parameters (see: https://godbolt.org/z/b5dn1ncvW).

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