[clang] [llvm] [HLSL] [DXIL] Implement the `AddUint64` HLSL function and the `UAddc` DXIL op (PR #125319)

[Finn Plummer via llvm-commits]

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@@ -19105,6 +19105,51 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
     return nullptr;
 
   switch (BuiltinID) {
+  case Builtin::BI__builtin_hlsl_adduint64: {
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inbelic wrote:

I suppose I know why we weren't able to re-use the `__builtin_add_c` but for other reviewers it would be good to add context as a pr comment here. Maybe they will have suggestions as to how we could use it.

https://github.com/llvm/llvm-project/pull/125319