[clang] [llvm] [HLSL] [DXIL] Implement the AddUint64 HLSL function and the UAddc DXIL op (PR #127137)

[Justin Bogner via cfe-commits]

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@@ -738,6 +739,16 @@ def UMin : DXILOp<40, binary> {
   let attributes = [Attributes<DXIL1_0, [ReadNone]>];
 }
 
+def UAddc : DXILOp<44, binaryWithCarryOrBorrow > {
+  let Doc = "Unsigned 32-bit integer arithmetic add with carry. uaddc(a,b) = (a+b, a+b overflowed ? 1 : 0)";
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bogner wrote:

We should be consistent and match the docs in [DXIL.rst](https://github.com/microsoft/DirectXShaderCompiler/blob/main/docs/DXIL.rst#operations-via-external-functions) for these (even though in this case that wording is a little awkward).
```suggestion
  let Doc = "unsigned add of 32-bit operand with the carry";
```

https://github.com/llvm/llvm-project/pull/127137