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

[Farzon Lotfi via cfe-commits]

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+; RUN: opt -S -dxil-op-lower -mtriple=dxil-pc-shadermodel6.3-library %s | FileCheck %s
+
+; CHECK: %dx.types.i32c = type { i32, i1 }
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farzonl wrote:

We need a vec2, and vec4 test that uses the vector scalarizer pass. What you will find is we can't scalarize UAddc without adding it to `llvm/lib/Target/DirectX/DirectXTargetTransformInfo.cpp` `isTargetIntrinsicTriviallyScalarizable`.

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