[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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+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -fnative-half-type -emit-llvm-only -disable-llvm-passes -verify
+
+uint2 test_too_few_arg() {
+  return __builtin_hlsl_adduint64();
+  // expected-error at -1 {{too few arguments to function call, expected 2, have 0}}
+}
+
+uint4 test_too_many_arg(uint4 a) {
+  return __builtin_hlsl_adduint64(a, a, a);
+  // expected-error at -1 {{too many arguments to function call, expected 2, have 3}}
+}
+
+uint2 test_mismatched_arg_types(uint2 a, uint4 b) {
+  return __builtin_hlsl_adduint64(a, b);
+  // expected-error at -1 {{all arguments to '__builtin_hlsl_adduint64' must have the same type}}
+}
+
+uint2 test_too_many_arg_elements(uint3 a, uint3 b) {
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inbelic wrote:

```suggestion
uint2 test_bad_num_arg_elements(uint3 a, uint3 b) {
```

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