[clang] [HLSL] Implement the `lit` intrinsic (PR #134171)

[Deric C. via cfe-commits]

================
@@ -280,6 +280,22 @@ constexpr bool4 isinf(double4 V) { return isinf((float4)V); }
 _DXC_COMPAT_TERNARY_DOUBLE_OVERLOADS(lerp)
 _DXC_COMPAT_TERNARY_INTEGER_OVERLOADS(lerp)
 
+//===----------------------------------------------------------------------===//
+// lit builtins overloads
+//===----------------------------------------------------------------------===//
+
+template <typename T>
+constexpr __detail::enable_if_t<__detail::is_arithmetic<T>::Value &&
+                                    (__detail::is_same<double, T>::value ||
----------------
Icohedron wrote:

I don't understand why `lit(bool,bool,bool)` isn't ambiguous.

C++ doesn't have half types, but defining two functions `lit(float,float,float)` and `lit(double,double,double)` and then calling `lit(bool,bool,bool)` results in a compilation error `error: call to 'lit' is ambiguous` as seen here: https://godbolt.org/z/Y3ThTfEs9
Is there special case handling for overload resolution implemented for HLSL?

https://github.com/llvm/llvm-project/pull/134171