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

[Kaitlin Peng via cfe-commits]

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@@ -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 ||
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kmpeng wrote:

The ambiguous error doesn't appear, but the half definition in `hlsl_instrinsics.h` doesn't seem to be used anymore when we're only checking `__detail::is_arithmetic<T>` in the overloads. The tablegen shows half inputs being casted to floats and then the float definition of `lit` being called.

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