[clang] [llvm] [HLSL] implement `clamp` intrinsic (PR #85424)

[Justin Bogner via llvm-commits]

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@@ -252,6 +252,116 @@ double3 ceil(double3);
 _HLSL_BUILTIN_ALIAS(__builtin_elementwise_ceil)
 double4 ceil(double4);
 
+//===----------------------------------------------------------------------===//
+// clamp builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn T clamp(T X, T Min, T Max)
+/// \brief Clamps the specified value \a X to the specified
+/// minimum ( \a Min) and maximum ( \a Max) range.
+/// \param X A value to clamp.
+/// \param Min The specified minimum range.
+/// \param Max The specified maximum range.
+///
+/// Returns The clamped value for the \a X parameter.
+/// For values of -INF or INF, clamp will behave as expected.
+/// However for values of NaN, the results are undefined.
+
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_clamp)
+half clamp(half, half, half);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_clamp)
+half2 clamp(half2, half2, half2);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_clamp)
+half3 clamp(half3, half3, half3);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_clamp)
+half4 clamp(half4, half4, half4);
+
+#ifdef __HLSL_ENABLE_16_BIT
----------------
bogner wrote:

This is pre-existing, so no change needed here, but maybe we should revisit it later. The difference between `_HLSL_16BIT_AVAILABILITY` (for half) and guarding with `#ifdef __HLSL_ENABLE_16BIT` (for int16/uint16) feels kind of subtle. I worry we could make mistakes here in the future.

https://github.com/llvm/llvm-project/pull/85424