[clang] [llvm] [HLSL] Implement `rsqrt` intrinsic (PR #84820)

[Damyan Pepper via cfe-commits]

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@@ -1153,6 +1153,38 @@ double3 rcp(double3);
 _HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
 double4 rcp(double4);
 
+//===----------------------------------------------------------------------===//
+// rsqrt builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn T rsqrt(T x)
+/// \brief RReturns the reciprocal of the square root of the specified value \a
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damyanp wrote:

Comparing this with the doc for rcp above, wonder if it should be more like:

`Returns the reciprocal of the square root of the specified value.  ie 1 / sqrt(\a x).`



https://github.com/llvm/llvm-project/pull/84820