[llvm] [CostModel] Handle vector struct results and cost `llvm.sincos` (PR #123210)

[David Sherwood via llvm-commits]

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@@ -285,6 +286,64 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     return false;
   }
 
+  /// Several intrinsics that return structs (including llvm.sincos[pi] and
+  /// llvm.modf) can be lowered to a vector library call (for certain VFs). The
+  /// vector library functions correspond to the scalar calls (e.g. sincos or
+  /// modf), which unlike the intrinsic return values via output pointers. This
+  /// helper checks if a vector call exists for the given intrinsic, and returns
+  /// the cost, which includes the cost of the mask (if required), and the loads
+  /// for values returned via output pointers. \p LC is the scalar libcall and
+  /// \p CallRetElementIndex (optional) is the struct element which is mapped to
+  /// the call return value. If std::nullopt is returned, the no vector library
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david-arm wrote:

nit: I think this should be `then no vector ...`

https://github.com/llvm/llvm-project/pull/123210