[llvm] [LV] Teach the vectorizer to cost and vectorize llvm.sincos intrinsics (PR #123210)

[Benjamin Maxwell via llvm-commits]

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@@ -285,6 +286,64 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
     return false;
   }
 
+  /// Several intrinsics struct-ret (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
+  /// call is available, so the intrinsic should be assigned the default cost
+  /// (e.g. scalarization).
+  std::optional<InstructionCost> getMultipleResultIntrinsicVectorLibCallCost(
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MacDue wrote:

Prefer `std::optional` as it does not overload the meaning of 'Invalid' for "no cost decided". You could accidentally return the 'Invalid' cost as the final cost, whereas an `std::optional` forces you to check it.

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