[llvm] [InstSimplify] Add basic constant folding for `llvm.sincos` (PR #114527)

[Benjamin Maxwell via llvm-commits]

================
@@ -3466,6 +3467,44 @@ ConstantFoldStructCall(StringRef Name, Intrinsic::ID IntrinsicID,
       return nullptr;
     return ConstantStruct::get(StTy, Result0, Result1);
   }
+  case Intrinsic::sincos: {
+    Type *Ty = StTy->getContainedType(0);
+    Type *TyScalar = Ty->getScalarType();
+
+    auto ConstantFoldScalarSincosCall =
+        [&](Constant *Op) -> std::pair<Constant *, Constant *> {
+      Constant *SinResult =
+          ConstantFoldScalarCall(Name, Intrinsic::sin, TyScalar, Op, TLI, Call);
+      if (!SinResult)
+        return {};
+      Constant *CosResult =
+          ConstantFoldScalarCall(Name, Intrinsic::cos, TyScalar, Op, TLI, Call);
+      if (!CosResult)
+        return {};
+      return std::make_pair(SinResult, CosResult);
+    };
+
+    if (auto *FVTy = dyn_cast<FixedVectorType>(Ty)) {
+      SmallVector<Constant *, 4> SinResults(FVTy->getNumElements());
+      SmallVector<Constant *, 4> CosResults(FVTy->getNumElements());
+
+      for (unsigned I = 0, E = FVTy->getNumElements(); I != E; ++I) {
+        Constant *Lane = Operands[0]->getAggregateElement(I);
+        std::tie(SinResults[I], CosResults[I]) =
+            ConstantFoldScalarSincosCall(Lane);
+        if (!SinResults[I])
+          return nullptr;
----------------
MacDue wrote:

> Are there really any cases where one can fail and not the other?

Probably not, but they both look like calls that could return null, so checking them both seems justified.

https://github.com/llvm/llvm-project/pull/114527