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

[Matt Arsenault via llvm-commits]

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@@ -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;
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arsenm wrote:

Inside ConstantFoldScalarSincosCall, you assume they can fail independently. Are there really any cases where one can fail and not the other? In any case, the error handling should be consistent in both places 

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