[llvm] [SDAG] Avoid creating redundant stack slots when lowering FSINCOS (PR #108401)

[Benjamin Maxwell via llvm-commits]

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@@ -2355,68 +2347,83 @@ static bool useSinCos(SDNode *Node) {
 }
 
 /// Issue libcalls to sincos to compute sin / cos pairs.
-void
-SelectionDAGLegalize::ExpandSinCosLibCall(SDNode *Node,
-                                          SmallVectorImpl<SDValue> &Results) {
-  RTLIB::Libcall LC;
-  switch (Node->getSimpleValueType(0).SimpleTy) {
-  default: llvm_unreachable("Unexpected request for libcall!");
-  case MVT::f32:     LC = RTLIB::SINCOS_F32; break;
-  case MVT::f64:     LC = RTLIB::SINCOS_F64; break;
-  case MVT::f80:     LC = RTLIB::SINCOS_F80; break;
-  case MVT::f128:    LC = RTLIB::SINCOS_F128; break;
-  case MVT::ppcf128: LC = RTLIB::SINCOS_PPCF128; break;
-  }
-
-  // The input chain to this libcall is the entry node of the function.
-  // Legalizing the call will automatically add the previous call to the
-  // dependence.
-  SDValue InChain = DAG.getEntryNode();
-
+void SelectionDAGLegalize::ExpandSinCosLibCall(
+    SDNode *Node, SmallVectorImpl<SDValue> &Results) {
   EVT RetVT = Node->getValueType(0);
   Type *RetTy = RetVT.getTypeForEVT(*DAG.getContext());
+  RTLIB::Libcall LC = RTLIB::getFSINCOS(RetVT);
+
+  // Find users of the node that store the results. The destination pointers
+  // can be used instead of creating stack allocations.
+  std::array<StoreSDNode *, 2> ResultStores = {nullptr};
+  for (SDNode::use_iterator UI = Node->use_begin(), UE = Node->use_end();
+       UI != UE; ++UI) {
+    SDUse &Use = UI.getUse();
+    SDNode *User = Use.getUser();
+    if (!ISD::isNormalStore(User))
+      continue;
+    auto *ST = cast<StoreSDNode>(User);
+    if (!ST->isSimple() || ST->getPointerInfo().getAddrSpace() != 0 ||
+        ST->getAlign() < DAG.getDataLayout().getABITypeAlign(RetTy))
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MacDue wrote:

Yeah, they're didn't seem to be a way to query that from the call, but I'm assuming that the call will expect the pointers to be aligned at least to the ABI requirement. 

I've renamed `RetTy`/`RetVT` to just `Ty`/`VT` (since it's both the return and argument type of the FSINCOS node).

https://github.com/llvm/llvm-project/pull/108401