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

[Matt Arsenault via llvm-commits]

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@@ -2355,68 +2347,73 @@ 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());
 
   TargetLowering::ArgListTy Args;
-  TargetLowering::ArgListEntry Entry;
+  TargetLowering::ArgListEntry Entry{};
+
+  // Find users of the node that store the results. The destination pointers
+  // can be used instead of creating stack allocations.
+  StoreSDNode *SinST = nullptr;
+  StoreSDNode *CosST = nullptr;
+  for (SDNode::use_iterator UI = Node->use_begin(), UE = Node->use_end();
+       UI != UE; ++UI) {
+    SDUse &Use = UI.getUse();
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arsenm wrote:

Need to make sure the address space of the pointer matches the address space of the store 

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