Fix a long standing tail call optimization bug. When a libcall is emitted

legalizer always use the DAG entry node. This is wrong when the libcall is
emitted as a tail call since it effectively folds the return node. If
the return node's input chain is not the entry (i.e. call, load, or store)
use that as the tail call input chain.

PR12419
rdar://9770785
rdar://11195178

llvm-svn: 154370

1 files changed, 8 insertions, 7 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index cf845c12462..22b5ae602ce 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1767,11 +1767,6 @@ SDValue SelectionDAGLegalize::ExpandBUILD_VECTOR(SDNode *Node) {
 // and leave the Hi part unset.
 SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
                                             bool isSigned) {
-  // 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();
-
   TargetLowering::ArgListTy Args;
   TargetLowering::ArgListEntry Entry;
   for (unsigned i = 0, e = Node->getNumOperands(); i != e; ++i) {
@@ -1787,9 +1782,15 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, SDNode *Node,
 
   Type *RetTy = Node->getValueType(0).getTypeForEVT(*DAG.getContext());
 
+  // By default, the input chain to this libcall is the entry node of the
+  // function. If the libcall is going to be emitted as a tail call then
+  // TLI.isUsedByReturnOnly will change it to the right chain if the return
+  // node which is being folded has a non-entry input chain.
+  SDValue InChain = DAG.getEntryNode();
+
   // isTailCall may be true since the callee does not reference caller stack
   // frame. Check if it's in the right position.
-  bool isTailCall = isInTailCallPosition(DAG, Node, TLI);
+  bool isTailCall = isInTailCallPosition(DAG, Node, InChain, TLI);
   std::pair<SDValue, SDValue> CallInfo =
     TLI.LowerCallTo(InChain, RetTy, isSigned, !isSigned, false, false,
                     0, TLI.getLibcallCallingConv(LC), isTailCall,
@@ -1825,7 +1826,7 @@ SDValue SelectionDAGLegalize::ExpandLibCall(RTLIB::Libcall LC, EVT RetVT,
   Type *RetTy = RetVT.getTypeForEVT(*DAG.getContext());
   std::pair<SDValue,SDValue> CallInfo =
   TLI.LowerCallTo(DAG.getEntryNode(), RetTy, isSigned, !isSigned, false,
-                  false, 0, TLI.getLibcallCallingConv(LC), false,
+                  false, 0, TLI.getLibcallCallingConv(LC), /*isTailCall=*/false,
                   /*doesNotReturn=*/false, /*isReturnValueUsed=*/true,
                   Callee, Args, DAG, dl);