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
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154370 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index cf845c1..22b5ae6 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1767,11 +1767,6 @@
// 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 @@
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 @@
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);