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

lib/CodeGen/Analysis.cpp

@@ -290,7 +290,7 @@ bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
 }
 
 bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
-                                const TargetLowering &TLI) {
+                                SDValue &Chain, const TargetLowering &TLI) {
   const Function *F = DAG.getMachineFunction().getFunction();
 
   // Conservatively require the attributes of the call to match those of
@@ -304,5 +304,5 @@ bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
     return false;
 
   // Check if the only use is a function return node.
-  return TLI.isUsedByReturnOnly(Node);
+  return TLI.isUsedByReturnOnly(Node, Chain);
 }