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

1 files changed, 4 insertions, 2 deletions

diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index c885d2a..720c9df 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1274,9 +1274,11 @@ public:
   }
 
   /// isUsedByReturnOnly - Return true if result of the specified node is used
-  /// by a return node only. This is used to determine whether it is possible
+  /// by a return node only. It also compute and return the input chain for the
+  /// tail call.
+  /// This is used to determine whether it is possible
   /// to codegen a libcall as tail call at legalization time.
-  virtual bool isUsedByReturnOnly(SDNode *) const {
+  virtual bool isUsedByReturnOnly(SDNode *, SDValue &Chain) const {
     return false;
   }