Set register kill flags on the SelectionDAG path, at least in the

easy cases.

llvm-svn: 102678

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index f857a1c8942..e944dfd17d0 100644
--- a/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -296,8 +296,19 @@ InstrEmitter::AddRegisterOperand(MachineInstr *MI, SDValue Op,
     }
   }
 
+  // If this value has only one use, that use is a kill. This is a
+  // conservative approximation. Tied operands are never killed, so we need
+  // to check that. And that means we need to determine the index of the
+  // operand.
+  unsigned Idx = MI->getNumOperands();
+  while (Idx > 0 &&
+         MI->getOperand(Idx-1).isReg() && MI->getOperand(Idx-1).isImplicit())
+    --Idx;
+  bool isTied = MI->getDesc().getOperandConstraint(Idx, TOI::TIED_TO) != -1;
+  bool isKill = Op.hasOneUse() && !isTied;
+
   MI->addOperand(MachineOperand::CreateReg(VReg, isOptDef,
-                                           false/*isImp*/, false/*isKill*/,
+                                           false/*isImp*/, isKill,
                                            false/*isDead*/, false/*isUndef*/,
                                            false/*isEarlyClobber*/,
                                            0/*SubReg*/, IsDebug));