Do not try and sink a load whose chain result has more than one use, when

trying to create RMW opportunities in the x86 backend.  This can cause a 
cycle to appear in the graph, since the other uses may eventually feed into
the TokenFactor we are sinking the load below.

llvm-svn: 81996

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index a900a69ba71..21681f9c4d0 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -364,7 +364,9 @@ static void MoveBelowTokenFactor(SelectionDAG *CurDAG, SDValue Load,
                              Store.getOperand(2), Store.getOperand(3));
 }
 
-/// isRMWLoad - Return true if N is a load that's part of RMW sub-DAG.
+/// isRMWLoad - Return true if N is a load that's part of RMW sub-DAG.  The 
+/// chain produced by the load must only be used by the store's chain operand,
+/// otherwise this may produce a cycle in the DAG.
 /// 
 static bool isRMWLoad(SDValue N, SDValue Chain, SDValue Address,
                       SDValue &Load) {
@@ -382,8 +384,9 @@ static bool isRMWLoad(SDValue N, SDValue Chain, SDValue Address,
     return false;
 
   if (N.hasOneUse() &&
+      LD->hasNUsesOfValue(1, 1) &&
       N.getOperand(1) == Address &&
-      N.getNode()->isOperandOf(Chain.getNode())) {
+      LD->isOperandOf(Chain.getNode())) {
     Load = N;
     return true;
   }