[llvm-commits] [llvm] r81996 - /llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp

[Nate Begeman]

Author: sampo
Date: Tue Sep 15 22:20:46 2009
New Revision: 81996

URL: http://llvm.org/viewvc/llvm-project?rev=81996&view=rev
Log:
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.


Modified:
    llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp?rev=81996&r1=81995&r2=81996&view=diff

==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelDAGToDAG.cpp Tue Sep 15 22:20:46 2009
@@ -364,7 +364,9 @@
                              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 @@
     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;
   }