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.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81996 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp
index a900a69..21681f9 100644
--- a/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -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;
}