simplify IsChainCompatible codegen, add comments. no

functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96453 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 4 deletions

diff --git a/include/llvm/CodeGen/DAGISelHeader.h b/include/llvm/CodeGen/DAGISelHeader.h
index f3eccf0..8cd11f6 100644
--- a/include/llvm/CodeGen/DAGISelHeader.h
+++ b/include/llvm/CodeGen/DAGISelHeader.h
@@ -26,9 +26,8 @@
 /// node list.
 SelectionDAG::allnodes_iterator ISelPosition;
 
-/// IsChainCompatible - Returns true if Chain is Op or Chain does
-/// not reach Op.
-static bool IsChainCompatible(SDNode *Chain, SDNode *Op) {
+/// ChainNotReachable - Returns true if Chain does not reach Op.
+static bool ChainNotReachable(SDNode *Chain, SDNode *Op) {
   if (Chain->getOpcode() == ISD::EntryToken)
     return true;
   if (Chain->getOpcode() == ISD::TokenFactor)
@@ -36,11 +35,20 @@ static bool IsChainCompatible(SDNode *Chain, SDNode *Op) {
   if (Chain->getNumOperands() > 0) {
     SDValue C0 = Chain->getOperand(0);
     if (C0.getValueType() == MVT::Other)
-      return C0.getNode() != Op && IsChainCompatible(C0.getNode(), Op);
+      return C0.getNode() != Op && ChainNotReachable(C0.getNode(), Op);
   }
   return true;
 }
 
+/// IsChainCompatible - Returns true if Chain is Op or Chain does not reach Op.
+/// This is used to ensure that there are no nodes trapped between Chain, which
+/// is the first chain node discovered in a pattern and Op, a later node, that
+/// will not be selected into the pattern.
+static bool IsChainCompatible(SDNode *Chain, SDNode *Op) {
+  return Chain == Op || ChainNotReachable(Chain, Op);
+}
+
+
 /// ISelUpdater - helper class to handle updates of the 
 /// instruciton selection graph.
 class VISIBILITY_HIDDEN ISelUpdater : public SelectionDAG::DAGUpdateListener {