Fix cycle in selection DAG introduced by extractelement legalization

[oota-llvm.git] / lib / CodeGen / SelectionDAG / LegalizeDAG.cpp

diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 3393e17b8e097c910d1a0a488f4c5abc0a70fd7e..f46767f6c4a1e4b59c7bdd44ea7e244673ece8b1 100644 (file)
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -1463,6 +1463,11 @@ SDValue SelectionDAGLegalize::ExpandExtractFromVectorThroughStack(SDValue Op) {
   // series of EXTRACT_VECTOR_ELT nodes are generated, one for each element in
   // the vector. If all are expanded here, we don't want one store per vector
   // element.
+
+  // Caches for hasPredecessorHelper
+  SmallPtrSet<const SDNode *, 32> Visited;
+  SmallVector<const SDNode *, 16> Worklist;
+
   SDValue StackPtr, Ch;
   for (SDNode::use_iterator UI = Vec.getNode()->use_begin(),
        UE = Vec.getNode()->use_end(); UI != UE; ++UI) {
@@ -1477,6 +1482,12 @@ SDValue SelectionDAGLegalize::ExpandExtractFromVectorThroughStack(SDValue Op) {
       if (!ST->getChain().reachesChainWithoutSideEffects(DAG.getEntryNode()))
         continue;
 
+      // If the index is dependent on the store we will introduce a cycle when
+      // creating the load (the load uses the index, and by replacing the chain
+      // we will make the index dependent on the load).
+      if (Idx.getNode()->hasPredecessorHelper(ST, Visited, Worklist))
+        continue;
+
       StackPtr = ST->getBasePtr();
       Ch = SDValue(ST, 0);
       break;