[DAGCombine] Enable more pre-indexed stores

    
The current check in CombineToPreIndexedLoadStore is too
conversative, preventing a pre-indexed store when the base pointer
is a predecessor of the value being stored. Instead, we should check
the pointer operand of the store.

Differential Revision: https://reviews.llvm.org/D56719

llvm-svn: 351933

1 files changed, 7 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b440bbe29fd..97b21e108ea 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -12652,7 +12652,13 @@ bool DAGCombiner::CombineToPreIndexedLoadStore(SDNode *N) {
   // Check #2.
   if (!isLoad) {
     SDValue Val = cast<StoreSDNode>(N)->getValue();
-    if (Val == BasePtr || BasePtr.getNode()->isPredecessorOf(Val.getNode()))
+
+    // Would require a copy.
+    if (Val == BasePtr)
+      return false;
+
+    // Would create a cycle.
+    if (Val == Ptr || Ptr->isPredecessorOf(Val.getNode()))
       return false;
   }