Delete a store whose input is a load from the same pointer:

  x = load p
  store x -> p


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45398 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 1 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6eaf7ae7f4..242fffd180 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -4223,7 +4223,7 @@ SDOperand DAGCombiner::visitSTORE(SDNode *N) {
   if (CombineToPreIndexedLoadStore(N) || CombineToPostIndexedLoadStore(N))
     return SDOperand(N, 0);
 
-  // FIXME: is there such a think as a truncating indexed store?
+  // FIXME: is there such a thing as a truncating indexed store?
   if (ST->isTruncatingStore() && ST->getAddressingMode() == ISD::UNINDEXED &&
       MVT::isInteger(Value.getValueType())) {
     // See if we can simplify the input to this truncstore with knowledge that
@@ -4243,6 +4243,17 @@ SDOperand DAGCombiner::visitSTORE(SDNode *N) {
       return SDOperand(N, 0);
   }
   
+  // If this is a load followed by a store to the same location, then the store
+  // is dead/noop.
+  if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(Value)) {
+    if (Chain.Val == Ld && Ld->getBasePtr() == Ptr &&
+        ST->getAddressingMode() == ISD::UNINDEXED &&
+        ST->getStoredVT() == Ld->getLoadedVT()) {
+      // The store is dead, remove it.
+      return Chain;
+    }
+  }
+  
   return SDOperand();
 }