Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -509,10 +509,11 @@
     bool isAndLoadExtLoad(ConstantSDNode *AndC, LoadSDNode *LoadN,
                           EVT LoadResultTy, EVT &ExtVT);
 
-    /// Helper function to calculate whether the given Load can have its
+    /// Helper function to calculate whether the given Load/Store can have its
     /// width reduced to ExtVT.
-    bool isLegalNarrowLoad(LoadSDNode *LoadN, ISD::LoadExtType ExtType,
-                           EVT &ExtVT, unsigned ShAmt = 0);
+    bool isLegalNarrowLdSt(LSBaseSDNode *LDSTN, ISD::LoadExtType ExtType,
+                           EVT &MemVT, unsigned ShAmt = 0,
+                           bool StrictInside = false);
 
     /// Used by BackwardsPropagateMask to find suitable loads.
    bool SearchForAndLoads(SDNode *N, SmallPtrSetImpl<LoadSDNode*> &Loads,
@@ -3960,64 +3961,78 @@
   return true;
 }
 
-bool DAGCombiner::isLegalNarrowLoad(LoadSDNode *LoadN, ISD::LoadExtType ExtType,
-                                    EVT &ExtVT, unsigned ShAmt) {
-  // Don't transform one with multiple uses, this would require adding a new
-  // load.
-  if (!SDValue(LoadN, 0).hasOneUse())
+bool DAGCombiner::isLegalNarrowLdSt(LSBaseSDNode *LDST,
+                                    ISD::LoadExtType ExtType, EVT &MemVT,
+                                    unsigned ShAmt, bool StrictInside) {
+  if (!LDST)
     return false;
-
-  if (LegalOperations &&
-      !TLI.isLoadExtLegal(ExtType, LoadN->getValueType(0), ExtVT))
+  // Only allow byte offsets.
+  if (ShAmt % 8)
     return false;
 
   // Do not generate loads of non-round integer types since these can
   // be expensive (and would be wrong if the type is not byte sized).
-  if (!ExtVT.isRound())
+  if (!MemVT.isRound())
     return false;
 
   // Don't change the width of a volatile load.
-  if (LoadN->isVolatile())
+  if (LDST->isVolatile())
     return false;
 
   // Verify that we are actually reducing a load width here.
-  if (LoadN->getMemoryVT().getSizeInBits() < ExtVT.getSizeInBits())
+  if (LDST->getMemoryVT().getSizeInBits() < MemVT.getSizeInBits())
     return false;
 
-  // For the transform to be legal, the load must produce only two values
-  // (the value loaded and the chain).  Don't transform a pre-increment
-  // load, for example, which produces an extra value.  Otherwise the
-  // transformation is not equivalent, and the downstream logic to replace
-  // uses gets things wrong.
-  if (LoadN->getNumValues() > 2)
+  // Ensure that this isn't going to produce an unsupported unaligned access.
+  if (ShAmt &&
+      !TLI.allowsMemoryAccess(*DAG.getContext(), DAG.getDataLayout(), MemVT,
+                              LDST->getAddressSpace(), ShAmt / 8))
     return false;
 
- // Only allow byte offsets.
-  if (ShAmt % 8)
+  // It's not possible to generate a constant of extended or untyped type.
+  EVT PtrType = LDST->getBasePtr().getValueType();
+  if (PtrType == MVT::Untyped || PtrType.isExtended())
     return false;
 
-  // Ensure that this isn't going to produce an unsupported unaligned access.
-  if (ShAmt && !TLI.allowsMemoryAccess(*DAG.getContext(), DAG.getDataLayout(),
-                                       ExtVT, LoadN->getAddressSpace(),
-                                       ShAmt / 8))
-    return false;
+  if (isa<LoadSDNode>(LDST)) {
+    LoadSDNode *Load = cast<LoadSDNode>(LDST);
+    // Don't transform one with multiple uses, this would require adding a new
+    // load.
+    if (!SDValue(Load, 0).hasOneUse())
+      return false;
 
+    if (LegalOperations &&
+        !TLI.isLoadExtLegal(ExtType, Load->getValueType(0), MemVT))
+      return false;
 
-  // If the load that we're shrinking is an extload and we're not just
-  // discarding the extension we can't simply shrink the load. Bail.
-  // TODO: It would be possible to merge the extensions in some cases.
-  if (LoadN->getExtensionType() != ISD::NON_EXTLOAD &&
-      LoadN->getMemoryVT().getSizeInBits() < ExtVT.getSizeInBits() + ShAmt)
-    return false;
+    // For the transform to be legal, the load must produce only two values
+    // (the value loaded and the chain).  Don't transform a pre-increment
+    // load, for example, which produces an extra value.  Otherwise the
+    // transformation is not equivalent, and the downstream logic to replace
+    // uses gets things wrong.
+    if (Load->getNumValues() > 2)
+      return false;
 
-  if (!TLI.shouldReduceLoadWidth(LoadN, ExtType, ExtVT))
-    return false;
+    // If the load that we're shrinking is an extload and we're not just
+    // discarding the extension we can't simply shrink the load. Bail.
+    // TODO: It would be possible to merge the extensions in some cases.
+    if ((StrictInside || Load->getExtensionType() != ISD::NON_EXTLOAD) &&
+        Load->getMemoryVT().getSizeInBits() < MemVT.getSizeInBits() + ShAmt)
+      return false;
 
-  // It's not possible to generate a constant of extended or untyped type.
-  EVT PtrType = LoadN->getOperand(1).getValueType();
-  if (PtrType == MVT::Untyped || PtrType.isExtended())
-    return false;
+    if (!TLI.shouldReduceLoadWidth(Load, ExtType, MemVT))
+      return false;
+  } else {
+    assert(isa<StoreSDNode>(LDST) && "It is not a Load nor a Store SDNode");
+    StoreSDNode *Store = cast<StoreSDNode>(LDST);
+    // Can't write outside the original store
+    if (Store->getMemoryVT().getSizeInBits() < MemVT.getSizeInBits() + ShAmt)
+      return false;
 
+    if (LegalOperations &&
+        !TLI.isTruncStoreLegal(Store->getValue().getValueType(), MemVT))
+      return false;
+  }
   return true;
 }
 
@@ -4050,7 +4065,7 @@
       auto *Load = cast<LoadSDNode>(Op);
       EVT ExtVT;
       if (isAndLoadExtLoad(Mask, Load, Load->getValueType(0), ExtVT) &&
-          isLegalNarrowLoad(Load, ISD::ZEXTLOAD, ExtVT)) {
+          isLegalNarrowLdSt(Load, ISD::ZEXTLOAD, ExtVT)) {
 
         // ZEXTLOAD is already small enough.
         if (Load->getExtensionType() == ISD::ZEXTLOAD &&
@@ -8787,7 +8802,7 @@
     return SDValue();
 
   LoadSDNode *LN0 = cast<LoadSDNode>(N0);
-  if (!isLegalNarrowLoad(LN0, ExtType, ExtVT, ShAmt))
+  if (!isLegalNarrowLdSt(LN0, ExtType, ExtVT, ShAmt))
     return SDValue();
 
   // For big endian targets, we need to adjust the offset to the pointer to