Prevent X86ISelLowering from merging volatile loads

Change isConsecutiveLoads to check that loads are non-volatile as this
is a requirement for any load merges. Propagate change to two callers.

Reviewers: RKSimon

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18546

llvm-svn: 265013

llvm/include/llvm/CodeGen/SelectionDAG.h

@@ -1284,10 +1284,12 @@ class SelectionDAG {
   /// vector op and fill the end of the resulting vector with UNDEFS.
   SDValue UnrollVectorOp(SDNode *N, unsigned ResNE = 0);
 
-  /// Return true if LD is loading 'Bytes' bytes from a location that is 'Dist'
-  /// units away from the location that the 'Base' load is loading from.
-  bool isConsecutiveLoad(LoadSDNode *LD, LoadSDNode *Base,
-                         unsigned Bytes, int Dist) const;
+  /// Return true if loads are next to each other and can be
+  /// merged. Check that both are nonvolatile and if LD is loading
+  /// 'Bytes' bytes from a location that is 'Dist' units away from the
+  /// location that the 'Base' load is loading from.
+  bool areNonVolatileConsecutiveLoads(LoadSDNode *LD, LoadSDNode *Base,
+                                      unsigned Bytes, int Dist) const;
 
   /// Infer alignment of a load / store address. Return 0 if
   /// it cannot be inferred.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -7251,14 +7251,9 @@ SDValue DAGCombiner::CombineConsecutiveLoads(SDNode *N, EVT VT) {
       LD1->getAddressSpace() != LD2->getAddressSpace())
     return SDValue();
   EVT LD1VT = LD1->getValueType(0);
-
-  if (ISD::isNON_EXTLoad(LD2) &&
-      LD2->hasOneUse() &&
-      // If both are volatile this would reduce the number of volatile loads.
-      // If one is volatile it might be ok, but play conservative and bail out.
-      !LD1->isVolatile() &&
-      !LD2->isVolatile() &&
-      DAG.isConsecutiveLoad(LD2, LD1, LD1VT.getSizeInBits()/8, 1)) {
+  unsigned LD1Bytes = LD1VT.getSizeInBits() / 8;
+  if (ISD::isNON_EXTLoad(LD2) && LD2->hasOneUse() &&
+      DAG.areNonVolatileConsecutiveLoads(LD2, LD1, LD1Bytes, 1)) {
     unsigned Align = LD1->getAlignment();
     unsigned NewAlign = DAG.getDataLayout().getABITypeAlignment(
         VT.getTypeForEVT(*DAG.getContext()));

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -6959,12 +6959,12 @@ SDValue SelectionDAG::UnrollVectorOp(SDNode *N, unsigned ResNE) {
                  EVT::getVectorVT(*getContext(), EltVT, ResNE), Scalars);
 }
 
-
-/// isConsecutiveLoad - Return true if LD is loading 'Bytes' bytes from a
-/// location that is 'Dist' units away from the location that the 'Base' load
-/// is loading from.
-bool SelectionDAG::isConsecutiveLoad(LoadSDNode *LD, LoadSDNode *Base,
-                                     unsigned Bytes, int Dist) const {
+bool SelectionDAG::areNonVolatileConsecutiveLoads(LoadSDNode *LD,
+                                                  LoadSDNode *Base,
+                                                  unsigned Bytes,
+                                                  int Dist) const {
+  if (LD->isVolatile() || Base->isVolatile())
+    return false;
   if (LD->getChain() != Base->getChain())
     return false;
   EVT VT = LD->getValueType(0);

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -5736,9 +5736,9 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, ArrayRef<SDValue> Elts,
     if (LoadMask[i]) {
       SDValue Elt = peekThroughBitcasts(Elts[i]);
       LoadSDNode *LD = cast<LoadSDNode>(Elt);
-      if (!DAG.isConsecutiveLoad(LD, LDBase,
-                                 Elt.getValueType().getStoreSizeInBits() / 8,
-                                 i - FirstLoadedElt)) {
+      if (!DAG.areNonVolatileConsecutiveLoads(
+              LD, LDBase, Elt.getValueType().getStoreSizeInBits() / 8,
+              i - FirstLoadedElt)) {
         IsConsecutiveLoad = false;
         IsConsecutiveLoadWithZeros = false;
         break;
@@ -5749,10 +5749,10 @@ static SDValue EltsFromConsecutiveLoads(EVT VT, ArrayRef<SDValue> Elts,
   }
 
   auto CreateLoad = [&DAG, &DL](EVT VT, LoadSDNode *LDBase) {
-    SDValue NewLd = DAG.getLoad(VT, DL, LDBase->getChain(),
-                                LDBase->getBasePtr(), LDBase->getPointerInfo(),
-                                LDBase->isVolatile(), LDBase->isNonTemporal(),
-                                LDBase->isInvariant(), LDBase->getAlignment());
+    SDValue NewLd = DAG.getLoad(
+        VT, DL, LDBase->getChain(), LDBase->getBasePtr(),
+        LDBase->getPointerInfo(), false /*LDBase->isVolatile()*/,
+        LDBase->isNonTemporal(), LDBase->isInvariant(), LDBase->getAlignment());
 
     if (LDBase->hasAnyUseOfValue(1)) {
       SDValue NewChain =