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

2 files changed, 9 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 09c7971c97d..8544c27263b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/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()));
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index ebf49b985a3..46986d7e0ad 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/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);