[SDAG] Teach Chain Analysis about BaseIndexOffset addressing.

While we use BaseIndexOffset in FindBetterNeighborChains to
appropriately realize they're almost the same address and should be
improved concurrently we do not use it in isAlias using the non-index
understanding FindBaseOffset instead. Adding a BaseIndexOffset check
in isAlias like should allow indexed stores to be merged.

FindBaseOffset to be excised in subsequent patch.

Reviewers: jyknight, aditya_nandakumar, bogner

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31987

llvm-svn: 301187

1 files changed, 13 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 4702d63cb61..91a56f81e97 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -16088,6 +16088,19 @@ bool DAGCombiner::isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1) const {
   if (Op1->isInvariant() && Op0->writeMem())
     return false;
 
+  unsigned NumBytes0 = Op0->getMemoryVT().getSizeInBits() >> 3;
+  unsigned NumBytes1 = Op1->getMemoryVT().getSizeInBits() >> 3;
+
+  // Check for BaseIndexOffset matching.
+  BaseIndexOffset BasePtr0 = BaseIndexOffset::match(Op0->getBasePtr(), DAG);
+  BaseIndexOffset BasePtr1 = BaseIndexOffset::match(Op1->getBasePtr(), DAG);
+  if (BasePtr0.equalBaseIndex(BasePtr1))
+    return !((BasePtr0.Offset + NumBytes0 <= BasePtr1.Offset) ||
+             (BasePtr1.Offset + NumBytes1 <= BasePtr0.Offset));
+
+  // FIXME: findBaseOffset and ConstantValue/GlobalValue/FrameIndex analysis
+  // modified to use BaseIndexOffset.
+
   // Gather base node and offset information.
   SDValue Base0, Base1;
   int64_t Offset0, Offset1;
@@ -16099,8 +16112,6 @@ bool DAGCombiner::isAlias(LSBaseSDNode *Op0, LSBaseSDNode *Op1) const {
                                       Base1, Offset1, GV1, CV1);
 
   // If they have the same base address, then check to see if they overlap.
-  unsigned NumBytes0 = Op0->getMemoryVT().getSizeInBits() >> 3;
-  unsigned NumBytes1 = Op1->getMemoryVT().getSizeInBits() >> 3;
   if (Base0 == Base1 || (GV0 && (GV0 == GV1)) || (CV0 && (CV0 == CV1)))
     return !((Offset0 + NumBytes0) <= Offset1 ||
              (Offset1 + NumBytes1) <= Offset0);