DAGCombiner: Merge store/loads when we have extload/truncstores

This is helps on architectures where i8,i16 are not legal but we have byte, and
short loads/stores. Allowing us to merge copies like the one below on ARM.

copy(char *a, char *b, int n) {
 do {
   int t0 = a[0];
   int t1 = a[1];
   b[0] = t0;
   b[1] = t1;

radar://13536387

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178546 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 19 insertions, 0 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ff98a04c5b..eb16095750 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7980,6 +7980,14 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
       EVT StoreTy = EVT::getIntegerVT(*DAG.getContext(), StoreBW);
       if (TLI.isTypeLegal(StoreTy))
         LastLegalType = i+1;
+      // Or check whether a truncstore is legal.
+      else if (TLI.getTypeAction(*DAG.getContext(), StoreTy) ==
+               TargetLowering::TypePromoteInteger) {
+        EVT LegalizedStoredValueTy =
+          TLI.getTypeToTransformTo(*DAG.getContext(), StoredVal.getValueType());
+        if (TLI.isTruncStoreLegal(LegalizedStoredValueTy, StoreTy))
+          LastLegalType = i+1;
+      }
 
       // Find a legal type for the vector store.
       EVT Ty = EVT::getVectorVT(*DAG.getContext(), MemVT, i+1);
@@ -8163,6 +8171,17 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
     StoreTy = EVT::getIntegerVT(*DAG.getContext(), StoreBW);
     if (TLI.isTypeLegal(StoreTy))
       LastLegalIntegerType = i + 1;
+    // Or check whether a truncstore and extload is legal.
+    else if (TLI.getTypeAction(*DAG.getContext(), StoreTy) ==
+             TargetLowering::TypePromoteInteger) {
+      EVT LegalizedStoredValueTy =
+        TLI.getTypeToTransformTo(*DAG.getContext(), StoreTy);
+      if (TLI.isTruncStoreLegal(LegalizedStoredValueTy, StoreTy) &&
+          TLI.isLoadExtLegal(ISD::ZEXTLOAD, StoreTy) &&
+          TLI.isLoadExtLegal(ISD::SEXTLOAD, StoreTy) &&
+          TLI.isLoadExtLegal(ISD::EXTLOAD, StoreTy))
+        LastLegalIntegerType = i+1;
+    }
   }
 
   // Only use vector types if the vector type is larger than the integer type.