Index: llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
@@ -1710,6 +1710,29 @@
   llvm_unreachable("cannot find MemSDNode in the pattern!");
 }
 
+/// Split \p COffsetVal into {immediate offset field, remainder offset} values.
+static std::pair<int64_t, int64_t> splitFlatOffset(int64_t COffsetVal,
+                                                   const SIInstrInfo *TII,
+                                                   unsigned AddrSpace,
+                                                   bool IsSigned) {
+  int64_t RemainderOffset = COffsetVal;
+  int64_t ImmField = 0;
+  const unsigned NumBits = TII->getNumFlatOffsetBits(IsSigned);
+  if (IsSigned) {
+    // Use signed division by a power of two to truncate towards 0.
+    int64_t D = 1LL << (NumBits - 1);
+    RemainderOffset = (static_cast<int64_t>(COffsetVal) / D) * D;
+    ImmField = COffsetVal - RemainderOffset;
+  } else if (static_cast<int64_t>(COffsetVal) >= 0) {
+    ImmField = COffsetVal & maskTrailingOnes<uint64_t>(NumBits);
+    RemainderOffset = COffsetVal - ImmField;
+  }
+
+  assert(TII->isLegalFLATOffset(ImmField, AddrSpace, IsSigned));
+  assert(RemainderOffset + ImmField == COffsetVal);
+  return {ImmField, RemainderOffset};
+}
+
 template <bool IsSigned>
 bool AMDGPUDAGToDAGISel::SelectFlatOffset(SDNode *N,
                                           SDValue Addr,
@@ -1742,22 +1765,10 @@
         // into two pieces that are both >= 0 or both <= 0.
 
         SDLoc DL(N);
-        uint64_t RemainderOffset = COffsetVal;
-        uint64_t ImmField = 0;
-        const unsigned NumBits = TII->getNumFlatOffsetBits(IsSigned);
-        if (IsSigned) {
-          // Use signed division by a power of two to truncate towards 0.
-          int64_t D = 1LL << (NumBits - 1);
-          RemainderOffset = (static_cast<int64_t>(COffsetVal) / D) * D;
-          ImmField = COffsetVal - RemainderOffset;
-        } else if (static_cast<int64_t>(COffsetVal) >= 0) {
-          ImmField = COffsetVal & maskTrailingOnes<uint64_t>(NumBits);
-          RemainderOffset = COffsetVal - ImmField;
-        }
-        assert(TII->isLegalFLATOffset(ImmField, AS, IsSigned));
-        assert(RemainderOffset + ImmField == COffsetVal);
+        uint64_t RemainderOffset;
 
-        OffsetVal = ImmField;
+        std::tie(OffsetVal, RemainderOffset)
+          = splitFlatOffset(COffsetVal, TII, AS, IsSigned);
 
         SDValue AddOffsetLo =
             getMaterializedScalarImm32(Lo_32(RemainderOffset), DL);