Index: llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp
@@ -1742,22 +1742,10 @@
         // 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)
+          = TII->splitFlatOffset(COffsetVal, AS, IsSigned);
 
         SDValue AddOffsetLo =
             getMaterializedScalarImm32(Lo_32(RemainderOffset), DL);
Index: llvm/lib/Target/AMDGPU/SIInstrInfo.h
===================================================================
--- llvm/lib/Target/AMDGPU/SIInstrInfo.h
+++ llvm/lib/Target/AMDGPU/SIInstrInfo.h
@@ -1039,6 +1039,12 @@
   bool isLegalFLATOffset(int64_t Offset, unsigned AddrSpace,
                          bool Signed) const;
 
+  /// Split \p COffsetVal into {immediate offset field, remainder offset}
+  /// values.
+  std::pair<int64_t, int64_t> splitFlatOffset(int64_t COffsetVal,
+                                              unsigned AddrSpace,
+                                              bool IsSigned) const;
+
   /// \brief Return a target-specific opcode if Opcode is a pseudo instruction.
   /// Return -1 if the target-specific opcode for the pseudo instruction does
   /// not exist. If Opcode is not a pseudo instruction, this is identity.
Index: llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -6976,6 +6976,26 @@
   return Signed ? isInt<13>(Offset) :isUInt<12>(Offset);
 }
 
+std::pair<int64_t, int64_t> SIInstrInfo::splitFlatOffset(int64_t COffsetVal,
+                                                         unsigned AddrSpace,
+                                                         bool IsSigned) const {
+  int64_t RemainderOffset = COffsetVal;
+  int64_t ImmField = 0;
+  const unsigned NumBits = 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(isLegalFLATOffset(ImmField, AddrSpace, IsSigned));
+  assert(RemainderOffset + ImmField == COffsetVal);
+  return {ImmField, RemainderOffset};
+}
 
 // This must be kept in sync with the SIEncodingFamily class in SIInstrInfo.td
 enum SIEncodingFamily {