Index: llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4096,13 +4096,14 @@
   // is a load, return the new registers in ValRegs. For a store, each elements
   // of ValRegs should be PartTy. Returns the next offset that needs to be
   // handled.
+  bool isBigEndian = MIRBuilder.getDataLayout().isBigEndian();
   auto MMO = LdStMI.getMMO();
   auto splitTypePieces = [=](LLT PartTy, SmallVectorImpl<Register> &ValRegs,
-                             unsigned Offset) -> unsigned {
+                             unsigned NumParts, unsigned Offset) -> unsigned {
     MachineFunction &MF = MIRBuilder.getMF();
     unsigned PartSize = PartTy.getSizeInBits();
     for (unsigned Idx = 0, E = NumParts; Idx != E && Offset < TotalSize;
-         Offset += PartSize, ++Idx) {
+         ++Idx) {
       unsigned ByteOffset = Offset / 8;
       Register NewAddrReg;
 
@@ -4118,16 +4119,19 @@
       } else {
         MIRBuilder.buildStore(ValRegs[Idx], NewAddrReg, *NewMMO);
       }
+      Offset = isBigEndian ? Offset - PartSize : Offset + PartSize;
     }
 
     return Offset;
   };
 
-  unsigned HandledOffset = splitTypePieces(NarrowTy, NarrowRegs, 0);
+  unsigned Offset = isBigEndian ? TotalSize - NarrowTy.getSizeInBits() : 0;
+  unsigned HandledOffset =
+      splitTypePieces(NarrowTy, NarrowRegs, NumParts, Offset);
 
   // Handle the rest of the register if this isn't an even type breakdown.
   if (LeftoverTy.isValid())
-    splitTypePieces(LeftoverTy, NarrowLeftoverRegs, HandledOffset);
+    splitTypePieces(LeftoverTy, NarrowLeftoverRegs, NumLeftover, HandledOffset);
 
   if (IsLoad) {
     insertParts(ValReg, ValTy, NarrowTy, NarrowRegs,
Index: llvm/test/CodeGen/M68k/GlobalISel/legalize-load-store.mir
===================================================================
--- llvm/test/CodeGen/M68k/GlobalISel/legalize-load-store.mir
+++ llvm/test/CodeGen/M68k/GlobalISel/legalize-load-store.mir
@@ -63,4 +63,36 @@
     RTS
 
 ...
+---
+name:            test_store_i128
+fixedStack:
+  - { id: 0, type: default, offset: 0, size: 4, alignment: 8, stack-id: default,
+      isImmutable: true, isAliased: false, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:             |
+  bb.1:
+    ; CHECK-LABEL: name: test_store_i128
+    ; CHECK: [[FRAME_INDEX:%[0-9]+]]:_(p0) = G_FRAME_INDEX %fixed-stack.0
+    ; CHECK-NEXT: [[LOAD:%[0-9]+]]:_(p0) = G_LOAD [[FRAME_INDEX]](p0) :: (load (p0) from %fixed-stack.0, align 8)
+    ; CHECK-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 1
+    ; CHECK-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 2
+    ; CHECK-NEXT: [[C2:%[0-9]+]]:_(s32) = G_CONSTANT i32 3
+    ; CHECK-NEXT: [[C3:%[0-9]+]]:_(s32) = G_CONSTANT i32 4
+    ; CHECK-NEXT: [[C4:%[0-9]+]]:_(s32) = G_CONSTANT i32 12
+    ; CHECK-NEXT: [[PTR_ADD:%[0-9]+]]:_(p0) = G_PTR_ADD [[LOAD]], [[C4]](s32)
+    ; CHECK-NEXT: G_STORE [[C]](s32), [[PTR_ADD]](p0) :: (store (s32) into unknown-address + 12)
+    ; CHECK-NEXT: [[C5:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
+    ; CHECK-NEXT: [[PTR_ADD1:%[0-9]+]]:_(p0) = G_PTR_ADD [[LOAD]], [[C5]](s32)
+    ; CHECK-NEXT: G_STORE [[C1]](s32), [[PTR_ADD1]](p0) :: (store (s32) into unknown-address + 8, align 8)
+    ; CHECK-NEXT: [[C6:%[0-9]+]]:_(s32) = G_CONSTANT i32 4
+    ; CHECK-NEXT: [[PTR_ADD2:%[0-9]+]]:_(p0) = G_PTR_ADD [[LOAD]], [[C6]](s32)
+    ; CHECK-NEXT: G_STORE [[C2]](s32), [[PTR_ADD2]](p0) :: (store (s32) into unknown-address + 4)
+    ; CHECK-NEXT: G_STORE [[C3]](s32), [[LOAD]](p0) :: (store (s32), align 16)
+    ; CHECK-NEXT: RTS
+    %1:_(p0) = G_FRAME_INDEX %fixed-stack.0
+    %0:_(p0) = G_LOAD %1(p0) :: (load (p0) from %fixed-stack.0, align 8)
+    %2:_(s128) = G_CONSTANT i128 316912650112397582603894390785; 0x4000000030000000200000001
+    G_STORE %2(s128), %0(p0) :: (store (s128))
+    RTS
 
+...