diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -4885,17 +4885,6 @@
   if (DstType.isVector())
     return UnableToLegalize;
 
-  uint64_t SizeOp0 = DstType.getSizeInBits();
-  uint64_t NarrowSize = NarrowTy.getSizeInBits();
-
-  // FIXME: add support for when SizeOp0 isn't an exact multiple of
-  // NarrowSize.
-  if (SizeOp0 % NarrowSize != 0)
-    return UnableToLegalize;
-
-  // Expand in terms of carry-setting/consuming G_<Op>E instructions.
-  int NumParts = SizeOp0 / NarrowTy.getSizeInBits();
-
   unsigned Opcode = MI.getOpcode();
   unsigned OpO, OpE, OpF;
   switch (Opcode) {
@@ -4929,28 +4918,37 @@
   unsigned NumDefs = MI.getNumExplicitDefs();
   Register Src1 = MI.getOperand(NumDefs).getReg();
   Register Src2 = MI.getOperand(NumDefs + 1).getReg();
-  Register CarryDst;
+  Register CarryDst, CarryIn;
   if (NumDefs == 2)
     CarryDst = MI.getOperand(1).getReg();
-  Register CarryIn;
   if (MI.getNumOperands() == NumDefs + 3)
     CarryIn = MI.getOperand(NumDefs + 2).getReg();
 
-  SmallVector<Register, 2> Src1Regs, Src2Regs, DstRegs;
-  extractParts(Src1, NarrowTy, NumParts, Src1Regs);
-  extractParts(Src2, NarrowTy, NumParts, Src2Regs);
+  LLT RegTy = MRI.getType(MI.getOperand(0).getReg());
+  LLT LeftoverTy, DummyTy;
+  SmallVector<Register, 2> Src1Regs, Src2Regs, Src1Left, Src2Left, DstRegs;
+  extractParts(Src1, RegTy, NarrowTy, LeftoverTy, Src1Regs, Src1Left);
+  extractParts(Src2, RegTy, NarrowTy, DummyTy, Src2Regs, Src2Left);
 
-  for (int i = 0; i < NumParts; ++i) {
-    Register DstReg = MRI.createGenericVirtualRegister(NarrowTy);
+  int NarrowParts = Src1Regs.size();
+  for (int I = 0, E = Src1Left.size(); I != E; ++I) {
+    Src1Regs.push_back(Src1Left[I]);
+    Src2Regs.push_back(Src2Left[I]);
+  }
+  DstRegs.reserve(Src1Regs.size());
+
+  for (int i = 0, e = Src1Regs.size(); i != e; ++i) {
+    Register DstReg =
+        MRI.createGenericVirtualRegister(MRI.getType(Src1Regs[i]));
     Register CarryOut = MRI.createGenericVirtualRegister(LLT::scalar(1));
     // Forward the final carry-out to the destination register
-    if (i == NumParts - 1 && CarryDst)
+    if (i == e - 1 && CarryDst)
       CarryOut = CarryDst;
 
     if (!CarryIn) {
       MIRBuilder.buildInstr(OpO, {DstReg, CarryOut},
                             {Src1Regs[i], Src2Regs[i]});
-    } else if (i == NumParts - 1) {
+    } else if (i == e - 1) {
       MIRBuilder.buildInstr(OpF, {DstReg, CarryOut},
                             {Src1Regs[i], Src2Regs[i], CarryIn});
     } else {
@@ -4961,7 +4959,10 @@
     DstRegs.push_back(DstReg);
     CarryIn = CarryOut;
   }
-  MIRBuilder.buildMerge(DstReg, DstRegs);
+  insertParts(MI.getOperand(0).getReg(), RegTy, NarrowTy,
+              makeArrayRef(DstRegs).take_front(NarrowParts), LeftoverTy,
+              makeArrayRef(DstRegs).drop_front(NarrowParts));
+
   MI.eraseFromParent();
   return Legalized;
 }
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll
@@ -80,7 +80,7 @@
   br label %block
 }
 
-; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %{{[0-9]+}}:_(s96) = G_ADD %{{[0-9]+}}:_, %{{[0-9]+}}:_ (in function: nonpow2_add_narrowing)
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: cannot select: %{{[0-9]+}}:gpr32(s32), %{{[0-9]+}}:gpr(s1) = G_UADDE %{{[0-9]+}}:gpr, %{{[0-9]+}}:gpr, %{{[0-9]+}}:gpr (in function: nonpow2_add_narrowing)
 ; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for nonpow2_add_narrowing
 ; FALLBACK-WITH-REPORT-OUT-LABEL: nonpow2_add_narrowing:
 define void @nonpow2_add_narrowing(i128 %x, i128 %y) {
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-add.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-add.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-add.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-add.mir
@@ -73,6 +73,89 @@
     %5:_(s64) = G_ANYEXT %4(s8)
     $x0 = COPY %5(s64)
 
+...
+---
+name:            test_scalar_add_narrowing
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_add_narrowing
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s64) = COPY $x2
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s64) = COPY $x3
+    ; CHECK: [[COPY4:%[0-9]+]]:_(s64) = COPY [[COPY]](s64)
+    ; CHECK: [[EXTRACT:%[0-9]+]]:_(s32) = G_EXTRACT [[COPY1]](s64), 0
+    ; CHECK: [[COPY5:%[0-9]+]]:_(s64) = COPY [[COPY2]](s64)
+    ; CHECK: [[EXTRACT1:%[0-9]+]]:_(s32) = G_EXTRACT [[COPY3]](s64), 0
+    ; CHECK: [[UADDO:%[0-9]+]]:_(s64), [[UADDO1:%[0-9]+]]:_(s1) = G_UADDO [[COPY4]], [[COPY5]]
+    ; CHECK: [[UADDE:%[0-9]+]]:_(s32), [[UADDE1:%[0-9]+]]:_(s1) = G_UADDE [[EXTRACT]], [[EXTRACT1]], [[UADDO1]]
+    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = G_IMPLICIT_DEF
+    ; CHECK: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[DEF]](s64)
+    ; CHECK: [[EXTRACT2:%[0-9]+]]:_(s32) = G_EXTRACT [[DEF]](s64), 0
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[EXTRACT2]](s32)
+    ; CHECK: [[COPY6:%[0-9]+]]:_(s64) = COPY [[UADDO]](s64)
+    ; CHECK: [[EXTRACT3:%[0-9]+]]:_(s32) = G_EXTRACT [[ANYEXT]](s64), 0
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[EXTRACT3]](s32)
+    ; CHECK: [[INSERT:%[0-9]+]]:_(s64) = G_INSERT [[ANYEXT1]], [[UADDE]](s32), 0
+    ; CHECK: $x0 = COPY [[COPY6]](s64)
+    ; CHECK: $x1 = COPY [[INSERT]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s64) = COPY $x2
+    %3:_(s64) = COPY $x3
+    %4:_(s128) = G_MERGE_VALUES %0(s64), %1(s64)
+    %5:_(s128) = G_MERGE_VALUES %2(s64), %3(s64)
+    %6:_(s96) = G_TRUNC %4(s128)
+    %7:_(s96) = G_TRUNC %5(s128)
+    %8:_(s96) = G_ADD %6, %7
+    %9:_(s128) = G_ANYEXT %8(s96)
+    %10:_(s64), %11:_(s64) = G_UNMERGE_VALUES %9(s128)
+    $x0 = COPY %10(s64)
+    $x1 = COPY %11(s64)
+
+...
+---
+name:            test_scalar_add_narrowing_s65
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_add_narrowing_s65
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s64) = COPY $x2
+    ; CHECK: [[COPY3:%[0-9]+]]:_(s64) = COPY $x3
+    ; CHECK: [[COPY4:%[0-9]+]]:_(s64) = COPY [[COPY]](s64)
+    ; CHECK: [[EXTRACT:%[0-9]+]]:_(s1) = G_EXTRACT [[COPY1]](s64), 0
+    ; CHECK: [[COPY5:%[0-9]+]]:_(s64) = COPY [[COPY2]](s64)
+    ; CHECK: [[EXTRACT1:%[0-9]+]]:_(s1) = G_EXTRACT [[COPY3]](s64), 0
+    ; CHECK: [[UADDO:%[0-9]+]]:_(s64), [[UADDO1:%[0-9]+]]:_(s1) = G_UADDO [[COPY4]], [[COPY5]]
+    ; CHECK: [[ZEXT:%[0-9]+]]:_(s32) = G_ZEXT [[EXTRACT]](s1)
+    ; CHECK: [[ZEXT1:%[0-9]+]]:_(s32) = G_ZEXT [[EXTRACT1]](s1)
+    ; CHECK: [[UADDE:%[0-9]+]]:_(s32), [[UADDE1:%[0-9]+]]:_(s1) = G_UADDE [[ZEXT]], [[ZEXT1]], [[UADDO1]]
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s1) = G_TRUNC [[UADDE]](s32)
+    ; CHECK: [[COPY6:%[0-9]+]]:_(s1) = COPY [[TRUNC]](s1)
+    ; CHECK: [[DEF:%[0-9]+]]:_(s64) = G_IMPLICIT_DEF
+    ; CHECK: [[EXTRACT2:%[0-9]+]]:_(s1) = G_EXTRACT [[DEF]](s64), 0
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[EXTRACT2]](s1)
+    ; CHECK: [[COPY7:%[0-9]+]]:_(s64) = COPY [[UADDO]](s64)
+    ; CHECK: [[EXTRACT3:%[0-9]+]]:_(s1) = G_EXTRACT [[ANYEXT]](s64), 0
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[EXTRACT3]](s1)
+    ; CHECK: [[INSERT:%[0-9]+]]:_(s64) = G_INSERT [[ANYEXT1]], [[COPY6]](s1), 0
+    ; CHECK: $x0 = COPY [[COPY7]](s64)
+    ; CHECK: $x1 = COPY [[INSERT]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s64) = COPY $x2
+    %3:_(s64) = COPY $x3
+    %4:_(s128) = G_MERGE_VALUES %0(s64), %1(s64)
+    %5:_(s128) = G_MERGE_VALUES %2(s64), %3(s64)
+    %6:_(s65) = G_TRUNC %4(s128)
+    %7:_(s65) = G_TRUNC %5(s128)
+    %8:_(s65) = G_ADD %6, %7
+    %9:_(s128) = G_ANYEXT %8(s65)
+    %10:_(s64), %11:_(s64) = G_UNMERGE_VALUES %9(s128)
+    $x0 = COPY %10(s64)
+    $x1 = COPY %11(s64)
+
 ...
 ---
 name:            test_vector_add