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
@@ -1814,6 +1814,26 @@
     return widenScalarMergeValues(MI, TypeIdx, WideTy);
   case TargetOpcode::G_UNMERGE_VALUES:
     return widenScalarUnmergeValues(MI, TypeIdx, WideTy);
+  case TargetOpcode::G_SADDO:
+  case TargetOpcode::G_SSUBO: {
+    if (TypeIdx == 1)
+      return UnableToLegalize; // TODO
+    auto LHSExt = MIRBuilder.buildSExt(WideTy, MI.getOperand(2));
+    auto RHSExt = MIRBuilder.buildSExt(WideTy, MI.getOperand(3));
+    unsigned Opcode = MI.getOpcode() == TargetOpcode::G_SADDO
+                          ? TargetOpcode::G_ADD
+                          : TargetOpcode::G_SUB;
+    auto NewOp = MIRBuilder.buildInstr(Opcode, {WideTy}, {LHSExt, RHSExt});
+    LLT OrigTy = MRI.getType(MI.getOperand(0).getReg());
+    auto TruncOp = MIRBuilder.buildTrunc(OrigTy, NewOp);
+    auto ExtOp = MIRBuilder.buildSExt(WideTy, TruncOp);
+    // There is no overflow if the re-extended result is the same as NewOp.
+    MIRBuilder.buildICmp(CmpInst::ICMP_NE, MI.getOperand(1), NewOp, ExtOp);
+    // Now trunc the NewOp to the original result.
+    MIRBuilder.buildTrunc(MI.getOperand(0), NewOp);
+    MI.eraseFromParent();
+    return Legalized;
+  }
   case TargetOpcode::G_UADDO:
   case TargetOpcode::G_USUBO: {
     if (TypeIdx == 1)
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 +73,66 @@
     %5:_(s64) = G_ANYEXT %4(s8)
     $x0 = COPY %5(s64)
 
+...
+---
+name:            test_scalar_uaddo_small
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_uaddo_small
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[TRUNC]], [[C]]
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s32) = G_TRUNC [[COPY1]](s64)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[TRUNC1]], [[C]]
+    ; CHECK: [[ADD:%[0-9]+]]:_(s32) = G_ADD [[AND]], [[AND1]]
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[ADD]], [[C]]
+    ; CHECK: [[ICMP:%[0-9]+]]:_(s32) = G_ICMP intpred(ne), [[ADD]](s32), [[AND2]]
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[ADD]](s32)
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[ICMP]](s32)
+    ; CHECK: $x0 = COPY [[ANYEXT]](s64)
+    ; CHECK: $x1 = COPY [[ANYEXT1]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s8) = G_TRUNC %0(s64)
+    %3:_(s8) = G_TRUNC %1(s64)
+    %4:_(s8), %5:_(s1) = G_UADDO %2, %3
+    %6:_(s64) = G_ANYEXT %4(s8)
+    %7:_(s64) = G_ANYEXT %5(s1)
+    $x0 = COPY %6(s64)
+    $x1 = COPY %7(s64)
+
+...
+---
+name:            test_scalar_saddo_small
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_saddo_small
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[SEXT_INREG:%[0-9]+]]:_(s32) = G_SEXT_INREG [[TRUNC]], 8
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s32) = G_TRUNC [[COPY1]](s64)
+    ; CHECK: [[SEXT_INREG1:%[0-9]+]]:_(s32) = G_SEXT_INREG [[TRUNC1]], 8
+    ; CHECK: [[ADD:%[0-9]+]]:_(s32) = G_ADD [[SEXT_INREG]], [[SEXT_INREG1]]
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[ADD]](s32)
+    ; CHECK: [[SEXT_INREG2:%[0-9]+]]:_(s32) = G_SEXT_INREG [[COPY2]], 8
+    ; CHECK: [[ICMP:%[0-9]+]]:_(s32) = G_ICMP intpred(ne), [[ADD]](s32), [[SEXT_INREG2]]
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[ADD]](s32)
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[ICMP]](s32)
+    ; CHECK: $x0 = COPY [[ANYEXT]](s64)
+    ; CHECK: $x1 = COPY [[ANYEXT1]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s8) = G_TRUNC %0(s64)
+    %3:_(s8) = G_TRUNC %1(s64)
+    %4:_(s8), %5:_(s1) = G_SADDO %2, %3
+    %6:_(s64) = G_ANYEXT %4(s8)
+    %7:_(s64) = G_ANYEXT %5(s1)
+    $x0 = COPY %6(s64)
+    $x1 = COPY %7(s64)
+
 ...
 ---
 name:            test_scalar_uaddo_32
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-sub.mir b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-sub.mir
--- a/llvm/test/CodeGen/AArch64/GlobalISel/legalize-sub.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/legalize-sub.mir
@@ -1,5 +1,6 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -march=aarch64 -run-pass=legalizer %s -o - | FileCheck %s
+
 ---
 name:            test_scalar_sub_big
 body:             |
@@ -92,6 +93,66 @@
     $w0 = COPY %2(s32)
     $w1 = COPY %4(s32)
 
+...
+---
+name:            test_scalar_usubo_small
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_usubo_small
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 255
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[AND:%[0-9]+]]:_(s32) = G_AND [[TRUNC]], [[C]]
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s32) = G_TRUNC [[COPY1]](s64)
+    ; CHECK: [[AND1:%[0-9]+]]:_(s32) = G_AND [[TRUNC1]], [[C]]
+    ; CHECK: [[ADD:%[0-9]+]]:_(s32) = G_ADD [[AND]], [[AND1]]
+    ; CHECK: [[AND2:%[0-9]+]]:_(s32) = G_AND [[ADD]], [[C]]
+    ; CHECK: [[ICMP:%[0-9]+]]:_(s32) = G_ICMP intpred(ne), [[ADD]](s32), [[AND2]]
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[ADD]](s32)
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[ICMP]](s32)
+    ; CHECK: $x0 = COPY [[ANYEXT]](s64)
+    ; CHECK: $x1 = COPY [[ANYEXT1]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s8) = G_TRUNC %0(s64)
+    %3:_(s8) = G_TRUNC %1(s64)
+    %4:_(s8), %5:_(s1) = G_UADDO %2, %3
+    %6:_(s64) = G_ANYEXT %4(s8)
+    %7:_(s64) = G_ANYEXT %5(s1)
+    $x0 = COPY %6(s64)
+    $x1 = COPY %7(s64)
+
+...
+---
+name:            test_scalar_ssubo_small
+body:             |
+  bb.0.entry:
+    ; CHECK-LABEL: name: test_scalar_ssubo_small
+    ; CHECK: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s64) = COPY $x1
+    ; CHECK: [[TRUNC:%[0-9]+]]:_(s32) = G_TRUNC [[COPY]](s64)
+    ; CHECK: [[SEXT_INREG:%[0-9]+]]:_(s32) = G_SEXT_INREG [[TRUNC]], 8
+    ; CHECK: [[TRUNC1:%[0-9]+]]:_(s32) = G_TRUNC [[COPY1]](s64)
+    ; CHECK: [[SEXT_INREG1:%[0-9]+]]:_(s32) = G_SEXT_INREG [[TRUNC1]], 8
+    ; CHECK: [[ADD:%[0-9]+]]:_(s32) = G_ADD [[SEXT_INREG]], [[SEXT_INREG1]]
+    ; CHECK: [[COPY2:%[0-9]+]]:_(s32) = COPY [[ADD]](s32)
+    ; CHECK: [[SEXT_INREG2:%[0-9]+]]:_(s32) = G_SEXT_INREG [[COPY2]], 8
+    ; CHECK: [[ICMP:%[0-9]+]]:_(s32) = G_ICMP intpred(ne), [[ADD]](s32), [[SEXT_INREG2]]
+    ; CHECK: [[ANYEXT:%[0-9]+]]:_(s64) = G_ANYEXT [[ADD]](s32)
+    ; CHECK: [[ANYEXT1:%[0-9]+]]:_(s64) = G_ANYEXT [[ICMP]](s32)
+    ; CHECK: $x0 = COPY [[ANYEXT]](s64)
+    ; CHECK: $x1 = COPY [[ANYEXT1]](s64)
+    %0:_(s64) = COPY $x0
+    %1:_(s64) = COPY $x1
+    %2:_(s8) = G_TRUNC %0(s64)
+    %3:_(s8) = G_TRUNC %1(s64)
+    %4:_(s8), %5:_(s1) = G_SADDO %2, %3
+    %6:_(s64) = G_ANYEXT %4(s8)
+    %7:_(s64) = G_ANYEXT %5(s1)
+    $x0 = COPY %6(s64)
+    $x1 = COPY %7(s64)
+
 ...
 ---
 name:            test_scalar_ssubo_32