Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3990,9 +3990,13 @@
       return SetResult(LHS, Builder.getFalse(), false);
 
     if (OCF == OCF_UNSIGNED_SUB) {
-      if (willNotOverflowUnsignedSub(LHS, RHS, OrigI))
+      OverflowResult OR = computeOverflowForUnsignedSub(LHS, RHS, &OrigI);
+      if (OR == OverflowResult::NeverOverflows)
         return SetResult(Builder.CreateNUWSub(LHS, RHS), Builder.getFalse(),
                          true);
+
+      if (OR == OverflowResult::AlwaysOverflows)
+        return SetResult(Builder.CreateSub(LHS, RHS), Builder.getTrue(), true);
     } else {
       if (willNotOverflowSignedSub(LHS, RHS, OrigI))
         return SetResult(Builder.CreateNSWSub(LHS, RHS), Builder.getFalse(),
Index: llvm/test/Transforms/InstCombine/with_overflow.ll
===================================================================
--- llvm/test/Transforms/InstCombine/with_overflow.ll
+++ llvm/test/Transforms/InstCombine/with_overflow.ll
@@ -544,8 +544,9 @@
 define { i8, i1 } @usub_always_overflow(i8 %x) nounwind {
 ; CHECK-LABEL: @usub_always_overflow(
 ; CHECK-NEXT:    [[Y:%.*]] = or i8 [[X:%.*]], 64
-; CHECK-NEXT:    [[A:%.*]] = call { i8, i1 } @llvm.usub.with.overflow.i8(i8 63, i8 [[Y]])
-; CHECK-NEXT:    ret { i8, i1 } [[A]]
+; CHECK-NEXT:    [[A:%.*]] = sub nsw i8 63, [[Y]]
+; CHECK-NEXT:    [[TMP1:%.*]] = insertvalue { i8, i1 } { i8 undef, i1 true }, i8 [[A]], 0
+; CHECK-NEXT:    ret { i8, i1 } [[TMP1]]
 ;
   %y = or i8 %x, 64
   %a = call { i8, i1 } @llvm.usub.with.overflow.i8(i8 63, i8 %y)