diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6224,9 +6224,9 @@
       std::swap(N1, N2);
     } else {
       switch (Opcode) {
-      case ISD::SIGN_EXTEND_INREG:
       case ISD::SUB:
         return getUNDEF(VT);     // fold op(undef, arg2) -> undef
+      case ISD::SIGN_EXTEND_INREG:
       case ISD::UDIV:
       case ISD::SDIV:
       case ISD::UREM:
diff --git a/llvm/test/CodeGen/AArch64/pr55178.ll b/llvm/test/CodeGen/AArch64/pr55178.ll
--- a/llvm/test/CodeGen/AArch64/pr55178.ll
+++ b/llvm/test/CodeGen/AArch64/pr55178.ll
@@ -10,8 +10,9 @@
 ; CHECK-NEXT:    mov w8, #-113
 ; CHECK-NEXT:    // kill: def $w0 killed $w0 def $x0
 ; CHECK-NEXT:    lsl w8, w8, w0
-; CHECK-NEXT:    cmp w8, w8, sxtb
-; CHECK-NEXT:    cset w0, lt
+; CHECK-NEXT:    sxtb w8, w8
+; CHECK-NEXT:    cmp w8, #0
+; CHECK-NEXT:    cset w0, gt
 ; CHECK-NEXT:    ret
   %1 = shl i8 -113, %X
   %cmp = icmp slt i8 undef, %1
diff --git a/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll b/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
--- a/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
+++ b/llvm/test/CodeGen/SystemZ/regcoal_remat_empty_subrange.ll
@@ -11,18 +11,19 @@
 @g_151 = external dso_local global i32, align 4
 @g_222 = external dso_local unnamed_addr global [7 x [10 x i8]], align 2
 
-define void @main() {
+define void @main(i16 %in) {
 ; CHECK-LABEL: main:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    lhi %r0, 1
+; CHECK-NEXT:    lhr %r2, %r2
 ; CHECK-NEXT:    larl %r1, g_151
 ; CHECK-NEXT:    lghi %r3, 0
-; CHECK-NEXT:    chi %r0, 0
+; CHECK-NEXT:    chi %r2, 0
+; CHECK-NEXT:    lhi %r0, 1
 ; CHECK-NEXT:    locghile %r3, 1
 ; CHECK-NEXT:    o %r0, 0(%r1)
-; CHECK-NEXT:    dsgfr %r2, %r0
 ; CHECK-NEXT:    larl %r1, g_222
 ; CHECK-NEXT:    lghi %r5, 0
+; CHECK-NEXT:    dsgfr %r2, %r0
 ; CHECK-NEXT:    stgrl %r2, g_39
 ; CHECK-NEXT:    stc %r5, 19(%r1)
 ; CHECK-NEXT:    br %r14
@@ -32,7 +33,7 @@
   %tmp5 = srem i64 0, %tmp4
   %tmp6 = trunc i64 %tmp5 to i8
   store i8 %tmp6, i8* getelementptr inbounds ([7 x [10 x i8]], [7 x [10 x i8]]* @g_222, i64 0, i64 1, i64 9), align 1
-  %tmp7 = icmp slt i16 undef, 1
+  %tmp7 = icmp slt i16 %in, 1
   %tmp8 = zext i1 %tmp7 to i64
   %tmp9 = srem i64 %tmp8, %tmp4
   store i64 %tmp9, i64* @g_39, align 8