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diff --git a/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ult-to-icmp-ugt.ll b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ult-to-icmp-ugt.ll
new file mode 100644
index 00000000000..287e3699932
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-ult-to-icmp-ugt.ll
@@ -0,0 +1,186 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; https://bugs.llvm.org/show_bug.cgi?id=38123
+
+; Pattern:
+;   x & C u< x
+; Should be transformed into:
+;   x u> C
+; Iff: isPowerOf2(C + 1)
+
+; ============================================================================ ;
+; Basic positive tests
+; ============================================================================ ;
+
+define i1 @p0(i8 %x) {
+; CHECK-LABEL: @p0(
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 [[X:%.*]], 3
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %tmp0 = and i8 %x, 3
+  %ret = icmp ult i8 %tmp0, %x
+  ret i1 %ret
+}
+
+define i1 @pv(i8 %x, i8 %y) {
+; CHECK-LABEL: @pv(
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i8 -1, [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ult i8 [[TMP0]], [[X:%.*]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %tmp0 = lshr i8 -1, %y
+  %tmp1 = and i8 %tmp0, %x
+  %ret = icmp ult i8 %tmp1, %x
+  ret i1 %ret
+}
+
+; ============================================================================ ;
+; Vector tests
+; ============================================================================ ;
+
+define <2 x i1> @p1_vec_splat(<2 x i8> %x) {
+; CHECK-LABEL: @p1_vec_splat(
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt <2 x i8> [[X:%.*]], <i8 3, i8 3>
+; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
+;
+  %tmp0 = and <2 x i8> %x, <i8 3, i8 3>
+  %ret = icmp ult <2 x i8> %tmp0, %x
+  ret <2 x i1> %ret
+}
+
+define <2 x i1> @p2_vec_nonsplat(<2 x i8> %x) {
+; CHECK-LABEL: @p2_vec_nonsplat(
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt <2 x i8> [[X:%.*]], <i8 3, i8 15>
+; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
+;
+  %tmp0 = and <2 x i8> %x, <i8 3, i8 15> ; doesn't have to be splat.
+  %ret = icmp ult <2 x i8> %tmp0, %x
+  ret <2 x i1> %ret
+}
+
+define <3 x i1> @p3_vec_splat_undef(<3 x i8> %x) {
+; CHECK-LABEL: @p3_vec_splat_undef(
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt <3 x i8> [[X:%.*]], <i8 3, i8 undef, i8 3>
+; CHECK-NEXT:    ret <3 x i1> [[TMP1]]
+;
+  %tmp0 = and <3 x i8> %x, <i8 3, i8 undef, i8 3>
+  %ret = icmp ult <3 x i8> %tmp0, %x
+  ret <3 x i1> %ret
+}
+
+; ============================================================================ ;
+; Commutativity tests.
+; ============================================================================ ;
+
+declare i8 @gen8()
+
+; The pattern is not commutative. instsimplify will already take care of it.
+define i1 @c0() {
+; CHECK-LABEL: @c0(
+; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    ret i1 false
+;
+  %x = call i8 @gen8()
+  %tmp0 = and i8 %x, 3
+  %ret = icmp ult i8 %x, %tmp0 ; swapped order
+  ret i1 %ret
+}
+
+; ============================================================================ ;
+; Commutativity tests with variable
+; ============================================================================ ;
+
+define i1 @cv0(i8 %y) {
+; CHECK-LABEL: @cv0(
+; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i8 -1, [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 [[X]], [[TMP0]]
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %x = call i8 @gen8()
+  %tmp0 = lshr i8 -1, %y
+  %tmp1 = and i8 %x, %tmp0 ; swapped order
+  %ret = icmp ult i8 %tmp1, %x
+  ret i1 %ret
+}
+
+define i1 @cv1(i8 %y) {
+; CHECK-LABEL: @cv1(
+; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    ret i1 false
+;
+  %x = call i8 @gen8()
+  %tmp0 = lshr i8 -1, %y
+  %tmp1 = and i8 %tmp0, %x
+  %ret = icmp ult i8 %x, %tmp1 ; swapped order
+  ret i1 %ret
+}
+
+define i1 @cv2(i8 %y) {
+; CHECK-LABEL: @cv2(
+; CHECK-NEXT:    [[X:%.*]] = call i8 @gen8()
+; CHECK-NEXT:    ret i1 false
+;
+  %x = call i8 @gen8()
+  %tmp0 = lshr i8 -1, %y
+  %tmp1 = and i8 %x, %tmp0 ; swapped order
+  %ret = icmp ult i8 %x, %tmp1 ; swapped order
+  ret i1 %ret
+}
+
+; ============================================================================ ;
+; One-use tests. We don't care about multi-uses here.
+; ============================================================================ ;
+
+declare void @use8(i8)
+
+define i1 @oneuse0(i8 %x) {
+; CHECK-LABEL: @oneuse0(
+; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[X:%.*]], 3
+; CHECK-NEXT:    call void @use8(i8 [[TMP0]])
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 [[X]], 3
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %tmp0 = and i8 %x, 3
+  call void @use8(i8 %tmp0)
+  %ret = icmp ult i8 %tmp0, %x
+  ret i1 %ret
+}
+
+; ============================================================================ ;
+; Negative tests
+; ============================================================================ ;
+
+define i1 @n0(i8 %x) {
+; CHECK-LABEL: @n0(
+; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[X:%.*]], 4
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult i8 [[TMP0]], [[X]]
+; CHECK-NEXT:    ret i1 [[RET]]
+;
+  %tmp0 = and i8 %x, 4 ; power-of-two, but invalid.
+  %ret = icmp ult i8 %tmp0, %x
+  ret i1 %ret
+}
+
+define i1 @n1(i8 %x, i8 %y, i8 %notx) {
+; CHECK-LABEL: @n1(
+; CHECK-NEXT:    [[TMP0:%.*]] = and i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult i8 [[TMP0]], [[NOTX:%.*]]
+; CHECK-NEXT:    ret i1 [[RET]]
+;
+  %tmp0 = and i8 %x, 3
+  %ret = icmp ult i8 %tmp0, %notx ; not %x
+  ret i1 %ret
+}
+
+define <2 x i1> @n2(<2 x i8> %x) {
+; CHECK-LABEL: @n2(
+; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X:%.*]], <i8 3, i8 16>
+; CHECK-NEXT:    [[RET:%.*]] = icmp ult <2 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    ret <2 x i1> [[RET]]
+;
+  %tmp0 = and <2 x i8> %x, <i8 3, i8 16> ; only the first one is valid.
+  %ret = icmp ult <2 x i8> %tmp0, %x
+  ret <2 x i1> %ret
+}