diff --git a/llvm/test/Transforms/InstCombine/signmask-of-sext-vs-of-shl-of-zext.ll b/llvm/test/Transforms/InstCombine/signmask-of-sext-vs-of-shl-of-zext.ll
new file mode 100644
index 000000000000..f529023e2a0d
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/signmask-of-sext-vs-of-shl-of-zext.ll
@@ -0,0 +1,174 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; If we zero-extend some value, and then immediately left-shift-out all the new
+; sign bits, and apply a mask to keep only the sign bit (which is the original
+; sign bit from before zero-extension), we might as well just sign-extend
+; and apply the same signmask.
+
+declare void @use32(i32)
+
+; Basic pattern
+
+define i32 @t0(i16 %x) {
+; CHECK-LABEL: @t0(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 16
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32
+  %i1 = shl i32 %i0, 16
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+define i32 @t1(i8 %x) {
+; CHECK-LABEL: @t1(
+; CHECK-NEXT:    [[I0:%.*]] = zext i8 [[X:%.*]] to i32
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 24
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i8 %x to i32
+  %i1 = shl i32 %i0, 24
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+
+; Some negative tests
+
+define i32 @n2(i16 %x) {
+; CHECK-LABEL: @n2(
+; CHECK-NEXT:    ret i32 0
+;
+  %i0 = zext i16 %x to i32
+  %i1 = shl i32 %i0, 15 ; undershifting
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+define i32 @n3(i16 %x) {
+; CHECK-LABEL: @n3(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[I1:%.*]] = shl i32 [[I0]], 17
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32
+  %i1 = shl i32 %i0, 17 ; overshifting
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+define i32 @n4(i16 %x) {
+; CHECK-LABEL: @n4(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 16
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -1073741824
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32
+  %i1 = shl i32 %i0, 16
+  %r = and i32 %i1, 3221225472 ; not a sign bit
+  ret i32 %r
+}
+
+; Extra-use tests
+
+define i32 @t5(i16 %x) {
+; CHECK-LABEL: @t5(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    call void @use32(i32 [[I0]])
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 16
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32
+  call void @use32(i32 %i0)
+  %i1 = shl i32 %i0, 16
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+define i32 @n6(i16 %x) {
+; CHECK-LABEL: @n6(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 16
+; CHECK-NEXT:    call void @use32(i32 [[I1]])
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32
+  %i1 = shl i32 %i0, 16 ; not one-use
+  call void @use32(i32 %i1)
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+define i32 @n7(i16 %x) {
+; CHECK-LABEL: @n7(
+; CHECK-NEXT:    [[I0:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    call void @use32(i32 [[I0]])
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw i32 [[I0]], 16
+; CHECK-NEXT:    call void @use32(i32 [[I1]])
+; CHECK-NEXT:    [[R:%.*]] = and i32 [[I1]], -2147483648
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %i0 = zext i16 %x to i32 ; not one-use
+  call void @use32(i32 %i0)
+  %i1 = shl i32 %i0, 16 ; not one-use
+  call void @use32(i32 %i1)
+  %r = and i32 %i1, -2147483648
+  ret i32 %r
+}
+
+; Some vector tests
+
+define <2 x i32> @t8(<2 x i16> %x) {
+; CHECK-LABEL: @t8(
+; CHECK-NEXT:    [[I0:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i32>
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw <2 x i32> [[I0]], <i32 16, i32 16>
+; CHECK-NEXT:    [[R:%.*]] = and <2 x i32> [[I1]], <i32 -2147483648, i32 -2147483648>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %i0 = zext <2 x i16> %x to <2 x i32>
+  %i1 = shl <2 x i32> %i0, <i32 16, i32 16>
+  %r = and <2 x i32> %i1, <i32 -2147483648, i32 -2147483648>
+  ret <2 x i32> %r
+}
+define <2 x i32> @t9(<2 x i16> %x) {
+; CHECK-LABEL: @t9(
+; CHECK-NEXT:    [[I0:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i32>
+; CHECK-NEXT:    [[I1:%.*]] = shl <2 x i32> [[I0]], <i32 16, i32 undef>
+; CHECK-NEXT:    [[R:%.*]] = and <2 x i32> [[I1]], <i32 -2147483648, i32 -2147483648>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %i0 = zext <2 x i16> %x to <2 x i32>
+  %i1 = shl <2 x i32> %i0, <i32 16, i32 undef>
+  %r = and <2 x i32> %i1, <i32 -2147483648, i32 -2147483648>
+  ; Here undef can be propagated into the mask.
+  ret <2 x i32> %r
+}
+define <2 x i32> @t10(<2 x i16> %x) {
+; CHECK-LABEL: @t10(
+; CHECK-NEXT:    [[I0:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i32>
+; CHECK-NEXT:    [[I1:%.*]] = shl nuw <2 x i32> [[I0]], <i32 16, i32 16>
+; CHECK-NEXT:    [[R:%.*]] = and <2 x i32> [[I1]], <i32 -2147483648, i32 undef>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %i0 = zext <2 x i16> %x to <2 x i32>
+  %i1 = shl <2 x i32> %i0, <i32 16, i32 16>
+  %r = and <2 x i32> %i1, <i32 -2147483648, i32 undef>
+  ; CAREFUL! We can't keep undef mask here, since high bits are no longer zero,
+  ; we must sanitize it to 0.
+  ret <2 x i32> %r
+}
+define <2 x i32> @t11(<2 x i16> %x) {
+; CHECK-LABEL: @t11(
+; CHECK-NEXT:    [[I0:%.*]] = zext <2 x i16> [[X:%.*]] to <2 x i32>
+; CHECK-NEXT:    [[I1:%.*]] = shl <2 x i32> [[I0]], <i32 16, i32 undef>
+; CHECK-NEXT:    [[R:%.*]] = and <2 x i32> [[I1]], <i32 -2147483648, i32 undef>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %i0 = zext <2 x i16> %x to <2 x i32>
+  %i1 = shl <2 x i32> %i0, <i32 16, i32 undef>
+  %r = and <2 x i32> %i1, <i32 -2147483648, i32 undef>
+  ; Here undef mask is fine.
+  ret <2 x i32> %r
+}