diff --git a/llvm/test/Transforms/InstCombine/reuse-constant-from-select-in-icmp.ll b/llvm/test/Transforms/InstCombine/reuse-constant-from-select-in-icmp.ll
new file mode 100644
index 000000000000..127cdf7e5187
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/reuse-constant-from-select-in-icmp.ll
@@ -0,0 +1,298 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; If we have a relational comparison with a constant, and said comparison is
+; used in a select, and there is a constant in select, see if we can make
+; those constants match.
+
+; We can't ever get non-canonical scalar predicates.
+
+; Likewise, while we can get non-canonical vector predicates, there must be an
+; extra use on that `icmp`, which precludes the fold from happening.
+
+;------------------------------------------------------------------------------;
+; Canonical scalar predicates
+;------------------------------------------------------------------------------;
+
+define i32 @p0_ult_65536(i32 %x, i32 %y) {
+; CHECK-LABEL: @p0_ult_65536(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65536
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+define i32 @p1_ugt(i32 %x, i32 %y) {
+; CHECK-LABEL: @p1_ugt(
+; CHECK-NEXT:    [[T:%.*]] = icmp ugt i32 [[X:%.*]], 65534
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ugt i32 %x, 65534
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+define i32 @p2_slt_65536(i32 %x, i32 %y) {
+; CHECK-LABEL: @p2_slt_65536(
+; CHECK-NEXT:    [[T:%.*]] = icmp slt i32 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp slt i32 %x, 65536
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+define i32 @p3_sgt(i32 %x, i32 %y) {
+; CHECK-LABEL: @p3_sgt(
+; CHECK-NEXT:    [[T:%.*]] = icmp sgt i32 [[X:%.*]], 65534
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp sgt i32 %x, 65534
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+
+;------------------------------------------------------------------------------;
+; Vectors
+;------------------------------------------------------------------------------;
+
+define <2 x i32> @p4_vec_splat_ult_65536(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p4_vec_splat_ult_65536(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 65536>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 65536>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @p5_vec_splat_ugt(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p5_vec_splat_ugt(
+; CHECK-NEXT:    [[T:%.*]] = icmp ugt <2 x i32> [[X:%.*]], <i32 65534, i32 65534>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ugt <2 x i32> %x, <i32 65534, i32 65534>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @p6_vec_splat_slt_65536(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p6_vec_splat_slt_65536(
+; CHECK-NEXT:    [[T:%.*]] = icmp slt <2 x i32> [[X:%.*]], <i32 65536, i32 65536>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp slt <2 x i32> %x, <i32 65536, i32 65536>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @p7_vec_splat_sgt(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p7_vec_splat_sgt(
+; CHECK-NEXT:    [[T:%.*]] = icmp sgt <2 x i32> [[X:%.*]], <i32 65534, i32 65534>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp sgt <2 x i32> %x, <i32 65534, i32 65534>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+
+; Vectors with undef
+
+define <2 x i32> @p8_vec_nonsplat_undef0(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p8_vec_nonsplat_undef0(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 undef>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 undef>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @p9_vec_nonsplat_undef1(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p9_vec_nonsplat_undef1(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 65536>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 undef>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 65536>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 undef>
+  ret <2 x i32> %r
+}
+define <2 x i32> @p10_vec_nonsplat_undef2(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p10_vec_nonsplat_undef2(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 undef>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 undef>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 undef>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 undef>
+  ret <2 x i32> %r
+}
+
+; Non-splat vectors
+
+define <2 x i32> @p11_vec_nonsplat(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @p11_vec_nonsplat(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 32768>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 32767>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 32768>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 32767>
+  ret <2 x i32> %r
+}
+
+;------------------------------------------------------------------------------;
+; Extra uses prevent the fold.
+;------------------------------------------------------------------------------;
+
+declare void @use1(i1)
+
+define i32 @n12_extrause(i32 %x, i32 %y) {
+; CHECK-LABEL: @n12_extrause(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65536
+; CHECK-NEXT:    call void @use1(i1 [[T]])
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65536
+  call void @use1(i1 %t)
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+
+;------------------------------------------------------------------------------;
+; Commutativity
+;------------------------------------------------------------------------------;
+
+; We don't care if the constant in select is true value or false value
+define i32 @p13_commutativity0(i32 %x, i32 %y) {
+; CHECK-LABEL: @p13_commutativity0(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 65535, i32 [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65536
+  %r = select i1 %t, i32 65535, i32 %y
+  ret i32 %r
+}
+
+; Which means, if both possibilities are constants, we must check both of them.
+define i32 @p14_commutativity1(i32 %x, i32 %y) {
+; CHECK-LABEL: @p14_commutativity1(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 65535, i32 42
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65536
+  %r = select i1 %t, i32 65535, i32 42
+  ret i32 %r
+}
+define i32 @p15_commutativity2(i32 %x, i32 %y) {
+; CHECK-LABEL: @p15_commutativity2(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 42, i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65536
+  %r = select i1 %t, i32 42, i32 65535
+  ret i32 %r
+}
+
+;------------------------------------------------------------------------------;
+; Negative tests
+;------------------------------------------------------------------------------;
+
+; For vectors, make sure we handle edge cases correctly
+define <2 x i32> @n17_ult_zero(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @n17_ult_zero(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult <2 x i32> [[X:%.*]], <i32 65536, i32 0>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ult <2 x i32> %x, <i32 65536, i32 0>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @n18_ugt_allones(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @n18_ugt_allones(
+; CHECK-NEXT:    [[T:%.*]] = icmp ugt <2 x i32> [[X:%.*]], <i32 65534, i32 -1>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp ugt <2 x i32> %x, <i32 65534, i32 -1>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @n19_slt_int_min(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @n19_slt_int_min(
+; CHECK-NEXT:    [[T:%.*]] = icmp slt <2 x i32> [[X:%.*]], <i32 65536, i32 -2147483648>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp slt <2 x i32> %x, <i32 65536, i32 -2147483648>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+define <2 x i32> @n20_sgt_int_max(<2 x i32> %x, <2 x i32> %y) {
+; CHECK-LABEL: @n20_sgt_int_max(
+; CHECK-NEXT:    [[T:%.*]] = icmp sgt <2 x i32> [[X:%.*]], <i32 65534, i32 2147483647>
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[T]], <2 x i32> [[Y:%.*]], <2 x i32> <i32 65535, i32 65535>
+; CHECK-NEXT:    ret <2 x i32> [[R]]
+;
+  %t = icmp sgt <2 x i32> %x, <i32 65534, i32 2147483647>
+  %r = select <2 x i1> %t, <2 x i32> %y, <2 x i32> <i32 65535, i32 65535>
+  ret <2 x i32> %r
+}
+
+; We don't do anything for non-relational comparisons.
+define i32 @n21_equality(i32 %x, i32 %y) {
+; CHECK-LABEL: @n21_equality(
+; CHECK-NEXT:    [[T:%.*]] = icmp eq i32 [[X:%.*]], -2147483648
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 2147483647, i32 [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp eq i32 %x, -2147483648
+  %r = select i1 %t, i32 2147483647, i32 %y
+  ret i32 %r
+}
+
+; We don't touch sign checks
+define i32 @n22_sign_check(i32 %x, i32 %y) {
+; CHECK-LABEL: @n22_sign_check(
+; CHECK-NEXT:    [[T:%.*]] = icmp slt i32 [[X:%.*]], 0
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 -1, i32 [[Y:%.*]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp slt i32 %x, 0
+  %r = select i1 %t, i32 -1, i32 %y
+  ret i32 %r
+}
+
+; If the types don't match we currently don't do anything.
+define i32 @n23_type_mismatch(i64 %x, i32 %y) {
+; CHECK-LABEL: @n23_type_mismatch(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i64 [[X:%.*]], 65536
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i64 %x, 65536
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}
+
+; Don't do wrong tranform
+define i32 @n24_ult_65534(i32 %x, i32 %y) {
+; CHECK-LABEL: @n24_ult_65534(
+; CHECK-NEXT:    [[T:%.*]] = icmp ult i32 [[X:%.*]], 65534
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[T]], i32 [[Y:%.*]], i32 65535
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %t = icmp ult i32 %x, 65534
+  %r = select i1 %t, i32 %y, i32 65535
+  ret i32 %r
+}