diff --git a/test/Transforms/GlobalDCE/comdats.ll b/test/Transforms/GlobalDCE/comdats.ll
new file mode 100644
index 00000000000..29ef848a586
--- /dev/null
+++ b/test/Transforms/GlobalDCE/comdats.ll
@@ -0,0 +1,178 @@
+; Test the behavior of GlobalDCE in conjunction with comdats.
+;
+; RUN: opt < %s -globaldce -S | FileCheck %s
+
+; First test checks that if one function in a comdat group is used, both other
+; functions and other globals even if unused will be preserved.
+$test1_c = comdat any
+; CHECK: $test1_c = comdat any
+
+; Second test checks that if one function in a comdat group is used, both other
+; functions and other globals even if unused will be preserved.
+$test2_c = comdat any
+; CHECK: $test2_c = comdat any
+
+; Third test checks that calling a function in a comdat group with an alias
+; preserves the alias.
+$test3_c = comdat any
+; CHECK: $test3_c = comdat any
+
+; Fourth test checks that calling an alias in a comdat group with a function
+; preserves the function. (This is the trivial case as the alias uses the
+; function.)
+$test4_c = comdat any
+; CHECK: $test4_c = comdat any
+
+; Fifth test checks that calling a function in a comdat group that is used as
+; the resolver of an ifunc doesn't preserve that ifunc. ifunc symbols don't
+; participate in the comdat group of their resolver function as they are
+; considered separate objects.
+$test5_c = comdat any
+; CHECK: $test5_c = comdat any
+
+; Sixth test checks that calling an ifunc whose resolver is in a comdat group
+; preserves the resolver. This is the trivial case as the ifunc uses the
+; resolver.
+$test6_c = comdat any
+; CHECK: $test6_c = comdat any
+
+; Seventh test checks that we can eliminate a comdat when it has only one dead function participant.
+$test7_c = comdat any
+; CHECK-NOT: $test7_c = comdat any
+
+; Eighth test checks that we can eliminate a comdat when it has only one dead global participant.
+$test8_c = comdat any
+; CHECK-NOT: $test8_c = comdat any
+
+; Ninth test checks that we can eliminate a comdat when there are multiple
+; dead participants.
+$test9_c = comdat any
+; CHECK-NOT: $test9_c = comdat any
+
+; Tenth test checks that we can eliminate a comdat when it has multiple
+; participants that form internal cyclic uses but are never used externally and
+; thus the entire ifunc can safely be eliminated.
+$test10_c = comdat any
+; CHECK-NOT: $test10_c = comdat any
+
+@test1_gv = linkonce_odr unnamed_addr global i32 42, comdat($test1_c)
+; CHECK: @test1_gv = linkonce_odr unnamed_addr global
+
+@test2_used = linkonce_odr unnamed_addr global i32 42, comdat($test2_c)
+; CHECK: @test2_used = linkonce_odr unnamed_addr global
+
+@test2_gv = linkonce_odr unnamed_addr global i32 42, comdat($test2_c)
+; CHECK: @test2_gv = linkonce_odr unnamed_addr global
+
+@test8_gv = linkonce_odr unnamed_addr global i32 42, comdat($test8_c)
+; CHECK-NOT: @test8_gv
+
+@test9_gv = linkonce_odr unnamed_addr global i32 42, comdat($test9_c)
+; CHECK-NOT: @test9_gv
+
+@test10_gv = linkonce_odr unnamed_addr global void ()* @test10_f, comdat($test10_c)
+; CHECK-NOT: @test10_gv
+
+@test3_a = linkonce_odr unnamed_addr alias void (), void ()* @test3_f
+; CHECK: @test3_a = linkonce_odr unnamed_addr alias
+
+@test4_a = linkonce_odr unnamed_addr alias void (), void ()* @test4_f
+; CHECK: @test4_a = linkonce_odr unnamed_addr alias
+
+@test10_a = linkonce_odr unnamed_addr alias void (), void ()* @test10_g
+; CHECK-NOT: @test10_a
+
+@test5_if = linkonce_odr ifunc void (), void ()* ()* @test5_f
+; CHECK-NOT: @test5_if
+
+@test6_if = linkonce_odr ifunc void (), void ()* ()* @test6_f
+; CHECK: @test6_if = linkonce_odr ifunc
+
+; This function is directly used and so cannot be eliminated.
+define linkonce_odr void @test1_used() comdat($test1_c) {
+; CHECK: define linkonce_odr void @test1_used()
+entry:
+  ret void
+}
+
+define linkonce_odr void @test1_f() comdat($test1_c) {
+; CHECK: define linkonce_odr void @test1_f()
+entry:
+  ret void
+}
+
+; Now test that a function, global variable, alias, and ifunc in the same
+; comdat are kept.
+define linkonce_odr void @test2_f() comdat($test2_c) {
+; CHECK: define linkonce_odr void @test2_f()
+entry:
+  ret void
+}
+
+define linkonce_odr void @test3_f() comdat($test3_c) {
+; CHECK: define linkonce_odr void @test3_f()
+entry:
+  ret void
+}
+
+define linkonce_odr void @test4_f() comdat($test4_c) {
+; CHECK: define linkonce_odr void @test4_f()
+entry:
+  ret void
+}
+
+declare void @test_external()
+
+define linkonce_odr void ()* @test5_f() comdat($test5_c) {
+; CHECK: define linkonce_odr void ()* @test5_f()
+entry:
+  ret void ()* @test_external
+}
+
+define linkonce_odr void ()* @test6_f() comdat($test6_c) {
+; CHECK: define linkonce_odr void ()* @test6_f()
+entry:
+  ret void ()* @test_external
+}
+
+define linkonce_odr void @test7_f() comdat($test7_c) {
+; CHECK-NOT: @test7_f
+entry:
+  ret void
+}
+
+define linkonce_odr void @test9_f() comdat($test9_c) {
+; CHECK-NOT: @test9_f
+entry:
+  ret void
+}
+
+define linkonce_odr void @test10_f() comdat($test10_c) {
+; CHECK-NOT: @test10_f
+entry:
+  %gv = load void ()*, void ()** @test10_gv
+  call void @test10_a()
+  ret void
+}
+
+define linkonce_odr void @test10_g() comdat($test10_c) {
+; CHECK-NOT: @test10_g
+entry:
+  call void @test10_f()
+  ret void
+}
+
+
+; An external function to pin as "used" various things above that shouldn't be
+; eliminated.
+define void @external_user() {
+  call void @test1_used()
+  %gv = load i32, i32* @test2_used
+
+  call void @test3_f()
+  call void @test4_a()
+
+  %fptr = call void() *@test5_f()
+  call void @test6_if()
+  ret void
+}
diff --git a/test/Transforms/GlobalDCE/pr20981.ll b/test/Transforms/GlobalDCE/pr20981.ll
deleted file mode 100644
index c3e06699da7..00000000000
--- a/test/Transforms/GlobalDCE/pr20981.ll
+++ /dev/null
@@ -1,17 +0,0 @@
-; RUN: opt < %s -globaldce -S | FileCheck %s
-
-$c1 = comdat any
-; CHECK: $c1 = comdat any
-
-@a1 = linkonce_odr alias void (), void ()* @f1
-; CHECK: @a1 = linkonce_odr alias void (), void ()* @f1
-
-define linkonce_odr void @f1() comdat($c1) {
-  ret void
-}
-; CHECK: define linkonce_odr void @f1() comdat($c1)
-
-define void @g() {
-  call void @f1()
-  ret void
-}