diff --git a/llvm/test/ThinLTO/X86/visibility-elf.ll b/llvm/test/ThinLTO/X86/visibility-elf.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/visibility-elf.ll
@@ -0,0 +1,137 @@
+; RUN: split-file %s %t
+; RUN: opt -module-summary %t/a.ll -o %ta.bc
+; RUN: opt -module-summary %t/b.ll -o %tb.bc
+
+;; Test visibility propagation. The prevailing definitions are all from %tb.bc.
+; RUN: llvm-lto2 run -save-temps -o %t1.bc %ta.bc %tb.bc \
+; RUN:   -r=%ta.bc,var1,l -r=%ta.bc,var2,l \
+; RUN:   -r=%ta.bc,hidden_def_weak_def,l -r=%ta.bc,protected_def_weak_def,l -r=%ta.bc,protected_def_weak_hidden_def,l \
+; RUN:   -r=%ta.bc,protected_def_hidden_ref,l -r=%ta.bc,not_imported,l -r=%ta.bc,hidden_def_ref,l \
+; RUN:   -r=%ta.bc,hidden_def_weak_ref,l \
+; RUN:   -r=%ta.bc,ext, -r=%ta.bc,main,plx \
+; RUN:   -r=%tb.bc,var1,plx -r=%tb.bc,var2,plx \
+; RUN:   -r=%tb.bc,hidden_def_weak_def,pl -r=%tb.bc,protected_def_weak_def,pl -r=%tb.bc,protected_def_weak_hidden_def,pl \
+; RUN:   -r=%tb.bc,protected_def_hidden_ref,pl -r=%tb.bc,not_imported,pl -r=%tb.bc,hidden_def_ref,pl \
+; RUN:   -r=%tb.bc,hidden_def_weak_ref,pl
+; RUN: llvm-dis < %t1.bc.1.3.import.bc | FileCheck %s
+
+;; %tb.bc does not import anything, so we just check 1.promote.
+; RUN: llvm-dis < %t1.bc.2.1.promote.bc | FileCheck %s --check-prefix=CHECK2
+
+;--- a.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK:      @var1 = external global i32, align 4
+; CHECK-NEXT: @var2 = available_externally hidden global i32 1, align 4
+
+@var1 = weak global i32 1, align 4
+@var2 = extern_weak global i32
+
+declare void @ext(void ()*)
+
+; CHECK: declare i32 @hidden_def_weak_def()
+; CHECK: declare void @protected_def_weak_def()
+; CHECK: declare hidden void @protected_def_weak_hidden_def()
+;; Currently the visibility is not propagated onto an unimported function,
+;; because we don't have summaries for declarations.
+; CHECK: declare extern_weak void @not_imported()
+; CHECK: define available_externally hidden void @hidden_def_ref() !thinlto_src_module !0
+; CHECK: define available_externally hidden void @hidden_def_weak_ref() !thinlto_src_module !0
+;; This can be hidden, but we cannot communicate the declaration's visibility
+;; to other modules because declarations don't have summaries, and the IRLinker
+;; overrides it when importing the protected def.
+; CHECK: define available_externally protected void @protected_def_hidden_ref() !thinlto_src_module !0
+
+; CHECK2: define hidden i32 @hidden_def_weak_def()
+; CHECK2: define protected void @protected_def_weak_def()
+; CHECK2: define protected void @protected_def_weak_hidden_def()
+; CHECK2: define hidden void @hidden_def_ref()
+; CHECK2: define hidden void @hidden_def_weak_ref()
+; CHECK2: define protected void @protected_def_hidden_ref()
+; CHECK2: define hidden void @not_imported()
+
+define weak i32 @hidden_def_weak_def() {
+entry:
+  %0 = load i32, i32* @var2
+  ret i32 %0
+}
+
+define weak void @protected_def_weak_def() {
+entry:
+  ret void
+}
+
+define weak hidden void @protected_def_weak_hidden_def() {
+entry:
+  ret void
+}
+
+declare extern_weak void @not_imported()
+
+declare void @hidden_def_ref()
+declare extern_weak void @hidden_def_weak_ref()
+declare hidden void @protected_def_hidden_ref()
+
+define i32 @main() {
+entry:
+  call void @ext(void ()* bitcast (i32 ()* @hidden_def_weak_def to void ()*))
+  call void @ext(void ()* @protected_def_weak_def)
+  call void @ext(void ()* @protected_def_weak_hidden_def)
+  call void @ext(void ()* @hidden_def_ref)
+  call void @ext(void ()* @hidden_def_weak_ref)
+  call void @ext(void ()* @protected_def_hidden_ref)
+  call void @ext(void ()* @not_imported)
+
+  ;; Calls ensure the functions are imported.
+  call i32 @hidden_def_weak_def()
+  call void @protected_def_weak_def()
+  call void @protected_def_weak_hidden_def()
+  call void @hidden_def_ref()
+  call void @hidden_def_weak_ref()
+  call void @protected_def_hidden_ref()
+  ret i32 0
+}
+
+;--- b.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@var1 = hidden global i32 1, align 4
+@var2 = hidden global i32 1, align 4
+
+define hidden i32 @hidden_def_weak_def() {
+entry:
+  %0 = load i32, i32* @var1
+  ret i32 %0
+}
+
+define protected void @protected_def_weak_def() {
+entry:
+  ret void
+}
+
+define protected void @protected_def_weak_hidden_def() {
+entry:
+  ret void
+}
+
+define hidden void @hidden_def_ref() {
+entry:
+  ret void
+}
+
+define hidden void @hidden_def_weak_ref() {
+entry:
+  ret void
+}
+
+define protected void @protected_def_hidden_ref() {
+entry:
+  ret void
+}
+
+define hidden void @not_imported() {
+entry:
+  ret void
+}
diff --git a/llvm/test/ThinLTO/X86/visibility-macho.ll b/llvm/test/ThinLTO/X86/visibility-macho.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/visibility-macho.ll
@@ -0,0 +1,91 @@
+; RUN: split-file %s %t
+; RUN: opt -module-summary %t/a.ll -o %ta.bc
+; RUN: opt -module-summary %t/b.ll -o %tb.bc
+
+;; Test visibility propagation. The prevailing definitions are all from %tb.bc.
+; RUN: llvm-lto2 run -save-temps -o %t1.bc %ta.bc %tb.bc \
+; RUN:   -r=%ta.bc,_var1,l -r=%ta.bc,_var2,l \
+; RUN:   -r=%ta.bc,_hidden_def_weak_def,l -r=%ta.bc,_not_imported,l -r=%ta.bc,_hidden_def_ref,l \
+; RUN:   -r=%ta.bc,_hidden_def_weak_ref,l \
+; RUN:   -r=%ta.bc,_ext, -r=%ta.bc,_main,plx \
+; RUN:   -r=%tb.bc,_var1,plx -r=%tb.bc,_var2,plx \
+; RUN:   -r=%tb.bc,_hidden_def_weak_def,pl -r=%tb.bc,_not_imported,pl -r=%tb.bc,_hidden_def_ref,pl \
+; RUN:   -r=%tb.bc,_hidden_def_weak_ref,pl
+; RUN: llvm-dis < %t1.bc.1.3.import.bc | FileCheck %s
+; RUN: llvm-dis < %t1.bc.2.1.promote.bc | FileCheck %s --check-prefix=CHECK2
+
+;--- a.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+; CHECK:      @var1 = external global i32, align 4
+; CHECK-NEXT: @var2 = available_externally hidden global i32 1, align 4
+
+@var1 = weak global i32 1, align 4
+@var2 = extern_weak global i32
+
+declare void @ext(void ()*)
+
+; CHECK: declare i32 @hidden_def_weak_def()
+;; Currently the visibility is not propagated for an unimported function.
+; CHECK: declare extern_weak dso_local void @not_imported()
+; CHECK: define available_externally hidden void @hidden_def_ref() !thinlto_src_module !0
+; CHECK: define available_externally hidden void @hidden_def_weak_ref() !thinlto_src_module !0
+
+; CHECK2: define hidden i32 @hidden_def_weak_def()
+; CHECK2: define hidden void @hidden_def_ref()
+; CHECK2: define hidden void @hidden_def_weak_ref()
+; CHECK2: define hidden void @not_imported()
+
+define weak i32 @hidden_def_weak_def() {
+entry:
+  %0 = load i32, i32* @var2
+  ret i32 %0
+}
+
+declare extern_weak void @not_imported()
+
+declare void @hidden_def_ref()
+declare extern_weak void @hidden_def_weak_ref()
+
+define i32 @main() {
+entry:
+  call void @ext(void ()* bitcast (i32 ()* @hidden_def_weak_def to void ()*))
+  call void @ext(void ()* @hidden_def_ref)
+  call void @ext(void ()* @hidden_def_weak_ref)
+  call void @ext(void ()* @not_imported)
+
+  ;; Calls ensure the functions are imported.
+  call i32 @hidden_def_weak_def()
+  call void @hidden_def_ref()
+  call void @hidden_def_weak_ref()
+  ret i32 0
+}
+
+;--- b.ll
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.15.0"
+
+@var1 = hidden global i32 1, align 4
+@var2 = hidden global i32 1, align 4
+
+define hidden i32 @hidden_def_weak_def() {
+entry:
+  %0 = load i32, i32* @var1
+  ret i32 %0
+}
+
+define hidden void @hidden_def_ref() {
+entry:
+  ret void
+}
+
+define hidden void @hidden_def_weak_ref() {
+entry:
+  ret void
+}
+
+define hidden void @not_imported() {
+entry:
+  ret void
+}