[NFC] [C++20] [Modules] Test that we can avoid adding more specializations in reduced BMI

Author: ChuanqiXu9

clang/test/Modules/avoid-specialization-update-in-reduced-bmi.cppm

@@ -0,0 +1,28 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/base.cppm -emit-module-interface -o %t/base.pcm
+// RUN: %clang_cc1 -std=c++20 %t/update.cppm -fmodule-file=base=%t/base.pcm -emit-module-interface -o %t/update.pcm
+// RUN: llvm-bcanalyzer --dump --disable-histogram %t/update.pcm | FileCheck %t/update.cppm --check-prefix=FULL
+//
+// RUN: %clang_cc1 -std=c++20 %t/base.cppm -emit-reduced-module-interface -o %t/base.pcm
+// RUN: %clang_cc1 -std=c++20 %t/update.cppm -fmodule-file=base=%t/base.pcm -emit-reduced-module-interface -o %t/update.pcm
+// RUN: llvm-bcanalyzer --dump --disable-histogram %t/update.pcm | FileCheck %t/update.cppm
+
+//--- base.cppm
+export module base;
+
+export template <typename T>
+struct base {
+    T value;
+};
+
+//--- update.cppm
+export module update;
+import base;
+export int update() {
+    return base<int>().value;
+}
+
+// FULL: TEMPLATE_SPECIALIZATION
+// CHECK-NOT: TEMPLATE_SPECIALIZATION