[C++20] [Modules] Don't import non-inline function bodies even if it is marked as always_inline

Close #80949

Previously, I thought the always-inline function can be an exception to
enable optimizations as much as possible. However, it looks like it
breaks the ABI requirement we discussed later. So it looks better to not
import non-inline function bodies at all even if the function bodies are
marked as always_inline.

It doesn't produce regressions in some degree since the always_inline
still works in the same TU.

Author: ChuanqiXu9

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3985,8 +3985,7 @@ bool CodeGenModule::shouldEmitFunction(GlobalDecl GD) {
   // behavior may break ABI compatibility of the current unit.
   if (const Module *M = F->getOwningModule();
       M && M->getTopLevelModule()->isNamedModule() &&
-      getContext().getCurrentNamedModule() != M->getTopLevelModule() &&
-      !F->hasAttr<AlwaysInlineAttr>())
+      getContext().getCurrentNamedModule() != M->getTopLevelModule())
     return false;
 
   if (F->hasAttr<NoInlineAttr>())

clang/test/CodeGenCXX/module-funcs-from-imports.cppm

@@ -53,11 +53,11 @@ int use() {
     return exported_func() + always_inline_func();
 }
 
-// Checks that none of the function (except the always_inline_func) in the importees
+// Checks that none of the function in the importees
 // are generated in the importer's code.
 // CHECK-O0: define{{.*}}_Z3usev(
 // CHECK-O0: declare{{.*}}_ZW1M13exported_funcv(
-// CHECK-O0: define{{.*}}available_externally{{.*}}_ZW1M18always_inline_funcv(
+// CHECK-O0: declare{{.*}}_ZW1M18always_inline_funcv(
 // CHECK-O0-NOT: func_in_gmf
 // CHECK-O0-NOT: func_in_gmf_not_called
 // CHECK-O0-NOT: non_exported_func
@@ -68,7 +68,7 @@ int use() {
 // O0 to keep consistent ABI.
 // CHECK-O1: define{{.*}}_Z3usev(
 // CHECK-O1: declare{{.*}}_ZW1M13exported_funcv(
-// CHECK-O1: define{{.*}}available_externally{{.*}}_ZW1M18always_inline_funcv(
+// CHECK-O1: declare{{.*}}_ZW1M18always_inline_funcv(
 // CHECK-O1-NOT: func_in_gmf
 // CHECK-O1-NOT: func_in_gmf_not_called
 // CHECK-O1-NOT: non_exported_func