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

This reverts commit 1ecbab5.

See the discussion in #86893.

The original commit receives too many complaints. Let's try to
workaround the issue to give better user experiences.

Author: ChuanqiXu9

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3952,7 +3952,8 @@ 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())
+      getContext().getCurrentNamedModule() != M->getTopLevelModule() &&
+      !F->hasAttr<AlwaysInlineAttr>())
     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 in the importees
+// Checks that none of the function (except the always_inline_func) in the importees
 // are generated in the importer's code.
 // CHECK-O0: define{{.*}}_Z3usev(
 // CHECK-O0: declare{{.*}}_ZW1M13exported_funcv(
-// CHECK-O0: declare{{.*}}_ZW1M18always_inline_funcv(
+// CHECK-O0: define{{.*}}available_externally{{.*}}_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: declare{{.*}}_ZW1M18always_inline_funcv(
+// CHECK-O1: define{{.*}}available_externally{{.*}}_ZW1M18always_inline_funcv(
 // CHECK-O1-NOT: func_in_gmf
 // CHECK-O1-NOT: func_in_gmf_not_called
 // CHECK-O1-NOT: non_exported_func