[C++20] [Modules] Treat constexpr/consteval member function as implicitly inline

Close llvm#107673

(cherry picked from commit 74ac96a)

Author: ChuanqiXu9

clang/lib/Sema/SemaDecl.cpp

@@ -9732,6 +9732,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     // the function decl is created above).
     // FIXME: We need a better way to separate C++ standard and clang modules.
     bool ImplicitInlineCXX20 = !getLangOpts().CPlusPlusModules ||
+                               NewFD->isConstexpr() || NewFD->isConsteval() ||
                                !NewFD->getOwningModule() ||
                                NewFD->isFromExplicitGlobalModule() ||
                                NewFD->getOwningModule()->isHeaderLikeModule();

clang/test/Modules/pr107673.cppm

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++20 %s -ast-dump | FileCheck %s
+export module a;
+export class f {
+public:
+    void non_inline_func() {}
+    constexpr void constexpr_func() {}
+    consteval void consteval_func() {}
+};
+
+// CHECK-NOT: non_inline_func {{.*}}implicit-inline
+// CHECK: constexpr_func {{.*}}implicit-inline
+// CHECK: consteval_func {{.*}}implicit-inline