[C++20] [Modules] Don't import function bodies from other module units even with optimizations

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3851,10 +3851,19 @@ CodeGenModule::isTriviallyRecursive(const FunctionDecl *FD) {
 bool CodeGenModule::shouldEmitFunction(GlobalDecl GD) {
   if (getFunctionLinkage(GD) != llvm::Function::AvailableExternallyLinkage)
     return true;
+
   const auto *F = cast<FunctionDecl>(GD.getDecl());
   if (CodeGenOpts.OptimizationLevel == 0 && !F->hasAttr<AlwaysInlineAttr>())
     return false;
 
+  // We don't import function bodies from other named module units since that
+  // behavior may break ABI compatibility of the current unit.
+  if (const Module *M = F->getOwningModule();
+      M && M->isModulePurview() &&
+      getContext().getCurrentNamedModule() != M->getTopLevelModule() &&
+      !F->hasAttr<AlwaysInlineAttr>())
+    return false;
+
   if (F->hasAttr<NoInlineAttr>())
     return false;
 

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

@@ -64,13 +64,13 @@ int use() {
 // CHECK-O0-NOT: non_exported_func_not_called
 // CHECK-O0-NOT: func_not_called
 
-// Checks that all the potentially called function in the importees are generated in the importer's code
-// with available_externally attribute.
+// Checks that the generated code within optimizations keep the same behavior with
+// O0 to keep consistent ABI.
 // CHECK-O1: define{{.*}}_Z3usev(
-// CHECK-O1: define{{.*}}available_externally{{.*}}_ZW1M13exported_funcv(
+// CHECK-O1: declare{{.*}}_ZW1M13exported_funcv(
 // CHECK-O1: define{{.*}}available_externally{{.*}}_ZW1M18always_inline_funcv(
-// CHECK-O1: define{{.*}}available_externally{{.*}}_ZW1M17non_exported_funcv(
-// CHECK-O1: define{{.*}}available_externally{{.*}}_Z11func_in_gmfv(
+// CHECK-O1-NOT: func_in_gmf
 // CHECK-O1-NOT: func_in_gmf_not_called
+// CHECK-O1-NOT: non_exported_func
 // CHECK-O1-NOT: non_exported_func_not_called
 // CHECK-O1-NOT: func_not_called

clang/test/CodeGenCXX/partitions.cpp

@@ -39,12 +39,13 @@ export int use() {
   return foo() + bar() + a + b;
 }
 
+// FIXME: The definition of the variables shouldn't be exported too.
 // CHECK: @_ZW3mod1a = available_externally global
 // CHECK: @_ZW3mod1b = available_externally global
 // CHECK: declare{{.*}} i32 @_ZW3mod3foov
 // CHECK: declare{{.*}} i32 @_ZW3mod3barv
 
 // CHECK-OPT: @_ZW3mod1a = available_externally global
 // CHECK-OPT: @_ZW3mod1b = available_externally global
-// CHECK-OPT: define available_externally{{.*}} i32 @_ZW3mod3foov
-// CHECK-OPT: define available_externally{{.*}} i32 @_ZW3mod3barv
+// CHECK-OPT: declare{{.*}} i32 @_ZW3mod3foov
+// CHECK-OPT: declare{{.*}} i32 @_ZW3mod3barv

clang/test/Modules/cxx20-importing-function-bodies.cppm

@@ -0,0 +1,72 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/a.cppm \
+// RUN:     -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/b.cppm \
+// RUN:     -emit-module-interface -fprebuilt-module-path=%t -o %t/b.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/c.cppm \
+// RUN:     -emit-module-interface -fprebuilt-module-path=%t -o %t/c.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/c.pcm -S \
+// RUN:     -emit-llvm -disable-llvm-passes -o - | FileCheck %t/c.cppm
+//
+// Be sure that we keep the same behavior as if optization not enabled.
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -O3 %t/a.cppm \
+// RUN:     -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -O3 %t/b.cppm \
+// RUN:     -emit-module-interface -fprebuilt-module-path=%t -o %t/b.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -O3 %t/c.cppm \
+// RUN:     -emit-module-interface -fprebuilt-module-path=%t -o %t/c.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -O3 %t/c.pcm \
+// RUN:     -S -emit-llvm -disable-llvm-passes -o - | FileCheck %t/c.cppm
+
+//--- a.cppm
+export module a;
+export int a() {
+    return 43;
+}
+
+template <int C>
+int implicitly_inlined_template_function() {
+    return C;
+}
+
+inline int reachable_inlined_a() {
+    return 45;
+}
+
+int reachable_notinlined_a() {
+    return 46;
+}
+
+export inline int inlined_a() {
+    return 44 + reachable_inlined_a() +
+           reachable_notinlined_a() +
+           implicitly_inlined_template_function<47>();
+}
+
+//--- b.cppm
+export module b;
+export import a;
+export int b() {
+    return 43 + a();
+}
+export inline int inlined_b() {
+    return 44 + inlined_a() + a();;
+}
+
+//--- c.cppm
+export module c;
+export import b;
+export int c() {
+    return 43 + b() + a() + inlined_b() + inlined_a();
+}
+
+// CHECK: declare{{.*}}@_ZW1b1bv
+// CHECK: declare{{.*}}@_ZW1a1av
+// CHECK: define{{.*}}@_ZW1b9inlined_bv
+// CHECK: define{{.*}}@_ZW1a9inlined_av
+// CHECK: define{{.*}}@_ZW1a19reachable_inlined_av
+// CHECK: declare{{.*}}@_ZW1a22reachable_notinlined_av
+// CHECK: define{{.*}}@_ZW1a36implicitly_inlined_template_functionILi47EEiv

clang/test/Modules/no-import-func-body.cppm

@@ -38,8 +38,8 @@ export int c() {
     return 43 + b() + a() + b_noinline() + a_noinline();
 }
 
-// CHECK: define{{.*}}available_externally{{.*}}@_ZW1b1bv(
-// CHECK: define{{.*}}available_externally{{.*}}@_ZW1a1av(
+// CHECK: declare{{.*}}@_ZW1b1bv(
+// CHECK: declare{{.*}}@_ZW1a1av(
 
 // CHECK: declare{{.*}}@_ZW1b10b_noinlinev()
 // CHECK: declare{{.*}}@_ZW1a10a_noinlinev()