[clang] [C++20] [Modules] Don't emit function bodies which is noinline and av… (PR #68501)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-modules

<details>
<summary>Changes</summary>

…ailabl externally

A workaround for https://github.com/llvm/llvm-project/issues/60996

As the title suggested, we can avoid emitting available externally functions which is marked as noinline already. Such functions should contribute nothing for optimizations.

The update for docs will be sent seperately if this god approved.

---
Full diff: https://github.com/llvm/llvm-project/pull/68501.diff


2 Files Affected:

- (modified) clang/lib/CodeGen/CodeGenModule.cpp (+3) 
- (added) clang/test/Modules/no-import-func-body.cppm (+45) 


``````````diff
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index cae9dd93bc55921..eeb923a29f9056b 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -3847,6 +3847,9 @@ bool CodeGenModule::shouldEmitFunction(GlobalDecl GD) {
   if (CodeGenOpts.OptimizationLevel == 0 && !F->hasAttr<AlwaysInlineAttr>())
     return false;
 
+  if (F->hasAttr<NoInlineAttr>())
+    return false;
+
   if (F->hasAttr<DLLImportAttr>() && !F->hasAttr<AlwaysInlineAttr>()) {
     // Check whether it would be safe to inline this dllimport function.
     DLLImportFunctionVisitor Visitor;
diff --git a/clang/test/Modules/no-import-func-body.cppm b/clang/test/Modules/no-import-func-body.cppm
new file mode 100644
index 000000000000000..9a111dca9855c09
--- /dev/null
+++ b/clang/test/Modules/no-import-func-body.cppm
@@ -0,0 +1,45 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: cd %t
+//
+// RUN: %clang_cc1 -std=c++20 -O1 -triple %itanium_abi_triple %t/a.cppm \
+// RUN:     -emit-module-interface -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 -O1 -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 -O1 -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 -O1 -triple %itanium_abi_triple %t/c.pcm -S \
+// RUN:     -emit-llvm -disable-llvm-passes -o - | FileCheck %t/c.cppm
+
+//--- a.cppm
+export module a;
+export int a() {
+    return 43;
+}
+export __attribute__((noinline)) int a_noinline() {
+    return 44;
+}
+
+//--- b.cppm
+export module b;
+export import a;
+export int b() {
+    return 43 + a();
+}
+
+export __attribute__((noinline)) int b_noinline() {
+    return 43 + a();
+}
+
+//--- c.cppm
+export module c;
+export import b;
+export int c() {
+    return 43 + b() + a() + b_noinline() + a_noinline();
+}
+
+// CHECK: define{{.*}}available_externally{{.*}}@_ZW1b1bv(
+// CHECK: define{{.*}}available_externally{{.*}}@_ZW1a1av(
+
+// CHECK: declare{{.*}}@_ZW1b10b_noinlinev()
+// CHECK: declare{{.*}}@_ZW1a10a_noinlinev()

``````````

</details>


https://github.com/llvm/llvm-project/pull/68501