From 1db7dc4d96deb01e7a03b4a9068a005789da1352 Mon Sep 17 00:00:00 2001 From: Alexey Bader Date: Thu, 9 Oct 2025 19:41:04 -0700 Subject: [PATCH 1/2] Fix use of funified-lto and save-temps flags together > clang -flto -funified-lto -save-temps test.c Fails with the following error message: ```bash module flag identifiers must be unique (or of 'require' type) !"UnifiedLTO" fatal error: error in backend: Broken module found, compilation aborted! clang: error: clang frontend command failed with exit code 70 (use -v to see invocation) ``` Here is what the driver does when `-save-temps` flag is set: > clang -flto -funified-lto -save-temps test.c -ccc-print-phases > +- 0: input, "test.c", c > +- 1: preprocessor, {0}, cpp-output > +- 2: compiler, {1}, ir > +- 3: backend, {2}, lto-bc > 4: linker, {3}, image The IR output of "compiler" step has "UnifiedLTO" module flag. "backend" step adds another module flag with "UnifiedLTO" identifier, which invalidates the LLVM IR module. --- clang/lib/CodeGen/BackendUtil.cpp | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp index 2d959827d6972..d28d886b3551e 100644 --- a/clang/lib/CodeGen/BackendUtil.cpp +++ b/clang/lib/CodeGen/BackendUtil.cpp @@ -1199,7 +1199,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline( } } - if (shouldEmitUnifiedLTOModueFlag()) + if (shouldEmitUnifiedLTOModueFlag() && + !TheModule->getModuleFlag("UnifiedLTO")) TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1)); } From 40e51fa8248b062c6126cca331cd3c3d4995f6d3 Mon Sep 17 00:00:00 2001 From: Alexey Bader Date: Thu, 9 Oct 2025 20:16:59 -0700 Subject: [PATCH 2/2] Add test. --- clang/test/CodeGen/unified-lto-module-flag.ll | 11 +++++++++++ 1 file changed, 11 insertions(+) create mode 100644 clang/test/CodeGen/unified-lto-module-flag.ll diff --git a/clang/test/CodeGen/unified-lto-module-flag.ll b/clang/test/CodeGen/unified-lto-module-flag.ll new file mode 100644 index 0000000000000..deefe826d1566 --- /dev/null +++ b/clang/test/CodeGen/unified-lto-module-flag.ll @@ -0,0 +1,11 @@ +; Test that we do not duplicate the UnifiedLTO module flag. +; +; RUN: %clang_cc1 -emit-llvm -flto=full -funified-lto -o - %s | FileCheck %s + +; CHECK: !llvm.module.flags = !{!0, !1, !2, !3} +!llvm.module.flags = !{!0, !1, !2, !3} + +!0 = !{i32 1, !"wchar_size", i32 2} +!1 = !{i32 7, !"frame-pointer", i32 2} +!2 = !{i32 1, !"EnableSplitLTOUnit", i32 1} +!3 = !{i32 1, !"UnifiedLTO", i32 1}