https://github.com/bader created
https://github.com/llvm/llvm-project/pull/162763
> 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.
>From 1db7dc4d96deb01e7a03b4a9068a005789da1352 Mon Sep 17 00:00:00 2001
From: Alexey Bader <[email protected]>
Date: Thu, 9 Oct 2025 19:41:04 -0700
Subject: [PATCH] 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));
}
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