[CIR] Correctly handle annotate attribute on C++ constructors/destructors

[Sharp0802]

This PR fixes an issue where the [[clang::annotate]] attribute on C++ constructors (CXXConstructorDecl) was not correctly lowered, and resolves a subsequent crash in the cir-to-llvm pipeline caused by the initial fix.

1. The Problem

There were two distinct problems:

• Initial Bug: The [[clang::annotate]] attribute was completely ignored when applied to a C++ constructor. While it worked for regular functions, the specific code path for handling CXXConstructorDecl in CIRGenModule did not process this attribute.

• Downstream Crash: After fixing the initial bug to generate the correct annotations and cir.global_annotations in the CIR dialect, the cir-translate tool would crash with a "redefinition of symbol" error for the annotation string (e.g., .str.annotation).

2. Analysis and Root Cause

• Cause of Initial Bug: In CIRGenModule::emitGlobalDefinition, the code path for constructors and destructors branches to ABI->emitCXXStructor. This path was missing the logic to check for an AnnotateAttr and add it to the deferredAnnotations map, which is correctly handled for regular FunctionDecls.

• Cause of Downstream Crash: The cir-to-llvm lowering pipeline has two mechanisms for handling annotations:

  1. The LoweringPrepare pass processes the cir.global_annotations attribute on the ModuleOp and generates the corresponding @llvm.global.annotations array and its associated global string constants.
  2. A later stage in the cir-translate binary also attempts to process the same cir.global_annotations attribute.

  The issue was that LoweringPreparePass did not consume (remove) the cir.global_annotations attribute after processing it. This left the attribute on the module, causing the later stage in cir-translate to re-process it, leading to the symbol redefinition crash.

3. Implementation

This PR addresses both issues with two key changes:

1. In CIRGenModule.cpp:

   • The logic to handle AnnotateAttr has been added to the CXXConstructorDecl / CXXDestructorDecl path within emitGlobalDefinition. This ensures that constructor annotations are correctly identified and deferred for processing, just like regular functions.

2. In LoweringPreparePass:

   • After the buildGlobalAnnotationValues() function successfully processes the cir.global_annotations attribute and generates the necessary LLVM globals, the pass now removes the cir.global_annotations attribute from the ModuleOp. This "consumes" the attribute, preventing any subsequent pass from redundantly processing it.

4. Verification

With these changes, a C++ constructor with a [[clang::annotate]] attribute is now correctly lowered through the entire pipeline:

• The ClangIR (cir dialect) correctly contains both the local annotations on the cir.func and the module-level cir.global_annotations.
• The cir-opt -cir-to-llvm pass successfully lowers this to the LLVM dialect.
• The cir-translate tool successfully converts the LLVM dialect to LLVM IR text without crashing.
• The final LLVM IR contains the expected @llvm.global.annotations metadata for the constructor.

This fix ensures that annotation metadata is preserved correctly and robustly for C++ constructors.

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 32e3971d31452620eb102f122259b429733b3ef0 67e6ac3525ffff8e95fdefd8d4cc0861a8234c8c --extensions cpp -- clang/lib/CIR/CodeGen/CIRGenModule.cpp clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp

View the diff from clang-format here.

diff --git a/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp b/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp
index 756416302b..069233d27b 100644
--- a/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp
+++ b/clang/lib/CIR/Dialect/Transforms/LoweringPrepare.cpp
@@ -1610,7 +1610,7 @@ void LoweringPreparePass::runOnOperation() {
   buildCXXGlobalInitFunc();
   buildGlobalCtorDtorList();
   buildGlobalAnnotationValues();
-  
+
   if (theModule && theModule->hasAttr("cir.global_annotations")) {
     theModule->removeAttr("cir.global_annotations");
   }

[bcardosolopes]

Thanks for the detailed explanation, some comments but this mostly ready to go

[bcardosolopes]

Remove the curly braces!

[bcardosolopes]

Same here!

[bcardosolopes]

Is this necessary? If cir.global_annotations have been removed in lowering prepare, how come it might show up here again?

[bcardosolopes]

Seems like some clang-format is needed