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[CIR] Support more declarations without any codegen #151076

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Jul 31, 2025
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[CIR] Support more declarations without any codegen #151076

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[CIR] Support more declarations without any codegen
mmha Jul 29, 2025
86ffcb5
Add support for deduction guides
mmha Jul 29, 2025
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8 changes: 7 additions & 1 deletion clang/lib/CIR/CodeGen/CIRGenModule.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1267,8 +1267,14 @@ void CIRGenModule::emitTopLevelDecl(Decl *decl) {
break;

// No code generation needed.
case Decl::UsingShadow:
case Decl::ClassTemplate:
case Decl::Concept:
case Decl::CXXDeductionGuide:
case Decl::Empty:
case Decl::FunctionTemplate:
case Decl::StaticAssert:
case Decl::TypeAliasTemplate:
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@xlauko xlauko Jul 29, 2025

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You can add Decl::VarTemplate, Decl::VarTemplatePartialSpecialization, Decl::Block, Decl::Binding to be complete and on par with classic codegen.

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@mmha mmha Jul 30, 2025

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Variable templates are covered in #151066.

I tinkered with Blocks a little bit and it seems like it's not possible to create a BlockDecl without a BlockExpr which requires codegen that's not implemented, yet. Likewise, a BindingDecl can only show up with a DecompositionDecl and while #151073 implements them on a function scope level we don't support them on in namespace scopes, yet. So these DeclKinds would be dead code which is why I didn't add them in this PR.

case Decl::UsingShadow:
break;

case Decl::CXXConstructor:
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32 changes: 32 additions & 0 deletions clang/test/CIR/CodeGen/empty.cpp
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@@ -0,0 +1,32 @@
// RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
// RUN: FileCheck --input-file=%t.cir %s --check-prefix=CIR

// These declarations shouldn't emit any code. Therefore the module is expected to be empty.

template<typename T>
concept some_concept = true;

template<some_concept T>
class class_template {};

; // Empty declaration

template<typename T>
void function_template();

static_assert(true, "top level static assert");

template<typename T>
using type_alias = T;

namespace N {
using ::class_template; // UsingShadow
}

template<typename T>
struct deduction_guide {};

deduction_guide() -> deduction_guide<int>;

// CIR: module {{.*}} {
// CIR-NEXT: }