https://github.com/zyn0217 created https://github.com/llvm/llvm-project/pull/186380
The MS ABI does not appear to have implemented C++20 concept mangling yet. This has led to a bug after CWG2369, where lambdas within a requires body become un-mangleable because the surrounding function templates might not be instantiated. Previously, we bypassed code emission for such lambdas. However, a lambda can also appear within a template argument, which breaks that workaround. I really wish for a correct concept implementation in the MS ABI. Fixes https://github.com/llvm/llvm-project/issues/173160 >From 24fd1007eb357f45840e25f2261be7bde7c43f10 Mon Sep 17 00:00:00 2001 From: Younan Zhang <[email protected]> Date: Fri, 13 Mar 2026 20:13:12 +0800 Subject: [PATCH] [Clang] Do not try emitting function body when substituting a constraint The MS ABI does not appear to have implemented C++20 concept mangling yet. This has led to a bug after CWG2369, where lambdas within a requires body become un-mangleable because the surrounding function templates might not be instantiated. Previously, we bypassed code emission for such lambdas. However, a lambda can also appear within a template argument, which breaks that workaround. I really wish for a correct concept implementation in the MS ABI. --- .../lib/Sema/SemaTemplateInstantiateDecl.cpp | 20 ++++------- clang/test/CodeGenCXX/ms-mangle-requires.cpp | 34 +++++++++++++++++++ 2 files changed, 40 insertions(+), 14 deletions(-) diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp index e74c41517ecbf..18a6f199adde6 100644 --- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp +++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp @@ -5965,20 +5965,12 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation, savedContext.pop(); } - // We never need to emit the code for a lambda in unevaluated context. - // We also can't mangle a lambda in the require clause of a function template - // during constraint checking as the MSI ABI would need to mangle the (not yet - // specialized) enclosing declaration - // FIXME: Should we try to skip this for non-lambda functions too? - bool ShouldSkipCG = [&] { - auto *RD = dyn_cast<CXXRecordDecl>(Function->getParent()); - if (!RD || !RD->isLambda()) - return false; - - return llvm::any_of(ExprEvalContexts, [](auto &Context) { - return Context.isUnevaluated() || Context.isImmediateFunctionContext(); - }); - }(); + // We never need to emit the code in constriant substitution. + // For example, we can't mangle a lambda in the require clause of a function + // template during constraint checking as the MS ABI would need to mangle the + // (not yet specialized) enclosing declaration. + // FIXME: This can be removed when MS ABI supports concepts. + bool ShouldSkipCG = inConstraintSubstitution(); if (!ShouldSkipCG) { DeclGroupRef DG(Function); Consumer.HandleTopLevelDecl(DG); diff --git a/clang/test/CodeGenCXX/ms-mangle-requires.cpp b/clang/test/CodeGenCXX/ms-mangle-requires.cpp index 88c432c54b117..755b151018fcf 100644 --- a/clang/test/CodeGenCXX/ms-mangle-requires.cpp +++ b/clang/test/CodeGenCXX/ms-mangle-requires.cpp @@ -69,3 +69,37 @@ void test() { } // CHECK-LABEL:define {{.*}} void @"??$f@$0CK@@GH147650@@YAXXZ"() } + +namespace GH173160 { + +template< typename TypeList, typename Func > +auto for_each_type(Func func) { + return func; +} + +template< class T > +struct X {}; + +template< class T > +concept Component = requires(T component) { + for_each_type<typename T::required_type>( []{} ); +}; + +struct EntityRegistry { + template< Component C > + auto get_component(const int id) -> X<C> { + return {}; + } +}; + +struct A { + struct required_type {}; +}; + +void foo() { + EntityRegistry entities; + entities.get_component<A>(0); + // CHECK: define {{.*}} @"??$get_component@UA@GH173160@@@EntityRegistry@GH173160@@QEAA?AU?$X@UA@GH173160@@@1@H@Z" +} + +} _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
