https://github.com/babadany2999 created https://github.com/llvm/llvm-project/pull/213534
### Summary Fixed an assertion failure (`Assertion 'MaybeODRUseExprs.empty() && "Leftover expressions for odr-use checking"' failed`) when evaluating C++26 `constexpr` structured binding packs during template instantiation. Fixes #170991. ### Root Cause When instantiating a C++26 `constexpr` structured binding pack (e.g. `constexpr auto [...xs] = s;`), building the member binding expressions in `checkMemberDecomposition` creates `DeclRefExpr` nodes referencing the `DecompositionDecl`. Because the declaration is `constexpr`, `BuildDeclRefExpr` defers ODR-use tracking and registers these `DeclRefExpr` nodes in `Sema::MaybeODRUseExprs`. However, `CheckCompleteDecompositionDeclaration` is executed after `ActOnFinishFullExpr` has already run for the variable initializer. As a result, `MaybeODRUseExprs` was left unflushed after decomposition bindings were created. When `ActOnFinishFunctionBody` completed the function body, it encountered leftover expressions in `MaybeODRUseExprs` and failed the assertion. ### Solution Added a call to `CleanupVarDeclMarking()` at the end of `Sema::CheckCompleteDecompositionDeclaration` in `clang/lib/Sema/SemaDeclCXX.cpp`. This flushes `MaybeODRUseExprs` and completes ODR-use tracking for the decomposition declaration bindings before returning. ### Test Plan - Added regression test case to `clang/test/SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp`. - Verified the test fails with an assertion failure on unpatched Clang and passes cleanly with the patch. - Ran full `clang/test/SemaCXX` and `clang/test/CXX` test suites. - Added release note to `clang/docs/ReleaseNotes.md` under *Bug Fixes to C++ Support*. >From 2d18b34ac45e66d8d2249819a01e9203def0127c Mon Sep 17 00:00:00 2001 From: Baba Dan Constantin <[email protected]> Date: Sun, 2 Aug 2026 14:35:25 +0300 Subject: [PATCH] [clang][constexpr] Fix assertion failure in constexpr structured binding pack evaluation (#GH170991) --- clang/docs/ReleaseNotes.md | 3 +++ clang/lib/Sema/SemaDeclCXX.cpp | 2 ++ .../SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp | 13 +++++++++++++ 3 files changed, 18 insertions(+) create mode 100644 clang/test/SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md index a38b99ff8e075..a169d065605e4 100644 --- a/clang/docs/ReleaseNotes.md +++ b/clang/docs/ReleaseNotes.md @@ -424,6 +424,9 @@ features cannot lower the translation-unit ABI level; copy so the union's object representation is copied, matching the defaulted union copy constructor. +- Fixed an assertion failure when evaluating C++26 `constexpr` structured binding packs during template + instantiation. (#GH170991) + #### Bug Fixes to AST Handling - Fixed a non-deterministic ordering of unused local typedefs that made diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp index 47b01b913b428..ebc1d8ba0008f 100644 --- a/clang/lib/Sema/SemaDeclCXX.cpp +++ b/clang/lib/Sema/SemaDeclCXX.cpp @@ -1701,6 +1701,8 @@ void Sema::CheckCompleteDecompositionDeclaration(DecompositionDecl *DD) { // E or of the same unambiguous public base class of E, ... if (checkMemberDecomposition(*this, Bindings, DD, DecompType, RD)) DD->setInvalidDecl(); + + CleanupVarDeclMarking(); } UnsignedOrNone Sema::GetDecompositionElementCount(QualType T, diff --git a/clang/test/SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp b/clang/test/SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp new file mode 100644 index 0000000000000..7ce4c5216ac94 --- /dev/null +++ b/clang/test/SemaCXX/cxx2c-binding-pack-constexpr-crash.cpp @@ -0,0 +1,13 @@ +// RUN: %clang_cc1 -fsyntax-only -std=c++26 %s + +namespace GH170991 { +struct S { int x{}; }; + +template <typename = void> +void f() { + constexpr S s; + constexpr auto [...xs] = s; +} + +template void f<void>(); +} _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
