Author: sethp Date: 2024-03-17T17:35:13+01:00 New Revision: 192be3c9c13363847d176f2c4bba2bd4be5e822f
URL: https://github.com/llvm/llvm-project/commit/192be3c9c13363847d176f2c4bba2bd4be5e822f DIFF: https://github.com/llvm/llvm-project/commit/192be3c9c13363847d176f2c4bba2bd4be5e822f.diff LOG: fix: constexpr bit_cast with empty base classes (#82383) Prior to this commit, clang would fail to produce a constant value for `b` in: ```c++ struct base { }; struct s : base { int z; }; constexpr auto b = std::bit_cast<s>(0x12); ``` e.g. https://godbolt.org/z/srrbTMPq4 Added: Modified: clang/docs/ReleaseNotes.rst clang/lib/AST/ExprConstant.cpp clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp Removed: ################################################################################ diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index ba9de1ac98de08..125d51c42d507f 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -392,6 +392,8 @@ Bug Fixes to C++ Support Fixes (#GH84368). - Fixed a crash while checking constraints of a trailing requires-expression of a lambda, that the expression references to an entity declared outside of the lambda. (#GH64808) +- Clang's __builtin_bit_cast will now produce a constant value for records with empty bases. See: + (#GH82383) Bug Fixes to AST Handling ^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp index fa9e8ecf654378..80f49714b64f0f 100644 --- a/clang/lib/AST/ExprConstant.cpp +++ b/clang/lib/AST/ExprConstant.cpp @@ -7347,9 +7347,6 @@ class BufferToAPValueConverter { for (size_t I = 0, E = CXXRD->getNumBases(); I != E; ++I) { const CXXBaseSpecifier &BS = CXXRD->bases_begin()[I]; CXXRecordDecl *BaseDecl = BS.getType()->getAsCXXRecordDecl(); - if (BaseDecl->isEmpty() || - Info.Ctx.getASTRecordLayout(BaseDecl).getNonVirtualSize().isZero()) - continue; std::optional<APValue> SubObj = visitType( BS.getType(), Layout.getBaseClassOffset(BaseDecl) + Offset); diff --git a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp index c5b8032f40b131..7520b43a194aba 100644 --- a/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp +++ b/clang/test/SemaCXX/constexpr-builtin-bit-cast.cpp @@ -90,7 +90,8 @@ void test_record() { struct tuple4 { unsigned x, y, z, doublez; - constexpr bool operator==(tuple4 const &other) const { + bool operator==(tuple4 const &other) const = default; + constexpr bool operator==(bases const &other) const { return x == other.x && y == other.y && z == other.z && doublez == other.doublez; } @@ -99,6 +100,9 @@ void test_record() { constexpr tuple4 t4 = bit_cast<tuple4>(b); static_assert(t4 == tuple4{1, 2, 3, 4}); static_assert(round_trip<tuple4>(b)); + + constexpr auto b2 = bit_cast<bases>(t4); + static_assert(t4 == b2); } void test_partially_initialized() { _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
