https://github.com/phoebewang updated https://github.com/llvm/llvm-project/pull/205040
>From afc371bbe15bf87b96ec434a6cb396262c746041 Mon Sep 17 00:00:00 2001 From: Phoebe Wang <[email protected]> Date: Sun, 21 Jun 2026 23:48:37 -0700 Subject: [PATCH 1/2] [clang] Exclude EmptyRecord calculating larger CXX records Fixes: #203760 Assisted-by: Claude Sonnet 4.6 --- clang/lib/CodeGen/Targets/X86.cpp | 1 + clang/test/CodeGen/X86/avx-cxx-record.cpp | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+) diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp index dbe4d656aabc5..abf903647336d 100644 --- a/clang/lib/CodeGen/Targets/X86.cpp +++ b/clang/lib/CodeGen/Targets/X86.cpp @@ -2085,6 +2085,7 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase, Class &Lo, Lo = merge(Lo, FieldLo); Hi = merge(Hi, FieldHi); if (returnCXXRecordGreaterThan128InMem() && + !isEmptyRecord(getContext(), I.getType(), true) && (Size > 128 && (Size != getContext().getTypeSize(I.getType()) || Size > getNativeVectorSizeForAVXABI(AVXLevel)))) { // The only case a 256(or 512)-bit wide vector could be used to return diff --git a/clang/test/CodeGen/X86/avx-cxx-record.cpp b/clang/test/CodeGen/X86/avx-cxx-record.cpp index b20bcdd616a43..e64cef32e78ec 100644 --- a/clang/test/CodeGen/X86/avx-cxx-record.cpp +++ b/clang/test/CodeGen/X86/avx-cxx-record.cpp @@ -46,3 +46,21 @@ YMM2 bar() { ((YMM1<1>*)&result)->x = UInt64x4{5, 6, 7, 8}; return result; } + +// Test that empty base classes do not prevent structs with a single wide +// vector member from being passed/returned in registers (issue #203760). +struct EmptyBase {}; + +struct YMMWithEmptyBase : EmptyBase { + UInt64x4 x; +}; + +// A struct with a single 256-bit vector and an empty base should use registers, +// matching the behavior with no base class. +// CHECK: define{{.*}} <4 x i64> @_Z18ymm_empty_base_retv() +// CLANG-20: define{{.*}} <4 x i64> @_Z18ymm_empty_base_retv() +YMMWithEmptyBase ymm_empty_base_ret() { return {}; } + +// CHECK: define{{.*}} i64 @_Z19ymm_empty_base_pass16YMMWithEmptyBase(<4 x i64> +// CLANG-20: define{{.*}} i64 @_Z19ymm_empty_base_pass16YMMWithEmptyBase(<4 x i64> +unsigned long long ymm_empty_base_pass(YMMWithEmptyBase x) { return x.x[0]; } >From 414b822387911924397a1e1981f894a2cb278748 Mon Sep 17 00:00:00 2001 From: Phoebe Wang <[email protected]> Date: Mon, 22 Jun 2026 23:17:11 -0700 Subject: [PATCH 2/2] Add release note --- clang/docs/ReleaseNotes.rst | 2 ++ 1 file changed, 2 insertions(+) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 5e7a0c76d4594..ea7d7908a5ff2 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -113,6 +113,8 @@ ABI Changes in This Version compilers. On most targets this is not a breaking change because ``fastcc`` and the platform C calling convention agree for ``void(ptr)``. It is an ABI break on i686, MIPS O32, PowerPC64 ELFv1, and Lanai. +- Fixed incorrect struct return when single large vector (256/512-bit) used on + x86-64 targets. (#GH203760) The bug was introduced since Clang 21. (#GH120670) AST Dumping Potentially Breaking Changes ---------------------------------------- _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
