https://github.com/kin4stat updated https://github.com/llvm/llvm-project/pull/113104
>From f7b8ed2e22b00a30ae8ecd7840747d6d808a75e4 Mon Sep 17 00:00:00 2001 From: Daniil Kustov <[email protected]> Date: Wed, 14 Oct 2026 18:38:09 +0300 Subject: [PATCH 1/2] [clang][CodeGen] Fix MSVC ABI for HVA/HFA returns with vectorcall on x86 Under __vectorcall, MSVC returns HVAs and HFAs in vector registers even if they are not C++14 aggregates, and even from instance methods. Other calling conventions keep the usual restrictions. Fixes #63417 --- clang/lib/CodeGen/MicrosoftCXXABI.cpp | 13 +++ .../microsoft-abi-vectorcall-hva-return.cpp | 88 +++++++++++++++++++ 2 files changed, 101 insertions(+) create mode 100644 clang/test/CodeGenCXX/microsoft-abi-vectorcall-hva-return.cpp diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp index 86916104d13440..422178c44abb01 100644 --- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp +++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp @@ -1195,6 +1195,19 @@ bool MicrosoftCXXABI::classifyReturnType(CGFunctionInfo &FI) const { // MSVC always returns structs indirectly from C++ instance methods. bool isIndirectReturn = !isTrivialForABI || FI.isInstanceMethod(); + // With __vectorcall on x86, HVAs (including HFAs) that can be passed in + // registers are returned in vector registers, even if they are not C++14 + // aggregates and even when returned from instance methods. + if (isIndirectReturn && + FI.getCallingConvention() == llvm::CallingConv::X86_VectorCall && + RD->canPassInRegisters()) { + const Type *Base = nullptr; + uint64_t NumElts = 0; + if (CGM.getABIInfo().isHomogeneousAggregate(FI.getReturnType(), Base, + NumElts)) + isIndirectReturn = false; + } + if (isIndirectReturn) { CharUnits Align = CGM.getContext().getTypeAlignInChars(FI.getReturnType()); LangAS SRetAS = CGM.getTargetCodeGenInfo().getSRetAddrSpace(RD); diff --git a/clang/test/CodeGenCXX/microsoft-abi-vectorcall-hva-return.cpp b/clang/test/CodeGenCXX/microsoft-abi-vectorcall-hva-return.cpp new file mode 100644 index 00000000000000..77fb3510fdf853 --- /dev/null +++ b/clang/test/CodeGenCXX/microsoft-abi-vectorcall-hva-return.cpp @@ -0,0 +1,88 @@ +// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -emit-llvm -o - %s | FileCheck %s --check-prefix=X64 +// RUN: %clang_cc1 -triple i686-pc-windows-msvc -emit-llvm -o - %s | FileCheck %s --check-prefix=X86 + +// Under __vectorcall, MSVC returns HVAs and HFAs in vector registers even if +// they are not C++14 aggregates, and even from instance methods. Other calling +// conventions keep the usual restrictions and return such types indirectly. +// See https://github.com/llvm/llvm-project/issues/63417. + +#define VC __attribute__((vectorcall)) +#define CD __attribute__((cdecl)) + +typedef float m128 __attribute__((__vector_size__(16), __aligned__(16))); + +// Non-aggregate HFA (base class, protected member, user-provided ctor). +struct B2 { float a; }; +struct HFA2 : B2 { HFA2(); protected: float b; }; + +HFA2 VC hfa2_vc(HFA2 *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HFA2 @"?hfa2_vc@@YQ?AUHFA2@@PEAU1@@Z"(ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.HFA2 @"?hfa2_vc@@YQ?AUHFA2@@PAU1@@Z"(ptr inreg noundef %x) + +HFA2 CD hfa2_cd(HFA2 *x) { return *x; } +// X64: define dso_local void @"?hfa2_cd@@YA?AUHFA2@@PEAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HFA2) align 4 %agg.result, ptr noundef %x) +// X86: define dso_local void @"?hfa2_cd@@YA?AUHFA2@@PAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HFA2) align 4 %agg.result, ptr noundef %x) + +// Non-aggregate HFA of doubles with only a user-provided constructor. +struct HFAD { HFAD(int); double a, b, c; }; + +HFAD VC hfad_vc(HFAD *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HFAD @"?hfad_vc@@YQ?AUHFAD@@PEAU1@@Z"(ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.HFAD @"?hfad_vc@@YQ?AUHFAD@@PAU1@@Z"(ptr inreg noundef %x) + +HFAD CD hfad_cd(HFAD *x) { return *x; } +// X64: define dso_local void @"?hfad_cd@@YA?AUHFAD@@PEAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HFAD) align 8 %agg.result, ptr noundef %x) +// X86: define dso_local void @"?hfad_cd@@YA?AUHFAD@@PAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HFAD) align 8 %agg.result, ptr noundef %x) + +// Non-aggregate HVA. +struct BV { m128 v1; }; +struct HVA2 : BV { HVA2(double); protected: m128 v2; }; + +HVA2 VC hva2_vc(HVA2 *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HVA2 @"?hva2_vc@@YQ?AUHVA2@@PEAU1@@Z"(ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.HVA2 @"?hva2_vc@@YQ?AUHVA2@@PAU1@@Z"(ptr inreg noundef %x) + +HVA2 CD hva2_cd(HVA2 *x) { return *x; } +// X64: define dso_local void @"?hva2_cd@@YA?AUHVA2@@PEAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HVA2) align 16 %agg.result, ptr noundef %x) +// X86: define dso_local void @"?hva2_cd@@YA?AUHVA2@@PAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HVA2) align 16 %agg.result, ptr noundef %x) + +// Non-trivial destructor. On x64, small classes with a non-trivial destructor +// can still be passed in registers, and MSVC returns them in XMM registers. On +// x86 they are returned indirectly. +struct HFADtor { ~HFADtor(); float a, b; }; + +HFADtor VC hfadtor_vc(HFADtor *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HFADtor @"?hfadtor_vc@@YQ?AUHFADtor@@PEAU1@@Z"(ptr noundef %x) +// X86: define dso_local x86_vectorcallcc void @"?hfadtor_vc@@YQ?AUHFADtor@@PAU1@@Z"(ptr dead_on_unwind inreg noalias writable sret(%struct.HFADtor) align 4 %agg.result, ptr inreg noundef %x) + +// Too many elements to be an HVA: still returned indirectly. +struct HFA5 { HFA5(); float a, b, c, d, e; }; + +HFA5 VC hfa5_vc(HFA5 *x) { return *x; } +// X64: define dso_local x86_vectorcallcc void @"?hfa5_vc@@YQ?AUHFA5@@PEAU1@@Z"(ptr dead_on_unwind noalias writable sret(%struct.HFA5) align 4 %agg.result, ptr noundef %x) +// X86: define dso_local x86_vectorcallcc void @"?hfa5_vc@@YQ?AUHFA5@@PAU1@@Z"(ptr dead_on_unwind inreg noalias writable sret(%struct.HFA5) align 4 %agg.result, ptr inreg noundef %x) + +// Instance methods. +struct Agg { float a, b; }; +struct S { + Agg VC agg_vc(Agg *x); + HFA2 VC hfa2_vc(HFA2 *x); + Agg agg_tc(Agg *x); + static HFA2 VC static_hfa2_vc(HFA2 *x); +}; + +Agg VC S::agg_vc(Agg *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.Agg @"?agg_vc@S@@QEAQ?AUAgg@@PEAU2@@Z"(ptr noundef nonnull align 1 dereferenceable(1) %this, ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.Agg @"?agg_vc@S@@QAQ?AUAgg@@PAU2@@Z"(ptr inreg noundef nonnull align 1 dereferenceable(1) %this, ptr inreg noundef %x) + +HFA2 VC S::hfa2_vc(HFA2 *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HFA2 @"?hfa2_vc@S@@QEAQ?AUHFA2@@PEAU2@@Z"(ptr noundef nonnull align 1 dereferenceable(1) %this, ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.HFA2 @"?hfa2_vc@S@@QAQ?AUHFA2@@PAU2@@Z"(ptr inreg noundef nonnull align 1 dereferenceable(1) %this, ptr inreg noundef %x) + +Agg S::agg_tc(Agg *x) { return *x; } +// X64: define dso_local void @"?agg_tc@S@@QEAA?AUAgg@@PEAU2@@Z"(ptr noundef nonnull align 1 dereferenceable(1) %this, ptr dead_on_unwind noalias writable sret(%struct.Agg) align 4 %agg.result, ptr noundef %x) +// X86: define dso_local x86_thiscallcc void @"?agg_tc@S@@QAE?AUAgg@@PAU2@@Z"(ptr noundef nonnull align 1 dereferenceable(1) %this, ptr dead_on_unwind noalias writable sret(%struct.Agg) align 4 %agg.result, ptr noundef %x) + +HFA2 VC S::static_hfa2_vc(HFA2 *x) { return *x; } +// X64: define dso_local x86_vectorcallcc %struct.HFA2 @"?static_hfa2_vc@S@@SQ?AUHFA2@@PEAU2@@Z"(ptr noundef %x) +// X86: define dso_local x86_vectorcallcc %struct.HFA2 @"?static_hfa2_vc@S@@SQ?AUHFA2@@PAU2@@Z"(ptr inreg noundef %x) >From 4d497f315cba8a70dac89b65b2eb81390645a31b Mon Sep 17 00:00:00 2001 From: Daniil Kustov <[email protected]> Date: Mon, 19 Oct 2026 02:19:09 +0300 Subject: [PATCH 2/2] Add a release note Assisted-by: Claude Opus 5.5 --- clang/docs/ReleaseNotes.md | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md index aba1dba5854fea..897c65f20cff35 100644 --- a/clang/docs/ReleaseNotes.md +++ b/clang/docs/ReleaseNotes.md @@ -126,6 +126,12 @@ features cannot lower the translation-unit ABI level; accesses to these fields. `__attribute__((packed))` on the field or the enclosing record still reduces the alignment. (#GH208256) +- Fixed Microsoft calling convention for returning HVAs and HFAs from + `__vectorcall` functions on x86 and x86-64. Such types are now returned in + vector registers even if they are not C++14 aggregates (for example, if they + have base classes, non-public data members, or user-provided constructors), + and also from instance methods, matching MSVC. (#GH63417) + ### AST Dumping Potentially Breaking Changes ### Clang Frontend Potentially Breaking Changes _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
