https://github.com/pranavk updated https://github.com/llvm/llvm-project/pull/120670
>From 4b6839317bcd2a014011cb91b5a3e58d4a47b0b1 Mon Sep 17 00:00:00 2001 From: Pranav Kant <p...@google.com> Date: Fri, 20 Dec 2024 02:17:23 +0000 Subject: [PATCH 1/3] [clang] Return larger CXX records in memory We incorrectly return CXX records in AVX registers when they should be returned in memory. This is violation of x86-64 psABI. Detailed discussion is here: https://groups.google.com/g/x86-64-abi/c/BjOOyihHuqg/m/KurXdUcWAgAJ --- clang/include/clang/Basic/LangOptions.h | 1 + clang/lib/CodeGen/Targets/X86.cpp | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+) diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h index 949c8f5d448bcf..0dd644eba559b9 100644 --- a/clang/include/clang/Basic/LangOptions.h +++ b/clang/include/clang/Basic/LangOptions.h @@ -245,6 +245,7 @@ class LangOptionsBase { /// construction vtable because it hasn't added 'type' as a substitution. /// - Skip mangling enclosing class templates of member-like friend /// function templates. + /// - Incorrectly return C++ records in AVX registers. Ver19, /// Conform to the underlying platform's C and C++ ABIs as closely diff --git a/clang/lib/CodeGen/Targets/X86.cpp b/clang/lib/CodeGen/Targets/X86.cpp index 7f73bf2a65266e..70d812057d0b01 100644 --- a/clang/lib/CodeGen/Targets/X86.cpp +++ b/clang/lib/CodeGen/Targets/X86.cpp @@ -1334,6 +1334,20 @@ class X86_64ABIInfo : public ABIInfo { return T.isOSLinux() || T.isOSNetBSD(); } + bool returnCXXRecordGreaterThan128InMem(unsigned Size, unsigned TypeSize, + unsigned NativeSize) const { + // Clang <= 19.0 did not do this. + if (getContext().getLangOpts().getClangABICompat() <= + LangOptions::ClangABI::Ver19) + return false; + + // The only case a 256(or 512)-bit wide vector could be used to return + // is when CXX record contains a single 256(or 512)-bit element. + if (Size > 128 && (Size != TypeSize || Size > NativeSize)) + return true; + return false; + } + X86AVXABILevel AVXLevel; // Some ABIs (e.g. X32 ABI and Native Client OS) use 32 bit pointers on // 64-bit hardware. @@ -2067,6 +2081,10 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase, Class &Lo, classify(I.getType(), Offset, FieldLo, FieldHi, isNamedArg); Lo = merge(Lo, FieldLo); Hi = merge(Hi, FieldHi); + if (returnCXXRecordGreaterThan128InMem( + Size, getContext().getTypeSize(I.getType()), + getNativeVectorSizeForAVXABI(AVXLevel))) + Lo = Memory; if (Lo == Memory || Hi == Memory) { postMerge(Size, Lo, Hi); return; >From 6e62d019db05601bb6d4046785b9a219f92cebe8 Mon Sep 17 00:00:00 2001 From: Pranav Kant <p...@google.com> Date: Mon, 30 Dec 2024 14:57:31 +0000 Subject: [PATCH 2/3] add a regression test --- clang/test/CodeGen/X86/avx-cxx-record.cpp | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) create mode 100644 clang/test/CodeGen/X86/avx-cxx-record.cpp diff --git a/clang/test/CodeGen/X86/avx-cxx-record.cpp b/clang/test/CodeGen/X86/avx-cxx-record.cpp new file mode 100644 index 00000000000000..0d5f070b7754fb --- /dev/null +++ b/clang/test/CodeGen/X86/avx-cxx-record.cpp @@ -0,0 +1,23 @@ +// RUN: %clang %s -c -S -emit-llvm -O2 -march=x86-64-v3 -o - | FileCheck %s + +using UInt64x2 = unsigned long long __attribute__((__vector_size__(16), may_alias)); + +template<int id> +struct XMM1 { + UInt64x2 x; +}; + +struct XMM2 : XMM1<0>, XMM1<1> { +}; + +// CHECK: define{{.*}} @_Z3foov({{.*}} [[ARG:%.*]]){{.*}} +// CHECK-NEXT: entry: +// CHECK-NEXT: store {{.*}}, ptr [[ARG]]{{.*}} +// CHECK-NEXT: [[TMP1:%.*]] = getelementptr {{.*}}, ptr [[ARG]]{{.*}} +// CHECK-NEXT: store {{.*}}, ptr [[TMP1]]{{.*}} +XMM2 foo() { + XMM2 result; + ((XMM1<0>*)&result)->x = UInt64x2{1, 2}; + ((XMM1<1>*)&result)->x = UInt64x2{3, 4}; + return result; +} >From 1f01309c237c8daf15be4ac1708e22e841935662 Mon Sep 17 00:00:00 2001 From: Pranav Kant <p...@google.com> Date: Mon, 30 Dec 2024 14:59:04 +0000 Subject: [PATCH 3/3] comment --- clang/include/clang/Basic/LangOptions.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/clang/include/clang/Basic/LangOptions.h b/clang/include/clang/Basic/LangOptions.h index 0dd644eba559b9..6df2fa414f4df8 100644 --- a/clang/include/clang/Basic/LangOptions.h +++ b/clang/include/clang/Basic/LangOptions.h @@ -245,7 +245,7 @@ class LangOptionsBase { /// construction vtable because it hasn't added 'type' as a substitution. /// - Skip mangling enclosing class templates of member-like friend /// function templates. - /// - Incorrectly return C++ records in AVX registers. + /// - Incorrectly return C++ records in AVX registers on x86_64. Ver19, /// Conform to the underlying platform's C and C++ ABIs as closely _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
