https://github.com/henrybw created
https://github.com/llvm/llvm-project/pull/157365
The MSVC ABI almost always returns vector types directly, but on x86 and
x86_64, there seems to be a special case for member functions, which return
vector types indirectly.
Fixes #104.
>From 8f42b86f8d487b9f488a7cf7ec5d0e127f736b12 Mon Sep 17 00:00:00 2001
From: Henry Baba-Weiss <henry.babawe...@gmail.com>
Date: Sun, 7 Sep 2025 14:16:16 -0700
Subject: [PATCH] [clang][CodeGen][MSVC] Return vector types from methods
indirectly
The MSVC ABI almost always returns vector types directly, but on x86 and x86_64,
there seems to be a special case for member functions, which return vector types
indirectly.
Fixes #104.
---
clang/docs/ReleaseNotes.rst | 3 ++
clang/lib/CodeGen/MicrosoftCXXABI.cpp | 23 +++++++-----
.../CodeGenCXX/microsoft-abi-vector-types.cpp | 36 +++++++++++++++++++
3 files changed, 53 insertions(+), 9 deletions(-)
create mode 100644 clang/test/CodeGenCXX/microsoft-abi-vector-types.cpp
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d1ef91b7e7c14..1be917221aa2c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -90,6 +90,9 @@ C++ Specific Potentially Breaking Changes
ABI Changes in This Version
---------------------------
+- Fixed Microsoft calling convention for returning vector types from C++ member
+ functions. Such vector types should be returned indirectly. (GH#104)
+
AST Dumping Potentially Breaking Changes
----------------------------------------
- How nested name specifiers are dumped and printed changes, keeping track of
clang AST changes.
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 88f0648660965..2d76eebcecd08 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1168,15 +1168,20 @@ static bool isTrivialForMSVC(const CXXRecordDecl *RD,
QualType Ty,
}
bool MicrosoftCXXABI::classifyReturnType(CGFunctionInfo &FI) const {
- const CXXRecordDecl *RD = FI.getReturnType()->getAsCXXRecordDecl();
- if (!RD)
- return false;
-
- bool isTrivialForABI = RD->canPassInRegisters() &&
- isTrivialForMSVC(RD, FI.getReturnType(), CGM);
-
- // MSVC always returns structs indirectly from C++ instance methods.
- bool isIndirectReturn = !isTrivialForABI || FI.isInstanceMethod();
+ bool isIndirectReturn = false;
+ if (const CXXRecordDecl *RD = FI.getReturnType()->getAsCXXRecordDecl()) {
+ bool isTrivialForABI = RD->canPassInRegisters() &&
+ isTrivialForMSVC(RD, FI.getReturnType(), CGM);
+
+ // MSVC always returns structs indirectly from C++ instance methods.
+ isIndirectReturn = !isTrivialForABI || FI.isInstanceMethod();
+ } else if (isa<VectorType>(FI.getReturnType())) {
+ // On x86, MSVC seems to only return vector types indirectly from non-
+ // vectorcall C++ instance methods.
+ isIndirectReturn =
+ CGM.getTarget().getTriple().isX86() && FI.isInstanceMethod() &&
+ FI.getCallingConvention() != llvm::CallingConv::X86_VectorCall;
+ }
if (isIndirectReturn) {
CharUnits Align = CGM.getContext().getTypeAlignInChars(FI.getReturnType());
diff --git a/clang/test/CodeGenCXX/microsoft-abi-vector-types.cpp
b/clang/test/CodeGenCXX/microsoft-abi-vector-types.cpp
new file mode 100644
index 0000000000000..e046fb4bb3169
--- /dev/null
+++ b/clang/test/CodeGenCXX/microsoft-abi-vector-types.cpp
@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -ffreestanding -emit-llvm %s -o -
-triple=i686-pc-windows-msvc | FileCheck %s
+// RUN: %clang_cc1 -ffreestanding -emit-llvm %s -o -
-triple=x86_64-pc-windows-msvc | FileCheck %s
+
+// To match the MSVC ABI, vector types must be returned indirectly from member
+// functions (as long as they do not use the vectorcall calling convention),
+// but must be returned directly everywhere else.
+
+#include <xmmintrin.h>
+
+struct Foo {
+ __m128 method_m128();
+ __m128 __vectorcall vectorcall_method_m128();
+};
+
+__m128 Foo::method_m128() {
+ return __m128{};
+// GH104
+// CHECK: store <4 x float>
+// CHECK: ret void
+}
+
+__m128 __vectorcall Foo::vectorcall_method_m128() {
+ return __m128{};
+// CHECK: ret <4 x float>
+}
+
+__m128 func_m128() {
+ return __m128{};
+// CHECK: ret <4 x float>
+}
+
+__m128 __vectorcall vectorcall_func_m128() {
+ return __m128{};
+// CHECK: ret <4 x float>
+}
+
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