[clang] fix: C++ empty record with align lead to va_list out of sync (PR #72197)
via cfe-commits
cfe-commits at lists.llvm.org
Fri Oct 10 08:45:54 PDT 2025
https://github.com/hstk30 updated https://github.com/llvm/llvm-project/pull/72197
>From e6835396eb6c3898f8c5c761ab7d144e8d9a952a Mon Sep 17 00:00:00 2001
From: hstk30 <hanwei62 at huawei.com>
Date: Fri, 10 Oct 2025 00:17:09 +0800
Subject: [PATCH] fix: C++ empty record with align break aarch64 AAPCS64
---
clang/docs/ReleaseNotes.rst | 3 +++
clang/lib/CodeGen/Targets/AArch64.cpp | 9 ++++++---
clang/test/CodeGen/AArch64/args.cpp | 20 ++++++++++++++++++-
.../AArch64/struct-coerce-using-ptr.cpp | 10 ++++++----
.../CodeGen/arm64-microsoft-arguments.cpp | 4 ++--
clang/test/CodeGenCXX/aarch64-arguments.cpp | 2 +-
clang/test/CodeGenCXX/arm64-darwinpcs.cpp | 2 +-
7 files changed, 38 insertions(+), 12 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 9a0d69c6c1b0e..cd89c6ff2bc9f 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -110,6 +110,9 @@ C++ Specific Potentially Breaking Changes
ABI Changes in This Version
---------------------------
+- Let C++ empty record fall through to the standard argument-handling path instead of
+ always pass a single ``i8`` according to aarch64 AAPCS rules.
+
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/Targets/AArch64.cpp b/clang/lib/CodeGen/Targets/AArch64.cpp
index d7deece232a9f..9adace69c06c6 100644
--- a/clang/lib/CodeGen/Targets/AArch64.cpp
+++ b/clang/lib/CodeGen/Targets/AArch64.cpp
@@ -422,6 +422,12 @@ ABIArgInfo AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadicFn,
}
// Empty records:
+ // AAPCS64 does not say that empty records are ignored as arguments,
+ // but other compilers do so in certain situations, and we copy that behavior.
+ // Those situations are in fact language-mode-specific, which seems really
+ // unfortunate, but it's something we just have to accept. If this doesn't
+ // apply, just fall through to the standard argument-handling path.
+ // Darwin overrides the psABI here to ignore all empty records in all modes.
uint64_t Size = getContext().getTypeSize(Ty);
bool IsEmpty = isEmptyRecord(getContext(), Ty, true);
if (!Ty->isSVESizelessBuiltinType() && (IsEmpty || Size == 0)) {
@@ -434,9 +440,6 @@ ABIArgInfo AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadicFn,
// behaviour here.
if (Size == 0)
return ABIArgInfo::getIgnore();
-
- // Otherwise, they are passed as if they have a size of 1 byte.
- return ABIArgInfo::getDirect(llvm::Type::getInt8Ty(getVMContext()));
}
// Homogeneous Floating-point Aggregates (HFAs) need to be expanded.
diff --git a/clang/test/CodeGen/AArch64/args.cpp b/clang/test/CodeGen/AArch64/args.cpp
index 3cb62d3119ecf..c284316a5e1b4 100644
--- a/clang/test/CodeGen/AArch64/args.cpp
+++ b/clang/test/CodeGen/AArch64/args.cpp
@@ -17,11 +17,29 @@ struct Empty {};
// DARWIN: define{{.*}} i32 @empty_arg(i32 noundef %a)
// C: define{{.*}} i32 @empty_arg(i32 noundef %a)
-// CXX: define{{.*}} i32 @empty_arg(i8 %e.coerce, i32 noundef %a)
+// CXX: define{{.*}} i32 @empty_arg(i64 %e.coerce, i32 noundef %a)
EXTERNC int empty_arg(struct Empty e, int a) {
return a;
}
+// CXX: define{{.*}} i32 @empty_align8_arg(i64 %a.coerce, i32 noundef %b)
+struct EmptyAlign8 { int __attribute__((aligned(8))) : 0; };
+EXTERNC int empty_align8_arg(struct EmptyAlign8 a, int b) {
+ return b;
+}
+
+// CXX: define{{.*}} i32 @empty_align16_arg(i128 %a.coerce, i32 noundef %b)
+struct EmptyAlign16 { long long int __attribute__((aligned(16))) : 0; };
+EXTERNC int empty_align16_arg(struct EmptyAlign16 a, int b) {
+ return b;
+}
+
+// CXX: define{{.*}} i32 @empty_align32_arg(ptr dead_on_return noundef %a, i32 noundef %b)
+struct EmptyAlign32 { long long int __attribute__((aligned(32))) : 0; };
+EXTERNC int empty_align32_arg(struct EmptyAlign32 a, int b) {
+ return b;
+}
+
// DARWIN: define{{.*}} void @empty_ret()
// C: define{{.*}} void @empty_ret()
// CXX: define{{.*}} void @empty_ret()
diff --git a/clang/test/CodeGen/AArch64/struct-coerce-using-ptr.cpp b/clang/test/CodeGen/AArch64/struct-coerce-using-ptr.cpp
index f0c9ef28201a5..97fdd0ce56c66 100644
--- a/clang/test/CodeGen/AArch64/struct-coerce-using-ptr.cpp
+++ b/clang/test/CodeGen/AArch64/struct-coerce-using-ptr.cpp
@@ -575,19 +575,21 @@ void TSpp_align16(SSpp_align16 s) { *s.a.x = 1; }
struct Sempty {
};
// CHECK-A64-LABEL: define dso_local void @_Z6Tempty6Sempty(
-// CHECK-A64-SAME: i8 [[S_COERCE:%.*]]) #[[ATTR0]] {
+// CHECK-A64-SAME: i64 [[S_COERCE:%.*]]) #[[ATTR0]] {
// CHECK-A64-NEXT: [[ENTRY:.*:]]
// CHECK-A64-NEXT: [[S:%.*]] = alloca [[STRUCT_SEMPTY:%.*]], align 1
// CHECK-A64-NEXT: [[COERCE_DIVE:%.*]] = getelementptr inbounds nuw [[STRUCT_SEMPTY]], ptr [[S]], i32 0, i32 0
-// CHECK-A64-NEXT: store i8 [[S_COERCE]], ptr [[COERCE_DIVE]], align 1
+// CHECK-A64-NEXT: [[COERCE_VAL_II:%.*]] = trunc i64 [[S_COERCE]] to i8
+// CHECK-A64-NEXT: store i8 [[COERCE_VAL_II]], ptr [[COERCE_DIVE]], align 1
// CHECK-A64-NEXT: ret void
//
// CHECK-A64_32-LABEL: define void @_Z6Tempty6Sempty(
-// CHECK-A64_32-SAME: i8 [[S_COERCE:%.*]]) #[[ATTR0]] {
+// CHECK-A64_32-SAME: i64 [[S_COERCE:%.*]]) #[[ATTR0]] {
// CHECK-A64_32-NEXT: [[ENTRY:.*:]]
// CHECK-A64_32-NEXT: [[S:%.*]] = alloca [[STRUCT_SEMPTY:%.*]], align 1
// CHECK-A64_32-NEXT: [[COERCE_DIVE:%.*]] = getelementptr inbounds nuw [[STRUCT_SEMPTY]], ptr [[S]], i32 0, i32 0
-// CHECK-A64_32-NEXT: store i8 [[S_COERCE]], ptr [[COERCE_DIVE]], align 1
+// CHECK-A64_32-NEXT: [[COERCE_VAL_II:%.*]] = trunc i64 [[S_COERCE]] to i8
+// CHECK-A64_32-NEXT: store i8 [[COERCE_VAL_II]], ptr [[COERCE_DIVE]], align 1
// CHECK-A64_32-NEXT: ret void
//
void Tempty(Sempty s) { }
diff --git a/clang/test/CodeGen/arm64-microsoft-arguments.cpp b/clang/test/CodeGen/arm64-microsoft-arguments.cpp
index a0a81be54325f..f7eb0cc765354 100644
--- a/clang/test/CodeGen/arm64-microsoft-arguments.cpp
+++ b/clang/test/CodeGen/arm64-microsoft-arguments.cpp
@@ -57,7 +57,7 @@ S4 f4() {
// Pass and return from instance method called from instance method.
// CHECK: define {{.*}} void @{{.*}}bar at Q1{{.*}}(ptr {{[^,]*}} %this, ptr dead_on_unwind inreg noalias writable sret(%class.P1) align 1 %agg.result)
-// CHECK: call void {{.*}}foo at P1{{.*}}(ptr noundef{{[^,]*}} %ref.tmp, ptr dead_on_unwind inreg writable sret(%class.P1) align 1 %agg.result, i8 %0)
+// CHECK: call void {{.*}}foo at P1{{.*}}(ptr noundef{{[^,]*}} %ref.tmp, ptr dead_on_unwind inreg writable sret(%class.P1) align 1 %agg.result, i64 %coerce.val.ii)
class P1 {
public:
@@ -76,7 +76,7 @@ P1 Q1::bar() {
// Pass and return from instance method called from free function.
// CHECK: define {{.*}} void {{.*}}bar{{.*}}()
-// CHECK: call void {{.*}}foo at P2{{.*}}(ptr noundef{{[^,]*}} %ref.tmp, ptr dead_on_unwind inreg writable sret(%class.P2) align 1 %retval, i8 %0)
+// CHECK: call void {{.*}}foo at P2{{.*}}(ptr noundef{{[^,]*}} %ref.tmp, ptr dead_on_unwind inreg writable sret(%class.P2) align 1 %retval, i64 %coerce.val.ii)
class P2 {
public:
P2 foo(P2 x);
diff --git a/clang/test/CodeGenCXX/aarch64-arguments.cpp b/clang/test/CodeGenCXX/aarch64-arguments.cpp
index ffb0cafa8882d..3206e38ad0090 100644
--- a/clang/test/CodeGenCXX/aarch64-arguments.cpp
+++ b/clang/test/CodeGenCXX/aarch64-arguments.cpp
@@ -1,5 +1,5 @@
// RUN: %clang_cc1 -triple arm64-none-linux -emit-llvm -w -o - %s | FileCheck -check-prefix=PCS %s
-// PCS: define{{.*}} void @{{.*}}(i8 %a
+// PCS: define{{.*}} void @{{.*}}(i64 %a.coerce)
struct s0 {};
void f0(s0 a) {}
diff --git a/clang/test/CodeGenCXX/arm64-darwinpcs.cpp b/clang/test/CodeGenCXX/arm64-darwinpcs.cpp
index a0b0d9efdd4c4..ef0e2da3effac 100644
--- a/clang/test/CodeGenCXX/arm64-darwinpcs.cpp
+++ b/clang/test/CodeGenCXX/arm64-darwinpcs.cpp
@@ -7,7 +7,7 @@ void test_extensions(bool a, char b, short c) {}
struct Empty {};
void test_empty(Empty e) {}
-// CHECK: define{{.*}} void @_Z10test_empty5Empty(i8
+// CHECK: define{{.*}} void @_Z10test_empty5Empty(i64 %e.coerce)
// CHECK-DARWIN: define{{.*}} void @_Z10test_empty5Empty()
struct HFA {
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