https://github.com/anondeveg created
https://github.com/llvm/llvm-project/pull/219661
Problem:
AIX has a rule where a double inside a struct is given 4-byte alignment and
then `preferred alignment` value should be upgraded from 4-bytes to 8-bytes.
the code that does the upgrade had an assertion:
```c++
assert(PreferredAlign == CharUnits::fromQuantity(4) && "No need to
upgrade the alignment value.")
```
that would fail if `__ms_struct__` was used.
Fix:
removed the assertion as alignment was working correctly without it.
made an if condition that would update the `preferred alignment` if and only if
it was 4-bytes.
added regression-test to `clang/test/Layout/aix-double-struct-member.cpp`.
>From c208bf30820c9591f324e0bd8aa6e0d08d1ca291 Mon Sep 17 00:00:00 2001
From: Anondev <[email protected]>
Date: Sat, 29 Aug 2026 12:23:30 +0300
Subject: [PATCH] [clang][AST] Fix assertion on AIX when ms_struct aligns a
double
---
clang/lib/AST/RecordLayoutBuilder.cpp | 9 +++--
.../test/Layout/aix-double-struct-member.cpp | 40 +++++++++++++++++++
2 files changed, 45 insertions(+), 4 deletions(-)
diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp
b/clang/lib/AST/RecordLayoutBuilder.cpp
index e6da6c78238c1..36442ea787afd 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -19,6 +19,8 @@
#include "clang/Basic/TargetInfo.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/MathExtras.h"
+#include <cassert>
+#include <llvm/Support/raw_ostream.h>
using namespace clang;
@@ -1996,10 +1998,9 @@ void ItaniumRecordLayoutBuilder::LayoutField(const
FieldDecl *D,
auto performBuiltinTypeAlignmentUpgrade = [&](const BuiltinType *BTy) {
if (BTy->getKind() == BuiltinType::Double ||
BTy->getKind() == BuiltinType::LongDouble) {
- assert(PreferredAlign == CharUnits::fromQuantity(4) &&
- "No need to upgrade the alignment value.");
- PreferredAlign = CharUnits::fromQuantity(8);
- }
+ if (PreferredAlign == CharUnits::fromQuantity(4)){
+ PreferredAlign = CharUnits::fromQuantity(8);
+ } }
};
const Type *BaseTy = D->getType()->getBaseElementTypeUnsafe();
diff --git a/clang/test/Layout/aix-double-struct-member.cpp
b/clang/test/Layout/aix-double-struct-member.cpp
index 6e091fcb1b1e1..7d183d24ac99d 100644
--- a/clang/test/Layout/aix-double-struct-member.cpp
+++ b/clang/test/Layout/aix-double-struct-member.cpp
@@ -431,3 +431,43 @@ int g = sizeof(G);
// CHECK-NEXT: | nvsize=20, nvalign=2, preferrednvalign=2]
} // namespace test11
+namespace test12 {
+// Fields whose base element is `double`/`long double` test their natural
+// 8-byte alignment under __ms_struct__.
+// See: issue 219627.
+struct __attribute__((__ms_struct__)) S { double d; };
+int a = sizeof(S);
+
+struct __attribute__((__ms_struct__)) LD { long double d; };
+int b = sizeof(LD);
+
+struct __attribute__((__ms_struct__)) CD { _Complex double d; };
+int c = sizeof(CD);
+
+struct __attribute__((__ms_struct__)) Arr { double d[4]; };
+int e = sizeof(Arr);
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct test12::S
+// CHECK-NEXT: 0 | double d
+// CHECK-NEXT: | [sizeof=8, dsize=8, align=8, preferredalign=8,
+// CHECK-NEXT: | nvsize=8, nvalign=8, preferrednvalign=8]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct test12::LD
+// CHECK-NEXT: 0 | long double d
+// CHECK-NEXT: | [sizeof=8, dsize=8, align=8, preferredalign=8,
+// CHECK-NEXT: | nvsize=8, nvalign=8, preferrednvalign=8]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct test12::CD
+// CHECK-NEXT: 0 | _Complex double d
+// CHECK-NEXT: | [sizeof=16, dsize=16, align=4, preferredalign=8,
+// CHECK-NEXT: | nvsize=16, nvalign=4, preferrednvalign=8]
+
+// CHECK: *** Dumping AST Record Layout
+// CHECK-NEXT: 0 | struct test12::Arr
+// CHECK-NEXT: 0 | double[4] d
+// CHECK-NEXT: | [sizeof=32, dsize=32, align=8, preferredalign=8,
+// CHECK-NEXT: | nvsize=32, nvalign=8, preferrednvalign=8]
+} // namespace test12
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