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The "aligned" attribute can only increase the alignment of a struct, or
struct member, unless it's used together with the "packed" attribute, or
used as a part of a typedef, in which case, the "aligned" attribute can
both increase and decrease alignment.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D107394
Files:
clang/lib/AST/ASTContext.cpp
clang/test/Layout/aix-alignof-align-and-pack-attr.cpp
clang/test/Layout/aix-alignof-align-attr.cpp
Index: clang/test/Layout/aix-alignof-align-attr.cpp
===================================================================
--- /dev/null
+++ clang/test/Layout/aix-alignof-align-attr.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -S -emit-llvm -x c++ < %s |
\
+// RUN: FileCheck %s
+
+struct __attribute__((__aligned__(2))) C {
+ double x;
+} c;
+
+// CHECK: @c = global %struct.C zeroinitializer, align 8
Index: clang/test/Layout/aix-alignof-align-and-pack-attr.cpp
===================================================================
--- /dev/null
+++ clang/test/Layout/aix-alignof-align-and-pack-attr.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -S -emit-llvm -x c++ < %s |
\
+// RUN: FileCheck %s
+
+struct __attribute__((__aligned__(2), packed)) C {
+ double x;
+} c;
+
+// CHECK: @c = global %struct.C zeroinitializer, align 2
Index: clang/lib/AST/ASTContext.cpp
===================================================================
--- clang/lib/AST/ASTContext.cpp
+++ clang/lib/AST/ASTContext.cpp
@@ -2478,11 +2478,19 @@
return ABIAlign;
if (const auto *RT = T->getAs<RecordType>()) {
- if (TI.AlignIsRequired || RT->getDecl()->isInvalidDecl())
+ const RecordDecl *RD = RT->getDecl();
+
+ if (RD->isInvalidDecl())
+ return ABIAlign;
+
+ // When used as part of a typedef, or together with a 'packed' attribute,
+ // the 'aligned' attribute can be used to decrease alignment.
+ if (TI.AlignIsRequired &&
+ (T->getAs<TypedefType>() != nullptr || RD->hasAttr<PackedAttr>()))
return ABIAlign;
unsigned PreferredAlign = static_cast<unsigned>(
- toBits(getASTRecordLayout(RT->getDecl()).PreferredAlignment));
+ toBits(getASTRecordLayout(RD).PreferredAlignment));
assert(PreferredAlign >= ABIAlign &&
"PreferredAlign should be at least as large as ABIAlign.");
return PreferredAlign;
Index: clang/test/Layout/aix-alignof-align-attr.cpp
===================================================================
--- /dev/null
+++ clang/test/Layout/aix-alignof-align-attr.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+struct __attribute__((__aligned__(2))) C {
+ double x;
+} c;
+
+// CHECK: @c = global %struct.C zeroinitializer, align 8
Index: clang/test/Layout/aix-alignof-align-and-pack-attr.cpp
===================================================================
--- /dev/null
+++ clang/test/Layout/aix-alignof-align-and-pack-attr.cpp
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple powerpc-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix-xcoff -S -emit-llvm -x c++ < %s | \
+// RUN: FileCheck %s
+
+struct __attribute__((__aligned__(2), packed)) C {
+ double x;
+} c;
+
+// CHECK: @c = global %struct.C zeroinitializer, align 2
Index: clang/lib/AST/ASTContext.cpp
===================================================================
--- clang/lib/AST/ASTContext.cpp
+++ clang/lib/AST/ASTContext.cpp
@@ -2478,11 +2478,19 @@
return ABIAlign;
if (const auto *RT = T->getAs<RecordType>()) {
- if (TI.AlignIsRequired || RT->getDecl()->isInvalidDecl())
+ const RecordDecl *RD = RT->getDecl();
+
+ if (RD->isInvalidDecl())
+ return ABIAlign;
+
+ // When used as part of a typedef, or together with a 'packed' attribute,
+ // the 'aligned' attribute can be used to decrease alignment.
+ if (TI.AlignIsRequired &&
+ (T->getAs<TypedefType>() != nullptr || RD->hasAttr<PackedAttr>()))
return ABIAlign;
unsigned PreferredAlign = static_cast<unsigned>(
- toBits(getASTRecordLayout(RT->getDecl()).PreferredAlignment));
+ toBits(getASTRecordLayout(RD).PreferredAlignment));
assert(PreferredAlign >= ABIAlign &&
"PreferredAlign should be at least as large as ABIAlign.");
return PreferredAlign;
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