[PATCH] D107598: [AIX] "aligned" attribute should not decrease type alignment returned by __alignof__

[Steven Wan via Phabricator via cfe-commits]

stevewan created this revision.
stevewan requested review of this revision.
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The "__alignof__()" operator, when used on a type, always returns the `ABIAlign` if the type is marked `__attribute__((aligned()))`. However, the "aligned" attribute should 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/D107598

Files:
  clang/lib/AST/ASTContext.cpp
  clang/test/Layout/aix-alignof-align-and-pack-attr.cpp


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 +1,21 @@
+// 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
+
+namespace test1 {
+struct __attribute__((__aligned__(2))) C {
+  double x;
+} c;
+
+// CHECK: @{{.*}}test1{{.*}}c{{.*}} = global %"struct.test1::C" zeroinitializer, align 8
+} // namespace test1
+
+namespace test2 {
+struct __attribute__((__aligned__(2), packed)) C {
+  double x;
+} c;
+
+// CHECK: @{{.*}}test2{{.*}}c{{.*}} = global %"struct.test2::C" zeroinitializer, align 2
+} // namespace test2
Index: clang/lib/AST/ASTContext.cpp
===================================================================
--- clang/lib/AST/ASTContext.cpp
+++ clang/lib/AST/ASTContext.cpp
@@ -2478,11 +2478,16 @@
     return ABIAlign;
 
   if (const auto *RT = T->getAs<RecordType>()) {
-    if (TI.AlignIsRequired || RT->getDecl()->isInvalidDecl())
+    const RecordDecl *RD = RT->getDecl();
+
+    // 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->isInvalidDecl())
       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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