[PATCH] D107394: [AIX] "aligned" attribute does not decrease alignment

[Steven Wan via Phabricator via cfe-commits]

stevewan created this revision.
stevewan requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

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;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D107394.363852.patch
Type: text/x-patch
Size: 2140 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20210803/2287e522/attachment.bin>