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

[Steven Wan via Phabricator via cfe-commits]

stevewan updated this revision to Diff 364350.
stevewan marked an inline comment as done.
stevewan added a comment.

Fix the same problem in field layout.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107394/new/

https://reviews.llvm.org/D107394

Files:
  clang/lib/AST/ASTContext.cpp
  clang/lib/AST/RecordLayoutBuilder.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/RecordLayoutBuilder.cpp
===================================================================
--- clang/lib/AST/RecordLayoutBuilder.cpp
+++ clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1961,6 +1961,12 @@
     }
   }
 
+  const Type *Ty = D->getType()->getBaseElementTypeUnsafe();
+  // When used as part of a typedef, the 'aligned' attribute can be used to
+  // decrease alignment.
+  bool AlignAttrCanDecreaseAlignment =
+      AlignIsRequired && Ty->getAs<TypedefType>() != nullptr;
+
   // The AIX `power` alignment rules apply the natural alignment of the
   // "first member" if it is of a floating-point data type (or is an aggregate
   // whose recursively "first" member or element is such a type). The alignment
@@ -1971,7 +1977,7 @@
   // and zero-width bit-fields count as prior members; members of empty class
   // types marked `no_unique_address` are not considered to be prior members.
   CharUnits PreferredAlign = FieldAlign;
-  if (DefaultsToAIXPowerAlignment && !AlignIsRequired &&
+  if (DefaultsToAIXPowerAlignment && !AlignAttrCanDecreaseAlignment &&
       (FoundFirstNonOverlappingEmptyFieldForAIX || IsNaturalAlign)) {
     auto performBuiltinTypeAlignmentUpgrade = [&](const BuiltinType *BTy) {
       if (BTy->getKind() == BuiltinType::Double ||
@@ -1982,7 +1988,6 @@
       }
     };
 
-    const Type *Ty = D->getType()->getBaseElementTypeUnsafe();
     if (const ComplexType *CTy = Ty->getAs<ComplexType>()) {
       performBuiltinTypeAlignmentUpgrade(CTy->getElementType()->castAs<BuiltinType>());
     } else if (const BuiltinType *BTy = Ty->getAs<BuiltinType>()) {
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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