From 69d27d2d054d23a106a5cf2a92ddd859b817dcc3 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Tue, 16 Jul 2013 00:21:28 +0000
Subject: [PATCH] Fix alignment of class derived from empty class.

The record layout code didn't properly take into account that
an empty class at offset 0 can have an alignment greater than 1.

Patch by Andrea Di Biagio.

llvm-svn: 186370
---
 clang/lib/AST/RecordLayoutBuilder.cpp         |  7 ++--
 .../SemaCXX/alignment-of-derived-class.cpp    | 41 +++++++++++++++++++
 2 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/SemaCXX/alignment-of-derived-class.cpp

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 51b1c062e0d2..5df372639daa 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1532,18 +1532,19 @@ CharUnits RecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
     }
   }
   
+  CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlign();
+  CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
+ 
   // If we have an empty base class, try to place it at offset 0.
   if (Base->Class->isEmpty() &&
       (!HasExternalLayout || Offset == CharUnits::Zero()) &&
       EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
     setSize(std::max(getSize(), Layout.getSize()));
+    UpdateAlignment(BaseAlign, UnpackedBaseAlign);
 
     return CharUnits::Zero();
   }
 
-  CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlign();
-  CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
-
   // The maximum field alignment overrides base align.
   if (!MaxFieldAlignment.isZero()) {
     BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
diff --git a/clang/test/SemaCXX/alignment-of-derived-class.cpp b/clang/test/SemaCXX/alignment-of-derived-class.cpp
new file mode 100644
index 000000000000..28c1fa9144b7
--- /dev/null
+++ b/clang/test/SemaCXX/alignment-of-derived-class.cpp
@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++11
+// expected-no-diagnostics
+
+// Test that the alignment of a empty direct base class is correctly
+// inherited by the derived class.
+
+struct A {
+} __attribute__ ((aligned(16)));
+
+static_assert(__alignof(A) == 16, "A should be aligned to 16 bytes");
+
+struct B1 : public A {
+};
+
+static_assert(__alignof(B1) == 16, "B1 should be aligned to 16 bytes");
+
+struct B2 : public A {
+} __attribute__ ((aligned(2)));
+
+static_assert(__alignof(B2) == 16, "B2 should be aligned to 16 bytes");
+
+struct B3 : public A {
+} __attribute__ ((aligned(4)));
+
+static_assert(__alignof(B3) == 16, "B3 should be aligned to 16 bytes");
+
+struct B4 : public A {
+} __attribute__ ((aligned(8)));
+
+static_assert(__alignof(B4) == 16, "B4 should be aligned to 16 bytes");
+
+struct B5 : public A {
+} __attribute__ ((aligned(16)));
+
+static_assert(__alignof(B5) == 16, "B5 should be aligned to 16 bytes");
+
+struct B6 : public A {
+} __attribute__ ((aligned(32)));
+
+static_assert(__alignof(B6) == 32, "B6 should be aligned to 32 bytes");
+
-- 
2.34.1