From a91d38a435431672404a65030f6b5896e4564d0e Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Fri, 2 Dec 2011 02:38:48 +0000
Subject: [PATCH] Fix bitfield handling for record layout with #pragma pack. 
 <rdar://problem/10494810> and PR9560.

llvm-svn: 145673
---
 clang/lib/AST/RecordLayoutBuilder.cpp |  8 +++--
 clang/test/Sema/pragma-pack-5.c       | 45 +++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/Sema/pragma-pack-5.c

diff --git a/clang/lib/AST/RecordLayoutBuilder.cpp b/clang/lib/AST/RecordLayoutBuilder.cpp
index 88a90a417291..c92116ac6c40 100644
--- a/clang/lib/AST/RecordLayoutBuilder.cpp
+++ b/clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1690,18 +1690,20 @@ void RecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
   UnpackedFieldAlign = std::max(UnpackedFieldAlign, D->getMaxAlignment());
 
   // The maximum field alignment overrides the aligned attribute.
-  if (!MaxFieldAlignment.isZero()) {
+  if (!MaxFieldAlignment.isZero() && FieldSize != 0) {
     unsigned MaxFieldAlignmentInBits = Context.toBits(MaxFieldAlignment);
     FieldAlign = std::min(FieldAlign, MaxFieldAlignmentInBits);
     UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignmentInBits);
   }
 
   // Check if we need to add padding to give the field the correct alignment.
-  if (FieldSize == 0 || (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)
+  if (FieldSize == 0 || (MaxFieldAlignment.isZero() &&
+                         (FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize))
     FieldOffset = llvm::RoundUpToAlignment(FieldOffset, FieldAlign);
 
   if (FieldSize == 0 ||
-      (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize)
+      (MaxFieldAlignment.isZero() &&
+       (UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
     UnpackedFieldOffset = llvm::RoundUpToAlignment(UnpackedFieldOffset,
                                                    UnpackedFieldAlign);
 
diff --git a/clang/test/Sema/pragma-pack-5.c b/clang/test/Sema/pragma-pack-5.c
new file mode 100644
index 000000000000..95bbe1fe7e94
--- /dev/null
+++ b/clang/test/Sema/pragma-pack-5.c
@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin9 %s -fsyntax-only -verify -ffreestanding
+// <rdar://problem/10494810> and PR9560
+// Check #pragma pack handling with bitfields.
+
+#include <stddef.h>
+#pragma pack(2)
+
+struct s0 {
+     char        f1;
+     unsigned    f2 : 32;
+     char        f3;
+};
+extern int check[sizeof(struct s0) == 6 ? 1 : -1];
+
+struct s1 {
+     char        f1;
+     unsigned       : 0;
+     char        f3;
+};
+extern int check[sizeof(struct s1) == 5 ? 1 : -1];
+
+struct s2 {
+     char        f1;
+     unsigned       : 0;
+     unsigned    f3 : 8;
+     char        f4;
+};
+extern int check[sizeof(struct s2) == 6 ? 1 : -1];
+
+struct s3 {
+     char        f1;
+     unsigned       : 0;
+     unsigned    f3 : 16;
+     char        f4;
+};
+extern int check[sizeof(struct s3) == 8 ? 1 : -1];
+extern int check[offsetof(struct s3, f4) == 6 ? 1 : -1];
+
+struct s4 {
+     char        f1;
+     unsigned    f2 : 8;
+     char        f3;
+};
+extern int check[sizeof(struct s4) == 4 ? 1 : -1];
+extern int check[offsetof(struct s4, f3) == 2 ? 1 : -1];