2 files changed, 31 insertions, 2 deletions
diff --git a/clang/lib/Sema/SemaAttr.cpp b/clang/lib/Sema/SemaAttr.cpp
index bf1e10e5b0b..37962ad1738 100644
--- a/clang/lib/Sema/SemaAttr.cpp
+++ b/clang/lib/Sema/SemaAttr.cpp
@@ -102,8 +102,11 @@ void Sema::ActOnPragmaPack(PragmaPackKind Kind, IdentifierInfo *Name,
   unsigned AlignmentVal = 0;
   if (Alignment) {
     llvm::APSInt Val;
+    
+    // pack(0) is like pack(), which just works out since that is what
+    // we use 0 for in PackAttr.
     if (!Alignment->isIntegerConstantExpr(Val, Context) ||
-        !Val.isPowerOf2() ||
+        !(Val == 0 || Val.isPowerOf2()) ||
         Val.getZExtValue() > 16) {
       Diag(PragmaLoc, diag::warn_pragma_pack_invalid_alignment);
       Alignment->Destroy(Context);
@@ -115,7 +118,6 @@ void Sema::ActOnPragmaPack(PragmaPackKind Kind, IdentifierInfo *Name,
   
   if (PackContext == 0)
     PackContext = new PragmaPackStack();
-
   
   PragmaPackStack *Context = static_cast<PragmaPackStack*>(PackContext);
   
diff --git a/clang/test/Sema/pragma-pack-2.c b/clang/test/Sema/pragma-pack-2.c
index e139be0be8f..c86136bf3e0 100644
--- a/clang/test/Sema/pragma-pack-2.c
+++ b/clang/test/Sema/pragma-pack-2.c
@@ -64,3 +64,30 @@ struct s2_4 {
 #pragma pack(pop)
 };
 extern int a2_4[offsetof(struct s2_4, f1) == 4 ? 1 : -1];
+
+#pragma pack(1)
+struct s3_0 {
+  char f0;
+  int f1;
+};
+#pragma pack()
+struct s3_1 {
+  char f0;
+  int f1;
+};
+extern int a3_0[offsetof(struct s3_0, f1) == 1 ? 1 : -1];
+extern int a3_1[offsetof(struct s3_1, f1) == 4 ? 1 : -1];
+
+// pack(0) is like pack()
+#pragma pack(1)
+struct s4_0 {
+  char f0;
+  int f1;
+};
+#pragma pack(0)
+struct s4_1 {
+  char f0;
+  int f1;
+};
+extern int a4_0[offsetof(struct s4_0, f1) == 1 ? 1 : -1];
+extern int a4_1[offsetof(struct s4_1, f1) == 4 ? 1 : -1];